Brain

Published on 01/04/2015 by admin

Last modified 22/04/2025

Print this page

This article have been viewed 1524 times

Chapter 13 Brain

Methods of imaging the brain

Imaging the brain’s structure and examining its physiology, both in the acute and elective setting, is now the domain of multiplanar, computer-assisted imaging. The imaging modalities in use today include the following:

1. Computed tomography (CT). This is the technique of choice for the investigation of serious head injury; for suspected intracranial haemorrhage, stroke, infection and other acute neurological emergencies. CT is quick, efficient and safer to use in the emergency situation than MRI.

2. Magnetic resonance imaging (MRI). This is the best and most versatile imaging modality for the brain, constrained only by availability, patient acceptability, and the logistics and safety of patient handling in emergency situations. New protocols and higher field strength magnets have raised the sensitivity of MRI in epilepsy imaging, acute stroke, aneurysm detection and follow-up post treatment of neoplastic and vascular disorders. It is the only effective way of diagnosing multiple sclerosis.

3. Angiography. This is very important in intracranial haemorrhage (ICH), especially subarachnoid haemorrhage (SAH). However, with the widespread availability of multi-detector CT scanners, CT angiography (CTA) is now preferentially used in ischaemic stroke, SAH and ICH. Angiography is still requested for pre-operative assessment of tumours and angiographic expertise is vital for the performance of many neurointerventional procedures.

4. Radionuclide imaging. There are two principal methods. The first is regional cerebral blood flow scanning, still more used in research than in clinical management, especially in the dementias and in movement disorders such as Parkinsonism; second is positron emission tomography (PET). By this method focal hyper-metabolism may be shown using F-18-fluorodeoxyglucose, for example in epilepsy, and cell turnover may be shown using¹¹C-methionine, for example in tumour studies.

5. Ultrasound (US). This is particularly helpful in neonates and during the first year of life to image haemorrhagic and ischaemic syndromes, developmental malformations, and hydrocephalus using the fontanelles as acoustic windows. In adults, transcranial Doppler may be used for intracerebral arterial velocity studies to assess the severity of vasospasm.

6. Plain films of the skull. These are of little value except in head injury.

COMPUTED TOMOGRAPHY OF THE BRAIN

Indications

CT is the imaging modality most commonly used in triaging acute neurological disease. For non-emergency indications CT is second best, but is still widely used, often because it is more broadly available and simpler to interpret. The indications include the following:

1. Following major head injury (if the patient has lost consciousness, has impaired consciousness, or has a neurological deficit). The presence of a skull fracture also justifies the use of CT. NICE (National Institute for Health and Clinical Excellence) guidance has been issued on the use of imaging for head injuries for adults and children, specifically CT, listing the criteria for assessment based on best relevant data and consensus recommendations.

2. In suspected intracranial infection (the use of contrast enhancement is recommended).

3. For suspected intracranial haemorrhage and cases of ischaemic and haemorrhagic stroke.

4. In suspected raised intracranial pressure, and as a precaution before lumbar puncture once certain criteria are fulfilled. These would include reduced consciousness (a Glasgow coma score of less than 12), definite papilloedema, focal neurological deficit, immune suppression and bleeding dyscrasias.

5. In other situations, such as epilepsy, migraine, suspected tumour, demyelination, dementia and psychosis CT is a lesser quality tool. If imaging can be justified, MRI is greatly preferable and is recommended by NICE in these situations except for first episode of psychosis.

Technique

1. Most clinical indications are adequately covered by 3-mm sections parallel to the floor of the anterior cranial fossa, from the foramen magnum to the midbrain, with 7-mm sections to the vertex. In all trauma cases, window width and level should be adjusted to examine bone and any haemorrhagic, space-occupying lesions. Review of all trauma studies should be done on brain windows, bone and ‘blood windows’ (i.e. W175 L75).

2. In suspected infection, tumours, vascular malformations and subacute infarction, the sections should be repeated following intravenous (i.v.) contrast enhancement. Standard precautions with regard to possible adverse reactions to contrast medium should be taken.

3. Dynamic studies using iodinated contrast are increasingly being used as a routine in high-velocity head trauma, the assessment of intracerebral bleeding in young patients, aneurysmal SAH, ruptured arteriovenous shunts and dural venous sinus thrombosis. CT angiography (CTA) on a typical 4-slice multidetector scanner is performed using 120 ml of contrast injected at 3 ml s⁻¹ with a delay of 20 s. Slices of 1.25 mm are reconstructed at increments of 0.8 mm. CT venography (CTV) involves a delay of 100 s. Images are usually reviewed both as three-dimensional rendered data and multiplanar reformats (MPRs).

Further reading

Bruening R., Flohr T. Protocols for Multislice CT 4- and 16-row Applications. Berlin: Springer Verlag, 2003.

Yates D., Aktar R., Hill J. Assessment, investigation, and early management of head injury: summary of NICE guidance. BMJ. 2007;335:719-720.

Magnetic Resonance Imaging of the Brain

Indications

MRI is indicated in all cases of suspected intracranial pathology. Techniques in use change with the development of new sequences and higher field strength magnets. The techniques described below are, therefore, only basic indications as to sequences in use. The greatest advantages in the use of MRI are the improved contrast resolution between grey and white matter, brain and cerebrospinal fluid (CSF); the removal of artifact due to bone close to the skull base and in the posterior fossa; and in obtaining multiplanar images for lesion localization.

Technique

1. Long TR sequences. The whole brain can be examined with 5-mm sections with 1-mm interspaces using T2-weighted turbo spin echo imaging. Proton density sequences, long TR and short TE, are used mostly for the assessment of demyelination and intra-articular disc changes in the temporomandibular joints.

2. Short TR sequences. T1-weighted sequences are used for the demonstration of detailed anatomy but gadolinium chelate contrast agents are required to view pathology. Common practice is to obtain a sagittal or coronal T1-weighted sequence as part of a standard brain study. Volumetric sequences pre and post contrast are used for image guidance software interfaces for insertion of deep brain stimulators for movement disorders and the removal of intra- and extra-axial tumours.

3. Gradient-echo T2-weighted sequences. Although suffering from various artifacts, the sensitivity of these sequences to susceptibility effects makes them very sensitive to the presence of blood products, as in cases of previous head injury, SAH and cavernomas. Haemosiderin produces marked focal loss of signal in such cases, and all patients with a history of head injury or other causes of haemorrhage should be imaged with this sequence.

4. FLAIR sequences (FLuid Attenuated Inversion Recovery) provide very good contrast resolution in the detection of demyelinating plaques and infarcts, and have the advantage that juxta-ventricular pathology contrasts with dark CSF, and is not lost by proximity to the intense brightness of the ventricular CSF, as in spin-echo T2-weighted studies.

5. Angiographic sequences. There are many methods, of which ‘time-of flight’ is one of the more commonly used. This is a very short TR, T1-weighted gradient echo three-dimensional sequence, with sequential presaturation of each partition so that only non-presaturated inflowing blood gives a high signal. Image display is by so-called ‘MIP’ or maximum intensity projection, giving a three-dimensional model of the intracranial vessels. Contrast-enhanced MR angiography requires a pump injector and is less susceptible to flow artifacts.

6. Echoplanar or diffusion weighted imaging (DWI). This sequence is becoming widely available on scanners. Most units perform DWI on all patients with suspected stroke, vasculitis, encephalitis, abscesses and in the workup of intracranial tumours. DWI examines the free movement, or Brownian motion, of water molecules at a cellular level. In acute infarcts cytotoxic oedema prevents free movement of water whereas in tumours there is no restriction. All DWI should be reviewed together with conventional sequences and apparent diffusion coefficient (ADC) maps. Acute infarcts are hyperintense on DWI and hypointense on ADC.

IMAGING OF INTRACRANIAL HAEMORRHAGE

Imaging of suspected intracranial haemorrhage is one of the most common requests of clinicians, usually in the emergency setting. Follow-up of haematomas and formulating a differential diagnosis can sometimes be quite challenging. In the acute setting CT and the neurophysiological information available as a result of multidetector technology is often the first and only modality used to assess these patients. MRI is more often used in situations where the initial workup has been negative and a more sensitive modality is required.

COMPUTED TOMOGRAPHY

A conventional study consists of 3-mm sections through the brainstem and posterior fossa, and 7-mm sections through the cerebrum. This is the basic multi-detector CT protocol for brain imaging. This is done without contrast to avoid diagnostic difficulty in deciding whether a parenchymal lesion is due to enhancement or blood. Acute blood is typically hyperdense on CT. An exhaustive differential diagnosis for bleeding in different compartments of the brain can be sourced elsewhere but in general bleeding can be extra-axial (i.e. epidural, subdural, subarachnoid, intraventricular) or intra-axial. Intra-axial bleeding can be due to head trauma, ruptured aneurysms or arteriovenous malformations, bleeding tumours (either primary disease or secondaries), hypertensive haemorrhages (cortical or striatal) or haemorrhagic transformation of venous or arterial infarcts. In the assessment of subarachnoid haemorrhage and ischaemic stroke CTA is becoming increasingly used as the screening modality for deciding further intervention. Neurosurgeons are increasingly using CTA alone as the modality for planning microsurgical clipping, especially in the cases where a haematoma exerting mass effect needs to be evacuated immediately adjacent to a freshly ruptured intracranial aneurysm. In ischaemic stroke CTA can localize an acute embolus and CT perfusion imaging can demonstrate the ischaemic core (irreversibly damaged brain) by calculating the relative cerebral blood volume and the ischaemic penumbra (recoverable brain parenchyma) by evaluating the relative cerebral blood flow (rCBF).

MAGNETIC RESONANCE IMAGING

MRI is used mostly to exclude the presence of an underlying tumour at an interval after the initial haemorrhage when there would be less perilesional brain swelling and obscuration of the anatomy due to blood degradation products. It is also used in the setting of subarachnoid bleeding where no aneurysm or arteriovenous malformation is found on CTA or catheter angiography. In these cases the entire neuraxis must be examined to exclude an ‘occult’ source of the haemorrhage. Diffuse axonal shear injuries, in patients with depressed coma scores post head injury, in light of a normal appearing CT scan, are best demonstrated on MRI with gradient echo imaging looking for susceptibility artifact due to ‘microbleeds’. Where resources are optimal, and MRI is used as part of the initial imaging pathway in ischaemic stroke, MR will help to determine the volumes of brain that can be recovered as well as the presence of early haemorrhage that is not visible on CT which would contraindicate thrombolysis.

Further reading

Wada R., Aviv R.I., Fox A.J., et al. CT angiography ‘spot sign’ predicts hematoma expansion in acute intracerebral hemorrhage. Stroke. 2007;38(4):1257-1262.

Westerlaan H.E., Gravendeel J., Fiore D., et al. Multislice CT angiography in the selection of patients with ruptured intracranial aneurysms suitable for clipping or coiling. Neuroradiology. 2007;49(12):997-1007.

Imaging of Gliomas

This is an all-encompassing term for a diverse group of primary brain tumours. This includes astrocytomas, oligodendrogliomas, choroid plexus tumours and ependymomas amongst others. The most commonly presenting tumour, however, is the WHO Grade IV astrocytoma or glioblastoma multiforme. Other brain tumours are derived from neuronal cell lines, mixed glial-neuronal cell lines, the pineal gland and embryonal cell lines, peripheral cranial nerves (such as the vestibular schwannoma), meningeal tumours and lymphoma. Appropriate differential diagnoses can be derived from noting the age of the patient, the tumour location (i.e. supra- or infratentorial, cortex or white matter, basal ganglia or brainstem, intra- or extra-axial), its consistency (i.e. cyst formation, mural nodule) and its enhancement characteristics.

COMPUTED TOMOGRAPHY

CT is often the first modality to demonstrate the presence of a brain tumour. The indications for scanning can include unrelenting morning headaches, drowsiness, stroke-like presentation and seizures. In addition to making the initial diagnosis, multidetector CT can be used for obtaining high-resolution datasets for image guidance for brain biopsies, with and without stereotactic frames. In the absence of advanced MR neuroimaging software and for patients who are unable to undergo MR, imaging multidetector CT can be used to obtain rCBF data for tumour matrix as well as the normal brain. Studies have been performed to correlate ratios of rCBF with tumour grade, assessment of radiation necrosis or dedifferentiation when following up tumours.

MAGNETIC RESONANCE IMAGING

MRI is the preferred modality for detailed assessment of brain tumours. In addition to using conventional imaging parameters to assess volume, location and tumour substance in multiple planes, advanced imaging techniques or ‘multi-modality’ imaging can reveal information about tumour grade and biology. Conventional T1 and T2 images are obtained. Diffusion-weighted imaging and diffusion tractography reveals information about tumour substance and effect on white matter tracts in the brainstem and the cerebrum. Multiple lesions, if present, can be better seen on post-contrast MRI, in which case metastatic disease becomes a consideration in the differential diagnosis. As grade IV gliomas can have a similar appearance, a search for a primary epithelial neoplasm elsewhere (for example breast and lung) would be indicated. MR spectroscopy is a technique whereby relative amounts of cell metabolites are detected to reflect the biochemical environment in a tumour. N-acetylaspartate, choline, creatine, lactate and myo-inositol are a few of the major metabolites assessed. Single voxel techniques are preferable using STEAM (stimulated echo acquisition mode) or point resolved spectroscopy (PRESS). Perfusion-weighted imaging can provide information about tumour grade and help to differentiate between tumour recurrence and radiation necrosis. Susceptibility perfusion imaging is most often used where gradient echo images are obtained of the entire brain during the first pass of gadolinium chelate and analysis of the collated data using small regions of interest is carried out looking at normal brain and the tumour. MPRAGE (magnetization-prepared rapid-acquisition gradient echo) volumetric data can also be used post contrast for image guidance for biopsy or tumour debulking.

Further reading

Al-Okaili R.N., Krejza J., Wang S., et al. Advanced MR imaging techniques in the diagnosis of intra-axial brain tumors in adults. RadioGraphics. 2006;26:S173-S189.

Stadlbauer A., Gruber S., Nimsky C., et al. reoperative grading of gliomas by using metabolite quantification with high-spatial-resolution proton MR spectroscopic imaging. Radiology. 2006;238:958-969.

Imaging of Acoustic Neuromas

MRI is the definitive diagnostic method. The neurophysiological methods, although quite sensitive, produce a large number of false-positive studies.

COMPUTED TOMOGRAPHY

Some departments use 2-mm section i.v. contrast-enhanced CT with bone and soft-tissue windowed images for suspected acoustic neuroma to relieve pressure on their MRI services. This approach is usually reserved for elderly patients, mostly to exclude the presence of large lesions that may require debulking or excision. Intracanalicular tumours cannot be shown by this method but surgically these will not be addressed.

MAGNETIC RESONANCE IMAGING

Most imaging departments will have a 1.5-T scanner where MR cisternography sequences are available, nulling the CSF pulsation artifact and highlighting the appearances of cranial nerves, arteries and veins which may also be contributing to sensorineural deafness and tinnitus. Nulling the pulsation artifact from CSF provides the contrast required and images as thin as 0.8 mm, with no gap, can be obtained. From this kind of data multiplanar, reformatted images can be reviewed. Post-contrast studies are obtained when a change in the contour of the nerve is observed or a filling defect is seen in the labyrinthine structures.

Further reading

Rupa V., Job A., George M., et al. Cost-effective initial screening for vestibular schwannoma: auditory brainstem response or magnetic resonance imaging. Otolaryngol. Head Neck Surg.. 2003;128(6):823-828.

Radionuclide Imaging of the Brain

There are currently two main modalities: regional cerebral blood flow imaging and PET imaging. Thallium imaging is also used in specialist centres for brain tumour assessment and there are niche agents in clinical practice used, for example in the diagnosis of Parkinson’s disease. Conventional radionuclide brain scanning (blood–brain barrier imaging) is essentially never used in modern clinical practice.

Further reading

Freeman L.M., Blaufox M.D., editors. Functional brain imaging. Sem. Nucl. Med.. 2003;33:1-2.

Conventional Radionuclide Brain Scanning (Blood–Brain Barrier Imaging)

This technique is not indicated if CT and/or MRI are available. It was a technique that used i.v. injection of the radiopharmaceuticals ^99mTc-DTPA and ^99mTc-pertechnetate to detect areas of blood–brain barrier breakdown and demonstrate cerebral metastases, meningioma and high-grade glioma.

REGIONAL CEREBRAL BLOOD FLOW IMAGING

This localizes rapidly in proportion to cellular metabolism rather than blood flow, and the distribution has some differences to that of HMPAO, which may need to be taken into consideration for clinical diagnosis.^1,² It currently has the advantage of greater stability than HMPAO and can be used for up to 6 h after reconstitution, which is of particular benefit for ictal epilepsy studies where an injection is only given once a seizure occurs.

Equipment

1. Single photon emission computed tomography (SPECT) gamma camera, preferably dual-headed

2. SPECT imaging couch with head extension

3. Low-energy high-resolution collimator (or more specialized slant-hole or fan-beam collimator).

Patient preparation

Since cerebral blood flow is continuously varying with motor activity, sensory stimulation, emotional arousal, etc., it is important to standardize the conditions under which the tracer is administered, especially if serial studies are to be undertaken in the same individual. Familiarization with the procedure to reduce anxiety and injection in a relaxing environment through a previously positioned i.v. cannula should be considered.

For localization of epileptic foci, ictal studies are much more sensitive than interictal, and if feasible the patient should be admitted under constant monitoring, with injection as soon as a seizure starts.

Technique

1. Administer 500 MBq of tracer

2. SPECT imaging is performed any time from 5 min to 2 h after injection with the patient supine.

Images

The acquisition protocol will depend upon the system available. Suitable parameters for a modern single-headed gamma-camera might be:

1. 360 ° circular orbit

2. 60–90 ° projections or continuous rotation over a 30-min acquisition

3. Combination of matrix size and zoom to give a pixel size of 3–4 mm.

Analysis

A cine film of the projections is looked at before the patient leaves to detect any movement. If significant movement has occurred and cannot be corrected by computer motion correction algorithms available, the patient must be re-scanned. SPECT reconstructions are made in three planes.

Additional techniques

1. If blood flow in the carotid and major cerebral arteries is of interest, a dynamic study during injection is performed.

2. Three-dimensional mapping of activity distributions onto standard brain atlases and image registration with MRI, CT and quantitative analysis are areas of increasing interest, particularly with the development of SPECT-CT scanners.

Aftercare

Radiation dose may be reduced by administration of a mild laxative on the day after the study and maintenance of good hydration to promote urine output.

Complications

None.

References

1 Asenbaum S., Brücke T., Pirker W., et al. Imaging of cerebral blood flow with technetium-99m-HMPAO and technetium-99m-ECD: a comparison. J. Nucl. Med.. 1998;39(4):613-618.

2 Koyama M., Kawashima R., Ito H., et al. SPECT imaging of normal subjects with technetium-99m-HMPAO and technetium-99m-ECD. J. Nucl. Med.. 1997;38(4):587-592.

Further reading

Murray A.D. The brain, salivary and lacrimal glands. In Sharp P.F., Gemmell H.G., Murray A.D., editors: Practical Nuclear Medicine, 3rd edn, London: Springer-Verlag, 2005.

Positron Emission Tomography

Indications

1. Localization of epileptic foci

2. Investigation of dementias

3. Grading of brain tumours.

Contraindications

1. Recent chemotherapy – minimum interval of 2–3 weeks recommended

2. Recent radiotherapy – minimum interval of 8–12 weeks recommended

3. Poorly controlled diabetes, i.e. serum glucose >8.5 mmol l at time of scanning.

Radiopharmaceuticals

Fluorine-18 fluorodeoxyglucose (¹⁸FDG) is a glucose analogue which is the most commonly used agent for oncological work and is also used for the investigation of dementias. There are other radiopharmaceuticals, e.g. L-[methyl-¹¹C]methionine ([¹¹C] MET) or 3′-deoxy-3′-[¹⁸F] fluorothymidine ([¹⁸F] FLT) which have the advantage of little normal cerebral uptake.

Patient preparation

Fasting for 4–6 h, with plenty of non-sugary fluids.

Alternative techniques

1. L-[methyl-¹¹C]methionine ([¹¹C] MET) or 3′-deoxy-3′-[¹⁸F] fluorothymidine ([¹⁸F] FLT) PET

2. ²⁰¹Thallium

3. MR spectroscopy.

Further reading

Hammoud D.A., Hoffman J.M., Pomper M.G., et al. Molecular neuroimaging: from conventional to emerging techniques. Radiology. 2007;245(1):21-42.

ULTRASOUND OF THE INFANT BRAIN

Indications

Any suspected intracranial pathology, particularly suspected germinal matrix haemorrhage, extra-axial haematomas and hydrocephalus.

Equipment

4–7-MHz, sector transducer. A 7.5- or 10-MHz transducer to visualize superficial structures.

Patient preparation

None is required, though a recently fed infant is more likely to submit to examination without protest. An agitated child should be calmed by the mother or carer by any appropriate method.

Methods

1. Via the anterior fontanelle

2. Through the squamosal portion of the temporal bone to visualize extracerebral collections and the region of the circle of Willis

3. Via the posterior fontanelle, for the posterior fossa.

Technique

Six coronal and six sagittal images are obtained and supplemented with other images of specific areas of interest. The base of the skull must be perfectly symmetrical on coronal scans. The first image is obtained with the transducer angled forward and subsequent images obtained by angling progressively more posteriorly. The anatomical landmarks that define each view are given below.

Coronal

1. The orbital roofs and cribriform plate (these combine to produce a ‘steer’s head’ appearance); anterior interhemispheric fissure; frontal lobes

2. Greater wings, lesser wings and body of sphenoid (these produce a ‘mask’ appearance); the cingulate sulcus; frontal horns of lateral ventricles

3. Pentagon view: five-sided star formed by the internal carotid, middle cerebral and anterior cerebral arteries

4. Frontal horns of lateral ventricles; cavum septum pellucidum; basal ganglia. Bilateral C-shaped echoes from the parahippocampal gyri; thalami

5. Trigones of lateral ventricles containing choroid plexus; echogenic inverted V from the tentorium cerebelli; cerebellum

6. Occipital horns of lateral ventricles; parietal and occipital cortex; cerebellum.

Sagittal

For the sagittal images, the reference plane should be a mid-line image with the third ventricle, septum pellucidum and fourth ventricle all on the same image. The more lateral parasagittal images are obtained with the transducer angled laterally and slightly oblique because the occipital horn of the lateral ventricle is more lateral than the frontal horn:

1. Two views of the mid-line

2. Parasagittal scans of the lateral ventricles. These are angled approximately 15 ° from the mid-line, to show the caudothalamic grooves

3. Steep parasagittal scans, approximately 30 ° from the mid-line, of the frontal, temporal and parietal cortices.

CEREBRAL ANGIOGRAPHY

Indications

1. Intracerebral and subarachnoid haemorrhage

2. Aneurysms presenting as space-occupying lesions

3. Brain arteriovenous shunts, carotico-cavernous fistulas (direct and indirect)

4. Cerebral ischaemia both of extracranial and intracranial origin

5. Pre-operative assessment of intracranial tumours.

Contraindications

1. Patients with unstable neurology (usually following subarachnoid haemorrhage or stroke)

2. Patients unsuitable for surgery

3. Patients in whom vascular access would be impossible or relatively risky

4. Iodine allergy. Relative contraindication as angiography could be performed with gadolinium chelates.

Equipment

A single or biplane digital subtraction angiography apparatus is required, with a C-arm allowing unlimited imaging planes, high-quality fluoroscopy, and road-mapping facility.

Three-dimensional rotational angiography is now increasingly available and forms an important part of the analysis of aneurysms during treatment. There should be access to the patient for both the radiologist and the anaesthetist, with appropriate head immobilization.

Preparation

When the patient is able to understand what is proposed, a clear explanation should be given, together with presentation of the risks and benefits. Most patients do not require sedation for diagnostic procedures and this would be contraindicated in acute neurological presentations. Children, patients who are excessively anxious, those who cannot cooperate because of confusion, or those who would be managed better during the procedure with full ventilation control are examined under general anaesthesia. Neurointerventional studies are done under general anaesthesia. Groin shaving is now regarded as unnecessary. Patients should not be starved unless general anaesthesia is to be used, but should, nevertheless, be restricted to fluid intake and only a light meal.

Technique

Catheter flushing solutions should consist of heparinized saline (2500 IU l⁻¹ normal saline). Using standard percutaneous catheter introduction techniques, the femoral artery is catheterized. There is a wide range of catheters available and there are proponents of many types. In patients up to middle age without major hypertension, there will be little difficulty with any standard catheter and a simple 4F polythene catheter with a slightly curved tip or 45 ° bend will suffice in the majority. Older patients and those with atherosclerotic disease may need catheters offering greater torque control such as the JB2 or Simmons (Figs 13.1 & 13.2) as appropriate. Catheter control will be better if passed through an introducer set, and this is also indicated where it is anticipated that catheter exchange may be required. Selective studies of the common carotids and the vertebrals are preferable to super selective studies of the internal and external carotids unless absolutely necessary. The following points should be noted:

1. The hazards of cerebral angiography are largely avoidable; they consist of the complications common to all forms of angiography (see Chapter 9) and those which are particularly related to cerebral angiography.

2. Any on-table ischaemic event has an explanation. Cerebral angiography does not possess an inherently unavoidable complication rate as has been suggested in the past. If an ischaemic event occurs there has been a complication, and its cause must be identified.

3. The most significant complications are embolic in origin, and the most important emboli are particulate. Air bubbles should be avoided as part of good angiographic practice, but are unlikely to cause a neurological complication.

4. Emboli may come from the injected solutions. Avoid contamination from glove powder, and dried blood or clot on gloves. Take care to avoid blood contamination of the saline or of the contrast medium, which is always dangerous. Avoid exposure of solutions to air. Contrast medium or heparin/saline in an open bowl is bad practice.

5. Emboli may arise from dislodgement of plaque or thrombus. Never pass a catheter or guidewire through a vessel that has not been visualized by preliminary injection of contrast medium. Use appropriate angled, hydrophilic guidewires. Do not try to negotiate excessively acute bends in vessels. The splinting effect of the catheter will cause spasm and arrest the flow in the artery. Dissections could occur which may lead to occlusion. Sharp curves can only be safely negotiated with microcatheters.

6. Emboli may arise from the formation of thrombus within a catheterized vessel. Always ensure that there is free blood flow past the catheter, and avoid forceful passage of a guidewire or catheter in such a way as may damage the intima of the vessel and cause thrombus formation.

7. Emboli may arise within the catheter. Do not allow blood to flow back into the catheter, or if it does occur then flush regularly or by continuous infusion. Never allow a guidewire to remain within a catheter for more than 1 min without withdrawal and flushing, and never introduce a guidewire into a contrast filled catheter, but fill the catheter with heparinized saline first.

8. Keep study time to a minimum, but not at the expense of the diagnostic usefulness of the study.

Figure 13.1 (a) Vertebrale or Berenstein, (b) JB 2, (c) Mani. End holes: 1 Side holes: 0.

Figure 13.2 Simmons (sidewinder) catheters. (a) For narrow aorta. (b) For moderately narrow aorta. (c) For wide aorta. (d) For elongated aorta. End holes: 1 Side holes: 0.

Contrast medium

Non-ionic monomer, e.g. iohexol, iopamidol. The concentration required is equipment-dependent, but with modern DSA, 150 g I ml⁻¹ will be suitable.

Contrast medium volume

1. Common carotid −10 ml by hand in about 1.5–2 s

2. Internal carotid – 7 ml by hand in about 1.5 s

3. Vertebral artery – 7 ml by hand in about 1.5 s, but this volume can be diluted by 2 ml of saline to opacify the contralateral vertebral on the same injection.

Projections

As required, but basically 20 ° anterior-posterior (AP), Townes, lateral, occipitomental and oblique views as indicated. Multiple projections are especially needed for aneurysm studies to open loops and profile aneurysms; however, with three-dimensional rotational angiography, contrast runs can now be cut down to a minimum, and computer models of aneurysms and vessels can analysed instead.

Films

From early arterial to late venous, about 8 s in total in most cases, system acquisitions will be at 2–4 frames s⁻¹ depending on the study. With digital fluoroscopy acquisitions typically will be 2 frames s⁻¹ for 4 s, then 1 frame every 2 s for 4 s.

Aftercare

1. Standard nursing care for the arterial puncture site

2. Most departments adopt the practice of maintaining neurological observation for a period of 4 h or so after the procedure

3. Good hydration should be maintained.

Recent Posts

Meta

Categories

Search Engine

Brain

Share this:

Related

Related posts: