Stump Pressure Research Articles

Division of the left renal vein during aortic surgery

Perirenal aortic exposure and control can be facilitated by division of the left renal vein (LRV), but only if adequate collateral venous drainage is present. When incremental elevations in LRV pressure were produced in nine dogs, we noted that left renal glomerular and tubular function (creatinine clearance, sodium retention, urine osmolality, and urine output) were virtually lost at pressures greater than 50 to 60 cm water. Between January 1967 and December 1989, 64 patients underwent LRV division during the performance of abdominal aortic aneurysm surgery (57 of 589 = 10%) or reconstruction for aortoiliac occlusive disease (7 of 506 = 1%). LRV stump pressures (LRVSPs) were measured in 44 of these patients and were less than or equal to 60 cm water in all but one instance. Ten of the 64 patients died, but none as a consequence of this maneuver. Post-operatively, all survivors had serial serum creatinine levels measured and either an intravenous pyelogram, renal scan, or arteriogram. One case of a non-functioning left kidney was identified. This occurred in the only patient who underwent re-anastomosis after LRV division. A LRVSP equal to or greater than 50 cm water and extreme venous distention after test clamping served as a contraindication to LRV division in seven other patients. We conclude that a LRVSP less than or equal to 50 to 60 cm water indicates that the LRV may be safely divided during juxtarenal aortic exposure. However, a pressure greater than or equal to 50 to 60 cm water suggests that LRV division should not be carried out unless absolutely essential and then only if right kidney function is known to be adequate.

Intraoperative Electroencephalographic Monitoring During Carotid Surgery with Routine Shunting

Fifty-nine patients undergoing sixty-four carotid reconstructions with routine intraluminal shunting had intraoperative electroencephalographic monitoring. The onset of rhythm or amplitude disturbances was demonstrated in 14 patients during exposure of the carotid artery, and in 24 patients during initial carotid clamping. Disturbances were seen in 15 patients during the period of intraluminal shunting and increased momentarily during the second clamping period. During closure of the surgical wound, all abnormalities disappeared except in one patient who ultimately developed a neurologic deficit upon awakening. Although patients who maintained normal electroencephalographic readings had higher carotid stump pressure (59 mm) than those who did not (42 mm), individual values were scattered. Intraoperative monitoring during carotid surgery with routine shunting has little usefulness.

Clinical observations on the effect of carotid artery occlusion on cerebral blood flow mapped by xenon computed tomography and its correlation with carotid artery back pressure

Xenon computed tomographic cerebral blood flow mapping was correlated with internal carotid artery stump pressures and clinical neurologic assessment during temporary internal carotid artery occlusion. One hundred fourteen patients with skull base tumors or intracranial aneurysms potentially requiring carotid resection or ligation underwent angiography, xenon CT cerebral blood flow mapping, and internal carotid artery blood pressure monitoring. The internal carotid artery was then temporarily occluded with a balloon catheter, stump pressure was measured through the catheter, and the xenon CT cerebral blood flow mapping was repeated. Adequate xenon CT cerebral blood flow was defined as >30 cc/100 gm/min. All patients had normal xenon CT cerebral blood flow before internal carotid artery occlusion. During internal carotid artery occlusion, xenon CT cerebral blood flow was found to be normal (group I, 40 patients), globally reduced but still within the normal range (group II, 50 patients), or low in the distribution of the ipsilateral middle cerebral artery (group III, 13 patients). With balloon occlusion, an immediate neurologic deficit developed in 11 patients (9%) requiring deflation of the balloon preceding xenon CT cerebral blood flow measurement (group IV). In group I internal carotid artery blood pressure was 128 mm Hg. (range 85 to 171 mm Hg) with stump pressure 86 mm Hg (range 46 to 125 mm Hg). In group II internal carotid artery blood pressure was 130 mm Hg. (range 78 to 199 mm Hg), with stump pressure 86 mm Hg (range 31 to 150 mm Hg). In group III internal carotid artery blood pressure was 135 mm Hg (range 95 to 194 mm Hg) with stump pressure 64 mm Hg (range 37 to 106 mm Hg). In group IV internal carotid artery blood pressure was 117 mm Hg (range 90 to 148 mm Hg), with stump pressure 62 mm Hg (range 23 to 100 mm Hg) p < 0.01 for stump pressure groups I and II versus III and IV. During subsequent operations one of the 23 patients in groups I and II requiring carotid occlusion or ligation had a stroke, but four of five patients (80%) in groups III and IV had strokes after internal carotid artery occlusion or resection. Although stump pressure correlates with xenon CT cerebral blood flow mapping, the wide range precludes its use alone as an absolute predictor of adequate cerebral blood flow after carotid occlusion. In addition, xenon CT cerebral blood flow mapping and trial internal carotid artery balloon occlusion are of value in predicting the hemodynamic consequences of carotid ligation.

頚動脈血流遮断時の２次元脳電図，３次元脳血流の変化とｓｔｕｍｐ ｐｒｅｓｓｕｒｅ

術前の脳血流, 脳波測定, 術中のモニタリングより頸動脈血流遮断による血行動態について検討を行った.Xe-433吸入法SPECTによる一側総頸動脈圧迫前及び圧迫中の中大脳動脈領域平均血流量は各々47ml, 37mlで, 圧迫により有意に減少した.頸動脈圧迫により二次元脳電図で同側delta-activityの出現, または増加が認められたのは21例中6例で, 他の15例では特に変化が認められなかった.このdelta-activityの出現あるいは増加した例の血流量は33mlで, 平均内頸動脈stump pressureは40mmHgであった.一方, 無変化群では42ml, 63mmHgであり, いずれにおいても変化群で有意に低値を示した.術中測定のSEPはearly componentの振幅で50%以上の高度低下を示したものは18例中5例で, この内4例では術後一過性の神経症状を示し, 術中脳虚血のよき指標となることが判明した.

Experience of Carotid Endarterectomy

The clinical course of 45 patients treated by carotid endarterectomy over the past 5 years is described with emphasis on the following three points: 1) Diagnostic methods, namely digital subtraction angiography (DSA) and B-mode Doppler imaging technique; 2) surgical procedure using an improved shunt tube and surgical instruments; and 3) monitoring before and during surgery. All operations were conducted using a shunt. Morbidity and mortality rates were both 0%. Postoperative transient hemiparesis lasting for 6 hours was recognized in only four cases. The total percentage of correct diagnoses using intravenous DSA compared with conventional angiography was approximately 80%. The accuracy of the non-invasive B-mode Doppler technique in measuring the degree of constriction compared with conventional angiography was 84%. The shunt was made of silicone tubing and was based on a tube 30 cm in length and 3.5 mm in diameter which was a T-shaped loop. Different sized bulbs were fixed to each end of the tube to prevent extravascular deviation. Modified bulldog clamps and Sugita clips were used for fixation in the vessel. Regional cerebral blood flow (rCBF) measurement and electroencephalography (EEG) under contralateral Matas procedure were conducted before surgery, and cross circulation during short-term occlusion of the common carotid artery was evaluated. The emergence or increase of delta waves in EEG during occlusion was observed in six cases. The rCBF of the affected middle cerebral artery territory in these patients was lower than that in patients with no increase of delta waves. Furthermore, the mean stump pressure during surgery in cases with preoperative EEG changes was 40 mmHg and that in cases without changes was 63 mmHg; these values were significantly different.(ABSTRACT TRUNCATED AT 250 WORDS)

Carotid Artery Stump Pressure: How Reliable Is It in Predicting the Need for a Shunt?

Carotid artery stump pressure was measured in 84 cases of carotid endarterectomy. The operations were performed in 71 patients over a period of five years. An altered neurological status during temporary occlusion of the carotid artery, assessed with the patient under local anesthesia, was the sole criterion for shunt placement. Stump pressure (SP) was significantly higher in the 69 unshunted cases (mean of 53.3 mmHg) than the 15 shunted cases (mean of 34.2 mmHg). Shunt was required in two of 41 cases (5%) with SP of greater than 50 mmHg, eight of 36 cases (22%) with SP of 25-50 mmHg, five of seven cases (71%) with SP of less than 25 mmHg. The clinical presentation, including history of prior stroke, and the presence of contralateral disease (including complete carotid occlusion), did not influence the need for a shunt. In this series, carotid artery stump pressure has greater predictive value for shunt requirement when it is greater than 50 mmHg or less than 25 mmHg. However, monitoring the neurological status of the patient in the awake state is still the most reliable method of determining shunt requirement. In our experience, this is associated with minimal morbidity and no mortality.

Continuous conjunctival oxygen tension (PcjO2) monitoring for assessment of cerebral oxygenation and metabolism during carotid artery surgery.

The clinical value of noninvasive continuous monitoring of conjunctival oxygen tension for assessment of cerebral perfusion during carotid endarterectomy performed under general anaesthesia has been evaluated. The patients (n = 17; mean age 62.5 +/- 1.7 years) were monitored as follows: conjunctival oxygen tension (PcjO2); internal jugular venous oxygen tension at the skull base level (PcijvO2); arterial blood pressure; arterial and internal jugular venous blood gases; acid-base data and lactate, pyruvate levels; end-tidal CO2 concentration. The mean preanaesthetic PcjO2 level of 4.86 +/- 0.40 kPa was significantly lower than PaO2(PcjO2)/PaO2 ratio of 0.48). Following anaesthesia, a larger PcjO2-PaO2 gradient (ratio 0.32) was seen in spite of the hyperoxic situation (FiO2 = 0.40) due to vasoconstriction induced by slight hypocapnia (reduction of PaCO2 from 5.13 +/- 0.08 to 4.64 +/- 0.10 kPa). The carotid artery crossclamping resulted in a rapid and pronounced decrease of PcjO2, while PcijvO2 remained unchanged. No relationship between PcjO2 and stump pressure was found, while a significant correlation (P less than 0.02) between PcjO2 and lactate in effluent venous blood from the brain was demonstrable. It is concluded that PcjO2 monitoring seems a clinically useful trend indicator of cerebral perfusion in the individual patient. Due to large interindividual variations in basal PcjO2 readings and in PcjO2 changes during carotid artery clamping, however, transconjunctival oxygen tension monitoring does not seem to allow early and accurate recognition of impending cerebral ischaemia during carotid endarterectomy, and its routine use therefore seems of limited value.

Carotid artery stump pressure: How reliable is it in predicting the need for a shunt?

Carotid artery stump pressure: How reliable is it in predicting the need for a shunt?

A Comparison of Computerized EEG with Internal Carotid Artery Stump Pressure for Detection of Ischemia During Carotid Endarterectomy

Previous investigations appear to indicate that an ischemic EEG is not observed during carotid cross-clamping when the stump pressure is >/=60 mm Hg. In this report of 124 carotid endarterectomies (CEA) performed with selective shunting based on computerized EEG (CEEG), we compared the CEEG and this previously established critical stump pressure level of 60 mm Hg as methods of detecting cerebral ischemia during carotid clamping. A significant association between stump pressure and CEEG findings during clamping existed (p <0.05). Only 1 of 44 patients with a stump pressure >/=60 mm Hg received a shunt based on CEEG signs of cerebral ischemia. However, 62 of the remaining 80 patients did not receive a shunt and awoke neurologically intact despite a stump pressure <60 mm Hg. A highly significant association between the postoperative neurologic exam and the CEEG findings during carotid clamping was demonstrated (p <0.001). In contrast, for stump pressure, a correlation with the neurologic exam was not found. Compared to CEEG, these results appear to indicate that a critical stump pressure of 60 mm Hg is a sensitive but not specific indicator for the placement of a shunt selectively during CEA. The combined use of these two monitors should lead to reliable shunt selection, especially when stump pressure is <60 mm Hg.

Does Anesthetic Technique Make a Difference? Augmentation of Systolic Blood Pressure During Carotid Endarterectomy

SMITH, J. S.; ROIZEN, M. F.; CAHALAN, M. K.; BENEFIEL, D. J.; BEAUPRE, P. N.; SOHN, Y. J.; BYRD, B. F.; SCHILLER, N. B.; STONEY, R. J.; EHRENFELD, W. K.; ELLIS, J. E.; ARONSON, S. Author Information

Hemodynamic performance of carotid artery shunts

Although the use of shunts for carotid artery surgery remains controversial, the hemodynamics of the shunts currently available have not been carefully evaluated in vivo. We developed an animal model using contralateral carotid artery ligation, which produced ipsilateral carotid blood flows (640 ± 44 ml/min) and internal carotid stump pressures (52 ± 4 mm Hg) over a range commonly seen in carotid artery surgery. Seven shunts were tested and included Javid; 10F and 8F Brener; and 14F, 12F, 10F, and 8F Argyle shunts. The hemodynamic features evaluated for each shunt included maximum shunt flow, the pressure gradients occurring across each shunt, the increase in cerebral perfusion pressure over occlusion pressure associated with shunt placement, and the distal pressure pulse waveform. The larger diameter shunts were consistently better than the smaller diameter shunts. The correlation between shunt flow and the increase in distal pressure produced by shunt placement was high (r = 0.98, p < 0.05), confirming that high flow rates maintained high perfusion pressure. By relating maximum shunt flow and the pressure gradient to the change in the pressure pulse contour for each shunt, it could be demonstrated that at the larger diameters, straight shunts displayed superior hemodynamic characteristics compared with tapered shunts, whereas at smaller diameters, tapered shunts were superior.

Repair of Abdominal Aortic Aneurysms in Patients with Renal, Iliac, or Distal Arterial Occlusive Disease

Appropriate preoperative vascular assessment of patients presenting with aortic aneurysms and arterial occlusive disease is essential to obtain the optimal results from aneurysm repair. The renal arteries should be evaluated in patients with hypertension or renal dysfunction, and stenosis must be addressed when seen on arteriograms. Hemodynamically significant lesions are candidates for bypass concomitant with aortic replacement. The stump pressure of a patent inferior mesenteric artery should be assessed intraoperatively, and bypass or reimplantation should be performed if colon ischemia might result from internal mesenteric artery ligation. If vasculogenic impotence is suggested by preoperative studies, meticulous nerve-sparing dissection and revascularization of the internal iliac arteries may result in recovery of erectile function in some patients. In all cases of aneurysm repair, the hypogastric circulation must be maintained through either direct revascularization or bypass to major collateral arteries. Iliac occlusive disease may be evaluated with several modalities, including physical examination, noninvasive laboratory testing, arteriography, and the papaverine test, to determine whether critical or subcritical stenoses are present. Aortic bifurcation grafts should be used to construct the distal anastomoses beyond areas of significant disease. The extent of lower-extremity occlusive disease directly affects the long-term patency of aortic replacement, and diligent follow-up is necessary for timely intervention to maintain patency of vascular reconstructions.

Hemodynamics of the hypogastric arterial circulation

This study was designed to assess the major sources of collateral supply to the hypogastric arterial bed (HGA). Peak systolic HGA and radial arterial pressure were obtained before and after clamping a patent HGA and after additional clamping of the contralateral HGA, the contralateral external iliac artery (EIA), or the ipsilateral EIA both selectively and in combinations. These procedures were performed in 10 patients with aortoiliac (AI) aneurysms or occlusive disease. In seven patients with aneurysms, clamping the contralateral HGA decreased the HGA stump pressure index from 0.57 to 0.49 (p less than 0.05), and clamping only the ipsilateral EIA decreased the stump pressure index to 0.38 (p less than 0.001). In three patients with occlusive disease, clamping the contralateral HGA did not decrease the stump pressure index, clamping both the contralateral HGA and EIA decreased the index from 0.61 to 0.57 (p greater than 0.05), and clamping only the ipsilateral EIA decreased the pressure index to 0.40 (p less than 0.01). These data suggest that branches of the ipsilateral EIA femoral arterial system provide a more significant collateral pathway than the contralateral HGA. These results suggest that it is important to relieve occlusive disease in the ipsilateral EIA femoral arterial system if a patent HGA is ligated or bypassed during AI reconstructions. Conversely, it is especially important to preserve forward perfusion in a patent HGA in a patient with compromised ipsilateral EIA femoral runoff.

Local versus general anaesthesia in carotid surgery. A prospective, randomised study

A randomised, prospective study was performed to compare local (LA) and general anaesthesia (GA) in carotid surgery with special emphasis on complications and the need for intra-operative shunting. Fifty-six patients were randomised to LA and 55 to GA. Eight patients in the LA group required a GA for various reasons. During the same period 14 patients were not randomised. Seven perioperative neurological deficits occurred (5.6%), four in the LA group, two in the GA group, and one in the non-randomised group (NS). Selective shunting was used, in the Ga group according to stump pressure or in cases with a previous stroke and in the LA group according to the appearance of neurological symptoms. In the GA group 25 patients were shunted and in the LA group five patients (P less than 0.001) needed a shunt. If strict pressure criteria for shunting had been used in the LA patients, ten would have been shunted and three of the patients who developed symptoms during clamping would not have been shunted. During surgery the highest recorded systolic pressure was significantly higher in the LA group (210 mmHg versus 173 mmHg, P less than 0.001). LA for carotid endarterectomy is comparable with general anaesthesia regarding peroperative complications but produces significantly higher blood pressures than general anaesthesia. On the other hand it allows the possibility of neurologic monitoring of the patient and leads to significantly less use of an intra-operative shunt.

Monitoring of Somatosensory Evoked Potentials during Extracranial Revascularization

Intraoperative somatosensory evoked potentials (SEPs) were measured in 17 patients during 21 extracranial revascularization and related procedures. The operations included 13 carotid endarterectomies (CEAs), two cervical internal carotid ligations, one vertebral artery (VA) clipping, one VA-common carotid artery (CCA) transposition, and four temporary balloon occlusion tests (TBOTs). Three of the 13 CEAs (23%) showed reduced amplitude and delayed latency of primary cortical SEPs during clamping of the carotid artery, followed by their recovery after emplacement of the internal shunt. Flattening of SEPs during clamping of the CCA was observed in the case of VA-CCA transposition; however, SEPs returned to normal immediately after insertion of a balloon indwelling shunt into the CCA. One of the four TBOTs showed alteration of SEPs during balloon occlusion of the subclavian artery proximal to the origin of the VA. In the others, SEPs remained stable during the entire procedure. Only one transient intraoperative ischemic complication was encountered among the cases of CEA. It was detected through flattening of SEPs, which led to the discovery of an internal shunt obstruction. Carotid stump pressure was also measured in 12 CEAs and two TBOTs, and seven of these 14 had pressure less than or equal to 50 mmHg. Four of the seven had carotid stump pressure less than or equal to 30 mmHg, and three of these four also showed altered SEPs. SEPs remained stable if the collateral flow was sufficient during vascular occlusion and showed obvious alteration when the blood flow was reduced to below the threshold. The authors conclude that monitoring of SEPs during extracranial revascularization is very useful.

Importance of cerebral collateral pathways during carotid endarterectomy.

Before surgery, we evaluated major intracranial collateral pathways using transcranial Doppler ultrasonography (TCD) in 50 patients who then underwent carotid endarterectomy with concurrent multimodality cerebral monitoring. Patients were grouped with respect to collateral pathways demonstrated preoperatively by TCD: Group 1, good collateralization with an anterior and/or posterior communicating artery ipsilateral to the operative carotid lesion (29 patients, 58%); Group 2, collateral pathways present but impeded by other proximal stenoses (nine patients, 18%); and Group 3, no collateralization identified (nine patients, 18%). Three patients (6%) could not be classified. TCD identified major collateral pathways with a sensitivity of 89% and a specificity of 80% when compared with arteriography. During carotid endarterectomy mean middle cerebral artery velocity, pulsatility index, and stump pressure were higher and the decrease in middle cerebral artery velocity with extracranial carotid artery cross clamping was significantly less among Group 1 patients than among Group 2 and 3 patients (p less than 0.05 for both groups). Group 1 patients required fewer intraoperative carotid artery shunts and developed fewer ischemic electroencephalographic abnormalities than did patients in Groups 2 and 3 (p less than 0.05 for both groups). TCD assessment of cerebral collateralization helps predict hemodynamic consequences of cross clamping during carotid endarterectomy.

Monitoring of subcortical and cortical somatosensory evoked potentials during carotid endarterectomy: comparison with stump pressure levels: Gigli GL, Caramia M, Marciani MG, et al. Electroencephalogr Clin Neurophysiol 1987;68:424–432

Monitoring of subcortical and cortical somatosensory evoked potentials during carotid endarterectomy: comparison with stump pressure levels: Gigli GL, Caramia M, Marciani MG, et al. Electroencephalogr Clin Neurophysiol 1987;68:424–432

Transcranial Doppler in the management of extracranial cerebrovascular disease: Implications in diagnosis and monitoring

Transcranial Doppler (TCD) insonation permits quantitative nonivasive evaluation of intracerebral arterial velocity. With the use of 2 MHz Doppler through a transtemporal approach, middle cerebral artery blood velocity (MCA-V, centimeters per second) and major collaterals were measured in 96 patients, including 15 normal control subjects, 66 patients with extracranial cerebrovascular disease (ECCVD), and 15 patients with other medical problems without ECCVD. MCA-V was higher in control subjects (62.7 ± 15.1) than in patients with ECCVD (45.0 ± 16.3, p < 0.05). There was no significant inverse correlation between MCA-V and the degree of internal carotid artery stenosis present by duplex examination. Twenty-three patients monitored during carotid endarterectomy had a mean MCA-V under anesthesia of 37.0 ± 16.9, which decreased to 22.4 ± 14.8 during cross-clamping (p < 0.01). MCA-V during cross-clamping correlated directly with stump pressure (R = 0.87) and was higher when major collaterals were identified before operation by TCD than when none were seen (31.7 ± 9.5 vs. 8.8 ± 8.5, p < 0.01). Shunt function was verified in all 11 patients shunted. Electroencephalographic changes occurred in four patients with an MCA-V of 14.7 ± 8.5 compared with an average of 24.1 ± 15.5 for patients with normal electroencephalograms. MCA-V increased from 46.6 ± 21.2 before operation to 61.0 ± 22.4 after carotid endarterectomy (p < 0.05). TCD can quantitate intracerebral blood flow in specific vessels, collateralization, the degree of cerebral ischemia caused by ECCVD, intraoperative changes in MCA-V that correlate with stump pressure and the electroencephalogram, shunt function, and the increases in cerebral blood flow resulting from carotid surgery. It is a new and important tool.

Carotid endarterectomy with local anesthesia: Results and advantages

In a collaborative prospective study from two institutions, we reviewed the clinical course of 969 consecutive patients who had 1200 carotid endarterectomies (CEs) for the treatment of occlusive arterial disease during the period of 1977 to 1987. The indications for CE comprised transient ischemic attacks (TIAs) in 581 cases (48.4%), cerebral infarction (CI) in 170 (14.2%), monocular blindness in 166 (13.8%), and asymptomatic stenosis in 283 (23.6%). Neurologic monitoring of the awake patient provided more reliable indication of the need for brain protection during operative arterial clamping than did electroencephalography or carotid stump pressure measurement. Of the 1200 cases, 113 (9%) required a shunt as determined by this method. Patients with contralateral carotid occlusion or severe stenosis required shunting six times more frequently than those with a unilateral lesion. Among all procedures, there were nine cases of transient neurologic deficit (0.9%), 11 cases of permanent neurologic deficit (0.9%), and eight deaths (0.67%). Among 283 CEs performed to treat asymptomatic lesions, no strokes and only one death (0.4%) occurred. One hundred sixty-six cases with amaurosis fugax were operated on without stroke or death. In the age group of 70 to 90 years, 508 procedures were carried out with four deaths (0.8%) and three strokes (0.6%). We conclude that CE performed with the patient under local anesthesia is safe and effective and permits satisfactory management of old and high-risk patients.

Monitoring of subcortical and cortical somatosensory evoked potentials during carotid endarterectomy: comparison with stump pressure levels

Monitoring of multichannel somatosensory evoked potentials (SEPs) has been performed in 40 cases of carotid endarterectomy (CEA). SEPs were obtained after median nerve stimulation at wrist, recording from 2nd cervical and from the scalp parietal (ipsi- and contralateral) and central (contralateral) positions. The reduction of CBF due to clamping of the carotid artery provoked SEP abnormalities in 10 of the 40 cases. None of the 30 patients with unmodified SEPs developed post-surgical neurological sequelae. SEP alterations were characterized exclusively by amplitude decrements and latency increases of the cortical components, the subcortical ones being unaffected. In 5 of these patients, SEPs returned to normal values before the end of the intervention and no neurological deficit was observed on awakening. In the remaining 5 cases SEPs retained their abnormalities and patients developed post-surgery neurological sequelae (4 immediately, 1 the day after). SEP alterations affected parietal and central components to a similar extent; however, in a few cases cerebral blood flow deficits provoked by carotid clamping modified differently the central P22 and the parietal N20–P25 waves. Comparisons with stump (back) pressure in the carotid artery revealed a higher sensitivity of the SEP technique in detecting vascularization problems due to carotid clamping. The time course of the appearance of SEP abnormalities seems to discriminate alterations secondary to collateral revascularization from those determined by embolization.