Etiology:

1. Acquired posthemorrhagic subependymal cyst:
   • hemorrhage
   • hypoxic-ischemic damage
     Site: caudothalamic notch
   • frequently in preterm infant
   • tear-shaped, 2–11 mm in size
2. Congenital subependymal cyst ← germinolysis
   • neurotropic infection: CMV, rubella
   • metabolic disorders (esp. Zellweger syndrome)
   • chromosomal abnormalities
   • maternal cocaine consumption
   • idiopathic in otherwise healthy newborn

Histo: cystic cavity with pseudocapsule of aggregates of germinal cells + glial tissue; NO epithelium; macrophage-like cells within fluid ← vascular origin