Rare Case of Tricompartmental Arachnoid Cyst Spanning Infratentorial, Supratentorial, and Extracranial Compartment and Presenting as Posterior Parietal Meningocele.

Abstract

Arachnoid cysts constitute a mere 1% of all nontraumatic intracranialspace-occupying lesions, and only 10% of these are present in theinfratentorial compartment. We hereby report a case of a 10-month-old femalechild with a tricompartmental arachnoid cyst. The arachnoid cyst spanned both the infratentorial and supratentorialcompartment of the intracranial space. In addition, the cyst was alsoherniating into the extracranial compartment through a congenital defect in theparietal bone. The child was brought to us with a disfiguring swelling over herscalp, which was progressively increasing in size. We managed the patient byexcision of the extracranial part and placed a cystoperitoneal shunt to take care of the intracranial part. Follow-up magneticresonance imaging after 6 months of intervention showed a significant reductionin the size of the intracranial portion of the cyst with no recurrence of theextracranial part. This case of arachnoid cyst involves multiplestructures. But interestingly, all these structures (arachnoid, dura, veins,and bone) are of mesodermal origin. So we would like to suggest that thispathology may be a result of developmental deviation during mesodermal differentiationrather than a simple expanding arachnoid cyst.