Diagnostic imaging in emergency patients

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Chapter 4 Diagnostic imaging in emergency patients

The aim of this chapter is to explain briefly the need and usefulness of diagnostic imaging services in emergency situations. Many of these emergencies arise ‘after hours’ and staff in most emergency departments have no immediate access to radiologists. The chapter also outlines the various diagnostic imaging modalities available, the basic principles involved in each modality and some clues to interpreting some of the most obvious lesions.

IMAGING MODALITIES

Plain X-rays

Plain X-rays are a commonly used modality. An X-ray beam is passed through the body.

Different tissues of the body absorb different amounts of X-rays. Unabsorbed X-rays are recorded on a film placed on the opposite side. Bone absorbs the most, hence it looks white on film. Air absorbs almost none, hence it looks black on film. Other tissues are demonstrated in shades between black and white.

Plain X-rays are performed as the first line of emergency investigations in many instances, as in fractures and abdominal or chest pain.

Ultrasound

Transducers used in this examination pass ultrasound into the body and also receive the echoes. The intensity of the echoes depends on the degree of absorption of sound waves by various tissues. On the image, echogenic areas appear white and sonolucent areas (that transmit sound, e.g. fluid) appear black.

Immediate and instant demonstration of organs by real-time ultrasound imaging and the fact that it is non-invasive and harmless (no radiation) have made this tool very popular. It is used in the following:

• To find out whether a lesion or lump is solid or cystic.

• Abdominal and pelvic organs—liver, gall bladder, bile ducts, pancreas, spleen, kidneys, aorta, inferior vena cava (IVC), bladder, prostate, uterus and ovaries, renal stones, gall stones, aortic aneurysm, traumatic and other haematomas—abscess and abnormal fluid collections can be demonstrated.

• To examine small parts (thyroid, testes and breast) and neonatal heads for ventricular size etc.

• For obstetrical work-up, including study of fetus for early detection of abnormalities, and for emergencies like ectopic pregnancy, vaginal ultrasound is extremely useful.

• Ultrasound-guided biopsy and interventional procedures.

• Musculoskeletal investigations, e.g. shoulder, knee, muscle and tendon injuries and acute tenosynovitis.

• Duplex and colour Doppler ultrasound:

• With the advent of duplex and colour flow Doppler it is now easy to identify arteries and veins non-invasively. This modality should be the first line of imaging for the detection of deep vein thrombosis (DVT) in the limbs. (This study can be difficult in extremely swollen, oedematous lower legs.) In difficult cases venography can be performed. It should be remembered that ultrasound is non-invasive and can be performed repeatedly even in pregnant patients with suspected DVT.

• Duplex ultrasound is useful in identifying superficial thrombophlebitis.

• While excluding thrombosis, ultrasound study can also diagnose other causes of a swollen, tender calf such as ruptured Baker’s cyst, haematoma in calf muscle, e.g. a gastrocnemius tear, mass in groin, axilla.

• Doppler ultrasound is useful in detecting and localising acute arterial occlusion in the limbs and in the investigation of peripheral vascular disease and carotid arterial disease.

• It is also useful in assessing renal artery stenosis and renal parenchymal vascular disease in the investigation of hypertension.

Computerised tomography (CT)

The same principles are applied in CT as in plain X-rays, but there are two main modifications:

1. The X-ray tube is rotated around the body in an axial plane.

2. Instead of an X-ray film, detectors are used on the opposite side. Multiple fixed detectors are placed around the body to pick up the signals as the X-ray tube rotates around the body. Signals from the detectors are digitalised and the computer builds up an image which can be seen on a TV monitor or recorded on a film.

The resulting images are transverse sections of the part examined. Using the stored information of consecutive thin transverse sections, the images can be reconstructed in sagittal, coronal and oblique planes. CT is now a proven diagnostic tool which delivers valuable information to help in the early diagnosis of many lesions and disease. Its use is greatly appreciated in many emergencies such as head injuries and some chest and abdominal emergencies. It is also useful in demonstrating fractures that are not shown by plain X-rays.

Helical CT scanning

Helical or spiral CT scanning is an improvement that allows very quick scanning of a patient (shorter scanning time than conventional CT) with increased accuracy of lesion detection resulting from volumetric data acquisition. In conventional CT, X-ray exposure and patient movement through the gantry alternate whereas, in helical CT, X-ray exposure and patient movement take place simultaneously giving a ‘spiral impression’.

Advantages

• Greater length of patient’s body can be scanned with one ‘breath-hold’ thus producing contiguous images without interruption, e.g. a 30-second scan can cover most of the chest.

• Eliminates respiratory artefacts and reduces partial volume effect, peristaltic and other movement artefacts.

• Produces overlapping images without extra radiation exposures.

• Using a window workstation the acquired images can be reconstructed in multiplanar and three-dimensional images with excellent clarity.

Multi-slice CT scans

This is a further advancement whereby the speed of scanning and resolutions are considerably improved by using more efficient detectors and obtaining thinner slices per rotation of the X-ray tube as the patient passes through the gantry.

Scanners are available to obtain 4, 8, 16, 32 or 64 slices (per rotation) of up to 0.5-mm thickness. A few 300-slice scanners are also available in Australia. These are faster than a heartbeat.

Advantages and uses

• Speed—some scanners can complete a body scan in 20 seconds; useful in ICU and in paediatric, elderly, trauma and postoperative patients, where a shorter breath-hold and quick scanning are required

• High resolution and fewer artefacts

• Less IV contrast usage by allowing the scanning to start when the contrast reaches the area of interest (contrast detection system)

• Multi-planer reconstruction without loss of resolution

• 3D reconstruction useful for surgical planning

• CT angiography (including pulmonary angiography to detect pulmonary embolism) and cholangiography

• CT fluoroscopy—useful in interventional work, e.g. placement of needle for biopsy, facet joint injection etc

• Virtual endoscopy—enables a bronchoscopic view or colonoscopic view to be obtained

• Coronary angiography—introduction of 300-slice CT will be useful for cardiac and coronary assessment without the need for catheterisation

Magnetic resonance imaging (MRI)

In the past 20 years MRI has gradually become the technique of first choice in the investigation of many diseases. The physics involved in MRI is more complex than for any other radiological technique. However, the basic principles are indicated by the original terminology, nuclear magnetic resonance (NMR).

Nuclear

Unlike X-ray images, which are produced by attenuation of X-ray photons by the outer orbital electrons in the atoms of the elements in the body tissue, the MRI signal arises from the centre of the atom—the nucleus. The nuclei used in MRI are those of hydrogen atoms.

Hydrogen is selected because:

• It makes up about 80% of the human body.

• Its nucleus has only 1 proton, which has magnetic property.

• The solitary proton gives it a larger magnetic field (or moment).

Magnetic

The hydrogen proton is a small, positively charged particle with associated angular momentum or spin. This situation represents a current loop and results in the formation of a magnetic field with north and south poles (dipoles). In other words, the protons behave as tiny magnets within the tissues. All nuclei used in MRI must have this property.

In the absence of influence from any external magnetic fields, the protons tend to orientate randomly in all directions. However, when a strong static external magnetic field is applied, these dipolar protons tend to align parallel to the direction of the external magnetic field (longitudinal plane).

The strong external magnetic field must be homogeneous over a volume large enough to contain the human body. This explains why the magnet tunnel is much longer than the CT gantry.

Resonance

This is a phenomenon whereby an object is exposed to an external oscillating disturbance that has a frequency similar to its own frequency of oscillation. Therefore, when a hydrogen proton is exposed to an external disturbance with a similar frequency to its own, the proton gains energy from the external disturbance. This is called resonance. This can happen only if the external disturbance is applied at 90° to the magnetic field of the proton. The oscillation frequency of the hydrogen proton in a static magnetic field of strength used in clinical MRI corresponds to the radiofrequency band (RF) in the electromagnetic spectrum.

Therefore, for resonance of hydrogen to take place, an RF pulse at the same frequency as the oscillation of the hydrogen proton must be applied at 90° to the magnetic field of the proton. The application of the RF pulse that causes resonance is called excitation, as it results in the nuclei gaining energy. This energy causes the magnetic field of the protons to change direction. Enough RF pulse energy is given to the proton to change the direction from the longitudinal to the transverse plane (flip angle of 90°). Now the protons are rotating in the transverse plane. According to the laws of electromagnetism, if a receiver coil is placed in the transverse plane, the transverse magnetisation produces a voltage in the coil. This voltage constitutes the MR signal.

When the RF pulse is turned off, the hydrogen protons return to their original orientations in the longitudinal plane. This is called relaxation. There are two main types of relaxation (T1 and T2). T1 is the return of net magnetisation to the longitudinal plane. T2 is the decay of magnetisation in the transverse plane. These two relaxations and their time variances are used to create imaging sequences. All relaxation times are based on fat and water. This is where most of the body’s hydrogen protons are.

T1 images are known for their anatomical details. In T1 images, fluid appears black and fat appears white.

T2 images are known for their contrast. In these images, fluid appears white and fat appears grey.

Proton density images are a combination of T1 and T2. These images specifically look at the concentration of hydrogen protons.

The above is a simple explanation of the basics, but more complex physics is involved in the formation of MR images which is beyond the scope of this chapter.

Summary

MRI involves the use of:

• large magnet to produce a static magnetic field

• RF generator to produce RF pulses

• hydrogen nuclei—different tissues have characteristic differences in hydrogen proton concentrations; therefore, the MR signal and hence the image obtained basically represent the different distributions of hydrogen protons in the body

• computer to convert the signals into images in various anatomical planes.

Advantages and uses of MRI

No ionising radiation.

Free of artefacts from adjacent bones and gas. Therefore it is excellent to demonstrate soft tissues adjacent to bones, e.g. base of brain and spinal cord.

Excellent resolution—even without contrast enhancement, MR is much more sensitive in detecting contrast differences between various tissues. This is due to the intrinsic differences in hydrogen proton density as well as T1 and T2 relaxation, magnetic susceptibility and motion in various tissues.

• Stroke—MRI can diagnose acute infarction within hours of onset when CT scan is still normal. This is done by using diffusion imaging which tracks the motion of water that becomes acutely restricted in the area of infarction. Once infarction has been diagnosed, an intravenous MRI angiogram can be performed at the same time to assess the calibre of the neck arteries.

• Haematoma—subdural and parenchymal haematoma and dural sinus thrombosis.

• Aneurysm and other vascular malformations—MRI angiography is very sensitive in finding small aneurysms up to about 2 mm and can also give some idea of the degree of any associated vasospasm.

• Intracranial mass—MRI can accurately stage both primary and metastatic tumours. It is more sensitive than CT for metastases. Some masses like abscess and epidermoid can be differentiated from other tumours with certainty as they have restricted water diffusion. In certain cases spectroscopy can also help in the differential diagnosis. MRI is also superior to CT in detecting lesions closer to the skull base such as acoustic neuroma and pituitary tumour.

• Other uses—demyelination, congenital anormality, meningeal disease and investigation of epilepsy.

• Spine—MRI is the modality of choice for assessing cord contusion and haematoma in the acute stage, especially when there is an associated spinal fracture and neurological signs. It is also excellent in demonstrating cord compression, infarction, tumour, neuromas, metastases, myelopathy, radiculopathy and brachial plexus avulsion. It is also useful in post-laminectomy complications such as haematoma or infection as well as investigation of infective spondylodiscitis where early changes, such as fluid in the disc, paraspinal collections and end plate erosions, are seen.

• Musculoskeletal—MRI has the ability to simultaneously characterise soft tissues (muscles, ligaments, tendons and cartilage) as well as bone marrow. It is very useful in the investigation of musculotendinous injury and pathology, joint injury and pathology (e.g. rotator cuff injury in shoulder, meniscal and ligamentus injury in knee) and fractures not detected by X-ray (e.g. fracture in the neck of femur) as well as bone infection, avascular necrosis, marrow disorders, bone and soft tissue tumours.

• Chest—constrictive pericarditis, aortic and great vessel dissection, congenital cardiac and great vessel abnormality, lung cancers closer to the chest wall and apex (e.g. Pancoast’s tumour).

• Abdomen—adrenal mass using chemical shift imaging, cholangiography etc.

• Pelvis—uterine and cervical tumours and abnormalities, differentiation of adenomyosis from fibroids, endometriosis assessment, bladder tumour etc.

Contrast enhanced MRI

In spite of the excellent tissue contrast definition without intravenous contrast, contrast-enhanced MRI (gadolinium) provides even better imaging sensitivity and specificity.

The enhanced contrast shows subtle parenchymal as well as leptomengingeal lesions not otherwise visible, e.g. very small metastatic lesions, acoustic neuromas of 2–3 mm, pituitary microadenomas, differentiation of the actual size of tumour from the surrounding oedema and differentiation of more malignant areas from less malignant areas. These are helpful for the purpose of treatment and to select the exact site for biopsy.

Ongoing research into the development of new contrast agents targeted at specific organs, disease processes, cells or gene type is likely to result in considerable expansion of the use of MRI.

MR angiography (MRA)

Protons in flowing blood (moving protons) produce a high signal against the background of little or no signal from the surrounding stationary tissues—hence the development of the MR angiogram with no display of the background soft tissue.

Contraindications

Cardiac pacemakers, ferromagnetic intracranial aneurysm clips (except where MR-compatible clips have been used), cochlear implants, intravascular stainless steel stents inserted less than 6 weeks previously, surgical clips in chest and abdomen inserted less than 1 week previously, metal workers with metallic foreign body in the eye.

Disadvantages

Because of the length of the magnet (tunnel), some patients may experience claustrophobia. This can mostly be overcome by sedation. Scanners are now available with open gantry which will alleviate claustrophobia, but these scanners are dedicated and are used mainly for musculoskeletal and spinal work-up.

Contrast study

The main limitation in the use of plain X-rays is the superimposition of the shadows of various organs. In many instances this can be overcome by introducing contrast:

• Barium to demonstrate the gastrointestinal tract (GIT).

• Intravenous pyelogram (IVP)—IV contrast demonstrates kidneys, collecting system and bladder. Helpful to assess function (excretion) and to detect stones, obstruction, space occupying lesion, deformities of renal tract etc.

• Micturating cystourethrogram (MCU)—to demonstrate urethra, bladder and vesicoureteral reflux.

• Arthrography—e.g. shoulder, to detect rotator cuff tears. Sometimes this is combined with a CT scan, which helps to identify glenoid labral injury etc. (Arthrograms may not be required if there is access to high resolution ultrasound and MRI scan.)

• Herniography—contrast injected into the peritoneal cavity to detect clinically undetectable inguinal or femoral hernia that is producing symptoms.

• Myelography—contrast injected via lumbar puncture demonstrates the subarachnoid space around the spinal cord and nerve roots. With the advent of CT and MRI the need for this examination is almost nil.

• Cholangiography—in the past, oral cholangiograms were performed, but this is now replaced by CT cholangiography. This examination requires slow infusion of contrast (which is excreted by bile) followed by helical CT scan and 3D reconstruction of the biliary tree.

• Sialography—contrast injected into the salivary ducts (parotid or submandibular) to identify stones, strictures, sialectasis and lesions in the glands.

• Hysterosalpingogram—contrast is injected into the uterine cavity to demonstrate the uterine cavity, fallopian tubes and to detect patency of the tube in the investigation of infertility.

• Sinogram and fistulogram—contrast injection shows the cavities and communications.

• Venography—could detect clots, incompetent perforators and varicose veins (current trend is to do Doppler and colour Doppler ultrasound examination).

• Arteriography—contrast injected into various arteries using catheters demonstrates the arteries in various organs. It is used to demonstrate occlusions, narrowing of arteries, aneurysms, bleeding points, AV malformation and tumours. Digital subtraction angiography (DSA) has replaced the conventional angiograms. In this technique, the X-ray images are digitalised and stored and manipulated by computer. The image signal of an area or organ obtained before the injection of contrast is subtracted from the image signal obtained after injection of contrast into the vessels. This is done by the computer.

Advantages

The resulting image will demonstrate the vessels and branches without superimposition of bones and other soft tissue shadows.

Owing to the fact that the image signals can be intensified by the computer, contrast media of low concentration and volume can be used with thinner catheters.

Interventional radiology

Radiologists are able to perform certain therapeutic and interventional diagnostic procedures using various types of imaging equipment (fluoroscopy, ultrasound, CT and MR), needles, catheters and guide wires.

• Dilatation of narrowed arteries—transluminal angioplasty, insertion of vascular stents.

• Embolisation—of bleeding vessels, preoperatve tumour embolisation to assist surgery by reducing blood loss and reducing the duration of surgery, palliative embolisation of tumours, embolisation of some vascular abnormalities.

• Thrombolysis—using local low-dose intra-arterial injection of thrombolytic agents to relieve thromboembolism in certain vessels such as coronary artery and peripheral arteries.

• Inferior vena cava filter insertion to prevent pulmonary embolism caused by clots arising from pelvis and lower limbs.

• Percutaneous insertion of stents to relieve biliary or ureteric obstruction.

• Percutaneous drainage of cysts, abscesses, pleural effusion etc.

• Percutaneous removal of renal or biliary stones when other methods are contraindicated.

• Biopsy of deep and superficial lesions—lesions in liver, pancreas, kidneys, other abdominal masses, chest lesions, breast, thyroid, lymph node and other superficial and deep lesions.

Intravenous contrast reaction

Even though the incidence of fatality is much lower than in street accidents, it is a great worry to doctors. Some statistics show that about 1 in 80,000 patients developed severe or fatal reaction when ionic contrast was used. Incidence of mild reaction is probably about 5–15%, moderate reaction about 1–2% and severe reaction is probably about 0.2%. However, with the use of non-ionic contrast and taking good precautions, the incidence of reaction is said to have reduced to about one-third to one-quarter of the frequency.

Usually patients who develop severe reaction have some other aggravating disease as well.

The exact pathogenesis of the reaction is not very clear. However, the following are possible mechanisms:

• chemotoxic effect

• hyperosmolar reactions causing erythrocyte or endothelial damage, blood–brain barrier damage and vasodilatation

• vasomotor reactions with release of vaso-active substances such as histamine, serotonin and bradykinin

• vaso-vagal reaction with inhibition of enzymes such as cholinesterase.

Symptoms and signs

Most reactions occur within minutes of injection. However, delayed reactions have also been reported.

Mild reactions—hot flush, burning sensation, arm pain, dizziness, nausea, vomiting, headache and urticaria—are thought to be due to systemic effects as a result of histamine liberation. Usually reassurance and restoration of the patient’s confidence is all that is required, but sometimes oral antihistamine for urticaria, mild analgesics and sometimes tranquillisers for anxiety (5 mg benzodiazepam) may also be helpful.

Moderate reactions involve a slightly more serious manifestation of the above symptoms, with or without a moderate degree of hypotension and bronchospasm. They usually respond to reassurance and antihistamine (IM or IV), benzodiazepam 5 mg, salbutamol inhalation for bronchospasm, hydrocortisone (100–500 mg IM or IV) and occasionally adrenaline 0.3–1 mL of 1/1000 IM. Oxygen by mask is administered.

Severe reaction can be life-threatening and involve a severe form of the above reactions plus convulsion, unconsciousness, laryngeal oedema, bronchospasm, pulmonary oedema, arrhythmia, hypotension, cardiac arrest, anaphylatic shock. Severe reactions require urgent treatment (see treatment of anaphylaxis in Chapter 40, ‘Dermatological presentations to emergency’).

Pre-deposing factors—in the presence of these, the incidence of reaction can be about 2–10 times as severe:

• Previous adverse reaction to contrast.

• Significant allergic history including iodides.

• Cardiac disease.

• Dehydration—all patients should be adequately hydrated as dehydration is dangerous, especially in patients with diabetes, renal impairment and multiple myeloma.

• Haematological and metabolic conditions such as sickle cell anaemia, patients with known phaeochromocytoma.

• Renal disease—patients with preexisting renal disease, especially patients with diabetes, have an increased risk of reaction as well as of renal failure. Metformin drugs used for diabetic treatment are excreted by the kidneys and in patients with renal impairment this has been known to cause lactic acidosis and lead to acute alteration of renal function. In view of this, all diabetic patients treated with metformin drugs must have serum urea and creatinine levels reviewed before the intravascular contrast injection (serum urea must be less than 6.7 mmol/L and serum creatinine must be less than 0.10 mmol/L). The metformin drugs should be discontinued from 48 hours before until 48 hours after the injection and should be recommenced only after checking the serum urea and creatinine. If required, another hypoglycaemic agent may be used during this period.

Prevention and precautions

1. Always try to use non-ionic contrast.

2. Like other drugs, contrast agents should be used only if indicated and should be used in the smallest possible dose and concentration that will result in adequate imaging.

3. Weigh the possible advantages of using contrast against the possible risk. In patients with a strong family history, contrast should be avoided. In many cases the contrast study may be replaced by another examination such as ultrasound, CT or MRI.

4. A test dose may not help. However, some authors advise a small test dose of about 1 mL IV in high-risk patients who definitely require contrast for diagnosis.

5. In some patients (e.g. asthmatic and allergic patients) premedication with oral corticosteroid and possibly antihistamines could be given during the 24 hours preceding the test. The patient should also be adequately hydrated.

IMAGING OF THE HEAD

Common emergencies are: trauma, severe headaches, collapse, syncope, seizures and stroke.

Trauma

Plain X-rays of skull

Indications

(Uncommon as CT is investigation of choice.)

• History of unconsciousness

• Palpable or visible depression on skull

• Laceration or penetrating wound

• Cerebrospinal fluid (CSF) or blood discharge from ear or nose

• Presence of neurological signs

Views

• Include anteroposterior, lateral, Towne’s and basal views.

• ‘Shoot through’ lateral (patient in supine position and X-ray beam horizontal) is useful to demonstrate air–fluid levels, especially in sinuses.

Interpretation

Every doctor working in the accident and emergency department should try to be familiar with the appearance of normal skull X-rays. The best way to detect abnormality is to know the normal. (This applies to every modality of imaging.)

One should be familiar with the skull sutures, vascular markings, venous lakes along the inner table of the skull vault, appearance of normal sinuses and normal intracranial calcifications (e.g. pineal body, choroid plexus).

Fracture of the skull can be an undepressed crack fracture or a depressed fracture.

Do not misinterpret sutures and vascular markings as fractures. You can avoid this by knowing the normal positions of sutures and vascular markings. Sutures are usually serrated. Fracture lines are usually ‘blacker’ than the vascular markings.

Beware of metopic sutures—in some patients such a suture may persist throughout life and may look like a fracture.

In depressed fractures, one or more fragments may be depressed. In some cases, oblique or tangential views may be needed to demonstrate depression.

If pineal calcification is present, look for shift. This indicates a space-occupying lesion such as a haematoma. (Towne’s view is ideal for this.)

Look for air–fluid level in sinuses or air in ventricles in the horizontal beam lateral view.

Plain X-rays of the face

Most facial injuries can be evaluated clinically. However, X-rays are performed for:

• confirmation

• assessment of the degree of displacement or depression of fragments

• detecting fractures in the presence of extreme facial swelling which makes palpation difficult.

In some cases facial fractures are associated with other serious emergencies, such as intracranial, neck or chest injuries, which may require emergency management such as maintenance of airway. In these patients, X-rays of the face can be postponed to the latter part of the management and may even be deferred for a few days.

Views

• Routine facial views—posteroanterior (PA), occipitomental (OM) and lateral

• Special views—nose (AP, lateral and axial), zygoma (Towne’s or modified basal view for the arch), orbital, mandible (PA, lateral, oblique and sometimes orthopantomogram—OPG—and occlusal view for symphysis menti)

Classification

For convenience, facial fractures can be divided into three types: upper third, middle third and lower third.

1. Upper third. The upper third, which is above the superior orbital margin, includes the superior orbital margin, the frontal sinuses and the adjacent frontal bone:

• Fracture of superior orbital margin appears as interrupted cortical margin with or without depression, either craniocaudally or posteriorly.

• Fracture of the frontal sinuses may involve anterior wall or both anterior and posterior walls.

• Fracture may be linear or comminuted, depressed or undisplaced.

• Fracture of sinus may extend into orbit—therefore look for orbital emphysema.

• Fractures causing laceration of mucosa in sinus or fractures communicating with skin laceration are compound fractures.

2. Middle third. This includes the nose, zygoma, orbit (floor, lateral and medial walls) and maxillae (mid-facial bones):

• Nose. Nasal fracture and deviations are easily detectable clinically, but X-rays are needed in patients with severe swelling or for confirmation of the degree of damage. Fractures of nasal bones are better seen in lateral view (soft tissue exposure). Deviation is seen in axial view. PA view may demonstrate fracture of frontal process of maxilla and also deviation of fracture of the bony part of nasal septum. Associated fractures in severe cases are: bony nasal septum, cribriform plate, frontal process of maxilla, anterior nasal spine of maxilla.

• Zygoma. Fracture of the arch usually involves three sites causing depression of the arch. A commonly seen severe form of fracture is of the zygomaticomaxillary complex. One fracture line extends from the zygomaticofrontal suture across the orbital process of zygoma (lateral wall of orbit) up to the lateral aspect of the inferior orbital fissure. Another fracture extends from the lateral wall of maxilla to the inferior orbital margin (near the inferior orbital foramen) and extends along the floor of the orbit to the lateral aspect of the inferior orbital fissure, thus completing a circle. This fracture can cause separation of the zygomatic bone from the maxilla and orbit. (This fracture can be well understood if the reader takes a dry skull and follows the line of the fracture described above).

• Orbit—blowout fracture. The orbital margin is stronger than the floor and medial wall of the orbit. The posterior half of the orbital floor is formed by the thin orbital plate of the maxilla. The medial wall is formed by the orbital plate of the ethmoid. These two orbital plates are very weak. Sometimes the orbital margin can be intact and the force of injury can be transmitted to the floor and medial walls of the orbit, causing blowout fractures into the adjacent sinuses. Therefore, in the presence of orbital emphysema, a blowout fracture should be suspected.

• Maxilla—fractures of mid-facial bones. These fractures tend to follow a certain pattern. There are three common patterns, which are named after the person who described them—Le Fort I, II and III fractures.

a. Le Fort I is the lowest and almost horizontal fracture through the maxilla, causing separation of the lower part of the maxilla. The fracture line extends from the inferolateral aspect of the nasal aperture horizontally across the lower part of the anterolateral and posterolateral walls of the maxilla. It then passes almost horizontally across the lower part of the medial and lateral pterygoid plates, reaches the medial wall of the maxillary antrum and extends to the inferolateral aspect of the nasal aperture, thus completing a circle.

b. Le Fort II fracture separates the midfacial bones from the cranium and the lateral aspect of the face. The medial part of the fracture line is across the nasal bone, nasal septum, frontal process of the maxilla, lacrimal bone and runs posteriorly along the ethmoidal bone. Laterally the fracture runs obliquely downwards from the inferior orbital margin (near the zygomaticomaxillary suture) along the anterolateral wall of the maxilla and then slightly ascends up the posterolateral wall of the maxilla to the inferior orbital fissure.

c. Le Fort III is the highest of the fractures and is bilateral causing complete separation of the midfacial bone from the base of the skull. The fracture line passes across the nasofrontal region to the ethmoid and runs posteriorly to the inferior orbital fissure. It also involves the pterygoid plates. Laterally the fracture involves the lateral wall of the orbit and the zygomatic arch.

The Le Fort fractures may occur in combination. The above description is useful for surgical planning.

3. Lower third. This includes the mandible. Common sites of fractures are the alveola (weakest part), condyles, angle of the mandible, body (usually the fracture is around the canine tooth because of maximum convexity). Bilateral fractures are common. Fractures of the body on one side and the angle on the other side are also common.

CT findings in head injury

If CT is available, it is the quickest way of detecting intracranial trauma. It has been reported that about 10–15% of patients with head injury with no neurological signs were found to have abnormal CT findings. In contrast, about 75% of patients with neurological signs demonstrated abnormal CT findings.

The lesions described in the following sections may be seen in CT.

Haematomas and contusions (acute and delayed)

Haematomas appear as high-density areas (white) on CT without contrast. Haematomas are fairly homogeneous, but contusion shows patchy dense and low-density areas. Low-density areas are due to oedema. Fresh blood appears as dense areas due to haemoglobin. (In anaemic patients it may be isodense with the rest of the brain or even hypodense if the haemoglobin level is low.)

Most haematomas become isodense in 1–3 weeks and in some cases get even smaller and hypodense. The isodense haematomas may be missed unless other signs of mass effect are looked for.

Delayed haematomas may appear from 2–7 days after trauma. Haematomas and associated oedema usually cause space-occupying effects—midline shift, compression on ventricles, cisterns etc.

Subdural haematomas

These usually appear as dense areas and follow the brain surface with a concave inner border and convex outer border. They tend to be diffuse and extend along the subdural space. Thin haematomas (e.g. less than 5 mm) and haematomas near the vertex may be difficult to identify. However, indirect evidence such as midline shift may help. Beware of bilateral subdural haematomas, which may not cause any shift.

Acute haematomas (occurring 0–1 week after trauma) are usually dense.

Subacute haematomas (occurring l–3 weeks after trauma) may be isodense.

Chronic haematomas (more than 3 weeks after trauma) are usually hypodense.

Acute-on-chronic haematomas show mixed density.

Epidural haematomas

These are caused by traumatic separation of the dura from the inner table causing damage to the middle meningeal arterial branches, venous branches or diploic veins. An epidural haematoma is usually seen as a biconvex density under the inner table of the skull. The biconvex appearance is due to firm adhesion of the dura to the inner table. For this reason the epidural haematomas are demarcated by sutures.

Oedema

Oedematous areas appear as low-density areas in the CT. They may be focal, patchy or diffuse. Due to the oedema there may be space-occupying effects, such as compression on the adjacent ventricles and midline shift.

Note: Oedema may have other causes such as infarction. Therefore it should be differentiated. A history of trauma and the site of involvement may be helpful.

Intraventricular and subarachnoid haemorrhage

These may occur with some head injuries and appear as dense areas within the ventricles, basal cistern, sylvian fissures, interhemispheric fissure or cerebral sulci. Resolution of the haemorrhage within the ventricular system and subarachnoid space is fairly quick and may disappear within a week.

Fractures and displaced or depressed bony fragments

These can be seen in CT when viewed with bone windows. The CT is useful to identify soft tissue contusion and foreign bodies in the scalp or in the intracranial region. It is also useful to identify any traumatic pneumocephalus.

Post-traumatic changes

Acute or delayed hydrocephalus is caused by blood in the subarachnoid space causing some obstruction to the CSF pathways.

Ischaemic infarction appears as low-density areas.

Post-traumatic atrophy is seen in almost one-third of patients with severe head injury. Due to the atrophy there may be compensatory dilation of the ventricles usually adjacent to the site of atrophy.

Post-traumatic abscess may be seen in penetrating injury or fracture, or as a complication following surgery. It appears as a low-density area with ring enhancement after contrast injection. This ring enhancement is usually surrounded by a large area of oedema. The lesion will also produce a space-occupying effect.

The use of CT in facial trauma

In some cases plain tomography is performed to demonstrate facial fractures. However, CT of facial bones in coronal, axial and sagittal planes is very useful, not only to demonstrate the fractures but also to show the extent, degree of depression of fragments and associated haematomas, especially in the adjacent sinuses, orbits etc.

Angiography in cerebral trauma

This has been almost eliminated by CT scanners. However, it is indicated if there is suspicion of vascular damage such as occlusion of an artery or injury to an AV malformation.

MRI in head injury

Even though MRI is superior to CT in detecting small haematomas, especially near the bones, CT is preferable as the initial investigation not only because the examination time is shorter but also because sometimes haematomas that are less than 1–2 days old may not be shown by MRI. CT shows acute haemorrhages well.

Head injury in children—CT appearance

Appearance of haematoma is almost the same as in adults. However, haemorrhagic contusions are less common than in adults due to greater pliability of the skull.

The paediatric brain may demonstrate acute generalised oedema causing narrowing of ventricles and subarachnoid space. Oedema is less marked in adults.

Acute severe headache and collapse

Sudden onset of severe headache or sudden collapse may be caused by intracranial haemorrhage. The haemorrhage could be from: aneurysm, AV malformation, capillary bleed in hypertension, bleeding disorders or bleeding from a tumour.

The haemorrhage may be intracerebral, subarachnoid or intraventricular.

In these cases CT is rewarding. Blood appears as dense areas. Valuable clues as to the site of bleeding and the cause may be shown by CT. However, in most cases angiograms (CT or DSA) will be required to show the exact site and cause of bleeding. Multiple vessel studies are necessary as there may be multiple aneurysms. An angiogram will also show the site of the lesion and, in cases of AV malformation, the feeding vessels to the malformation. Angiograms are not necessary in cerebral parenchymal haemorrhage.

In suspected subarachnoid haemorrhage, CT scan is performed before lumbar puncture. If haemorrhage is marked, or hydrocephalus or space-occupying effect is detected, lumbar puncture is avoided. However, in cases where no haemorrhage is detected, lumbar puncture could be performed. This is because very small haemorrhages may not be shown by CT. Small amounts of blood are not enough to change the CSF density, or in some (anaemic) patients the haemoglobin content may not be enough to change the CSF density.

Syncope and seizures

Of the many causes of syncope only a few need radiological assistance for diagnosis or confirmation:

• Syncope caused by reduced cardiac output may need echocardiography, cardiac catheterisation and angiography.

• Syncope is rarely caused by cerebrovascular disease, e.g. transient ischaemic attacks, subclavian steal, vertebrobasilar insufficiency. In these cases Doppler ultrasound or angiography will be useful.

• In cases of seizures, CT of the head may be required to exclude any underlying pathology.

Stroke

Transient ischaemic attacks (TIAs) may represent an early warning sign of impending stroke. Therefore arteriography (DSA) of the neck vessels and cerebral arteries is performed in cases of TIA.

Even though arteriography gives a more definite answer, ultrasound examination of the neck vessels (Duplex and colour Doppler studies) could be performed initially.

In all patients with stroke, CT should be the initial radiological examination. However, if MRI is available, it is preferred to CT as MRI is better at detecting early infarction (within a few hours of vascular occlusion). CT sometimes gives negative results within the first 24–48 hours.

EMERGENCIES IN THE NECK

Major emergencies are trauma, foreign bodies, and croup and laryngeal inflammation in children.

Trauma

Cervical spine injuries are common and can be life-threatening. They range from nerve root compression and paralysis to death. Therefore, X-ray or CT evaluation of the cervical spine is important in trauma.

Plain X-ray views

1. The first film to obtain is a ‘brow up—shoot through’ lateral view. (Patient in supine position; movement of neck should be avoided.) Film should be well penetrated. All the cervical vertebrae and possibly the upper thoracic vertebrae should be demonstrated. Demonstration of the lower cervical and upper thoracic spine may be difficult in most patients. Swimmer’s lateral projection or a lateral film with shoulder traction could be useful. Sometimes the patient’s condition may not permit this. Alternative ways to demonstrate this area are tomography in lateral projection or CT scan if available.

2. If no abnormality is seen in the first film, do an open-mouth AP view of ‘peg’ to exclude any fracture of the ‘peg’. In suspicious cases the rest of the views are done only after expert examination of the film: a radiologist should be consulted if available.

3. If no abnormality is seen in the above two views, do the rest of the views, i.e. AP and two obliques. Patients must move the neck themselves.

4. Lastly, if there are no neurological signs, a flexion and extension view (functional view) could be done. Do not force the neck—the patient must move the neck. In suspicious cases the oblique and functional views should be done under the supervision of the attending doctor.

5. If no abnormality is seen in the above and the symptoms are still suspicious of fracture, tomography of selected areas could be done. If CT is available, it will be useful to show the vertebrae in transverse plane and to detect haematomas. If a helical or multiple-slice scanner is available, high-resolution images could be obtained in sagittal and coronal planes as well as 3D images.

Clues for interpretation of X-rays

1. For proper interpretation one should be familiar with the normal appearance of the vertebrae, facetal joints, disc spaces and the soft tissues around the spine.

2. Lateral and peg views should be inspected first.

3. Look for fracture lines or deformities in each vertebral body, neural arch and the facets. Look for dislocation or subluxation of facetal joints and any malalignment of vertebrae.

4. Loss of lordosis and scoliosis may indicate bony injury or soft tissue injury.

5. If the disc is damaged the space may be narrow

6. Soft tissues anterior to the spine (prevertebral soft tissue) should be inspected for swelling (haematomas). Normal AP distance of the prevertebral soft tissue in the retropharyngeal region (at the anteroinferior angle of C2) is about 6–7 mm in adults and children. Retrotracheal soft tissue at the level of the anteroinferior angle of C6 is about 14–15 mm in children and about 15–20 mm in adults (these measurements are upper limit of normal). Haematoma may be due to fracture or rupture of the anterior spinal ligament.

7. To identify upper cervical subluxation in the lateral view, draw a line along the anterior cortical margin of the spinous processes from C1 to C3 (posterior cervical line). If there is more than 2 mm displacement, it is diagnostic. This is usually seen in odontoid fracture or Hangman’s fracture.

Note: In children slight anterior subluxation of the body of C2 on C3, especially in the flexion view, is normal. In these cases note the posterior cervical line, which will be normal.

8. Look for common fractures. Fractures are common at the C1–C2 articulation, ‘peg’, and from C5 to C7.

9. Pitfalls: In the AP view of the peg, watch for superimposed shadow of an incisor tooth which will look like a fracture. Also look for a separate ossification centre of the peg. (In some cases tomography of the peg may be needed to identify the fracture.)

10. CT can be performed to determine the state of soft tissue structures around the spine.

11. It is also useful in cases of suspected instability at the fracture and also to identify suspected bony fragments within the vertebral canal.

12. CT (in bone windows) will demonstrate the neural arches and facetal joints. This will be useful to identify fractures or dislocation at the joints. Modern CT scanners can image the spine in various anatomical planes.

13. MRI is more sensitive than CT in demonstrating the spinal cord.

Classification of cervical spine injury

Cervical spine injuries can be classified according to the type of injury—flexion injury or extension injury. However, in many instances the patient is unconscious or cannot describe the injury. As far as the treatment is concerned, it is important to decide whether the fracture is stable or unstable. The X-ray findings are useful in making this decision.

Flexion injury

The various kinds of flexion injury are described below in order of severity.

Hyperflexion sprain. Partial damage to posterior ligaments including interspinous ligaments. Flexion lateral view may demonstrate widening or fanning of the space between adjacent spinous processes.

Unilateral or bilateral facetal dislocation.

• In lateral view, look for anterior displacement of one vertebral body on the other by less than 50%.

• In AP view look for malalignment of spinous processes (especially in unilateral dislocation). Facets may be locked, i.e. inferior articular facet of the vertebra above is locked in front of the superior facet of the vertebra below.

Anterior wedging of vertebral bodies or compression fractures. If the neural arches are not fractured this may be a stable fracture.

Comminuted fracture of vertebral body (‘teardrop’ fractures). In these fractures look for any fragments in the vertebral canal. These fragments could cause damage to the spinal cord. CT scan would be useful in these cases to identify any fragments in the canal.

Extension injury

The various kinds of extension injury are described below in order of severity.

Hyperextension sprain. This causes damage to the anterior longitudinal ligament. Due to hyperextension there may be protrusion or bulging of the disc posteriorly. There may also be some haematoma and swelling from the ligamentum flavum. The disc bulging and the swelling from the ligamentum flavum can cause compression on the spinal cord. In these cases the X-ray may be normal. CT scan or MRI would be useful in these patients.

• Sometimes lateral plain X-ray may show soft tissue swelling (haematoma) within prevertebral tissue.

• Extension injuries may be associated with fractures of the anterior angles of the vertebral bodies.

• Extension injuries may not be stable in extended positions of the neck but are stable in flexion.

Hangman’s fracture. Fracture of both pedicles of axis with displacement of the body of C2 anteriorly and posterior displacement of neural arch of C2. This is well seen in the lateral view.

Jefferson bursting fracture. This fracture is unusual and is caused mainly by vertical compression injury causing bilateral fractures of anterior and posterior arches of C1. In the open-mouth AP view there will be lateral displacement—both lateral masses of C1.

Fracture of peg. Look for fracture line (not to be confused with superimposed shadows and separate ossification centres). Also look for alignment in lateral view—posterior cervical line.

Stable fractures

• Unilateral fracture of lamina pedicle or lateral mass

• Unilateral facetal fracture or dislocation

• Wedge fracture

• Burst fracture—disc forced into fractured end plates of body

• Fracture of spinous process

Unstable fractures

• Bilateral fracture of lamina

• Bilateral dislocation of facets

• Comminuted fracture body (any fracture dislocation)

• Hangman’s fracture

• Peg fracture

Foreign body in neck—pharynx and upper oesophagus

Most swallowed foreign bodies lodge at the level of cricopharyngeal muscle or in the upper oesophagus. Commonest foreign bodies are fish bone, meat or chicken bone, large pieces of meat and coins.

Lateral film of the neck is the most useful view. Film of soft tissue exposure may be necessary to identify faintly calcified bones. Radio-opaque materials are fairly easy to detect. Superimposition of calcified hyoid, thyroid, cricoid and laryngeal cartilages will be a problem. However, an understanding of their normal expected anatomical position will help to distinguish a foreign body. Pattern of calcification of cartilages (irregular) will also help. Swallowed bone may have a linear cortex. In difficult cases a barium swallow may help to identify the foreign body. Swallowing cottonwool soaked in barium (usually under fluoroscopic control) will occasionally help. This may get caught on the foreign body.

CT is also useful to locate smaller foreign bodies not shown by X-ray.

Epiglottitis and croup

Young children may develop severe acute inflammation of the epiglottis and larynx. In most cases where the condition is severe, radiological examination is postponed until the patient’s condition is stable.

A lateral view of the neck (soft tissue exposure) is the best view. Rarely, a single midline tomogram in lateral projection may be necessary.

• A swollen epiglottis will look like a thumb—the swollen aryepiglottis may also be seen.

• In croup usually the subglottic region from the vocal cord to the level of the inferior border of the thyroid cartilage shows mucosal swelling which causes narrowing of the airway. Vocal cords will also be affected. The need for radiology is debatable. However, if the patient’s condition permits, it will be useful to perform an AP and lateral view of the neck. Swollen vocal cords, obliteration of laryngeal ventricles and narrowing of the subglottic airway by swelling can be easily seen.

Helical CT scan of larynx and trachea with sagittal and coronal reconstruction would be useful if clinically reasonable.

EMERGENCIES IN THORACIC AND LUMBAR SPINE

Injury and acute disc prolapse or rupture

Views

• If the patient is immobilised, a ‘shoot through’ lateral view is initially performed.

• Lateral film of the thoracic spine is obtained while the patient is breathing. This is to ‘blur’ the superimposed ribs.

• Swimmer’s lateral or lateral tomography may be required for demonstration of upper 3/4 thoracic vertebrae.

• AP view is fairly easy to obtain.

• In cases of suspected ligamentous rupture, flexion and extension views in lateral projection are obtained.

• In lumbar spine, if the condition of the patient permits, oblique views are also performed. These demonstrate the laminae and facetal joints well.

• CT scan is useful to demonstrate the integrity of disc and bony elements. They are also useful to detect facetal dislocation, subluxation and any posterior dislodgment of bony fragments into the vertebral canal. It is also useful to demonstrate the soft tissues around the spine.

Unstable injury

• Transverse fractures through vertebral bodies and neural arches

• Fracture dislocation

• Rupture of ligaments (in the lateral view, the interspinous distance is wide, especially in flexion view)

Disc prolapse

Plain X-ray may show disc narrowing—this is not always seen. Therefore, if symptoms persist, CT scan of the disc would be useful to show disc prolapse.

High resolution scanners can differentiate disc material, nerve roots etc.

MRI scan is superior in demonstrating spinal cord, nerve roots, discs, ligaments and bone oedema from trauma.

CHEST EMERGENCIES

Routine views

• PA and lateral—obtained in erect position, both in full inspiration.

• If patient cannot stand, erect PA or AP and lateral in sitting position (in full inspiration) are obtained.

• If patient cannot sit or stand, supine AP is obtained. This is unsatisfactory because the patient may not be able to take a full inspiration and the diaphragm appears elevated. It also causes magnification, especially of the mediastinum. mobile views are AP.

Additional views

• Oblique views for ribs.

• Apical lordotic view to demonstrate lung apices (to get the superimposed clavicle out of the way).

• Inspiration and expiration films to demonstrate pneumothorax.

• Penetrated film to see mediastinum or lung bases.

• Lateral decubitus (patient lying down on one side—right or left, and film obtained with horizontal beam). This demonstrates mobility of pleural fluid on the dependent side.

Interpretation

There are two ways to interpret:

1. An experienced person will use a problem-oriented approach, depending on the clinical information.

2. An inexperienced person should look at a chest film in a routine, systematic manner.

a. Start looking at the mediastinal shadows. Cast your eyes along the:

• anterior mediastinal structures—thymus (enlargement in infants; tumour in adults), thyroid (retrosternal), lymph nodes (if enlarged)

• middle mediastinum—heart, aortic arch and branches, pulmonary artery, superior and inferior vena cavae.

• posterior mediastinal structures—trachea, bronchi, oesophagus, descending thoracic aorta, lymph nodes, (abnormal) neural tissues, look for hiatus hernia, spine.

b. Look at the hilar shadows.

c. Look at the lung parenchyma and other lung markings (pulmonary vasculature and bronchi).

d. Look at the pleura.

e. Look at the chest wall (including ribs).

f. Cast your eyes along the periphery of the film, e.g. the shoulder, under the diaphragm.

Trauma

Rib fractures

First, second and third rib fractures are seen only in severe trauma. Commonest are from fourth to ninth ribs. Flail chest is seen when three or more ribs are fractured at two points. These are usually seen from the fourth to eighth ribs. A common site of fracture is usually the lateral angle. Because of this, oblique views are essential. Rib fractures can cause pneumothorax and haemothorax. Fracture of tenth, eleventh and twelfth ribs can cause damage to the liver, spleen and kidneys.

Lung contusion

Appears as an area of consolidation. It is not always associated with rib fracture. It may not appear immediately (sometimes a day later) and begins to resolve 2–3 days after injury. It usually resolves completely in about 10–15 days.

Rupture of thoracic aorta

Seen in motor vehicle accidents—usually seen near the ligamentum arteriosum. In this region the aorta is relatively fixed. Sudden deceleration and compression injury causes laceration at this relatively fixed portion of the aorta.

In chest X-rays there will be evidence of superior mediastinal widening, shift of the trachea to the right with obscuring of the aortic arch, and there may be haemothorax on the left. CT scan and aortography are the other radiological investigations in these patients.

Rupture of trachea or bronchus

Common findings in chest X-rays are pneumomediastinum, pneumothorax and surgical emphysema. Occlusion of fractured bronchus can cause collapse of the corresponding lung, lobe or segment.

Rupture of diaphragm

Seen in direct blunt trauma and penetrating injury. Sometimes not diagnosed immediately. In an X-ray the outline of the dome may not be normal. It may be elevated; there may be haemothorax or segmental lung collapse. On the left side, the bowel may herniate into the thorax and, on the right side, the liver may herniate. Rupture in blunt trauma is common on the left side.

CT in chest trauma. If a helical or multislice scanner is available, it will be useful for better demonstration of chest in sagittal and coronal planes as well as in 3D format. CT angiogram could be performed to demonstrate aorta and great vessels.

Breathlessness

Asthma and acute-on-chronic airflow limitation (CAL)

In CAL, chest X-ray shows overinflated lung, flattened domes of diaphragm, widened retrosternal space, hyper-radiolucency, a barrel-shaped chest, a relatively small and elongated heart shadow, prominent main pulmonary arteries and pruning of peripheral pulmonary arteries (associated pulmonary artery hypertension), and thickened bronchial walls (end-on ring shadows and tramline shadows).

In asthma, overinflation of lungs and bronchial wall thickenings may be seen. Other findings may include atelectasis caused by mucous plugging or consolidation.

High resolution CT of 1-mm thickness is useful for investigation of CAL, especially to identify bronchiectasis, emphysematous bullae and interstitial fibrosis.

Radiological appearance in acute heart failure

Heart failure may be divided into left and right heart failure.

X-ray findings in left heart failure

• Distension of upper lobe veins (normally the upper lobe veins are smaller in calibre than the lower lobe veins).

• Interstitial pulmonary oedema. In the early stages the oedema forms around the hilar region, causing blurring of the hilar markings. Septal lines are due to accumulation of fluid along the lymphatics: ‘A’ lines are long and radiate from the hilar region to the periphery; ‘B’ lines are short and are seen in the region of the costophrenic angles.

• Alveolar pulmonary oedema. This is due to filling of the alveolar spaces with exudates. It is seen as haziness radiating from the hilar region and produces a butterfly-wing appearance. In the severe form, the alveolar oedema produces a patchy or cottonwool appearance.

X-ray appearances in right ventricular failure

• Prominence of superior vena cava (SVC) and azygous vein.

• Pleural effusion. In heart failure often more fluid is seen on the right side. In the early stages, pleural effusions are seen in the costophrenic angles as a homogeneous density demonstrating a ‘meniscus sign’. The meniscus sign is seen in the erect position. The fluid in the base changes to a haziness in the supine films. This indicates mobility of the fluid. Small fluid collections are first detected in the lateral view—in the posterior costophrenic angles. In the average chest, the posterior costophrenic angle can accumulate about 150–200 mL of fluid without being seen in the PA view. In the early stages fluid can also accumulate in the fissures between the lobes. This appears as thick oblique fissures.

Pleural effusion

Pleural effusion may have various other causes, e.g. tumour. Large pleural effusions can obscure the underlying cause. If the fluid is mobile a lateral decubitus view would be useful to demonstrate the lung bases. (Alternatively, CT scan could be performed to identify any mass in the lung base.)

Chest pain

Only the causes where radiology plays a part are included in this section.

Myocardial infarction

Chest X-rays are performed to look at the heart size and shape, and also to look for evidence of heart failure. Upper limit of normal cardiothoracic ratio (CTR) is 50% (CTR = transverse diameter of the heart divided by transverse diameter of the chest).

Pericardial effusion

Chest X-ray is also useful to identify pericardial effusion. In the supine position the heart appears globular in shape and in the erect position it produces a ‘tent shape’. The angle between the right atrium and the right diaphragm is lost. On fluoroscopic examination poor pulsation may be demonstrated in cases of pericardial effusion. (For proper demonstration of pericardial effusion, echocardiography or CT scan is more useful.)

Pulmonary embolism

• Within 24–48 hours there may not be any radiological change. However, if large pulmonary arterial branches are blocked, there may be a cut-off sign (i.e. abrupt ending of an arterial branch).

• Raised hemidiaphragm—on the side of infarction.

• After about 24–48 hours an almost triangular density with its base towards the periphery of the chest may appear.

• There may be a small associated pleural effusion.

• Sometimes the main pulmonary artery on the affected side may enlarge.

• Later in the process, in the area of infarction there may be atelectasis or scar formation.

• Nuclear isotope ventilation perfusion scans are performed for diagnosis, but sometimes this is not confirmatory. However, a normal chest X-ray and abnormal isotope scan could be indicative of pulmonary embolism.

• Pulmonary arteriography is the best means of establishing or excluding pulmonary embolism. This is rarely performed because of adverse reactions and the cost. However, recently, with the introduction of multislice scanners, CT pulmonary angiograms are performed. This would be sensitive to detect emboli in pulmonary arteries up to about the fourth or fifth level of branching.

• Doppler study or venogram of the lower limb veins may show the origin of the clot.

Dissecting aneurysm

• In the PA view there may be widening of the superior mediastinum with the ascending aorta bulging to the right.

• The lateral view may show bulging of the ascending aorta anteriorly. A long-standing aneurysm of the ascending aorta can cause erosion of the posterior aspect of the sternum.

• Leak from the aneurysm into the pericardium causes a large globular heart.

• When the dissection extends into the arch and descending thoracic aorta, the diameter widens towards the left. Sometimes a double aortic knuckle shadow can be seen. Some aneurysms leak into the pleural cavity and appear as a pleural effusion. In some patients uniform haziness can be seen in the left lung, due to blood spread along the bronchi and pulmonary arterial planes.

• CT scan can demonstrate a dissecting aneurysm and its extent.

• In order to demonstrate the exact site of rupture some surgeons prefer an aortogram.

Pneumothorax

• Usually PA films in expiratory and inspiratory phases are obtained in the erect position.

• A large pneumothorax is well seen in a normal PA film. A small pneumothorax is usually demonstrated in the expiratory film.

• In order to identify the pneumothorax, follow the lung markings towards the periphery. The markings stop well short of the chest wall. A white visceral pleural line can be seen at this level.

• Do not confuse the accompanying shadow caused by intercostal muscles along the ribs for visceral pleura.

• Look for an associated pneumomediastinum (air can leak from bronchi in asthmatics) and subcutaneous emphysema along the chest wall and neck.

Haemoptysis

Pulmonary infarction

See ‘Pulmonary embolism’, above.

Tumour

A mass, either solitary or multiple, can be seen in the hilar region or elsewhere in the lung. If there is any doubt about the diagnosis, CT would be useful. CT may also demonstrate any enlarged lymph nodes.

Other accidents

Drowning

Pulmonary oedema is seen in cases of near-drowning in both fresh and sea water. Pulmonary oedema may not develop for up to 2 days. Therefore, negative findings in immediate CXRs do not exclude later development of oedema.

Inhalation of toxic gases/smoke

In toxic gas inhalation, pulmonary oedema develops quickly—in about 4–24 hours.

In smoke inhalation, the oedema may not develop for up to 2–4 days.

In CXRs oedema appears as patchy infiltrates. There may be segmental atelectasis. These changes usually resolve faster.

Ingestion of hydrocarbons (e.g. petroleum)

May develop patchy pneumonic consolidation in lung bases, usually within 1–2 hours. Severity depends on the amount ingested. Takes up to 2 weeks to resolve.

Foreign body

Radio-opaque foreign bodies in bronchi are easily seen in CXRs. Foreign bodies like nuts, seeds and plastics may be difficult to see.

Radiological signs are usually indirect, i.e. signs of obstruction.

In children obstruction is usually ball-valve type, causing air trapping.

PA films are obtained in inspiration and expiration. The inspiratory film may be normal but, in the expiratory film, there will be hyperradiolucency and signs of increased volume on the affected side (flat diaphragm and shift of mediastinum to the opposite side).

Chest screening is very useful to detect air trapping. Normal lungs show normal density and change of volume during breathing in comparison with the affected lung, which shows fixed volume and density.

In adults, obstruction usually causes collapse of the lung or lobes.

RADIOLOGY IN ABDOMINAL EMERGENCIES

Almost all modalities of imaging (plain X-ray, contrast study, CT and ultrasound) are used in abdominal emergencies. Of these, plain X-rays are the most commonly used.

Views

• Routine views—AP in supine and erect position.

• Additional views—lateral decubitus in patients who cannot stand up, to look for fluid levels or free peritoneal gas.

• In some cases an erect chest X-ray is also performed to look for gas under the diaphragm or any pleural fluid in the lung bases.

Interpretation

An inexperienced person finds it difficult to interpret an abdominal X-ray due to superimposition of various organs. This difficulty can be greatly reduced if the film is looked at in a routine manner, for example as follows.

1. Look at the bowel shadows—these are easily identifiable because of gas and faeces. Stomach, small and large bowel can be differentiated by their anatomical site and their pattern of mucosal folds and wall—valvulae conniventes in jejunal loops and haustral pattern in large bowel. Note any fluid levels and bowel dilation.

2. Look at the four major organs: liver, spleen, kidneys and bladder, for their size, position, outline and density.

3. Look at the psoas shadows and fat planes in the flank and along the pelvic walls.

4. Look for radio-opaque stones (gall and renal) and abnormal calcification (pancreatic, hepatic and abdominal aortic).

5. Look above and below the diaphragm for abnormal gas, fluid or air collections.

6. Any abnormal mass causing displacement of adjacent structures.

7. Look at the bony elements (lower ribs, lumbar spine and pelvis).

Acute abdomen

In the plain X-ray of the abdomen the main aim is to identify obstruction, perforation or ileus in the bowel shadows.

Radiological signs of bowel obstruction

There may be gaseous distension of the bowel up to the site of obstruction. In complete or almost complete obstruction, very little gas is seen in the bowel distal to the obstruction.

Multiple fluid levels are seen in erect films.

A step-ladder pattern of air fluid levels is seen in small bowel obstruction. In large bowel obstruction fluid levels are seen around the periphery. In complete obstruction of large bowel there may be fluid levels in the small bowel as well.

In gastric outlet or duodenal obstruction, a distended stomach with a large air-fluid level is seen.

Volvulus. In sigmoid volvulus look for a dilated loop of bowel in the form of an inverted U in the left hypochondrium. In caecal volvulus the base of the dilated caecum usually points to the right iliac fossa. The volvulus can be confirmed by performing a limited dilute barium or gastrograffin enema.

Intussusception. A sharp cut-off of bowel gas pattern is seen. Common intussusception is at the ileocaecal junction. There may be dilated small bowel with multiple fluid levels. Limited barium enema examination may show a coil-spring appearance. In children the barium enema can be therapeutic and in most cases will be able to reduce the intussusception.

Radiological signs of ileus

Generalised. Slight to moderate gaseous distension of small and large bowel with multiple small fluid levels can be seen. Generalised ileus is usually seen in postoperative patients, peritonitis and retroperitoneal conditions.

Localised. The bowel loops in close proximity to an inflammatory area may show slight dilation and some fluid levels. One or two loops may be involved. This is called sentinel loop, e.g. jejunal loops and transverse colon are involved in pancreatitis and acute deep gastric ulcers. Terminal ileum is involved in conditions such as appendicitis. Hepatic flexure and some small bowel in the right hypochondrium may show fluid levels in cholecystitis. In renal colic there may be sentinel loops on the affected side.

Radiological signs in perforation

Free peritoneal gas is usually seen under the diaphragm in the erect position. In a lateral decubitus film, free gas may be seen along the flank. The free gas is sometimes seen only after 24 hours.

Loculated peritoneal gas, e.g. in perforation of a duodenal ulcer there may be loculated gas along the inferior liver margin. If there is a collection of gas in the lesser sac, in the plain X-ray there may be a double gas shadow projected over the fundus of the stomach.

Retroperitoneal gas from perforation of the retroperitoneal portion of the large bowel.

In order to identify the site of perforation, gastrograffin contrast may be used (extravasated contrast is absorbed by the bloodstream and excreted by the kidney). In cases of suspected upper GIT perforation the contrast may be given orally. In cases of colonic perforation it may be given rectally. Not all perforations can be demonstrated by this technique.

GIT bleeding and ischaemia

1. It is difficult to demonstrate bleeding points by barium study. However, this examination may be useful in demonstrating the presence of oesophageal varices, peptic ulcers, diverticula or tumours.

2. Highly selective coeliac, superior or inferior mesenteric arteriograms may demonstrate bleeding points. Angiography is also useful to demonstrate occluded arteries causing mesenteric ischaemia. A bleeding rate of 1 mL/min is usually required.

Pancreatitis

1. Plain X-rays may show only indirect evidence such as sentinel loops or calcification in the region of the pancreas.

2. Barium meal may show a widened loop of duodenum due to enlargement of the pancreas.

3. Ultrasound is able to demonstrate the size and texture of the pancreas. It may also demonstrate oedematous change or any pseudocyst formation. However, sometimes it is difficult to demonstrate the pancreas by ultrasound due to obesity of the patient and presence of excessive gas.

4. A CT scan is the ideal examination to demonstrate the pancreas, especially in the obese patient. The sensitivity is such that it can demonstrate inflammatory changes, a small amount of calcification, a mass, a pseudocyst and also the state of surrounding tissues. It is also useful for follow-up study.

5. Skinny needle biopsy under CT or ultrasound control has greatly improved the diagnostic ability.

6. Endoscopic retrograde cholangiopancreatography (ERCP) demonstrates the state of the pancreatic ducts.

Cholecystitis

1. Plain X-ray may demonstrate radio-opaque gallstones and sometimes demonstrates sentinel loops (localised ileus).

2. Ultrasound is the diagnostic tool of choice. It can demonstrate stones, thickness of the wall of the gall bladder and any oedematous change. It can also demonstrate the size of the bile ducts or any stones in the duct. However, demonstration of the lower common bile duct may be difficult.

3. In a post-cholecystectomy patient with symptoms of biliary colic, CT cholangiography could be useful to exclude any retained stones in the bile duct, strictures etc.

Aortic aneurysm

The majority of aneurysms are asymptomatic. However, these patients usually present to emergency departments when there is a rupture or leak. Severe rupture is fatal. If a slow leak is suspected radiological investigation is carried out.

1. Plain X-ray (AP and lateral) shows a soft tissue mass, especially in the posterior abdominal wall. This is usually on the left side of the lumbar spine and is better seen in the lateral view. 50% of aortic aneurysms may have some calcification in the wall of the artery, which is very useful for identification of an aneurysm.

2. Ultrasound or CT scans are non-invasive, easier and quicker methods of diagnosing aneurysms. A CT scan is superior to ultrasound. It can demonstrate the site and length of the aneurysm. It can also demonstrate the diameter of the aneurysm and the presence of clot. CT is the study of choice in many patients, especially in obese patients. With the modern scanners CT aortography gives excellent results which also show the relationship of renal arteries to the neck of the aneurysm. This is useful for surgical planning.

3. Digital angiography is still used by surgeons to demonstrate the aneurysm and the branches of the abdominal aorta. However, this would show only the lumen and not the actual diameter of the aneurysm or the intraluminal clot.

Renal colic

1. Plain X-rays may show radio-opaque calculi and may demonstrate localised ileus. CT is commonly used.

2. An IVP may demonstrate: obstruction (partial or complete), radiolucent stones, state of kidneys and collecting system.

3. If there is a non-functioning kidney and there are no radio-opaque stones, retrograde pyelography would be warranted.

4. Ultrasound may not detect all the stones in the kidney. It would demonstrate hydronephrosis in the case of ureteric obstruction.

Haematuria

Severe cases of haematuria may present to the emergency department.

1. An IVP may reveal tumour in the kidneys, ureters or bladder.

2. CT is used to demonstrate renal and bladder tumours as well as any extension of the tumour.

3. Ultrasound can be used if CT scan is not available or if the patient is allergic to contrast medium.

Abdominal trauma

Blunt trauma is more common. Radiological investigations depend on the patient’s condition. The investigations include: plain abdominal X-ray, IVP, arteriograms, ultrasound and CT.

Renal contusion and laceration

1. Plain X-ray may show: loss of renal outline, loss of psoas shadow, scoliosis with concavity towards the side of injury, localised ileus on the side of injury, fracture of lower ribs, vertebrae (including transverse processes) and pelvic bones.

2. IVP may show: non-functioning kidney or delayed nephrogram; extravasation of contrast from ruptured kidney, ureter or bladder; clots, seen as filling defects within the pelvicalyceal system, ureter or bladder.

3. Arteriogram. If an IVP shows non-function and renal laceration is suspected, an emergency renal arteriogram is performed to assess the state of the renal arteries. (Renal vessel repair should be performed within a few hours.)

4. Ultrasound and CT, if available, are useful. They can demonstrate rupture, contusion and haematoma. CT is superior to ultrasound.

Renal vein thrombosis

1. An IVP shows an enlarged kidney, prolonged nephrographic phase and reduced excretion.

2. Ultrasound with Doppler may assist but helical CT in rapid sequential imaging after contrast injection has about 90% success in detecting renal vein thrombosis. Other findings include prolonged parenchymal enhancement and delayed excretion.

3. MR imaging is also an excellent method of demonstrating renal vein thrombosis.

Bladder trauma

• May be contusion or rupture (either intraperitoneal or extraperitoneal).

• In these cases a cystogram will be useful to demonstrate the site of the rupture.

Urethral rupture

• Usually seen in males.

• Site of rupture can be demonstrated by a retrograde urethrogram.

Spleen and liver injury

Splenic injury is more common than liver. Sometimes the plain X-ray signs may be non-specific. If there are some signs, further investigations may be necessary to confirm the diagnosis. Radiological signs depend on whether there is capsular damage or not.

Plain X-ray of abdomen and chest

• Elevation of left diaphragm in splenic injury and right in liver injury.

• Left or right effusion in spleen or liver injury, respectively.

• There may be atelectasis at the left or right base.

• There may be fracture of the lower ribs.

• Blurred liver or splenic outline.

• In splenic haematoma, the stomach may be displaced medially and the splenic flexure of colon downwards. In liver injury, the hepatic flexure may be displaced.

• In cases of rupture there may be loss of flank stripes, separation of walls of bowel loops by peritoneal fluid, obliteration of splenic or hepatic outline and general haziness of abdomen.

Ultrasound

• May show fluid (haemoperitoneum). Blood (fluid) is seen in the lateral gutters and pelvic recesses.

• May show contused areas of the organ.

CT

This is the best examination. If CT is not available, ultrasound is performed. CT can demonstrate intracapsular haematomas, laceration and haemoperitoneum.

Angiogram

Selective arteriograms would be useful to study the state of the arteries and also to demonstrate rupture.

Hollow viscus

Rupture or perforation rarely occurs with blunt trauma, but may be seen in penetrating injury. When it occurs, there may be gas collections in the peritoneal cavity. Sometimes retroperitoneal and mediastinal gas can be seen. This can be detected in plain abdominal and chest X-rays. Gastrograffin study may be useful to demonstrate the site of perforation but this is not usually required.

CT is useful to identify free peritoneal air and also any other injury to the adjacent organs.

SOME OBSTETRIC EMERGENCIES

Bleeding in pregnancy

This can be due to: abortion—threatened, incomplete, complete or missed; ectopic pregnancy; placenta praevia; hydatidiform mole; placental separation (abruptio placentae).

All the above causes can be assessed by ultrasound (using transabdominal and transvaginal probes), which is the examination of choice. The fetal viability can also be assessed.

Intrauterine fetal death

This can be confirmed by ultrasound.

Intrauterine trauma

Ultrasound is also used to assess the fetus after abdominal trauma.

FRACTURES OF PELVIS AND LIMBS

Most fractures are easy to recognise on X-rays. However, some are difficult, e.g. hairline undisplaced fractures. In suspicious cases repeat examination by CT in 10–14 days could be performed (e.g. scaphoid fracture).

In about 10–14 days some bone absorption occurs adjacent to the fracture line, which makes the fracture visible. In addition periosteal reaction (callus) may begin to form.

Undisplaced fractures through the epiphysial plates are also difficult to recognise. These fractures will also demonstrate bone resorption and callus in about 2 weeks time.

1. In minor fractures, look at the cortical bone for any discontinuity or dents. Also look for any irregularity in the trabecular pattern.

2. In some areas, e.g. femoral neck and scaphoid, tomogram, CT or nuclear scan may be required to demonstrate an undisplaced crack fracture.

3. If suspicious areas are encountered, oblique views should be done (thin fracture lines are visible only when the X-rays pass perpendicular to the fracture line).

4. In oblique fractures of the metaphysis, always look at the depth of the epiphyseal plates, as the fracture might extend along the plate causing widening of the growth plate.

5. In the forearm and leg, if one of the bones is shortened or dislocated, usually the other bone will have a fracture or dislocation. Therefore, in the distal limbs have a good look at the entire length of the bones, especially the proximal and distal ends and the adjacent joints.

6. In young patients look at the location of ossification centres around the joints to identify any dislocation of the epiphysis, e.g. elbow. If in doubt consult a radiologist or do a comparative view of the opposite joint.

7. In the wrist, do not miss dislocation of carpal bones, e.g. lunate. Try to identify the position of carpal bones in the lateral view.

8. In the joints, look for indirect signs of haemarthrosis, i.e. displacement of adjacent fat pad. If there is haemarthrosis, always look hard to identify any hairline fracture or epiphyseal displacement. If in doubt, X-ray again in 10–14 days.

9. Look for soft tissue swelling in the X-ray (sometimes the X-ray has to be viewed under bright light). If found, concentrate on this area to identify any fracture.

10. The pelvis is like a ring—in compression injuries it might break in two or more places. Fracture of pelvic bones may be associated with dislocation or subluxation at the sacroiliac joints or pubic symphysis.

RADIATION ISSUES

Ionising radiation can be from natural or artificial sources.

Natural radiation. Heat and light are types of radiation that we can feel or see, but there are other kinds of radiation that human senses cannot detect. We constantly receive invisible radiation from the sky (cosmic radiation), earth’s crust, air and even food and drinks.

Artificial radiation. Are from X-rays, nuclear industries and weapons. Unlike natural radiation, these are fully controllable.

Measuring radiation. The radiation dose received by people (whole body) is measured in Gray (Gy). The adverse effective dose (absorbed dose that may cause biological effects or cancer) is measured in Sievert (Sv).

Radiation exposure and limits

• Exposure from natural radiation is about 1.5 mSv per year.

• The International Commission on Radiological Protection (ICRP) has set the following limits:

a. For radiation workers, 20 mSv per year.

b. For general public, 1 mSv per year (over and above the natural radiation).

c. For patients, considering the diagnostic benefits over radiation risk, a definite limit for dose from radiological procedures has not been set. However, scientists have calculated the possible radiation dose associated with some radiological investigations, as indicated in Table 4.1. (These figures are a guide only and may vary from patient to patient as they are highly dependent on the size of the patient and the exposure factors used. In CT, the dose also depends on the number of slices as well as the number of examinations, e.g. pre- and post-contrast studies. Thin slices produce a higher radiation dose due to more overlap between the slices.)

Table 4.1 Possible effective doses of radiation associated with some radiological investigations

Examination	Possible effective dose (mSv)
Dental OPG	0.01
Foot/hand (1 film)	0.02
Skull (2 films)	0.04
Chest (2 films)	0.06–0.1
Mammogram (4 films)	0.13
Cervical spine (6 films)	0.3
Abdomen/pelvis (1 film)	0.7
Thoracic spine (2 films)	1.4
Lumbar spine (5 films)	1.8
IVP (6 films)	2.5
Ba meal (11 films fluoro)	2.5–3.8
Ba enema (10 films)	6–7
Coronary angiogram	1.6–5
CT head	2.5
CT chest	5–8
CT lumbar	5
CT abdomen	7–10
CT coro-angio (64-slice)	5–10
CT whole body	15
Lung scan (nuclear)	2–3
Bone scan	3–5
Sestamibi scan	13
Radiotherapy (6 weeks)	2000
Air travel (crew)	3.8/year
Air travel (passengers)	0.05/7 h
Computer/TV use	0.01/year

Ba, barium; CT, computerised tomography; IVP, intravenous pyelogram; OPG, orthopantomogram; TV, television

Summary

It is now known that, in diagnostic radiology, CT is a major contributor of radiation.

Referring doctors, radiologists and radiographers should be aware that CT is a high-dose procedure. At the same time, doctors and patients must be assured that CT is a highly beneficial X-ray and should not be feared when the benefit of the examination clearly outweighs the risk.

Doctors should order CT examination with caution, especially when ordering multiple examinations, CT with and without contrast and CT of the whole body.

Imaging professionals should make every effort to reduce radiation as low as reasonably achievable, while obtaining adequate diagnostic information in the image.

EDITOR’S COMMENTS

Although long, this chapter contains a wealth of practical information. Very few emergency patients escape diagnostic tests. Always, if there is any doubt, talk to the radiographers/radiologists about any study. Always arrange for follow-up of the formal report as emergency physicians are not radiologists. Even if the images and reconstructions look easy—you are not an expert and are simply giving the patients an impression.

RECOMMENDED READING

Dogra V.S., Bhatt S., editors. Emergency cross-sectional imaging. Radiologic Clinics of North America, May 2007;45(3):395-608.

Grainger R.G., Allison D.J. Grainger and Allison’s diagnostic radiology: a textbook of medical imaging, 4th edn. London: Churchill Livingstone; 2001.

Lau L.S., James P., Acton C.M., et al. Imaging guidelines, 4th edn. Sydney: Royal Australian and New Zealand College of Radiologists; 2001.

Mirvis S.E., Shanmuganathan K., editors. Emergency chest imaging. Radiologic Clinics of North America, March 2006;44(2):165-322.

Radiologic Clinics of North America. Advances in emergency radiology. Philadelphia: WB Saunders; September 1999. I: May 1999; II:

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