Porencephalic cyst

Q: What is the most likely diagnosis? show answer

A: Porencephalic cyst.

Q: How do you define a proencephalic cyst? show answer

A: This is harder than you think it would be. Some authors use the term very broadly to encompass essentially all brain clefts / cysts (and thus include schizencephaly), whilst others reserve the term for an ecephaloclastic cleft (most common usage). The necessity of a cyst communicating with the ventricular system and / or subarachnoid space to earn the designation porencephaly is also a point of contention. Some authors use the term for cysts whether or not communication exists. Others reserve the term of cysts that communicate with at least one space, in which case they divide porencephalic cysts into internal (communicating with the ventricle) or external (communicating with the subarachnoid space). Still others require communication with both.

Q: Assuming the narrower more common definition of porencephaly (i.e encephaloclastic process), what is the main distinguishing feature of schizencephaly? show answer

A: Schizencephalic clefts are lined by abnormal grey matter, whereas porencephalic cysts are lined by white matter.

Q: What does the presence of adjacent white matter gliosis imply about the timing of the insult? show answer

A: Usually is taken to imply that the insult occurred in the third trimester or postnatally. It may be that gliosis can occur as early as 20 weeks of gestation [1].