Reports differ on which nerve fibers are affected by radiofrequency lesions made in peripheral nerves, some stating that primarily the myelinated delta and unmyelinated C fibers are destroyed, others stating that the destruction affects all sizes of nerve fibers and both myelinated and unmyelinated fibers. This study was designed to confirm one of those two findings, and to study the role that different temperatures might play in determining which fibers are affected. Radiofrequency lesions (85 degrees C for 2 minutes) were made in dogs by placing a temperature-monitored electrode into the lumber intervertebral foramina. The dogs were killed at intervals up to 6 weeks after rhizotomy, and the lesions were studied by light and electron microscopy. In all lesions, there was a total loss of unmyelinated fibers and a nearly total loss of myelinated fibers. In other dogs, 2-minute lesions were made at 45 degrees, 55 degrees, 65 degrees, and 75 degrees C, and the lesions examined 1 week later. Again, all sizes and all types of fibers were destroyed.

Eighty patients sustaining head injuries and presenting with Glasgow Coma Scale scores of 8 or less were entered into a prospective randomized study to assess the benefit of intracranial pressure (ICP) monitoring with two regimens of mannitol administration. Group I was treated with mannitol for ICP elevations greater than 25 mm Hg, while Group II received empirical mannitol therapy irrespective of ICP readings. No statistically significant differences in mortality rate or neurological outcome were demonstrated between the two groups. These results are comparable to those of several published series of head-injured patients receiving similar treatment from 1977 to 1982. However, those series must be reassessed in light of recently published studies with treatment initiated at lower levels of ICP.

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Although meningiomas are known to cause varying degrees of cerebral edema, the relative importance of their location, size, histological subtype, and other histological features in the production of cerebral edema has not been studied adequately. Therefore, we undertook a retrospective analysis of 43 meningiomas excised between 1975 and 1980. The results indicate that histological subtype has no relationship to the production of cerebral edema, with one exception. Meningiomas containing partly or completely a hemangiopericytic component were the only histological subtype associated consistently with cerebral edema. The location of a meningioma per se may not determine the production of cerebral edema. A relationship between size, aggressive histological features, vascular proliferative changes, and the production of cerebral edema was seen. The need for and the nature of further studies required to explain the cerebral edema that may be associated with small meningiomas are discussed.