An infantile case of posterior fossa arachnoid cyst presenting with marked engorgement of contralateral supraorbital vein.

A 6-month-old, previously healthy boy presented with poor feeding and vomiting for 2 weeks. At presentation, his left supraorbital vein was found to engorge considerably. A cranial computed tomography (CT) scan revealed a large cyst in the posterior fossa with a prominent left superior ophthalmic vein (SOV). Magnetic resonance imaging delineated the well-demarcated cyst markedly compressing the right cerebellar hemisphere. The patient underwent microscopic fenestration of the cyst wall through lateral suboccipital craniotomy. The cyst wall, comprising multi-layered, opacified membranes, was extensively resected and communicated with the prepontine cistern. The histological appearance of the cyst wall was consistent with an arachnoid cyst. Engorgement of the left supraorbital vein resolved immediately after surgery. A postoperative CT scan did not identify the SOV in the left orbit. In the present case, engorgement of the supraorbital vein might reflect the increased venous pressure of the SOV caused by compression of the contralateral cerebellar hemisphere.