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  • Timing of Angiography and Patient Considerations A ngiography for SAH should be performed promptly, considering the patient’s overall medical and neurologic condition to establish the diagnosis and facilitate timely treatment . In cases of aneurysmal SAH, the peak incidence of rebleeding occurs within the first 24 hours (4.1%), then drops to approximately 1.5% per day for a cumulative rebleed rate of 26.5% for the first 2 weeks in patients not receiving antifibrinolytics . For selected patients, early therapeutic intervention prevents acute aneurysmal rehemorrhage and allows for effective medical or endovascular treatment for delayed ischemic neurologic complications (vasospasm). Patients considered good candidates for early surgical or endovascular treatment require early angiography. Angiography for very ill or unstable patients may be deferred. When surgery has been significantly delayed after initial angiography has been performed, it may be necessary to repeat the study. The development of vasospasm and cerebral ischemia may influence surgical planning, whereas the resolution of vasospasm may allow the visualization of additional vascular pathology missed on the initial study. There are several reports of spontaneous thrombosis of cerebral aneurysms occurring 2 weeks to 2 years following initial angiography Conversely, recanalization of previously thrombosed aneurysms or de novo aneurysm development has also been reported. Acute SAH patients may be gravely ill and special attention to their clinical condition is mandatory. In the angiography suite, the patient should be adequately monitored, minimally requiring frequent vital signs and electrocardiographic monitoring. An automated sphygmomanometer and a pulse oximeter are desirable. A nurse may help to assess the patient’s neurologic and hemodynamic status, as well as administer oxygen, intravenous fluids, and medications. It is safest and most efficient for the neuroradiologist to be able to concentrate on the performance and interpretation of the study; however, it must be remembered that during the procedure, care for the patient is the operator’s responsibility and should remain the highest priority. For stuporous, comatose, or hemodynamically unstable patients, proper medical care, intubation before the procedure, and use of intravenous sedation or general anesthesia by anesthesia personnel is recommended. A moving, uncooperative, or unstable patient is subject to higher risk during the procedure and increased likelihood of poor quality or nondiagnostic images. If adequate clinical care cannot be given to a seriously ill patient during angiography, the study should be deferred until the necessary arrangements can be made. Cerebral angiography is an invasive procedure and carries inherent risks. A study reviewing 1000 consecutive transfemoral cerebral angiograms disclosed a 1% transient and a 0.5% permanent neurologic deficit within 24 hours secondary to the procedure. Complications correlated with age, length of procedure, and contrast burden
  • and occurred more frequently in patients presenting with a history of stroke, transient ischemic attack, and carotid bruit. Referring to the annual risk of aneurysmal rupture, and the morbidity and mortality of SAH, the benefit derived from the angiographic information outweighs the potential risks. Postangiography headache, possibly due to catheter or contrast-induced release of vasoactive substances, occurs in up to 33% of patients, may be accompanied by nausea, vomiting, photophobia, and phonophobia, and should be differentiated from rehemorrhage. One recent study reported a 4.8% incidence of angiography-induced rerupture when performed within 6 hours of the initial SAH. This incidence is lower than previously reported and is not much different than the natural incidence of rehemorrhage; thus, early angiography should not be discouraged. Pan Cerebral Angiography Versus Limited Study As discussed earlier, patients with intracranial aneurysms often harbor multiple lesions. The possibility of associated unruptured aneurysms in the setting of aneurysmal SAH mandates the performance of pan cerebral angiography to assess the entire cerebral circulation.. Although incomplete angiography is not encouraged, it has been suggested that in cases of medically unstable or neurologically deteriorating patients, or when inexperienced angiographers are performing emergent studies, limited angiography may be performed. The estimated risk of erroneous surgical exploration given a suggestive CT and a limited angiogram is less than 0.4%. Conversely, demonstration of multiple aneurysms by pan cerebral angiography allows the surgeon the opportunity to perform a single-stage approach to clip all accessible unruptured aneurysms while attending to the ruptured one, obviating the need for additional surgery. Additionally, it may significantly affect patient management with regard to hypertensive or hypervolemic therapy, as well as influence decisions regarding endovascular therapy for these aneurysms. Unless prohibited by special anatomic considerations, four vessel is routinely performed angiography. If bilateral internal carotid and vertebral artery injections do not reveal intracranial lesions, external carotid artery angiography should be done specifically to evaluate the potential presence of dual vascular pathology. Follow-up for an Initial Negative Angiogram In patients with acute spontaneous SAH, pan cerebral angiography will not reveal a finding in approximately 10% to 20% of cases .Several factors may account for this negative evaluation. Focal vasospasm may prevent adequate opacification of an aneurysm and reduces the certainty of a negative angiogram. The presence of vasospasm influences the decision regarding the timing and number of follow-up
  • angiograms and is discussed later in this article. Spontaneous thrombosis of a ruptured intracranial aneurysm has been described in 9% to 13% of various autopsy series. Several theories have been proposed concerning the pathogenesis of spontaneous thrombosis, relating it to stasis, hypercoagulability, or endothelial injury. Cerebral vasospasm, systemic hypotension, local damage to the arterial wall due to aneurysmal rupture, and antifibrinolytic agents have also been implicated. The relationship between the size of the aneurysmal neck and the volume of the aneurysmal sac has also been suggested as a predisposing factor because a narrow neck may facilitate stasis and thrombosis. Conversely, recanalization of acutely thrombosed aneurysmshas also been described Traditionally, the interval between the initial study and repeat angiography has been 3 to 6 weeks to allow for possible vasospasm to resolve. However, a change in clinical status or a significant finding by noninvasive imaging may affect the decision to repeat angiography at an earlier time. Angiographic Considerations Cerebral angiography for the evaluation of saccular aneurysms should achieve more than simply demonstrating the presence or absence of a lesion. Detailed anatomic information is required for optimal planning of surgical or endovascular intervention. Using anatomic principles and radiographic techniques the angiographer should try to demonstrate the following: • The size, shape, and orientation of the aneurysm; the angiographic lumen should be compared with axial imaging for correlation. • The location, size, and extent of the aneurysm neck in relation to the aneurysm fundus and parent vessel. The angiographic neck may differ from that demonstrated by axial imaging. Accurate delineation of the neck is mandatory for endovascular treatment considerations. The parent vessel from which the aneurysm arises, including size, configuration, and anatomic variations. • The relationship of the aneurysm to the surrounding vasculature. • Collateral blood flow patterns pertinent to the vascular territory at the level of the circle of Willis and leptomeningeal pathways. • Multiplicity of aneurysms. In patients with SAH, sufficient characterization is necessary to suggest which aneurysm has hemorrhaged. Correlation with axial imaging is recommended. • The presence of thrombus within the aneurysm and associated thromboembolic complications. Evidence of vasospasm (localized or generalized) or cerebral ischemia. Mass effect or vascular displacement secondary to intraparenchymal hemorrhage or by the aneurysm itself. • Associated vascular anomalies and diseases (AVMS, fibromuscular dysplasia, vasculitis, atherosclerosis, moyamoya).
  • • Growth or change in aneurysm morphology compared with prior studies. • Demonstration of external carotid artery branches when bypass surgery is anticipated. The anatomic information related to the aneurysm and the parent vessel, as well as information concerning the “physiologic neck,” inflow and outflow sites and vortex flow may prove useful in designing strategies and predicting longevity of endo- vascular treatment as well as deciding among therapeutic modalities. To acquire this complex information, the angiographer needs to be aware of patient positioning, radiographic projection, centering, and collimation. Because DSA systems are prevailing, most of these are performed with live fluoroscopy by the operator. These tasks were previously performed and mastered in conventional film screen angiography by the radiologic technologist with position change of the patient’s head according to projection protocols. The fluoroscopic recognition of different projections, as described previously in the literature, is mandatory to obtain them efficiently by rotating and moving the x-ray tube and image intensifier. It is helpful to recognize the relationship between the orbital rim and the superior aspect of the petrous bone in the anterior- posterior (AP) plane . Variations of oblique views are routinely used to evaluate different segments of the intracranial circulation . Ongoing adaptation and modification are necessary because anatomic variants, vessel tortuosity, structural changes, head position, and angiographic equipment may influence the projection of vessels. When faced with multiple aneurysms in,SAH, it is necessary to decide which aneurysm ruptured .CT localization, angiographic signs, and aneurysmal size and shape.are important in determination of the beeding anerysms ACommA had the highest probability of rupture (62%) followed by BA and PICA aneurysms (50% each) and PCommA aneurysms (38%). Larger and more irregular aneurysms are more likely to have bled, with irregular shape being the more consistent predictor. Angiographic signs suggesting hemorrhage include contrast dye extravasation (pathognomonic), focal mass effect, focal vasospasm, and presence of a nipple. New focal vasospasm or a change in aneurysm shape, determined by sequential angiograms, are highly suggestive. Identifying the symptomatic aneurysm is important because studies suggest that the morbidity and mortality of patients with multiple aneurysms and SAH is related to the ruptured aneurysm and not the asymptomatic lesions. Angiography of Unusual Aneurysms Serpentine aneurysms arise most commonly from the MCA (51 %). The PCA, vertebrobasilar junction, and supraclinoid ICA constitute most of the remaining locations. Angiography is pathognomic revealing an irregular, serpiginous vascular channel with markedly slow flow and separate entrance and exit sites, terminating in normal vessels supplying vital tissue. Angiographic evaluation should provide information regarding collateral sources of blood supply to cerebral tissue in the distribution of the aneurysm, including the relevant leptomeningeal circulation. The external carotid artery (ECA) should also be selectively studied because therapy often will include consideration of a vascular bypass graft to support distal vascular territories. Mass effect from the thrombosed portion of the aneurysm may be appreciated. Superselective angiography, test occlusions, and functional amytal testing may be performed .
  • Dissecting aneurysms have a distinctly different distribution from that of saccular aneurysms. Reportedly, the most frequent locations are MCA, 41 %; VB, 23%; ICA, 21%; and ACA, 13%.” Angiography remains the most accurate study for the delineation of these lesions .four angiographic features are described: (1) retention of contrast mediainside an aneurysm through the late arterial and venous phases; (2) double lumen with an aneurysmally dilated false lumen; (3) irregular narrowmg proximal or distal to the aneurysm; and (4) rapid changes with disappearance or emergence of fusiform-like aneurysms upon repeated studies. Additional angiographic description refers to irregular “pearl and string” dilatations and narrowings of the vessel wall without definite aneurysm. Treatment combines supportive measures for any ischemic sequela and aneurysm exclusion, usually by parent vessel occlus ion. Erroneous Angiographic Diagnosis of Cerebral Aneurysms An erroneous angiogram is a false-negative study in which an aneurysm is missed Or a false-positive study in which something is mistakenly identified as an aneurysm. Superimposition of vessel loops projecting as an aneurysm is a cause for a false-positive study. The true nature of the anatomy may be delineated by using different projections, increased magnification, and high- frame rate acquisition. Typically, superimposed vascular loops may be suggested by the presence of a “double density” without contour abnormality. The presence of an infundibular dilatation at a vessel origin, particularly the PCommA, may occasionally be difficult to distinguish from a small aneurysm. Infundibula are identified by the following criteria 1. size less than 3 mm 2. triangular (funnel) shape 3. vessel arises from the apex of the dilatation. Because some authors caution that infundibular dilatations are not always “normal” and may on rare occasion be the cause of SAH, these criteria should be strictly applied when excluding the possibility of an aneurysm. Vertebral artery angiography to opacify the posterior communicating ICA junction in a retrograde fashion may be helpful to delineate an infundibulum from an aneurysm. Failure to identify a small-sized aneurysm may simply be due to the inability to project the lesion adequately. Small aneurysms may be obscured by surrounding vasculature and additional projections are required to reveal or exclude them. Conversely, several inherent physiologic and anatomic conditions may produce a false- negative study including aneurysm thrombosis , parent vessel thrombosis, or vasospasm. Because these conditions are potentially reversible, repeat angiography is mandatory. MR angiography may demonstrate a thrombosed aneurysm that failed to opacify by angiography and may be complementary to a negative study. It has been suggested that MR angiography may demonstrate an aneurysm not identified by conventional angiography, although suboptimal angiographic technique may also play an important role . Technical error, such as inadequate contrast injection, may prevent aneurysmal opacification especially in areas where washout by collateral flow exists (ACommA and PCommA). The neuroangiographer should be mindful of the pitfalls and thus avoid the erroneous study.
  • Angiography for Vasospasm Clinically significant vasospasm develops in up to 30% of patients following aneurysmal SAH. The incidence of this complication is highest 4 to 12 days following the initial bleed. Although the etiology is still obscure, there is evidence to support the concept that vasospasm is induced by vasoconstrictive substances released by lysed blood cells. A patient’s response to vasospasm correlates with several factors including the volume of blood within the subarachnoid spaces, cerebral perfusion pressure, hematocrit, and collateral blood supply to the cerebrovascular territory at risk . Early exclusion of a ruptured aneurysm from the circulation in combination with calcium channel blockers, cerebrospinal fluid drainage, intracranial pressure monitoring, and “triple H” therapy (hemodilution, hypertension, hypervolemia) are used to improve the patient’s outcome. Transcranial Doppler ultrasonography is used routinely as a noninvasive method for early diagnosis and quantitative monitoring of the development and course of vasospasm. Changes in the Doppler wave form and velocity, in conjunction with frequent neurologic examinations, serve to select patients for repeat angiography and possible endovascular treatment because early detection and treatment improves outcome. Angiography performed in delayed cerebral ischemia may show widespread vessel narrowing or localized caliber changes, mainly involving vascular segments within the basal cisterns. Percutaneous angioplasty is directed toward dilatation of arteries supplying the vascular territorie most likely accounting for a specific neurologic deficit . s Mechanical vessel dilatation is performed with a balloon or microcatheter, whereas “chemical angioplasty” uses intra-arterial infusion of papavarine. experience indicates that the vasodilatory effect of mechanical angioplasty is permanent whereas that following papavarine may be only transient and often is associated with increases in intracranial pressure . Angiographic improvement is judged by vessel caliber and vascular filling and usually correlates with immediate improvement in transcranial Doppler parameters. When performed early in the clinical course, neurologic improvement ensues. ruptured aneurysm from the circulation is well established, we may approach the time when diagnostic cerebral angiography can offer an early diagnosis in combination with early endovascular therapy, allowing supportive treatment for the complications of SAH.