Remote cerebellar hemorrhage after supratentorial surgery.

OBJECTIVE: Remote cerebellar hemorrhage (RCH) is an infrequent and poorly understood complication of supratentorial neurosurgical procedures. We retrospectively compared 42 patients who experienced RCH with a case-matched control cohort, to delineate risk factors associated with the occurrence of this complication. METHODS: Between 1988 and 2000, 42 patients experienced RCH after supratentorial neurosurgical procedures at our institution. Diagnoses were made on the basis of postoperative computed tomographic or magnetic resonance imaging findings in all cases. The medical records for these patients were reviewed and compared with those for a control cohort of 43 patients, matched for age, sex, surgical lesion, and type of craniotomy, who were treated during the same period. RESULTS: RCH most commonly occurred after frontotemporal craniotomies for unruptured aneurysm repair or temporal lobectomy and was frequently an incidental finding on postoperative computed tomographic scans. However, some cases of RCH were associated with significant morbidity, and two patients died. Preoperative aspirin use and elevated intraoperative systolic blood pressure were significantly associated with RCH (P = 0.026 and P = 0.036, respectively). Pathological findings for two cases demonstrated hemorrhagic infarctions in both. CONCLUSION: RCH most commonly follows supratentorial neurosurgical procedures, performed with the patient in the supine position, that involve opening of cerebrospinal fluid cisterns or the ventricular system (such as unruptured aneurysm repair or temporal lobectomy). Preoperative aspirin use and moderately elevated intraoperative systolic blood pressure are potentially modifiable risk factors associated with the development of RCH. Although RCH can cause death or major morbidity, most cases are asymptomatic or exhibit a benign course. Cerebellar "sag" as a result of cerebrospinal fluid hypovolemia, causing transient occlusion of superior bridging veins within the posterior fossa and consequent hemorrhagic venous infarction, is the most likely pathophysiological cause of RCH.

Venous air embolism in sitting and supine patients undergoing vestibular schwannoma resection.

OBJECTIVE: This study retrospectively compares the incidence of venous air embolism (VAE) detection and morbidity in the sitting and supine positions. All patients underwent vestibular schwannoma resection via the retrosigmoid approach by a single surgical team. METHODS: A total of 432 consecutive operations were reviewed, 222 of which were performed with the patients in the sitting position and 210 of which were performed with the patients in the supine position. Charts were reviewed for evidence of intraoperative VAE, intraoperative hypotension secondary to VAE, postoperative morbidity related to VAE, and other variables to compare the groups. RESULTS: This study demonstrated a 28% incidence of VAE detection when patients were in the sitting position compared to a 5% incidence of VAE detection when patients were in the supine position (P < 0.0001). Intraoperative hypotension secondary to VAE was noted in 1.8% of the sitting patients and 1.4% of the supine patients (P=0.72, no significant difference). Postoperative morbidity caused by VAE was noted in one sitting patient (0.5%) (pulmonary edema) and in no supine patients (P=0.48, no significant difference). Blood loss was slightly greater in the supine group, and operative times were similar in both groups, despite that the average tumor size of patients operated on in the sitting position was 2.8 cm versus 2.2 cm in the supine group (P < 0.0001). CONCLUSION: Our results indicate that although there is a higher incidence of VAE detection in sitting patients, the morbidity is not statistically greater. We conclude that because morbidity from VAE is similar in either position, patient positioning should be based on surgical team preference.

Localized cystic subdural hygroma: case report.

We report a new variant of subdural hygroma previously undocumented in the literature. A 29-year-old man had a skull mass and a progressive headache of 6 to 7 years duration. He was involved in a car crash 8 years earlier and had an unrecognized skull fracture. During surgery the lesion was found to be a localized, cystic subdural hygroma communicating with the subarachnoid space through a narrow opening. This lesion is unique because: (1) the subdural hygroma was limited by an adhesion between the dura and the arachnoid; (2) the actual communication between the subdural hygroma and the subarachnoid space was clearly identified; and (3) localized bulging of the skull is exceptional for a subdural hygroma. Differentiation from more common cystic lesions such as congenital arachnoid cysts, traumatic arachnoid cysts, intradiploic arachnoid cysts, and chronic subdural hematomas is discussed.

Spinal arterial aneurysm: case report.

Isolated aneurysms of the spinal artery (not associated with arteriovenous malformations) are exceptionally rare. Fewer than 17 cases have been reported in the literature. We report a case of an isolated spinal artery aneurysm causing acute subarachnoid hemorrhage. Spinal artery aneurysms are contrasted with the more common intracranial aneurysms in terms of presentation and pathogenesis. The various clinical presentations of spinal artery aneurysms are discussed as well. A summary of all reported cases of spinal aneurysms, with and without associated arteriovenous malformations, is listed.

Glass-ceramics for high precision reflective-optic applications.

Titania- and zirconia-nucleated glasses in the basic Li(2)Al(2)O(4)-SiO(2) system were found suitable for casting relatively large mirror blanks. Upon heat treatment, these glasses crystallized uniformly to yield transparent, very low expansion beta quartz solid solution glass-ceramics. Special care was required in processing large diameter blanks, owing to localized temperature increases resulting from the exothermic heat of crystallization. Glass-ceramics with a wide range of beta quartz solid solution stability resulted in a uniform product. Transparent glass-ceramic mirror blanks were obtained with average expansion coefficients from 5 degrees C to 50 degrees C of 0 +/- 0.3 x 10(-7)/ degrees C. Ware up to 15 cm thick was processed to less than 10 micro/cm strain, with no change in expansion or transparency through the blank. Work with thick ware provided additional insight into the problems that might be encountered in the fabrication of very large castings.