Hypodense extracerebral images on computed tomography in children. "External hydrocephalus": a misnomer?

External hydrocephalus (EH) was identified in 58 infants under 3 years of age during the period 1 June 1986 to 28 February 1990. Radiological images and clinical features were compared with 11 cases of cerebral atrophy (CA). Significant differences were found in delivery, head circumference, and the incidence of motor and developmental abnormalities. The population with EH was found to be quite heterogeneous, with a male preponderance. Intracranial pressure was normal in 15 cases in which lumbar puncture was done. The flow of cerebral spinal fluid was considered to be within the normal range in 6 cases. The results of a few cases examined with metrizamide cisternography are presented. The prognosis in our cases was not as benign as previously published, and use of the name EH is questioned. The less committal term "hypodense extracerebral images" is proposed when computed tomography (CT) is the only study done. The hypothesis that encephalocranial disproportion is the basic underlying entity for the CT images is proposed.