[Idiopathic Pericerebral Swelling (external Hydrocephalus) of Infants]

Benign enlargement of the subarachnoid spaces was diagnosed in 41 infants on the basis of ultrasound and/or CT scan findings. 10 MHz transfontanellar ultrasonography is without doubt the most reliable investigation in this condition (skull-to-cortex distance greater than 5 mm). Patients with extracerebral collections due to a clearly identifiable pathologic process (e.g., prematurity, IUGR, neonatal distress, malnutrition) were excluded from the study. Macrocrania developed rapidly in 72% of patients, either as the single manifestation (30%) or with delayed motor development and hypotonia (30%). Other clinical patterns included evidence of intracranial hypertension (15%) and hypotonia without macrocrania (20%). The two main findings of this study were the high rate of familial forms and the severity of early hemorrhagic complications, i.e., spontaneous subdural hematoma (5/41 cases), with permanent neurologic impairment in some instances (2/5 cases). These complications call into question the benignity of this syndrome whose long-term outcome, particularly in terms of cognitive function, is as yet unknown.