EMERGENCY NEURORADIOLOGY - PART 4 doc

114 I. CEREBROVASCULAR EMERGENCIES Fig. 1.97 (cont.) - c) MRA of neck vessels: occlusion at the be- ginning of the right internal carotid artery. Fig. 1.98 - a) Basic SE T2 MRI; blurred signal hyperintensity in right occipital location; b) SE T1 image after gadolinium: non- homogeneous contrast enhancement due to blood-brain barri- er damage caused by the presence of an acute ischaemic area; c) MRA of the vessels of the circle of Willis: stenosis in the proximal segment of the right posterior cerebral artery. c a b c detachable embolization coils. This has shown a good correspondence between MRA and selective DSA with regard to the evaluation of aneurysms occluded with coils. It has in fact been possible to evaluate any residual aneurysm neck and flow within the residual aneurysmatic sack if present. However, to be fair, certain vascular details are obviously less easy to evaluate in the single MRA partitions. Arteriovenous malformations Generally speaking, MRA used in combina- tion with MRI is sufficient for the detection of most cerebral arteriovenous malformations. The TOF MRA technique gives good documen- tation of the major arterial feeding arteries (Fig. 1.100). Venous drainage and the central nidus are better studied using PC MRA. The use of in- travenous gadolinium improves visualization of the venous vascular components of AVM’s. MRA also permits in-depth studies of the nidus, its dimensions and its relationship with the surrounding neural tissue, which are important elements for treatment planning. This technique is also useful during follow-up after therapy; invasive selective DSA is nevertheless required in order to obtain precise images of the exact anatomical architecture and the dynamic aspects of the AVM. CONCLUSIONS MRA is an important non-invasive method for studying the brachiocephalic and cerebral blood vessels. Its main application in neuroradiological emergencies is for the evaluation 1.9 MR ANGIOGRAPHY 115 Fig. 1.99 - 3D TOF MRA of the vessels of the circle of Willis: presence of an aneurysm on the anterior communicating artery. b a Fig. 1.100 - AVM: a) basic SE T2 MRI: numerous serpigenous images with signal void in the left temporoparietal region; b) 3D TOF MRA: presence of a large AVM, supplied by branches orig- inating from the Sylvian artery and left posterior cerebral artery. of cerebral circulation in suspected cases of ischaemic stroke or thrombosis of the dural venous sinuses. In such cases, MRA can be performed together with conventional MRI aimed at obtaining a rapid and complete diagnostic analysis of the problem, thereby al- lowing optimal specific treatment choices to be made. It is also widely used to screen for cerebral aneurysms in high risk groups, and more recently to monitor aneurysms following treatment with Gugielmi’s detachable embolization coils. It is important to underline the importance of having access to high performance MRI sys- tems that allow the rapid execution of both the static conventional imaging as well as the angiographic acquisitions. REFERENCES 1. Anderson CM, Edelman RR, Turki PA: Clinical Magnetic Resonance Angiography. Raven Press New York, 1993. 2. Atlas SW: MR angiography in neurologic disease. Radio- logy 193:1-6, 1994. 3. Atlas SW, Sheppard L, Godberg HI et al: Intracranial aneurysms: detection and characterization with MR angiography with use of an advanced post-processing technique in a blinded-reader study. Radiology 203:807-814, 1997. 4. Atkinson D, Brant-Zawadzki M, Gilliam G et al.: Improved MR angiography: magnetization transfer suppression with variable flip angle excitation and increased resolution. Ra- diology 190:890-894, 1994. 5. Bowen BC, Quencer RM, Margosian P et al.: MR angiography of occlusive disease of the arteries in the head and neck: current concepts. AJR 162: 9-18, 1994. 6. Edelman RR, Ahn SS, Chien D et al.: Improved time-of- fligth MR angiography of the brain with magnetization transfer contrast. Radiology 184: 395-399, 1992 7. Furst G, Hofer M, Steinmetz H et al.: Intracranial stenooc- clusive disease: MR angiography with magnetization transfer and variable flip angle. AJNR 17:1749-1757, 1996. 8. Heiserman JE, Drayer BP, Keller PJ et al.: Intracranial vascular stenosis and occlusion: evaluation with tree-dimensional time-of-flight MR angiography. Radiology 185:667-673, 1992. 9. Kim JK, Farb RI, Wright GA: Test bolus examination in the carotid artery at dynamic gadolinium-enhanced MR angiography. Radiology 206:283-289, 1998. 10. Korogi Y, Takahashi M, Mabuchi N: Intracranial aneurysms: diagnostic accuracy of MR angiography with evaluation of maximum intensity projection and surce images. Ra- diology 199:199-207, 1996. 11. Korogi Y, Takahaski M, Nakagawa T et al.: Intracranial vascular stenosis and occlusion: MR angiography findings. AJNR 18:135-143, 1997. 12. Levy C, Laissy JP, Raveau V: Carotid and vertebral artery dissections: three dimensional time of fligth MR angiography and MR versus conventional angiography. Radio- logy 190:97-103, 1994. 13. Levy RA, Prince MR: Arterial-phase three-dimensional contrast-enhanced MR angiography of the carotid arteries. AJR 167:211-215, 1996. 14. Litt AW, Eidelman EM, Pinto RS et al.: Diagnosis of carotid artery stenosis: comparison of 2D time of fligth MR angiography with contrast angiography in 50 patients. AJNR 12:149-154, 1991. 15. Mathews VP, Elster AD, King JC et al: Combined effects of magnetization transfer and gadolinium in cranial MR imaging and MRA. AJR 164:167-172, 1995. 16. Mattle HP, Wentz KU et al: Cerebral venography with MR. Radiology 178:453-458, 1991. 17. Mohr JP, Biller J, Hilal SK et al: Magnetic resonance imaging in acute stroke. Stroke 26:807-812, 1995. 18. Parker DL, Blatter DD: Multiple thin slab magnetic resonance angiography. Neuroimag Clin North AM 2:677-692, 1992. 19. Provenzale JM: Dissection of the internal carotid and vertebral arteries: imaging features. AJR 165:1099-1104, 1995. 20. Prince MR, Grist TM, Bebatin JE et al: 3D contrast MR angiography. Springer-Verlag (New-York) 1997. 21. Ruggeri PM, Poulos N, Masaryk TJ et al: Occult intracranial aneurysms in polycystic kidney disease: screening with MR angiography. Radiology 191:33-39, 1994. 22. Sardanelli F, Zandrino F et al: MR angiography of internal- carotid arteries:breath-hold gd-enhanced 3D fast imaging with steady-state precession versus unenhanced 2D and 3D time-of-fligth techniques. J Cat 23:208-215, 1999. 23. Scarabino T, Carriero A et al: MR angiography in carotid stenosis: a comparison of three techniques. Eur J Radiol 28:117-125, 1998. 24. Sorensen AG, Buonanno FS, Gonzales RG et al: Hypera- cute stroke: evaluation with combined multisection diffusion-weighted and hemodynamically weighted echoplanar MR imaging. Radiology 199:991-401, 1996. 25. Stock KW, Wetzel S, Kirsch E et al: Anatomic evaluation of the circle of Willis: MR angiography versus intraarterial digital subtraction angiography. AJNR 17:1495-1499, 1996. 26. Warach S, Gaa J et al: Acute human stroke studied by who- le brain echo planar diffusion-weithted magnetic resonance imaging. Ann Neurol 37:231-241, 1995. 116 I. CEREBROVASCULAR EMERGENCIES 117 INTRODUCTION The relatively recent advent of sophisticated imaging techniques such as CT and MR has dra- matically reduced the demand for conventional invasive selective cerebral angiography in radiological diagnosis. Despite the fact that conventional angiography is now considered comple- mentary to other techniques in neurological emergencies, it has been shown not to be completely replaceable because there are certain questions that angiography alone can answer. In recent years, there has been a return to the use of angiography based on the improvement in the technique’s safety, speed and sophistication (e.g., hard- and software improvements, atrau- matic catheterization materials, and new low osmolarity contrast agents), and on the progres- sively increasing experience of vascular interventional radiology treatment techniques (8). This last factor has led to angiography being considered as having a dual purpose: an instrument used in both diagnosis and therapy. CLINICAL INDICATIONS The clinical indications for emergency angiography are cerebral ischaemia and haemorrhage, as well as some forms of cranial trauma and thrombotic pathology of the venous structures. The initial diagnostic evaluation is nevertheless left to non-invasive methods such as CT, MR and Doppler ultrasound, which are now able to satisfy the most urgent diagnostic requirements. Generally speaking, angiography is presently used in those cases in which non-invasive techniques have ex- hausted their usefulness, and, above all, when treatment using endovascular techniques is being considered. Cerebral ischaemia In cerebral ischaemia, depending on whether it manifests itself as TIA or frank infarction, angiography is not routinely used except in specific cases during certain time periods following the ischaemic ictus. a) Transient ischaemic attacks: TIA’s do not usually constitute an angiographic emergency; patients with TIA’s are typically subjected to angiography only after a certain period of time during which the clinical evolution and the less invasive diagnostic techniques (e.g., ultrasound) have indicated the presence of a vascular lesion that might be amenable to surgery. Although in- 1.10 CONVENTIONAL ANGIOGRAPHY F. Florio, M. Nardella, S. Balzano, V. Strizzi, T. Scarabino frequently encountered, angiographic examinations can be mandatory in patients suffering from repeated ischaemic attacks and having a non-invasive imaging diagnosis of subtotal occlusion of one of the cervicocranial vessels; in such cases urgent surgery or angioplasty may be able to prevent total vascular thrombosis. b) Cerebral infarction: Angiography is rarely used today in cases of frank cerebral infarction, and is in any case usually delayed until partial functional clinical recovery is observed. Trends recently have pointed towards utiliz- ing very early angiographic examinations, within hours following the acute ischaemic event, when the clinical syndrome can be attributed to an arterial occlusion that may be susceptible to treatment using transcatheter fibrinolysis. This is one of the more recent innovations of interventional neuroradiology, although its real clinical efficacy merits further investigation (2). Cerebral haemorrhage Angiography plays a more important role in cases of cerebral haemorrhage. a) Parenchymal haemorrhages do not usually require angiographic analysis when the origin of the haemorrhage is thought to be sponta- neous (i.e., elderly patient with hypertension). However, when clinical and anatomical condi- tions favour a different aetiology for the haemorrhage (e.g., relatively young patient, nor- motensive, atypical position, etc.), angiography becomes mandatory and should be performed urgently, especially when the haemorrhage de- mands emergency surgery. b) In cases of epidural/subdural haemorrages emergency angiography has varying diagnostic importance. It is unusual for posttrau- matic epidural/subdural haemorrages to gain diagnostic benefit from angiography. Angiogra- phy can only be justified when associated lesions of the cerebral vessels are suspected (e.g., dissection or rupture of a vessel wall, posttrau- matic aneurysms, arteriovenous malformations/fistulae). c) Angiography has a different importance in the case of subarachnoid haemorrhage. With its often abrupt onset and typical clinical picture, subarachnoid haemorrhage is the most frequently encountered of the potential neurological angiographic emergencies. Thrombosis of the cerebral veins and dural venous sinuses This type of pathology, now somewhat rare, can require emergency angiography when intracranial hypertension dominates the clinical picture. In such cases, angiography is used to confirm the clinicoradiological suspicions. However, while the cranial dural venous sinuses are more critically assessed angiographically, digital subtraction angiography (DSA) is only capable of providing indirect information on the thrombosis of cortical venous structures (e.g., slow arterial and venous circulation, areas of paucity of venous vessels, presence of collateral venous circulation). TECHNIQUES Angiography performed in emergency con- ditions is relatively difficult and requires a certain degree of experience as it is almost always performed in less than ideal circumstances. This difficulty is due both to the patient’s state of consciousness and ability to cooperate as well as to the gravity of the clinical picture, which requires the utmost rapidity of angiographic examination execution and immediate interpretation. The use of conventional angiography has been much improved by the advent of modern DSA appliances with high spatial definition (1024 x 1024 matrix). DSA allows, above all, reduced examination times, while the marked simplification of the radiographic technique has made it possible to limit the total amount of contrast medium required for each individual injection. In addition, the use of low concentration, low osmolarity, non-ionic contrast agents has reduced the potential contrast agent toxicity risk. In short, DSA has evolved into the a much simpler imaging modality with less risk to the patient. 118 I. CEREBROVASCULAR EMERGENCIES The only drawback of DSA is its sensitivity to even the slightest patient motion; this requires complete patient immobilization, which is typically only possible with deep sedation or general anaesthesia. If there are no specific con- traindications, such as underlying cerebral haemorrhage, minimal heparinization can be undertaken. With these exceptions, no other particular patient preparation is usually required. Patient vital functions and neurological sta- tus should be monitored constantly during the examination, and the patient should be kept under observation for 12-24 hours after the procedure. In the absence of contraindica- tions, the angiogram is performed through transfemoral access. Other routes of access (e.g., axillary, common carotid arteries) have a higher risk of local complications. Preliminary arch aortography used to explore the large supra-aortic arterial branches is preferable in general and specifically indispensable for identifying vacular variations and ostial/proximal atherosclerotic lesions. In order to study the aortic arch and its branches, the left anterior oblique projection is used with an angulation of 15-20 degrees; generally speaking, 20-25 ml of contrast medium are required with a flow rate of 10-15 ml/sec delivered over 1-2 sec- onds (total contrast volume: 25-50 ml). Stud- ies of the carotid bifurcation require both oblique projections in order to project the internal carotid free from the external carotid artery, as well as to study the walls and lumen of the vascular structures circumferentially. Although panoramic imaging of the cranial vasculature can be useful as a preliminary approach to locating major lesions and to analyse overall haemodynamic balance of flow between the cerebral hemispheres, selective catheterization of the cerebral vessels is almost always essential. Each arterial injection examined requires at least the two orthogonal projections during DSA; in many cases oblique projection imaging also needs to be performed in order to properly define the pathology. Each individual injection usually requires not more than 6-9 ml of contrast medium delivered at a rate of 6 ml per second (more in cases of arteriovenous malformation or large arteriovenous fistula). In latest generation angiographic appliances, the examination is fa- cilitated by improvements such as rotational angiography or even 3D angiography (20). APPLICATIONS We will examine the dual diagnostic and therapeutic role of angiography in ischaemic and haemorrhagic pathology, and omit trauma and thrombotic pathology of the venous structures, which are more rarely observed at emergency diagnostic cerebral angiography. Diagnostic role In cases of ischaemia and haemorrhage, angiography is usually principally responsible for identifying the vascular lesion(s) responsible for the clinical syndrome and for definitively determining the plan for therapy. a) Cerebral ischaemia: Regardless of whether it involves transient ischaemic attacks or frank infarction, the principle role of DSA is simply to identify the vascular lesion(s) responsible for the ischaemia. Further goals include the analysis of the degree of the stenotic/occlusive pathology and an estimation of its haemodynamic significance, exclusion of the presence of other lesions that could affect treatment and provision of a complete picture of cerebral haemodynamics. Another important factor is the characterization of such lesions: whether they are atherosclerotic, dysplastic (e.g., fibro- muscular dysplasia) or related to trauma (e.g., arterial dissection); and whether there are associated complications (e.g., intraluminal thrombus, ulceration of atherosclerotic plaques) (Fig. 1.101). In actual fact, today there are a number of examination techniques available (Echo- Colour-Doppler, MR angiography, CT angiography and SPECT), which alongside angiography contribute to this global evaluation and fi- nally to the formulation of treatment choices. b) Cerebral Haemorrhage: In the presence of haemorrhages, cerebral angiography plays a 1.10 CONVENTIONAL ANGIOGRAPHY 119 120 I. CEREBROVASCULAR EMERGENCIES Fig. 1.101 - (a-e) Cerebral ischaemia. (a-c) selective catheterism of the common carotid artery. In (a) plaque at the start of the internal carotid artery, with “rose thorn” image due to ulcer (arrow); kinking in the precranial stretch (small arrows); in b) irregular plaque (ulcerated). (d-e) Ultrasound of the carotid bifurcation. In (d) marked intimal thickening with flat plaques (arrowhead); in (e) coarse sclerocalcific plaque (arrow). a cd e b more complex role. Nevertheless, in cases of intraparenchymal haemorrhage, when performed correctly using proper techniques, angiography is able to identify or exclude the existence of associated underlying aneurysms or vascular malformations. With AVM’s, utmost attention must be paid to determining the arterial feeders, venous drainage and other singular anatomical and haemodynamic characteristics of the malformation (Fig. 1.102). This information is essential for treatment planning and for optimally choos- ing between surgery and transcatheter embolic therapy. The recent interest in intraoperative angiography made possible by the new portable and manageable DSA appliances have allowed to conduct angiographic examinations directly on the operating table. This approach could prove invaluable in immediate preoperative, intraoperative and postoperative evaluations of vascular malformations in patients with intraparenchymal haemorrhage. In the presence of subarachnoid haemorrhage the use of angiography is even more important and is essential in most cases to de- termine the optimal surgical approach. An- giography is the most suitable method for directly demonstrating the cause of the bleed (e.g., aneurysm or malformation) in such cases. At present, MR angiography and CT angiography can identify large and many of the smaller aneurysms; however, in patients with subarachnoid haemorrhage, negative MR angiography does not rule out the presence of an underlying aneurysm or vascular malformation. Therefore, although invasive selective angiography is not completely devoid of risks, at the present time it remains the most sensitive angiographic technique. Selecting the time at which to perform the examination is particularly difficult, and is much dependent upon the presence or absence of arterial vasospasm and the timing of surgery. Perform- ing angiography in the period during which vasospasm is most likely to be present (3-10 days after the bleed) can lead to a masking of the presence of the aneurysm sack due to non- filling. The decision as to whether to perform angiography either in the early phase (day one) following subarachnoid haemorrhage or later (two weeks) depends upon the decision of the surgical team and the patient’s clinical condition. This examination requires experience and diligence, paying particular attention to detail. It should also be pointed out that in certain situations, despite the utmost care in angiographic examination execution and interpretation, the study can be negative due to partial or total thrombotic occlusion of the aneurysmal lumen or to the persistence of the arterial vasospasm (18). Angiography permits an evaluation of the size of the aneurysm, its shape and its neck (Fig. 1.103). Angiography is also required to evaluate the entire cerebral arterial system both to search for other possible aneurysms as well as to perform a complete presurgical haemodynamic assessment. To this end, it can be useful to perform cross- compression of the contralateral cervical carotid artery during carotid injections in order to study the cross-filling, and therefore the collateral circulatory capacity, of the elements of the circle of Willis. Therapeutic role The interest and utility of interventional radiology is increasing in the neuroradiological field, especially in certain emergency situations where it can provide support for or even replacement of traditional therapeutic approaches. Cerebral ischaemia: In cerebral ischaemia, the principal therapeutic use of angiography is selective intraarterial fibrinolysis and percutaneous angioplasty. a) For some years now, selective intraarterial fibrinolysis has been used in treating acute ischaemia of the lower extremities as well as other regions of the body (e.g., renal, mesen- teric, coronary ischaemia). This has occurred primarily because of the introduction of new, efficient fibrinolytic drugs that are easy to han- dle and have low incidence of untoward side effects. Its use in the treatment of cerebral ischaemia, which in industrialized countries ac- counts for the third largest cause of death and 1.10 CONVENTIONAL ANGIOGRAPHY 121 is the most common cause of lifetime disabil- ity, is now available in many centres world- wide. Treatment must be begun within 6-8 hours from onset of the ischaemic ictus, once angiography has demonstrated the obstructive nature of the ischaemia. A microcatheter is in- troduced via the transfemoral route into the occluded artery; the distal tip of the catheter is positioned in contact with the thrombus and injecting from 200,000 to 1,000,000 Urokinase; 1/3 of the total amount of the dose is administered as a bolus, and the remainder as a continuous infusion over the subsequent 1-2 hours. The main hindrance to the wider use of this technique is the extreme sensitivity of the cerebral tissue to anoxia, which leaves a very small time margin between onset and the start of treatment, and the potential risk of peripheral non-cerebral and cerebral haemorrhagic complications (Fig. 1.104). The procedure requires a high degree of specific physician experience and a high level of organization of the medical and paramedical team involved. It is therefore typically only performed in highly specialized centres and in selected patients. However, statistics reveal encouraging figures for this technique. By re- specting rigid patient selection criteria, re- canalization of the occluded vessel varies from 44% to 100% of cases, and partial or total re- gression of the clinical picture is observed in 31% - 100% of cases (3, 7, 22). b) Until recently, percutaneous angioplasty, has found fertile ground in areas of the body outside the brachiocephalic region. The continuous technical evolution of the materials used (e.g., small calibre PTA catheters, thin- ner guide wires and flexible stents), the experience gained in other body regions and the 122 I. CEREBROVASCULAR EMERGENCIES Fig. 1.102 - (a-c) Intraparenchymal haemorrhage. a) CT: volu- minous intraparenchymal haematoma in right temporoparietal position of recent onset, with intraventricular expansion. (b-c) Selective catheterism of the right internal carotid artery, early and late arteriographic phase of same case: arteriovenous malformation (arrow) sustained by branches of the middle cerebral artery and the rear choroid arteries, with venous drain through ascending superficial veins (arrowheads). a b c perfection of medical support have made it possible to extend PTA to the supraaortic vessels, albeit with application and selection criteria that are yet to be universally accepted. It may be that PTA is not absolutely required in hyperacute emergency situations, however, it may be useful to perform this therapeutic procedure in a timely manner subacutely in patients with rapidly worsening transient ischaemic syndromes, when preceding angiography demonstrates the presence of a severe stenosis that is felt to be responsible for the 1.10 CONVENTIONAL ANGIOGRAPHY 123 Fig. 1.103 - (a-d) Subarachnoid haemorrhage. a) CT: subarachnoid blood expansion, at the occipital region of the cortical sulci (arrows). b) selective catheterism of the left vertebral artery (same case): small aneurysm of the left posterior cerebral artery, near to the start of the temporooccipital artery (arrow). c) selective catheterism of the left internal carotid artery: small sac-shaped aneurysm of the anterior communicating artery (arrow). d) selective catheterism of the left internal carotid artery: aneurysm of the anterior communicating artery (arrowhead); spasm of the anterior cerebral artery (arrow). a c b d [...]... that can occur b Fig 2.10 - (a-b) A large epidural haematoma is seen in left temporal-parietal region (a) associated with an overlying skull fracture (b) Tab 2.5 - Post-traumatic sequelae of head injuries 1) - Cortical atrophy 2) - Encephalomalacia 3) - Pneumocephalus 4) - Leptomeningeal cyst formation 5) - Cranial nerve lesions 6) - Diabetes insipidus (pituitary injury) 7) - Hydrocephalus (communicating... 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AJNR 14: 34 6-3 47 ,1993. 14. Milburn JM, Moran CJ, Cross DT et al: Effect of intraarterial papaverine on cerebral circulation time. AJNR 18: 108 1-1 085, 1997 angulation of 1 5-2 0 degrees; generally speaking, 2 0-2 5 ml of contrast medium are required with a flow rate of 1 0-1 5 ml/sec delivered over 1-2 sec- onds (total contrast volume: 2 5-5 0 ml). Stud- ies of