Trinh Nguyen, MD
Hydranencephaly is a rare cephalic disorder with prevalence 1-2:10, 000. It is characterized by the absence of the cerebral hemispheres, incomplete or absent falx cerebri. Brainstem, basal ganglia and cerebellum are usually present, surrounded by cerebrospinal fluid.
Etiology of this disorder includes: bilateral occlusion of the internal carotid or middle cerebral arteries; necrotizing vasculitis caused by infection (HSV, CMV, Toxoplasmosis); diffuse hypoxic-ischemic brain necrosis based on fetal hypoxia; leukomalacia formed by confluence of multiple cystic cavities. The occlusion of internal carotid arteries results in ischemic insult of the areas supplied by anterior and middle cerebral artery. Blood supply for the posterior brain fossa stays intact which explains the presence of brainstem and cerebellum.
Diagnosis can be done prenatally by ultrasound which shows a large cystic mass filling the entire cranial cavity; no cerebral cortex can be seen. Falx cerebri is partially missing or absent and brainstem is preserved.
Differential diagnosis includes alobar holoprosencephaly, porencephaly and extreme hydrocephaly which can be distinguished by presence of at least minimum of the frontal cortex. The prognosis is very poor. Affected infants usually display reflex activity and limb movements but do not survive the first year of life.
The following images show a case of hydranencephaly which was diagnosed at 29 weeks of pregnancy. A 24 year old G2P2 with non-contributive family history was referred to our department for the anomaly of the baby’s head. Diagnosis of hydranencephaly was based on following ultrasound findings. Patient opted for pregnancy termination. A 1400 g preterm boy died after delivery.
Image 1: Image shows cranial cavity filled with fluid and partial falx cerebri.
Images 2,3: Images present intracranial cavity with cerebellum, no cerebral cortex is visible.
Images 4,5: Images 4 and 5 (3D view) shows a posterior fossa with preserved cerebellum and partial falx cerebri; intracranial cavity filled with fluid.