DURING the past two years the authors have identified in living infants seven examples of a cerebral anomaly which presents some of the clinical characteristics of hydrocephalus but which consists essentially of serious maldevelopment, or even complete absence, of the cerebral hemispheres, with intact meninges and cranium.The AnomalyThe anomaly consists primarily of absence of the cerebral hemispheres within intact meninges and skull, the resulting cavity being filled with cerebrospinal fluid. The fluid circulation may be normal or the outlets of the ventricles may be closed; "hydrocephalus" results in either case. At operation or autopsy the most striking feature noted is absence of the cerebrum, although a few islands or bands of it may persist. The pia-arachnoid usually is intact, although in some cases it also may have broken down. In the authors' surgical cases the transparent membrane was intact and the attenuated major branches of the middle cerebral artery were pulsating vigorously. As the fluid is aspirated, two egg-shaped, white, glistening bodies representing the basal ganglia are seen on the floor of the skull. Different specimens reveal variable amounts of residual cerebral tissue in the periphery of the tremendously expanded and freely communicating lateral ventricles. The anatomic description of these residual masses of nervous tissue as investigated in autopsy specimens (Cases 1, 3, 6 and 7) will be presented elsewhere.Etiology and Terminology: The cause of the condition remains controversial, but since the meninges and cranium are intact, it must be assumed that the anlage of the neopallium was present during the period of formation of these layers. Cruveilhier described the anomaly as hydrocephalic anencephaly ("l'anencéphalie hydrocéphalique") and contrasted it with anencephaly associated with absence of the cranial vault.
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