The middle cerebral artery (MCA) carries about 80% of the flow volume received by the cerebral hemisphere. 8 The normal MCA blood velocity (V MCA ) under resting conditions ranges from 35 to 90 cm/sec, with a mean of about 60 cm/sec.3 ' 4 This range probably reflects the well-known individual MCA diameter variation as well as individual differences in cerebral blood flow. In healthy individuals, V MCA shows CO 2 reactivity of 3.4 ± 0.8%/mm Hg, 9 which is very close to the 4.1 ± 1% CO 2 reactivity of cerebral blood flow determined by means of the xenon washout technique. Received October 14, 1986; accepted June 9, 1987. good impression of variations in MCA flow volumeThe present study was conducted to examine in further detail the relation between concomitant variations in V MCA and QMCA in clinical situations. A special emphasis was placed on evaluating blood velocity measurements as a clinical tool in labile vascular situations since flow measurements using the well-established xenon washout techniques have definite limitations under such circumstances. Clinical ModelDirect recording of QMCA using miniaturized cuff probes 12 is a highly specialized technique; moreover, this invasive method is incompatible with simultaneous transcranial blood velocity measurements in the clinical setting. However, during carotid endarterectomy (CEA), recording of the flow volume in the extracranial internal carotid artery (ICA) is available. This method provides a great number of sampling points from each individual investigated. Given that the ipsilateral MCA receives a constant proportion of the ICA flow volume (QICA). relative changes in Q ICA will reflect relative changes in Q MC A-This model includes some assumptions. First, since the ICA usually also supplies the anterior cerebral artery, a constant proportional relation between Q ICA and Q M CA can be assumed only when the carotid system investigated is neither receiving flow through collaterals nor supplying collaterals into other intracranial artery territories. This condition is met only when there is no cerebral artery stenosis either extracranially or intracranially.

We measured regional cerebral blood flow and cerebral vasoreactivity before and 3 months after carotid endarterectomy using xenon-133 inhalation with single-photon emission computed tomography and the acetazolamide test in 14 selected patients who had suffered cerebral transient ischemic attacks due to an ipsilateral internal carotid artery stenosis. The patients had neither clinical nor cerebral computed tomographic evidence of infarction. Baseline regional cerebral blood flow was symmetrical before and unchanged after endarterectomy. Before endarterectomy, vasoreactivity in the middle and anterior cerebral artery territories of the symptomatic side was significantly reduced (p<0.05); however, vasoreactivity was normalized 3 months after surgery. Our findings strongly suggest that the stenoses caused a reduction in perfusion reserve that was improved by carotid endarterectomy. A lthough carotid endarterectomy is one of the / \ most common vascular operations, 1 its effect -Z A . on cerebral blood flow (CBF) and intracranial hemodynamics have not been fully clarified. -10The diversity of results presumably reflects differences in studies with regard to patient selection, timing of the postoperative evaluation, and methodology used to measure CBF.The purposes of our study were to assess regional cerebral blood flow (rCBF) using xenon-133 inhalation and single-photon emission computed tomography (SPECT) and cerebral vasoreactivity using the carbonic anhydrase inhibitor acetazolamide 11 before and 3 months after carotid endarterectomy. Subjects and MethodsWe studied 14 patients (12 men and two women) aged 52-70 (mean 62) years. They had experienced cerebral transient ischemic attacks (TIA) due to ipsilateral internal carotid artery (ICA) stenosis, and they were treated with carotid endarterectomy. The interval from the last TIA to endarterectomy varied from 10 to 33 (median 15) days. Patients who had a history of stroke, clinical findings suggestive of cere- Received May 17, 1989; accepted February 28, 1990. bral infarction, or cerebral computed tomographic evidence of infarction were excluded. The patients had experienced no symptoms from the contralateral cerebral hemisphere or the brain stem. This selection was made in order to exclude the effects of cerebral infarction on the rCBF studies. No patient had orthostatic provoked symptoms. The study was performed in accordance with the Helsinki Declaration, and informed consent was given by all patients. Stenosis was assessed preoperatively using conventional arteriography and pulsed Doppler ultrasound studies.12 Three stenoses (22%) reduced the diameter of the ICA by 50%-75%, two (14%) by 75%-90%, and the remaining nine (64%) by >90%. Ten stenoses were in the left and the other four were in the right ICA. In the contralateral ICA, a stenosis of <50% was found in three patients, a stenosis of 75% in one patient, and a stenosis of 90% in another; the contralateral ICA was occluded in two patients and normal in the remaining seven (50%). One patient had a vertebral...

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Ventral perforation is a rare complication of lumbar diskectomy. Injury to retroperitoneal vessels is the most common serious complication to such perforation. Ventral perforation with damage to the bowel is rarely reported. The authors present the first case report of injury to the small bowel during a microsurgical lumbar diskectomy. The case illustrates the importance of awareness of bowel injury as a possible complication of diskectomy. Possible pre- and postoperative considerations are also discussed. A brief review of the literature on bowel injuries after this common surgical procedure is also given.