Specific Imaging Findings

Porencephalic cysts are smooth-walled CSF-filled cavities within the substance of the brain which abut with an enlarged lateral ventricle or the subarachnoid space. The cysts may be enclosed by a thin membrane or communicate directly with ventricles or/and other CSF-containing spaces. When large they may appear as a direct communication between the lateral ventricle and the subarachnoid space. Porencephalic cysts are lined by a thin layer of gliotic white matter, and the surrounding tissue often has normal signal characteristics. The contents of the cysts follow CSF on CT and on all MRI sequences and there is no enhancement after contrast administration.

Pertinent Clinical Information

Porencephalic cysts are primarily found in children, although they can occur in adults. As they are often the result of hemorrhage or ischemia, perinatally acquired cysts are associated with cerebral palsy, epilepsy, and psychomotor retardation. The presence and severity of symptoms depends on the location and extent of tissue destruction.

Differential Diagnosis

Schizencephaly (84)

1. • dysplastic gray matter lines the cleft

Arachnoid Cyst (142)

1. • tissue subjacent to the cyst is displaced and compressed but the cortical stripe is preserved

2. • no communication with lateral ventricles

Ependymal Cyst (146)

1. • entirely intraventricular

2. • may be difficult to distinguish when large but will not communicate with the subarachnoid space

Background

Porencephalic cysts may occur pre- or postnatally and both result from destruction of cerebral tissue from trauma, infarction, infection, or hemorrhage. Antenatally derived porencephalic cysts most commonly result from periventricular hemorrhage, followed by cerebral infarction and CNS infection during the late second or early third trimester.