Clinical History
Fourteen-year-old boy with history of two attacks of seizures in the past two months.
Imaging Findings
A moderate-size cyst lined by white matter located in the right frontal lobe measuring 4 x 4 x 3.8 cm in size. The lesion extends near the right caudate head, however, no communication is seen with the lateral ventricle.
The lesion follows CSF signal in all sequences, with no diffusion restriction.
It is not lined by grey matter and there is no significant adjacent gliosis. A thin hypo T2* rim is present.
No significant mass effect on the adjacent parenchyma.
Discussion
Background
Congenital porencephaly is a rare disorder. It is defined as a cystic intracranial lesion resulting from an encephaloclacic insult (e.g. intrauterine infections and ischaemia), lined by white matter, which communicates with the ventricles and/or the subarachnoid space [1]. When communicating with the subarachnoid space it is called "External porencephalic cyst"[1]. Porencephaly can be unilateral or bilateral [2] and the location often corresponds to territories supplied by the cerebral arteries[2, 3].
Clinical perspective
The clinical presentation varies according to the size and site of the lesion as well as associated abnormalities; ranging from asymptomatic patients to profoundly impaired [3].
Imaging perspective
Antenatal ultrasonography may show the lesion as intracranial cysts that communicate with the ventricular system and/or subarachnoid space. Computed tomography demonstrates a CSF attenuating cyst with a well-defined borders. Usually no mass effect is seen. No contrast enhancement or solid component are present [1, 3].
MR imaging demonstrates that the cyst is lined by white matter. Gliosis may or may not be seen; depending on the age at which the insult occurred. The content of the cyst follows CSF signal on all sequences [1, 3].
The important differential for this entity is schizencephaly [1] that can be differentiated with MR imaging as the lesion in schizencephaly is lined by grey matter [3].
Treatment and prognosis
Usually no treatment is needed, however, the most important indication for surgery is mass effect [3]. Non-surgical symptomatic cases can be treated supportively [1]. The prognosis is somewhat related to the size and location of the lesion as well as associated abnormalities [1].
Take home message:
Congenital porencephaly is a rare disorder that can be depicted by neuroimaging. The white matter coverage of the lesion differentiates it from schizencephaly (lined by grey matter) [1, 2, 3].
Differential Diagnosis List
Congenital porencephalic cavity (External type)
Closed lip schizencephaly
Arachnoid cyst
Final Diagnosis
Congenital porencephalic cavity (External type)
