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The infratentorial compartment represents the second most common location of arachnoid malformations. Ten arachnoid cysts of the posterior fossa, operated on between 1970 and 1983, are reviewed. These lesions, although congenital and developmental in nature, may present at any age, and males are more frequently affected. A high rate of birth-related trauma (50% in this series) is conceivably due to fetal macrocranium, and the enlarged head and psychomotor retardation prevail in infancy and childhood. In arachnoid cysts occurring during adulthood, symptoms and signs more clearly indicate a dysfunction of the posterior fossa. Besides computerized tomography, pneumoencephalography and metrizamide techniques are recommended to rule out a Dandy-Walker syndrome in doubtful cases, and to obtain information about the cerebrospinal fluid (CSF) circulation. It is particularly important to establish the presence and type of communication of cysts with the CSF pathways. Although infratentorial cysts often communicate, they can be space-occupying masses because of increasing CSF retention, which may be due to a ball-valve mechanism or to inadequate communication. The frequently associated hydrocephalus (seven of the 10 cases in this series had hydrocephalus) seemed to be dependent mainly upon mechanical factors. The authors discuss the indications for intracranial surgery versus shunting procedures and report the results achieved by direct cyst excision.

Four young adults with spontaneous dissection of the vertebrobasilar system are reported. Clinically, two patients presented with subarachnoid hemorrhage and two with brain-stem ischemia. In two cases of ruptured arterial dissection of the posterior cerebral artery, angiography demonstrated fusiform and "sausage-like" dilatation of the involved vessel. In two cases of occlusive dissection of the basilar artery, angiography revealed the typical "string sign." All four patients were treated conservatively: three survive in good clinical condition and one remains disabled. Follow-up angiograms showed spontaneous healing of the lesion with return to an almost normal arterial configuration in two cases; residual narrowing corresponding to the dissection was the most notable finding in the other two. It is recommended that, in a subset of neurologically stable patients, angiographic monitoring is undertaken to assess the tendency for spontaneous repair before surgical intervention is planned.

The cases of 10 normotensive patients with chronic intracerebral hematomas are reported. The patients' median age at diagnosis was 42 years. The median duration of symptoms was 22 days. Seizures were the presenting symptom in 50% of the cases. Computerized tomography almost consistently demonstrated ring-shaped lesions with mass effect and perifocal edema. Arteriography revealed that all but one of the lesions were avascular. All patients had superficial white matter lesions, mostly in the frontoparietal region. All patients were treated surgically. Most of the hematomas were encapsulated and contained blood in various stages of organization. The thick capsule consisted of an outer layer of collagenous tissue and an inner layer of granulation tissue. Occult cerebrovascular malformations were detected in two instances. There were two deaths, both related to recurrent postoperative hemorrhage. This entity can present much like a brain malignancy and should be considered in the differential diagnosis of ring-shaped lesions whatever the clinical presentation. Strategies of treatment are discussed.