Diagnostic performance of quantitative signal intensity measurements on magnetic resonance imaging for distinguishing cerebellopontine angle meningioma from acoustic schwannoma.

OBJECTIVE: Our study investigated magnetic resonance imaging measurements for differentiating cerebellopontine angle (CPA) meningioma from vestibular schwannoma (VS). PATIENTS AND METHODS: This retrospective study compared 36 meningioma and 36 VS patients. The tumor volume (Vtumor) and peritumor edema index (EI) relationship was analyzed. T2-weighted three-dimensional gradient-echo image signal intensity (T23D) and apparent diffusion coefficient (ADC) differentiation cutoff values were defined. Mann-Whitney U test, independent-samples t-test, receiver operating characteristic curve, and Spearman's correlation analyses were applied. RESULTS: Meningioma had higher Vtumor (p=0.009) and EI (p=0.031) values than VS. Meningioma had significantly (p<0.001) lower values than VS for mean ADC (ADCmean: 0.841±0.083×10-3 vs.1.173±0.190×10-3 mm2/s), minimum ADC (ADCmin: 0.716±0.078×10-3 vs.1.045±0.178×10-3 mm2/s), tumor:white matter ADC ratio (rADC: 1.198±0.19 vs. 1.59±0.30), mean T23D (T23Dmean: 142.91±19.9 vs. 218.72±84.73), and tumor:adipose T23D ratio (rT23d: 0.19±0.06 vs. 0.30±0.28) Cutoff, sensitivity (Se), and specificity (Sp) values were ADCmin, 0.856×10-3 mm2/s (Se: 96.6%, Sp: 100%); ADCmean, 0.963×10-3 mm2/s (Se: 96.6%, Sp: 95.5%); rADC, 1.3189 (Se: 93.1%, Sp: 81.8%), T23Dmean (Se: 96.6%, Sp: 100%); rT23D, 0.1951 (Se: 89.7%, Sp: 100%), Vtumor, 14828.65 mm3 (Se: 75.0%, Sp: 66.7%), and EI, 1.1025 (Se: 47.2%, Sp: 100%). CONCLUSIONS: ADCmin, ADCmean, rADC, T23Dmean, rT23D, Vtumor, and EI, effectively discriminated meningioma from VS.

Diagnostic value of cerebral vasospasm by transcranial doppler ultrasound in Vietnamese patients with subarachnoid hemorrhage.

OBJECTIVE: Although the application of transcranial Doppler (TCD) ultrasonography in clinical diagnosis of cerebral vasospasm is popular in clinical practice in Vietnam, available evidence of the predictive value of vasospasm on TCD in the literature was mostly reported from large institutions in developed countries. Hence, this study was conducted to evaluate the value of TCD ultrasonography in the diagnosis of vasospasm in patients with subarachnoid hemorrhage (SAH) in Vietnam. PATIENTS AND METHODS: This is a prospective observational study of all aneurysmal SAH patients consecutively admitted to a single center between 2008 and December 2011. TCD and 64-slice computed tomographic angiography (CTA) were used to cerebral vasospasm in SAH patients. RESULTS: 316 patients were analyzed (mean age = 52.97±12.27 years, 52.2% males). There were statistically significant difference rates of the cerebral vasospasm by Hunt and Hess Classification and Fisher classification (p <0.01). The proportion of the patients with cerebral vasospasm who were diagnosed exactly by TCD was 95.2%, while the proportion of the patients without cerebral vasospasm diagnosed exactly was 91.5%. TCD predictive diagnostic value was the highest, with the sensitivity of 0.95 (95% CI: 0.91-0.98), specificity of 0.91 (95% CI: 0.85-0.96), positive predictive value of 0.94 (5% CI: 0.90-0.97) and negative predictive value of 0.93 (95 CI: 0.87-0.97). Hemiplegia was the clinical symptom with the highest diagnostic value with the sensitivity of 0.34 (95% CI: 0.27-0.41), specificity of 0.92 (95% CI: 0.86-0.96), positive predictive value of 0.86 (95% CI: 0.76-0.93) and negative predictive value of 0.49 (95% CI: 0.41-0.54). CONCLUSIONS: Evidence of vasospasm diagnosis on TCD ultrasonography was found with high accuracy. Current study enables to suggest the wide application of TCD in Vietnam health facilities from central to grassroots levels instead of the CTA use.

Dysarthria during basilar artery balloon occlusion.

A 49-year-old woman presenting with recurrent, reversible brainstem symptoms and a distal basilar artery aneurysm underwent balloon test occlusion. Five minutes after balloon inflation she developed a reversible isolated dysarthria. Despite failing the test occlusion (and after an additional brainstem event), the patient underwent surgery with placement of a clip across the basilar artery. The operation was tolerated without complication. The authors conclude that 1) pure dysarthria may be a symptom of temporary basilar artery occlusion and 2) balloon testing may overestimate the risk of basilar artery clipping.

Reconstruction of the hypoplastic posterior arch of the atlas with calvarial bone grafts for posterior atlantoaxial fusion: technical report.

Posterior atlantoaxial fusion is a common procedure performed for instability at C1-C2. This operation requires intact posterior elements of both the atlas and the axis. When this is not the case, the incorporation of the occiput and the lower spinal segments is usually required for adequate posterior fusion, but such a procedure limits the mobility of the upper cervical spine. A technique for the reconstruction of the posterior arch of the atlas with calvarial bone is described in this report. This technique allowed the successful fusion of the C1 and C2 vertebrae in a patient with traumatic atlantoaxial subluxation who also had a congenital absence of the posterior arch of the atlas.

Measurement of tumor resection volumes from computerized images. Technical note.

The authors describe a method for quantitation of the area and volume of the resection cavity in patients who have undergone surgery for brain tumors. Using a slide scanner and Image 1.27, a public domain program for the Apple Macintosh II computer, computerized tomography scans and magnetic resonance images can be digitized and analyzed for a particular region of interest, such as the area and volume of tumor on preoperative and postresection scans. Phantom scans were used to analyze the accuracy of the program and the program users. User error was estimated at 2%, program error was 4.5%. This methodology is proposed as a means of retrospectively calculating the extent of tumor resection.

The influence of electric fields on the epileptiform bursts induced by high potassium in CA3 region of rat hippocampal slice.

The effects of pulsed direct current (dc) electric fields on the frequency of spontaneous bursting in a model epileptic focus were studied. The high potassium hippocampal slice model was used to generate spontaneous burst firing activity similar to interictal spikes in the pyramidal cell layer of CA3. Electric fields were generated from platinum subdural electrodes placed in the perfusion bath. Three hundred and seventy-eight experimental trials were performed on 10 hippocampal slices from 10 rats and the effects of field polarity, field strength and duration of stimuli on firing frequency was examined. Hippocampal slices were oriented horizontally with the CA3 layer towards the positive electrode, the average interburst interval did not correlate significantly with polarity of the delivering pulses (one-way ANOVA, p = 0.96). Average interburst interval showed a significant correlation with pulse duration of 200 and 400 msec (p = 0.030 and p = 0.004, respectively). As a function of field strength, there were significant average interval changes for fields of 33, 46, and 73 mV/mm (p = 0.024, p = 0.001 and p = 0.001, respectively). In conclusion, CA3 burst firing activity in high potassium concentration can therefore be altered by electric fields.

Risk Score Estimation: a new method to determine optimal timing of aneurysm clipping for improved management outcome.

The outcome of 703 patients who underwent surgery following aneurysmal subarachnoid hemorrhage were analyzed with regards to age, associated medical conditions, vasospasm and clinical status at the time of operation. Patients with Hunt and Hess grade I, II, and III had a 96%, 90% and 93% favorable (good and fair) outcome respectively. In contrast only 58% of patients with grade IV had the same result. The outcome was unfavorable in 13% of the patients who were older than 60 years of age and only in 9% of the patients between 30-59 years of age. All the patients younger than 30 years old had a good outcome. Associated medical condition increased the incidences of poor outcome (7% vs. 12%). Patients harboring vertebro basilar aneurysms had a poorer outcome, as opposed to those with aneurysms located in the anterior circulation (20% vs. 8%). The presence of angiographic vasospasm alone did not influence outcome. A proposed point value was given for each of the adverse factors and from this the optimal surgical time was determined for each individual patient. This concept of Risk Score Estimation approach may improve the management outcome of patients with ruptured intracranial aneurysms.

Effect of intracarotid papaverine on human cerebral blood flow and vascular resistance during acute hemispheric arterial hypotension.

This study assessed the feasibility of augmenting cerebral blood flow (CBF) and decreasing hemispheric cerebrovascular resistance (CVR) by intracarotid papaverine during acute cerebral hypotension. Awake patients (n = 10) undergoing transfemoral balloon occlusion of an internal carotid artery (ICA) with nitroprusside (SNP)-induced systemic hypotension (10% reduction of mean arterial pressure) were studied. We measured mean femoral artery pressure (MAP), mean distal ICA pressure (P(ica)), and CBF (intracarotid 133Xe) at two time points: before and after intracarotid papaverine infusion (1 or 7 mg/min). Two patients became symptomatic immediately after ICA occlusion and were excluded. One patient developed a focal seizure during papaverine infusion. In another, the occlusion balloon deflated prematurely. Of the remaining six patients, two of the three patients who received high-dose papaverine (7 mg/min) developed transient obtundation. The remaining three patients, who received low-dose papaverine (1 mg/min), did not develop any neurologic symptoms. There was a trend for intracarotid papaverine to increase hemispheric CBF by 36% (33 +/- 10 versus 45 +/- 22 ml x 100 g(-1) x min(-1), P = .084, n = 6); papaverine decreased CVR from 1.3 +/- 0.4 to 1.0 +/- 0.3 mm Hg x ml(-1) x 100 g(-1) x min(-1) (P = .049). There was no significant change in heart rate, MAP, or P(ica) during experimental protocol. Manipulation of CVR by intracarotid papaverine during acute hemispheric arterial hypotension appears to be feasible. Further studies are needed to establish safety and efficacy.

Ophthalmoplegia resulting from an intraorbital hematoma.

BACKGROUND: A case is described in which an intraorbital hematoma was found to complicate recovery from attempted aneurysm clipping 5 days into the postoperative period. The etiology, management, and complication avoidance are discussed. CASE DESCRIPTION: Five days after attempted surgical clipping of an internal carotid artery aneurysm via a frontotemporal craniotomy with orbital osteotomy, a patient underwent coiling of the aneurysm. Shortly after the endovascular procedure, the patient developed exophthalmos and ophthalmoplegia involving the right side followed by decline in her level of consciousness. An emergency computed tomography (CT) scan revealed an epidural hematoma with intraorbital extension. After evacuation of the hematoma, the patient recovered extraocular function and returned to her baseline mental status. CONCLUSION: Exophthalmos and ophthalmoplegia in a patient recovering from cranial surgery using skull base techniques warrants immediate attention, especially after endovascular procedures. Delay in intervention may result in loss of neurologic function or life. The authors discuss the relevant literature and management of this uncommon complication.

Cerebral vasospasm after tumor resection. A case report.

OBJECTIVE AND IMPORTANCE: Symptomatic cerebral vasospasm can occur after resection of tumors in or adjacent to the basal cisterns, causing delayed neurological deterioration. This potentially treatable condition may go unrecognized. Delay in its recognition will adversely affect the outcome of the patients. There has been a few cases of vasospasm after tumoral resection reported in the literature, mostly in adults. We report a case of vasospasm after resection of a third nerve schwannoma in a pediatric patient. This is the youngest patient reported to date with vasospasm after resection of a brain tumor. CLINICAL PRESENTATION: A six years old girl presented with sudden onset diplopia. Radiological work-up revealed a third nerve mass. She underwent a craniotomy for resection of her mass. Pathological findings were consistent with a third nerve schwannoma. One week postoperatively, her mental status deteriorated. A CT scan revealed a diffuse hypodense area involving the right frontal and temporal lobes in the middle cerebral artery distribution as well as the midbrain. The absence of these findings on the MRI imaging performed on the first postoperative day made us evoke a vascular etiology. A cerebral angiogram was performed and revealed vasospasm in the right internal carotid artery and in the right middle and posterior cerebral arteries. Hyperdynamic hypervolemic hemodilutional therapy was instituted. CONCLUSION: Delayed clinical deterioration from vasospasm is a potentially reversible condition, if recognized early. A high index of suspicion should be maintained in case delayed clinical deterioration occurs after surgery of tumors in the basal cisterns. Cerebral angiography will confirm the diagnosis. Early institution of hyperdynamic hypervolemic hemodilutional therapy and angioplasty may reverse the deficit and improve outcome.

Use of intra-aortic balloon pump counterpulsation for refractory symptomatic vasospasm.

Delayed neurologic deficits secondary to vasospasm remain a vexing problem. Current treatments include: hypertensive hypervolemic hemodilution (Triple-H) therapy, angioplasty, and intra-arterial papaverine administration. Significant morbidity and mortality still result from vasospasm despite these therapies. We present two patients with symptomatic vasospasm who received intra-aortic balloon pump counterpulsation (IABP) to improve cerebral blood flow when they were unable to tolerate Triple-H therapy. One patient (L.T.) developed vasospasm after resection of a meningioma that encased the carotid and middle cerebral artery. The other patient (D.F.) suffered a subarachnoid hemorrhage (Fisher Grade III, Hunt/Hess Grade III) from a basilar tip aneurysm. Postoperatively, both patients developed vasospasm. Treatment with Triple-H therapy, angioplasty, and papaverine yielded modest results. When they experienced cardiac ischemia, Triple-H therapy was stopped, but their neurologic condition deteriorated markedly. Because of this, IABP was started. Both patients had an immediate improvement in cardiac function. IABP was able to reverse some of the neurologic deficits, and was weaned off after several days of support. Both patients had a substantial improvement in function, and are now capable of caring for themselves. We conclude that IABP may play an important role for improving cerebral blood flow in patients with vasospasm. It may be particularly useful in those patients with limited cardiac reserve.

Postoperative hydrocephalus in cranial base surgery.

The incidence of postoperative hydrocephalus and factors relating to it were analyzed in 257 patients undergoing cranial base surgery for tumor resection. A total of 21 (8%) patients developed postoperative hydrocephalus, and all required shunting, Forty-two (17%) patients developed cerebrospinal fluid (CSF) leak that required placement of external drainage systems (ventriculostomy or lumbar drain, or both); 10 (23%) of these 42 patients eventually needed shunt placement to stop the leak because of hydrocephalus. Prior craniotomy, prior radiation therapy, and postoperative CSF infection were also associated with an increased risk of developing hydrocephalus (48% versus 6%, 19% versus 8%, and 14% versus 7%, respectively). Prior radiation and postoperative CSF infection increased the risk of CSF leak in patients with hydrocephalus (30% versus 18% and 30% versus 9%, respectively). CSF leak and hydrocephalus commonly occurred in patients who underwent resection of a glomus tumor. In conclusion, 8% of patients who underwent cranial base surgery for tumors developed de novo hydrocephalus; half of them also had CSF leak in addition to hydrocephalus; and all required shunt placement for CSF diversion.

Multiple intracerebral intravascular papillary endothelial hyperplasia.

Intravascular papillary endothelial hyperplasia (IPEH) is a rare benign reactive lesion usually found in thrombosed subcutaneous blood vessels. It uncommonly occurs in the central nervous system and may be mistaken for a more malignant type of tumour such as angiosarcoma. We present a first case of multiple IPEH occurring intracranially in a 51-year-old woman. She developed neurological compromises secondary to the mass affect of the haematoma arising from one of the lesions. Prompt surgical evacuation of the haematoma stabilized her condition. Surgical treatment, pathological findings, radiographic characteristics, and a review of the literature are presented.

Pediatric cerebellar hemorrhages.

Cerebellar hemorrhage is a devastating condition with morbidity and mortality related not only to the etiology of the hemorrhage, but also to the timing of the intervention. Sixteen consecutive pediatric patients with acute cerebellar hemorrhages are presented: 6 had vascular abnormalities, 3 had tumors, and 2 had hemorrhages of unknown etiology. Thirteen of the 16 patients survived with only 1 of the 13 having persistent vegetative state as a neurologic outcome. Six of 8 patients presenting in a moribund condition had good outcomes, and 3 of 4 patients presenting with fixed and dilated pupils also had good outcomes. Thus, in contrast to adults, rapid evaluation by CT scanning, followed by the judicious use of ventricular drainage and prompt surgical treatment, have resulted in favorable outcomes in pediatric patients despite their poor clinical presentations. None of the neonates having cerebellar hemorrhages required surgical intervention; their courses could be followed clinically and with transfontanel ultrasound.

Profound hypothermia and circulatory arrest with skull base approaches for treatment of complex posterior circulation aneurysms.

OBJECTIVE: Cardiopulmonary bypass with profound hypothermia and circulatory arrest has seen a resurgence as an adjunct technique in neurological surgery. We report our experience with this technique in treating seven complex vertebro-basilar aneurysms. METHODS: Skull base approaches were used in all cases, providing excellent exposure and minimizing brain retraction. There were six basilar artery aneurysms and one giant fusiform vertebro-basilar artery aneurysm. All aneurysms but one had an apparent neck, which could be clipped. The fusiform vertebro-basilar artery aneurysm was trapped, partially resected, and the circulation was reestablished with a saphenous vein graft from the cervical internal carotid artery to the mid-basilar artery. RESULTS: Five patients had an excellent outcome and two had a good outcome at one year or at latest follow up. Two of the patients showed improvement of neurological deficits which were present before the surgical intervention. CONCLUSION: Applying very strict selection criteria in this small series of patients with posterior circulation aneurysms, excellent or good results were achieved using the profound hypothermic circulatory arrest technique.

Controlling chaos in the brain.

In a spontaneously bursting neuronal network in vitro, chaos can be demonstrated by the presence of unstable fixed-point behaviour. Chaos control techniques can increase the periodicity of such neuronal population bursting behaviour. Periodic pacing is also effective in entraining such systems, although in a qualitatively different fashion. Using a strategy of anticontrol such systems can be made less periodic. These techniques may be applicable to in vivo epileptic foci.

Recovery of brain function during induced cerebral hypoperfusion.

We used the setting of clinically indicated internal carotid artery balloon test occlusions in 44 patients with inoperable carotid cavernous aneurysms or head and neck tumours to examine real-time changes in higher cerebral function that correlate with specific levels of cerebral blood flow. By making detailed haemodynamic and neurobehavioural measurements during the 30 min the carotid artery was occluded, we were able to quantify higher cerebral function patterns in relation to absolute cerebral blood flow (CBF) levels. We found that once the carotid artery was occluded, patients whose CBF averaged 47 ml/100 g/min (no different from baseline) maintained consistent performance on a sustained attention task; those whose CBF dropped to an average 37 ml/100 g/min had a reversible deterioration of sustained attention, and those whose CBF fell to 27 ml/100 g/min had impaired sustained attention that persisted until the carotid occlusion was reversed. The relevance of these results to the pathological state of clinical stroke is discussed with respect to the haemodynamic and physiological mechanisms that may determine how brain function is lost and regained in the setting of acute cerebral hypoperfusion.

Manipulation of cerebrovascular resistance during internal carotid artery occlusion by intraarterial verapamil.

UNLABELLED: Occlusion of the internal carotid artery (ICA) results in acute cerebral hypotension. We hypothesized that during acute cerebral hypotension, in addition to physiological autoregulation, further arteriolar relaxation is possible by pharmacological means. We tested the feasibility of using intracarotid verapamil, a calcium channel blocker, to decrease the cerebrovascular resistance (CVR) and augment cerebral blood flow (CBF) at low postocclusion distal ICA pressures (PICA). Eleven patients undergoing trial occlusion of ICA were enrolled. Distal ICA or stump pressure, hemispheric CBF, and CVR were determined before and after carotid occlusion. During ICA occlusion, CBF and other physiological variables were determined before and after intracarotid verapamil. Two patients were excluded from the study. Carotid occlusion (n = 9) significantly decreased PICA (mean +/- SD, from 82 +/- 22 to 46 +/- 11 mm Hg, P = 0.001) and CBF (from 42 +/- 11 to 33 +/- 11 mL.100 g-1.min-1, P < 0.05). During occlusion, after intracarotid verapamil (3.9 +/- 1.6 mg), hemispheric CBF tended to increase from 31 +/- 11 to 35 +/- 14 mL.100 g-1.min-1 (P = 0.067). However, the percent increase in CBF after verapamil was a linear function of PICA (y = 1.01 x -32, n = 9, r2 = 0.84, P = 0.006). The decrease in CBF during carotid occlusion suggests that near maximal cerebral autoregulatory vasodilation had occurred, although our results indicate that it may be feasible to further augment CBF by pharmacological means during acute cerebral hypotension. IMPLICATIONS: When the internal carotid artery is occluded during neurosurgical procedures, there may be a significant reduction in cerebral perfusion. The authors have demonstrated that the intraarterial administration of verapamil increases cerebral blood flow as a linear function of cerebral artery pressure. Intracarotid injection of vasodilators may augment cerebral blood flow during acute cerebral hypotension.

Intracarotid infusion of the nitric oxide synthase inhibitor, L-NMMA, modestly decreases cerebral blood flow in human subjects.

BACKGROUND: The authors hypothesized that if nitric oxide (NO) was a determinant of background cerebrovascular tone, intracarotid infusion of NG-monomethyl-L-arginine (L-NMMA), a NO synthase (NOS) inhibitor, would decrease cerebral blood flow (CBF) and intracarotid L-arginine would reverse its effect. METHODS: In angiographically normal cerebral hemispheres, after the initial dose-escalation studies (protocol 1), the authors determined the effect of intracarotid L-NMMA (50 mg/min for 5 min) on CBF and mean arterial pressure (MAP) over time (protocol 2). Changes in CBF and MAP were then determined at baseline, during L-NMMA infusion, and after L-NMMA during L-arginine infusion (protocol 3). To investigate effects of higher arterial blood concentrations of L-NMMA, changes in CBF and MAP were assessed at baseline and after a bolus dose of L-NMMA (250 mg/1 min), and vascular reactivity was tested by intracarotid verapamil (1 mg/min, protocol 4). CBF changes were also assessed during induced hypertension with intravenous phenylephrine (protocol 5). RESULTS: Infusion of L-NMMA (50 mg/min for 5 min, n = 7, protocol 2) increased MAP by 17% (86 +/- 8 to 100 +/- 11 mmHg; P < 0.0001) and decreased CBF by 20% (45 +/- 8 to 36 +/- 6 ml. 100 g-1. min-1; P < 0.005) for 10 min. Intracarotid l-arginine infusion after L-NMMA (protocol 3) reversed the effect of L-NMMA. Bolus L-NMMA (protocol 4) increased MAP by 20% (80 +/- 11 to 96+/-13 mmHg; P< 0.005), but there was no significant decrease in CBF. Intracarotid verapamil increased CBF by 41% (44+/- 8 to 62 +/- 9 ml. 100 g-1. min-1; P< 0.005). Phenylephrine-induced hypertension increased MAP by 20% (79 +/- 9 to 95 +/- 6 mmHg; P = 0.001) but did not affect CBF. CONCLUSIONS: The results suggest that intracarotid L-NMMA modestly decreases CBF, and the background tone of cerebral resistance vessels may be relatively insensitive to NOS inhibition by the intraarterial route.

Morbidity of intracranial hemorrhage in patients with cerebral arteriovenous malformation.

BACKGROUND AND PURPOSE: Decisions on invasive arteriovenous malformation (AVM) treatment are currently based on natural-course risk estimates of AVM bleeding and assumptions on morbidity from cerebral hemorrhage in general. However, morbidity of AVM hemorrhage has rarely been reported. We sought to assess the morbidity of intracranial hemorrhage in patients with cerebral AVMs. METHODS: From a prospective AVM database, 119 patients were analyzed: 115 had a hemorrhage as the diagnostic event, and 27 of them suffered a second hemorrhage during follow-up; an additional 4 patients had other diagnostic symptoms but bled during follow-up. The type (parenchymal, subarachnoid, intraventricular) and location of AVM hemorrhage were determined by CT/MR brain imaging. Disability and neurological impairment were assessed with the Barthel Index, the Rankin Scale, and the National Institutes of Health Stroke Scale, with a mean follow-up time of 16.2 months. RESULTS: Of the 115 incident hemorrhages, 34 (30%) were subarachnoid, 27 (23%) parenchymal, 18 (16%) intraventricular, and 36 (31%) in combined locations. In 54 patients (47%; 95% confidence interval [CI], 38% to 56%) the incident hemorrhage resulted in no neurological deficit, and an additional 43 patients (37%; 95% CI, 28% to 46%) were independent in their daily activities (Rankin 1). Fifteen patients (13%; 95% CI, 7% to 19%) were moderately disabled (Rankin 2 or 3), and 3 (3%; 95% CI, 0% to 6%) were severely disabled (Rankin > or =4). Parenchymal hemorrhages were most likely to result in a neurological deficit (52%). Type and morbidity of hemorrhage during follow-up were similar to incident events. Twenty (74%) of 27 patients with both incident and follow-up hemorrhages were normal or independent (Rankin 0 or 1). None of the patients with a hemorrhage during follow-up died during the observation period. CONCLUSIONS: Hemorrhage from cerebral AVMs appears to have a lower morbidity than currently assumed. This finding encourages a reevaluation of the risks and benefits of invasive AVM treatment.