Investigative procedures

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CHAPTER 3 Investigative procedures

This chapter describes various investigative procedures commonly used in surgery. The procedures are described briefly, together with their indications and possible complications.

Conventional radiology

Radiographs penetrate differentially through tissues of the body, resulting in different exposure of the silver salts in the radiograph film. On a plain radiograph, gas and fat absorb few X-rays and consequently appear dark, while bone and calcified defects are poorly penetrated and appear white or radio-opaque.

• A plain radiograph is one where no contrast medium is administered to the patient, e.g. routine CXR.

• A contrast study involves administration of a contrast medium, which outlines or delineates the structure under study, e.g. barium in GI studies or iodinated benzoic acid derivatives in arteriography.

Plain films

Chest X-ray (CXR)

• Always check the name of the film and the right and left markers.

• Make sure the whole chest and diaphragm are clearly on the film. You may need to count the ribs to exclude a cervical rib.

• Check that the trachea is central.

• Check the mediastinal width.

• Check cardiothoracic ratio. Maximum width of heart divided by maximum ‘bony’ (rib-to-rib) diameter of chest should be <50% in normal adults.

• Check vascular pattern, e.g. reduced in recent pulmonary embolus, distension of upper lobe veins in pulmonary venous hypertension.

• Check lung fields, e.g. lobar collapse, pneumonic consolidation, bronchial carcinoma, pneumothorax.

• Check bony thoracic cage, e.g. fractures, secondary deposits, notching (coarctation of aorta).

• Check soft tissues, e.g. surgical emphysema, mastectomy.

• Check for free air under the diaphragm on erect chest X-ray.

Abdominal X-ray (AXR)

Check for the following:

• Dilated hollow viscus with or without air/fluid levels, e.g. small and large bowel obstruction

• Free intraperitoneal gas (check position in which film was taken, e.g. air under the diaphragm with perforated hollow viscus)

• Abnormal gas patterns, e.g. air in biliary tree with cholecystoduodenal fistula and gallstone ileus, bladder with colovesical fistula

• Calcified calculi – kidney, ureter, bladder, gallbladder; 10% of gallbladder stones are radio-opaque and 85% of renal stones are radio-opaque

• Foreign bodies, e.g. swallowed keys, etc.; trauma, e.g. bullet wounds; carelessness, e.g. swabs

• Abnormal calcification, e.g. arteriosclerotic vessels, pancreatic calcification seen with chronic pancreatitis (rarely carcinoma of the pancreas calcifies), uterine fibroids

• Retroperitoneum, e.g. absence of psoas shadows with retroperitoneal haemorrhage, retroperitoneal gas with retroperitoneal perforation of a viscus

• Bones, e.g. bony metastases, fractures, osteoarthritis (plain radiographs of the limbs and skulls are dealt with in Chapters 4, 17 and 18).

Contrast studies

Gastrointestinal tract

Biliary tree

Ultrasound

Ultrasound is now the first-line test for diagnosis of gallstones. It will also show a dilated biliary tree but will rarely pick up stones in the common bile duct due to the fact that the lower end of the common bile duct is likely to be obscured by gas from the transverse colon.

Magnetic resonance cholangiopancreatography (MRCP)

MRCP is now the initial imaging test of choice for biliary tree abnormalities, e.g. obstruction. It is a non-invasive method of imaging the biliary and pancreatic ducts. The technique does not require intravenous contrast material and uses specialized MRI sequences (i.e. heavily T2-weighted) to make the fluid in the ducts appear bright, while the surrounding organs and tissues are suppressed and appear dark. Heavily T2-weighted images give excellent anatomical detail. MRCP may be used as a screening examination in patients with a low or intermediate probability of choledocholithiasis, failed or incomplete ERCP, demonstrating variations in ductal anatomy, demonstrating postoperative anatomy (e.g. biliary-enteric anastomoses, sclerosing cholangitis), complications of chronic pancreatitis (e.g. ductal dilatation, strictures).

Endoscopic retrograde cholangiopancreatography (ERCP)

Contrast medium is injected retrogradely through the ampulla of Vater via a side-viewing duodenoscope. The technique is described more fully in the section on endoscopy, below.

Percutaneous transhepatic cholangiography (PTC)

This is used for diagnosis of obstructive jaundice. A long fine needle (22G Chiba) is passed percutaneously into the liver until a duct is pierced, witnessed by the aspiration of bile. Contrast is then injected to outline the biliary tree. Jaundiced patients may have clotting defects, e.g. abnormal prothrombin time (PT), and therefore a clotting screen should be carried out prior to this investigation. Vitamin K or fresh frozen plasma (FFP) should be administered i.v. if the PT is abnormal. Complications include haemorrhage, bile peritonitis, cholangitis and septicaemia. This technique however, has been largely superseded by MRCP.

Operative cholangiogram

At operation for cholecystectomy, the ducts should be checked for stones. Contrast is injected via a cannula inserted into the common bile duct via the stump of the cystic duct and radiographs are carried out or the image intensifier used. The diameter of the ducts, presence of filling defects and failure of contrast to pass into the duodenum are significant.

T-tube cholangiogram

If the common bile duct has been explored to exclude or remove stones, a latex T-tube is usually inserted. The horizontal bar of the T is in the duct and the vertical bar is brought out through the skin. Contrast is injected down the T-tube 8–10 days postoperatively to check for any residual stones, biliary leakage or stenosis prior to removal of the tube. There should be free flow of contrast medium into the duodenum and no filling defects.

Urinary tract

Intravenous urography (IVU)

Intravenous contrast is administered, which is excreted by the kidneys and eventually delineates the renal pelvis, ureters and bladder. A plain film is taken first so that any opacities seen can be compared with the films after contrast is given. It is useful for the diagnosis of obstruction, tumours, infection, congenital abnormalities and trauma. The only contraindication is allergy to the contrast medium. Caution must be exercised in diabetes mellitus, renal failure, multiple myeloma and cardiac failure.

Cystography

The patient is catheterized and the bladder filled with contrast medium. Bladder leaks, tumours, vesicoureteral reflux, and diverticulae can be diagnosed. A post-micturition film will diagnose residual urine. This technique has largely been superseded by ultrasonography.

Urethrography

A water soluble contrast medium is injected per urethram. Ruptures of the urethra, strictures or tumours may be seen.

Retrograde pyelography

This is carried out via cystoscopy by passing a ureteric catheter into each ureteric orifice. Clear views of the ureter and pelvicalyceal system are obtained. This test is used in patients with impaired renal function with poor concentration of contrast or if incomplete filling of the collecting structures is seen on IVU. The ureteric catheter may be left in situ to allow drainage of an obstructed system and for renal function tests to normalize prior to operative procedures.

Antegrade pyelography

The pelvicalyceal system of the kidney is punctured with a fine 22G needle. Contrast is injected and allows accurate assessment of the ureter and pelvicalyceal system, as well as assessing drainage.

Vascular system

Arteriography

Contrast medium is injected directly into the lumen of an artery. The catheter is usually introduced via the Seldinger wire technique into a suitable and easily accessible artery. The femoral artery at the groin is the usual portal of entry, although the brachial and axillary may be used. A careful history of allergies to contrast media needs to be ascertained. A clotting screen should be carried out prior to vascular radiology. With a catheter in situ, water soluble contrast medium is injected directly into the artery and images recorded in rapid sequences. Stenosis, thrombosis, embolism or aneurysm can be demonstrated. Complications include haemorrhage at the puncture site, dislodgement of atheromatous plaques, embolism, thrombosis.

Digital subtraction angiography (DSA)

DSA is now commonly used. Vascular images may be obtained with lower concentrations of contrast medium. The digital images are processed by subtracting unnecessary background, e.g. bones, and enhancing contrast between the tissues. Where high resolution is not needed, the contrast can be given intravenously into a fast-flowing vein, e.g. via a central line or into the femoral vein, and the arteries imaged when the contrast reaches them. These studies are known as intravenous digital subtraction angiography (IVDSA) or digital intravenous angiography (DIVA).

Venography

Contrast is injected into a superficial vein, i.e. a vein on the dorsum of the foot in the lower limb, and a tourniquet is placed around the ankle to direct the contrast into the deep veins. Lower limb venography is used to confirm or exclude DVT or to investigate deep venous insufficiency, i.e. it would demonstrate the site of incompetent perforating veins. This technique has been largely superseded by Doppler ultrasound.

Ultrasonography

Ultrasound works on the principle that the ultrasound emitted as a pulse from a transducer travels at constant velocity into tissue and is reflected by varying amounts from different tissue interfaces and travels back to the receiver at the same speed. The transducer is a piezoelectric crystal that both transmits and receives the ultrasound. The time required for the pulse to travel to the interface and back can be used to determine the depth of that interface. An image of the slice of the body is obtained by directing a narrow beam of high-energy sound waves into the body and recording the manner in which the sound is reflected by different structures. Sound is transmitted well through any fluid but poorly or not at all through air or bone. Returning echoes are electronically converted into a video image on a monitor, the resulting picture being a wedge-shaped slice of the area of interest.

Advantages

• It does not employ ionizing radiation and therefore produces no biological injury in the tissues.

• Any plane can be employed to examine the region of interest.

• It is less expensive than CT or MRI.

• It can be used at the bedside if the patient is too ill to be moved.

Dimensions of organs or lesions can be measured and the volume of the bladder and the left ventricle can also be assessed. Stones cause marked changes in acoustic impedance with almost complete reflection of ultrasound, showing echogenic foci with fan-shaped acoustic shadowing.

Very little preparation is necessary. For pelvic ultrasound the bladder should be full, providing a fluid-filled non-reflective medium for the ultrasound to reach the pelvic organs. The patient should be starved for biliary ultrasound to allow the gallbladder to fill with bile and to minimize gas shadows.

Ultrasound is non-invasive, painless, safe and cheap in comparison with CT and MRI, although it does not produce as sharp an image.

Ultrasound may be used for the following:

• Assessment of abdominal masses

• Distinguishing solid from cystic lesions, e.g. Renal carcinoma from a renal cyst

• Assessment of liver secondaries

• Detecting stones in the gallbladder or urinary bladder

• Measuring the size of lesions, e.g. The diameter of an abdominal aortic aneurysm or the width of a dilated bile duct

• Guided biopsy, e.g. biopsy of liver secondary or other mass

• Guided drainage, e.g. of localized collections of fluid or subphrenic or pelvis abscesses.

Disadvantages

Although limitations are few, lesions of the lower end of the common bile duct and head of the pancreas may be obscured by bowel gas. Bone completely reflects ultrasound and the method is therefore useless for studying organs encased by bone, e.g. brain and spinal cord.

Doppler ultrasound

Doppler ultrasound is used in vascular monitoring to study blood flow. A beam of ultrasound is directed at a vessel using a special probe. Ultrasound is reflected from the red cells, which cause a frequency shift related to their velocity. The shift can be heard as a noise or recorded as a waveform or sonogram. The faster the flow of red cells past the probe the higher the sound pitch. The Doppler probe is coupled to the skin with acoustic gel and angled towards the direction of arterial flow. Stenoses and occlusions cause diminished signals distal to a proximal obstruction.

Uses of Doppler ultrasound

Measurement of systolic pressure in peripheral arteries

A sphygmomanometer cuff is applied to occlude the artery. The probe is placed over the artery (dorsalis pedis, posterior tibial in the case of the lower limb), the tourniquet released and the pressure recorded when a signal is picked up. This pressure is compared with a normal brachial pressure, i.e. the ankle/brachial pressure index. The normal value is 1.0–1.2.

Other methods include analysis of waveforms to assess stenoses and occlusions.

Duplex scanning

This combines real-time B-mode imaging with a pulsed Doppler spectral analysis of flow velocity pattern. Blood vessels are identified by their characteristic B-mode images with prominent wall echoes and dark sonar-lucent lumina. Calcified plaques show bright echoes with acoustic shadowing behind. The pulsed Doppler beam is placed in the centre of the identified vessel and the spectral analysis allows classification of the degree of stenosis. Duplex scanning may be applied to analyse carotid disease, lower extremity arterial disease, intestinal arteries, renal arteries, and venous thromboses. Colour coding of flow direction may give further information.

Computerized tomography (CT)

CT produces cross-sectional images of the body, taking a series of transverse slices through the body. Sensitive X-ray detectors measure the X-ray attenuation through the patient in a large number of different directions, and a fast digital computer then uses the measurements to compute an image. These images are displayed on a screen and subsequently recorded on film. CT scanning may be used in conjunction with contrast medium enhancement. This may be given i.v. to show, for example, hepatic tumours, renal parenchyma and collecting system, aorta and IVC. It may enhance brain lesions when the blood–brain barrier is breached. Contrast may also be given by mouth or enema to outline the GI tract.

A new generation of spiral CT scanners is in use. The patient passes quickly through the scanner and a volume of data is obtained and analysed. Scanning is performed in a single breath-hold, decreasing motion artefact and allowing accurate timing of intravascular contrast enhancement. Images are superior to conventional CT. Specific applications include CT angiography and imaging of pulmonary emboli.

Advantages

CT has many uses but is the investigation of choice in head injuries. It is also useful for studying the retroperitoneum, pancreas, mediastinum, and lungs. It can be used for staging tumours, e.g. lymphomas, and can be used for guided biopsy.

CT angiography

Scan is performed simultaneously with high speed contrast media injection. It may be used for visualizing vessels anywhere in the body. Specific uses include:

• Examination of the pulmonary arteries in suspected pulmonary embolism

• Visualizing blood flow in the renal arteries in suspected renal artery stenosis

• Assessment of prospective kidney donors to visualize the arterial anatomy of the kidney

• Identification of aortic aneurysms

• Identification of aortic dissection

• Identification of deep vein thrombosis.

CT urography

Multidetector CT urography is a single examination that allows evaluation of potential urinary tract calculi, renal parenchymal masses and both benign and malignant urothelial lesions. Upper tract urothelial malignancies, including small lesions <5 mm in diameter can be detected with high sensitivity. It is useful in the assessment of haematuria and also trauma to the urinary tract,

Magnetic resonance imaging (MRI)

MRI is also known as nuclear magnetic resonance (NMR). MRI is based on the fact that certain atomic nuclei placed in a magnetic field and acted on by a suitable radiofrequency pulse undergo changes in their energy states, which result in the emission of measurable radio signals. The signals are then manipulated in a computer to provide sectional radiographic images. No ionizing radiation is involved. The procedure is non-invasive and can be carried out as an outpatient procedure. It is relatively time consuming, with extensive studies taking in excess of 1 h. MRI gives high soft tissue contrast and the body can be imaged in coronal, sagittal or transverse planes.

Advantages

The technique is particularly useful for studies of the CNS (lipids have a high hydrogen content), soft tissues of the pelvis, soft tissue tumours, and orthopaedic problems. Magnetic resonance angiography is also being increasingly used to assess the heart, renal arteries, and peripheral vessels. Magnetic resonance cholangiopancreatography (MRCP) can also be used to image the biliary tract.

Disadvantages

These include high cost, limited availability, low patient throughput, poor detail of bone and calcified tissues, and image artefacts from respiratory and cardiac movement and bowel peristalsis. The patient is in the ‘tube’ for long periods and it is difficult to monitor the ill patient. Contraindications include patients with cardiac pacemakers, and cranial surgery with metal clips.

Positron emission tomography (PET)

PET is an imaging technology which produces a 3-dimensional image or picture of functional processes within the body. The system detects a pair of gamma rays emitted by a positron-emitting radionuclide which is introduced into the body on a biologically active molecule, usually a sugar. The most common form of tracer used is FDG, a glucose analogue. The concentrations of tracer image then give tissue metabolic activity in terms of glucose intake. Images of the tracer concentration in 3-dimensional space within the body are then reconstructed by computer analysis. PET scans are increasingly read alongside CT scans, a combination giving both anatomic and metabolic information. Modern PET scanners are integrated with high-end multi-detector row CT scanner. PET scanning is advantageous in the management of malignancy, as it can often detect tumours before structural changes are seen on CT or MRI. Its extreme sensitivity makes it possible to detect cancers at their earliest stages and to outline their exact locations. It is useful in follow-up looking for cancer recurrence and monitoring the effectives of chemotherapy and other treatments. It is also useful in neurological diseases such as Alzheimer’s disease.

Advantages

Advantages of PET scanning include more detailed diagnostic information not available from other investigations such as CT or MRI, shorter time for definitive diagnosis, earlier detection of disease with the need for less invasive diagnostic procedures, precise staging of disease and improved monitoring of recurrences and more effective assessment of results of chemotherapy. Its ability to distinguish between benign and malignant tumours can result in the avoidance of unnecessary surgery.

Disadvantages

These include high cost and limited availability. The radioactive component used in PET scanning means that there is only a limited number of times a patient can undergo this procedure.

Mammography

A mammogram is a soft tissue radiograph of the breast. The tissues constituting the breast have a very low inherent contrast. Soft tissue mammography depends on the fact that tumour tissue is denser than breast tissue, particularly in the older patient (age 40+), where glandular tissue has been replaced by fat. The study is uncomfortable and somewhat undignified for the patient, since compression of the breast is essential in order to ‘spread’ the breast over the film cassette, immobilize the breast and reduce the radiation dose. A radiolucent, translucent compression plate is used. Two projections are usually taken – superoinferior and mediolateral. For screening programmes, two projections are used on the first attendance and one projection only on follow-up, unless the patient is symptomatic, and then two projections are used. Careful viewing of the film under high intensity light with magnification is essential. An infiltrating radio-opaque mass is suggestive of malignancy but fine-stippled calcification (like salt grains scattered on the film) strongly suggests the diagnosis. Mammography is used for the following:

• To assess palpable lumps

• To exclude lumps in other symptomatic patients, e.g. painful breasts

• Screening.

If a non-palpable lump is picked up on mammography, preoperative localization with wires is undertaken via mammography. The wire is left in the breast and acts as a guide to the surgeon to the location of the radiological abnormality. When the specimen of breast tissue has been removed it is submitted to radiography to confirm that the abnormal area has in fact been excised.

Radioisotope scanning

A suitable tracer agent is given intravenously or orally. The tracer agent is a substance taken up by the target tissue. This substance is combined with a radioactive label, the most commonly used being technetium-99m (^99mTc). A gamma camera is placed over the area of interest and simultaneously collects and counts the level of radioactivity. Dynamic imaging involves measuring the changing level of radioactivity over a period of time and storing this in a computer for later analysis. Renal blood flow measurement is an example of dynamic imaging. The following are applications of radioisotope scanning which are used in clinical practice.

Bone scans

Phosphates labelled with technetium are tracer agents. The tracer is taken up in areas of increased bone deposition and resorption. Uptake occurs in sites of infection, secondary tumour and acute arthritis. Indications for bone scanning include suspected bony secondaries, suspected osteomyelitis, abnormal biochemical profiles suggesting bone disease, e.g. raised calcium or alkaline phosphatase.

Renal scans

Two isotopes are commonly used, i.e. mercaptoacetyltriglycine (MAG3) and dimercaptosuccinic acid (DMSA). MAG3 is excreted dynamically through the kidney while DMSA remains in cortical tissue. They are useful in assessing asymmetrical renal function. Dynamic computer analysis allows assessment of renal blood flow as well as excretory activity. Practical applications include investigation of renal artery stenosis, and also differentiating acute tubular necrosis (ATN), renal ischaemia and obstruction in transplanted kidneys.

Lung scanning

This is important in the diagnosis of pulmonary embolism (PE), although it is being somewhat superseded by CT pulmonary angiography. Emboli obliterate areas of pulmonary arterial circulation but ventilation remains intact. A ventilation/perfusion scan (V/Q scan) is usually carried out. The perfusion scan involves the injection of radioactive particles small enough to temporarily block a small number of pulmonary capillaries. Technetium-labelled albumen microspheres are usually used. A ventilation scan using an inert radioactive gas, e.g. xenon, is performed simultaneously. The scans are compared. Areas that are ventilated and not perfused suggest embolism. Areas that are perfused but not ventilated suggest consolidation or collapse.

Scanning for infection

Ultrasonography or CT scanning will locate a collection of pus but in equivocal cases, white cell scanning may help. The patient is bled and the white cells separated. These are then labelled with indium-111 (¹¹¹In) and reinjected. The body is then scanned and areas of interest noted. The test is useful in patients with pyrexia of unknown origin or septicaemia, where other methods have failed to locate an area of sepsis.

Screening for GI bleeding

The patient’s own red cells are labelled with technetium and reinjected. The abdomen is scanned at intervals over the next 24 h. The investigation reveals only the general area of bleeding, e.g. stomach, right or left colon, rather than the exact site.

Endoscopy

Endoscopy implies examination of part of the body through an instrument. This may be through a natural orifice, e.g. oesophagoscopy or sigmoidoscopy, or through a surgically created hole, e.g. laparoscopy or arthroscopy. Endoscopy may be carried out with a rigid instrument, e.g. oesophagoscopy or sigmoidoscopy, the latter two being the most commonly used rigid endoscopy instruments. More recently, fibreoptic instruments have become more sophisticated and more widely used, e.g. gastroscopy, colonoscopy.

Use of endoscopes

Rigid endoscopes

Sigmoidoscope

This is probably the most commonly used rigid endoscope. It is 25 or 30 cm long. Examination is usually carried out in the left lateral position. The position of a lesion is usually indicated by measuring its distance in centimetres from the anal verge. Biopsies may be taken with long forceps inserted through the scope.

Oesophagoscopy

This has largely been superseded by the flexible instrument. The rigid one, however, remains useful for removing large foreign bodies from the oesophagus.

Cystoscopy

The rigid instrument has been widely used for many years but has now been largely superseded by the flexible scope. The rigid instrument remains useful for retrograde ureteric catheterization. Transurethral resection of the prostate has been carried out for many years via the rigid cystoscope.

Laparoscopy

This technique was widely used by gynaecologists but is now being more widely used by the general surgeon, particularly for minimally invasive surgery. A cannula is introduced into the peritoneal cavity and the peritoneal cavity distended with carbon dioxide gas. It is useful not only for diagnosis and biopsy but invasive procedures are now being carried out through it, e.g. cholecystectomy, appendicectomy.

Flexible endoscopes

Gastroscope (oesophago-gastro-duodenoscope)

This is used with intravenous sedation and a pharyngeal local anaesthetic spray. A clear view can be obtained of the oesophagus, stomach, duodenum, and with a side viewing scope the ampulla of Vater may be clearly seen. It is used for the identification and biopsy of lesions; tracing sources of GI haemorrhage; injection of oesophageal varices; lasering of bleeding lesions; dilatation of oesophageal strictures; cannulation of the ampulla of Vater for ERCP. With the technique of ERCP a diathermy wire can be used down the gastroscope for dividing the sphincter of Oddi and allowing stones to pass out into the GI tract.

Colonoscopy

It is possible to inspect the whole of the colon after adequate bowel preparation. Biopsies can be carried out. Polyps can be removed by a wire snare or diathermy. Routine follow-up of patients having had previous carcinomas resected or ulcerative colitis can be carried out, avoiding the need for repeated barium enemas.

Bronchoscopy

Narrow fibreoptic bronchoscopes can be passed under local anaesthetic. They are mainly used for diagnostic purposes but can also be used postoperatively for removing mucus plugs that have caused segmental collapse.

Other flexible scopes

These include cystoscopes, sigmoidoscopes, choledochoscopes (for inspecting the common bile duct at open surgery to assess for stones, tumours, etc.), and arterioscopes, which will show areas of stenosis, embolus and allow inspection of arterial anastomoses for patency.

Tissue diagnosis

Biopsy

This is removal of a piece of tissue from the living to provide a diagnosis. Incisional biopsy is the surgical removal of a piece of accessible tissue. Excisional biopsy is the complete removal of a discrete lesion without a wide margin and without it being considered curative of the disease.

Lesions may be biopsied as follows:

• direct vision, e.g. skin lesion

• forceps via an endoscope, e.g. sigmoidoscopic biopsy of a rectal lesion

• percutaneously using a Tru-Cut punch needle, e.g. breast lesions

• percutaneously by guided needle under ultrasound or CT control

• laparoscopically

• by open surgical excision, e.g. lymph node biopsy.

Cytology

Specimens obtained by scraping or fine-needle aspiration are spread on a slide and stained. The earliest example of this technique was cervical smears stained by the Papanicolaou technique.

Cytological diagnosis requires a skilled pathologist. The method must be both specific and sensitive. False positives and false negatives may occur. Cytological diagnosis is useful in the following situations in general surgery:

• Aspiration of ascites or pleural effusions

• Aspiration of solid masses, e.g. breast, thyroid, pancreas or lymph nodes.

Interventional radiology

Interventional radiology has increased markedly over the past two decades and has probably been most marked in the areas of vascular radiology, urological radiology and the treatment of obstructive jaundice. The areas listed below have seen advances in interventional radiology.

Tissue diagnosis

• Automated Tru-Cut needle biopsy under ultrasound or CT control, e.g. liver biopsy

• Fine-needle aspiration cytology (FNAC). A 22G needle can usually be safely passed through most organs to aspirate the suspicious lesion under ultrasound or CT control, e.g. lesions in the head of the pancreas.

Biliary tract

In obstructive jaundice caused by malignant compression, either intrinsic (cholangiocarcinoma) or extrinsic (nodes at porta hepatis), the site can be accurately located by PTC and treated by stenting. A guide wire is passed through the stenosis and the stenosis dilated, following which a stent is passed over the guide wire to lie across the stenosis. This procedure may also be carried out at ERCP and is likely to be associated with fewer complications by the latter method.

Urinary tract

The renal pelvis can be punctured by percutaneous insertion of a needle under ultrasound or CT control. The tract can be dilated to allow tubes to be inserted and this allows for removal of stones from the renal pelvis or the insertion of nephrostomy tubes to drain the kidney prior to definitive treatment of a distal obstruction. The procedure is known as percutaneous nephrostomy.

Vascular system

Percutaneous transluminal angioplasty (PTA)

Arteriography is carried out by the Seldinger technique. A flexible guide wire is then passed across the stenosis. A catheter with a rigid plastic inflatable balloon is then placed along the guide wire to lie within the stenosis and its position is checked under the image intensifier. The balloon is inflated to dilate the stenosis. Measurement of pressures above and below the site of the dilatation is used to assess the success of the procedure. The complications include arterial rupture, embolism, thrombosis or dissection. It is also possible to insert percutaneously a stent across the dilated stenosis in an attempt to prevent restenosis. A vascular surgeon should always be available to deal with any complications that may arise.

Thrombolysis

This is used very rarely nowadays. Acute-on-chronic ischaemia of a limb without gross neurological deficit may be treated with thrombolytic therapy. Systemic thrombolysis carries dangers of haemorrhage, e.g. GI or cerebral, and local thrombolysis is safer. Arteriography is carried out to confirm the diagnosis. The tip of a catheter is then placed within the clot and a thrombolytic agent, e.g. streptokinase, urokinase or tissue plasminogen activator, is infused directly into the clot. Radiographs are repeated at 8–12-h intervals to check progress. At each radiograph the catheter is advanced further into the dissolving clot. When the clot is cleared any stenoses demonstrated radiologically may be submitted to angioplasty if suitable.

Embolization

This is suitable for highly vascular tissues, e.g. arteriovenous malformations, or to treat lesions not amenable to surgery, e.g. liver metastases or extensive renal carcinoma. The main arterial supply is identified via arteriography and a catheter placed within it. An occlusive material is then injected. Suitable agents include gelatin foam or minute steel coils. Embolization is being increasingly used to arrest haemorrhage following trauma or from the GI tract.

Prevention of pulmonary emboli

Recurrent pulmonary emboli in the presence of adequate anticoagulation is an indication for interrupting the IVC. It is possible to insert a filter in the cava percutaneously via the internal jugular vein or femoral vein. A commonly used filter is the Greenfield, which is shaped like a shuttlecock and is held closed with a special introducing catheter. This catheter is inserted through a sheath in the femoral vein. It is positioned in the inferior vena cava below the renal veins and released. The feet of the filter hook into the vein wall to prevent it becoming dislodged.

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