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SUMMARY Four patients with mass lesions of the posterior fossa experienced protracted vomiting as their only symptom for extended periods of time. The responsible lesions were a cerebellar tumour in two patients, a ventricular cysticercus in one patient, and a giant vertebral artery aneurysm in another. All four cases had compression or displacement of the floor of the fourth ventricle, where the "vomiting centre" has been located. occurring in the early morning, frequently related to postural changes, and at times being described as "explosive". She lost 20 kg in weight over this period. During the last 2 months prior to evaluation, she experienced recurrent dizziness and gait unsteadiness. On neurological examination, multidirectional nystagmus and mild gait ataxia were detected. Computed tomography (CT) revealed a mass lesion in the cerebellar vermis, which at surgery was found to be a Grade III astrocytoma of the vermis, attached to the inferior portion of the floor of the fourth ventricle. Vomiting ceased after operation. Patient 2 A 29 year old woman presented early postprandial vomiting 3 to 4 times a week during the first and second trimester of her fourth pregnancy. Although vomiting occurred less frequently in the last trimester of pregnancy, it continued after delivery. One month later she started experiencing headaches and was admitted to the hospital in November 1974. General physical and neurologic examinations were within normal limits. She had had a weight loss of 12 kg. Contrast radiology of the gastrointestinal tract and an electroencephalogram (EEG) were normal. Plain skull radiographs showed an enlargement of the sella turcica. A pneumoencephalogram showed no entry of air into the ventricular system, and contrast ventriculography revealed a mass lesion in the caudal aspect of the floor of the fourth ventricle, with associated hydrocephalus. A ventriculoperitoneal shunt was inserted, and a cysticercus cyst firmly attached to the floor of the fourth ventricle was incompletely resected. She became asymptomatic after operation.

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