Porencephalic Cyst

2-year-old female with spasticity and seizures. There is a large CSF fluid signal intensity collection which occupies the majority of the left cerebral hemisphere. The cyst lies in continuity with the atrium of the left lateral ventricle, and the walls of the cyst are lined by white matter. There is no suspicious abnormality on the diffusion weighted images. There is partial effacement of the left lateral ventricle with slight rightward shift of the septum pellucidum. The findings are compatible with a large, left hemispheric, porencephalic cyst. A porencephalic cyst results from a focal region of cystic encephalomalacia lying in continuity with the ventricular system. The differential includes arachnoid and ependymal cysts as well as lissencephaly. Etiologies include perinatal cerebral ischemia, parenchymal hemorrhage, trauma, infection and certain familial disorders. Clinical symptoms include seizures and spasticity in the first year of life. Later, language impairment, motor deficits, and mental retardation may be seen.