Hydranencephaly: Transillumination may not illuminate diagnosis

Hydranencephaly describes the condition of extensive absence of cerebral tissue that is replaced by a saclike accumulation of fluid. It first may be suspected by neonatal bedside transillumination, which is a screening tool but is not diagnostic. When noted at birth, it is imperative to rapidly distinguish this condition from extensive hydrocephalus, holoprosencephaly, large porencephalic cyst, and other conditions so that those conditions with indications for prompt treatment are identified. An illustrative case of hydranencephaly is presented with discussion of imaging techniques to distinguish between the diagnostic possibilities. Etiologies of the neuropathology of hydranencephaly are discussed. The importance of distinguishing this condition, with an associated poor prognosis, from extensive hydrocephalus, with potential for improved prognosis with early shunting procedures, is emphasized.