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Stanley L. Barnwell, Van V. Halbach, Christopher F. Dowd, Randall T. Higashida, Grant B. Hieshima, and Charles B. Wilson

✓ Dural arteriovenous (AV) fistulas are thought to be acquired lesions that form in an area of thrombosis within a sinus. If the sinus remains completely thrombosed, venous drainage from these lesions occurs through cortical veins, or, if the sinus is open, venous drainage is usually into the involved sinus. Among 105 patients with dural A V fistulas evaluated over the the past 5 years, seven had a unique type of dural AV fistula in the superior sagittal, transverse, or straight sinus in which only cortical venous drainage occurred despite a patent involved sinus; the fistula was located within the wall of a patent dural sinus, but outflow was not into the involved sinus. This variant of dural AV fistulas puts the patient at serious risk for hemorrhage or neurological dysfunction caused by venous hypertension. Three patients presented with hemorrhage, one with progressive neurological dysfunction, one with seizures, and two with bruit and headaches. A combination of surgical and endovascular techniques was used to close the fistula while preserving flow through the sinus.

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Epidermoid cysts of the brain stem

Report of three cases

William G. Obana and Charles B. Wilson

✓ The authors report the cases of three patients with epidermoid cysts which insinuated themselves into the brain stem. In all three patients, the tumor occupied the pons, although in one it was predominantly located in the medulla. The cyst contents and nonadherent tumor capsule were removed in all three patients, but no attempt was made to remove tumor densely adherent to the brain stem. One patient's cyst was removed in one operation, but maximal resection in the other two required two operations. After surgery, sixth nerve function completely returned in one patient; another patient had a stable pontine gaze palsy but developed new facial weakness; and the third patient had stable cranial nerve deficits with a diminished hemiparesis. The last patient developed a pseudomeningocele and communicating hydrocephalus, and required a lumboperitoneal shunt. In all three patients, computerized tomography scans demonstrated hypodense tumors not enhanced by contrast material. Magnetic resonance imaging was performed on two patients; in both, the tumors showed increased signal intensity relative to brain on T1-weighted images and decreased signal intensity relative to brain on T2-weighted studies. Magnetic resonance imaging, the most accurate modality for localizing these lesions and determining their extent, was also invaluable for postoperative monitoring and follow-up evaluation. Safe and adequate resection includes decompression of cyst contents and removal of nonadherent portions of the cyst capsule. Cyst wall adherent to the brain stem, however, should not be removed.

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Neil A. Martin, Wesley A. King, Charles B. Wilson, Stephen Nutik, L. Phillip Carter, and Robert F. Spetzler

✓ Eight patients with dural arteriovenous malformations (AVM's) of the anterior cranial fossa are presented, and the pertinent literature is reviewed. Unlike cases of dural AVM's in other locations, sudden massive intracerebral hemorrhage was the most frequent reason for presentation. Other symptoms included tinnitus, retro-orbital headache, and a generalized seizure. The malformations were supplied consistently by the anterior ethmoidal artery, usually in combination with other less prominent feeding vessels. The lesion's venous drainage was through the superior sagittal sinus via a cortical vein; in addition, in two cases a subfrontal vein drained the AVM. A venous aneurysm was encountered near the site of anastomosis with the dural feeder in most cases, and was found in all patients who presented with hemorrhage. The AVM was obliterated surgically in six patients, with favorable results achieved in five. One patient died postoperatively from a pulmonary complication. Because of their anatomy and proclivity for hemorrhage, these vascular malformations represent a unique group of dural AVM's. Surgical management of anterior fossa dural AVM's carries low morbidity, and is indicated when the lesions have caused hemorrhage or when there is an associated venous aneurysm.

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The treatment of medulloblastoma

Results of a prospective randomized trial of radiation therapy with and without CCNU, vincristine, and prednisone

Audrey E. Evans, R. Derek T. Jenkin, Richard Sposto, Jorge A. Ortega, Charles B. Wilson, William Wara, Inta J. Ertel, Simon Kramer, Chu H. Chang, Sanford L. Leikin, and G. Denman Hammond

✓ In a prospective randomized trial designed to study the effectiveness of adjuvant chemotherapy following standard surgical treatment and radiation therapy, 233 eligible patients with medulloblastoma were treated by members of the Childrens Cancer Study Group and the Radiation Therapy Oncology Group. Eligible patients were randomly assigned to receive radiation therapy with or without adjuvant chemotherapy consisting of 1-(2-chloroethyl)-3-cyclohexyl-nitrosourea (CCNU), vincristine, and prednisone. The estimated 5-year event-free survival probability was 59% for patients treated with radiation therapy and chemotherapy and 50% for patients treated with radiation therapy alone, a difference which is not statistically significant. The 5-year survival probability was 65% for both groups. Although the treatment difference was not statistically significant when all patients were combined, in the small number of patients with more extensive tumors, event-free survival was better in the group receiving chemotherapy (48% vs. 0%, p = 0.006). In these latter patients the survival time is also significantly prolonged. Extent of disease (as measured by the M staging criteria described by Chang) and age at diagnosis were significantly associated with outcome; advanced disease and young age had a worse prognosis. The extent of tumor resection was not an independent prognostic factor. It is concluded that chemotherapy does not benefit patients with low-stage medulloblastoma, but may benefit those with more advanced stages of disease.

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Stanley L. Barnwell, Christopher F. Dowd, Richard L. Davis, Michael S. B. Edwards, Philip H. Gutin, and Charles B. Wilson

✓ The cases of seven patients with intramedullary, cryptic vascular malformations of the spinal cord are reported. In all patients, the clinical course was progressive; a Brown-Séquard syndrome was the most common presenting symptom complex. Magnetic resonance (MR) imaging was performed in all patients. The pattern seen most often was a focus of high signal (on both T1- and T2-weighted MR images) surrounded by a larger zone of low signal (best seen on T2-weighted images), and was remarkably similar for all patients. Six patients underwent surgical exploration; removal of the lesions halted the progression of symptoms in five patients, and one patient had worsened sensory function after surgery. Motor function did not decrease postoperatively in any patient. The one patient who refused surgery has continued to decline neurologically. Histopathological examination of surgical specimens showed a cavernous malformation in one patient, a venous malformation in one, venous varices in two, and organizing hematomas in two; these findings are markedly different from those in previously reported cases of cryptic vascular malformations.

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Joshua B. Bederson, Griffith R. Harsh IV, John A. Walker, and Charles B. Wilson

✓ The authors report a case in which bilateral cystic temporal lobe necrosis developed after treatment of nasopharyngeal lymphoepithelioma with 7000 cGy of external beam radiation. The patient presented with an isolated memory deficit that was documented by neuropsychological testing. After fenestration and internal shunting of both cysts, there was striking resolution of the lesions and of the memory deficit.

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Samuel F. Ciricillo, Richard L. Davis, and Charles B. Wilson

✓ The authors report the case of a patient harboring a posterior fossa neuroepithelial cyst who presented with positional facial weakness and syncope. The patient recovered rapidly after cyst fenestration and placement of an internal cyst-cisternal shunt. The pathogenesis and principles of diagnosis and management of these rare lesions are reviewed.

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Complex dural arteriovenous fistulas

Results of combined endovascular and neurosurgical treatment in 16 patients

Stanley L. Barnwell, Van V. Halbach, Randall T. Higashida, Grant Hieshima, and Charles B. Wilson

✓ Of the 88 patients evaluated for symptomatic dural arteriovenous (AV) fistula over the past 8 years, 16 had large or complicated lesions that could not be treated with standard transvascular approaches or in which such treatment had been unsuccessful. Eleven fistulas were located in the transverse sinus, two in the cavernous sinus, two in the straight sinus, and one in the falx-tentorial region near the vein of Galen. The patients were treated with a combination of endovascular and neurosurgical techniques. Fourteen patients underwent preoperative transarterial embolization; this procedure closed the fistula in one patient. In the remaining 15 patients, surgery was performed to provide access to the fistula for embolization from either the venous or the arterial side, or for excision of the fistula. Transvenous embolization completely obliterated the fistula in seven of nine patients; the fistulas were embolized incompletely through the feeding arteries in two patients; and complete surgical resection of the lesion was accomplished in four patients. Complications related to venous occlusion occurred in two patients and one patient suffered communicating hydrocephalus that was effectively treated by shunting. There were no deaths. The results suggest that combined endovascular and neurosurgical techniques are a safe and effective means for the treatment of selected complex dural AV fistulas.

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Joshua B. Bederson and Charles B. Wilson

✓ Outcome after 252 posterior fossa explorations for the treatment of trigeminal neuralgia was determined by a retrospective review. Patients with distortion of the fifth nerve root caused by extrinsic vascular compression underwent microvascular decompression, those with no compression underwent partial sensory rhizotomy, and those with vascular contact but no distortion of the nerve root underwent decompression and rhizotomy. The mean follow-up period was 5.1 years. An excellent (75%) or good (8%) clinical outcome was achieved in 208 patients; 13 patients (5%) experienced little or no pain relief. Thirty-one patients (12%) suffered recurrent trigeminal neuralgia an average of 1.9 pain-free years after operation; recurrence continued at a rate of approximately 2% per year thereafter. Reoperation for recurrent or persistent pain provided excellent or good results in 85% of reoperated patients, but partial sensory rhizotomy was required in most of these patients. Outcome was affected by previous surgical procedures. A previous percutaneous radiofrequency lesion was associated with a significantly greater incidence of fifth nerve complications and a worse outcome after posterior fossa exploration. Because of this finding, the authors recommend that percutaneous radiofrequency rhizolysis be reserved for patients who have failed posterior fossa exploration or who are not candidates for surgery. Patients with compressive nerve root distortion and a short duration of symptoms before surgery had a significantly better outcome than patients with a longer duration of symptoms. In contrast, there was no relationship between the duration of symptoms and outcome of patients without nerve root distortion. Vascular decompression may cause dysfunction of the trigeminal system in tic douloureux, but in patients who remain untreated for long periods an intrinsic abnormality develops that may perpetuate pain even after microvascular decompression. Posterior fossa exploration is recommended as the procedure of choice for patients with trigeminal neuralgia who are surgical candidates.