Arachnoid Cyst in Middle Cranial Fossa With Intraorbital Cyst (Orbital Meningocele)

Intracranial arachnoid cysts are extra-axial non-enhancing cerebrospinal fluid (CSF) density lesions. These are usually incidental findings on radiological investigations. Usually, the patients with arachnoid cysts are asymptomatic until the cyst grows large while symptomatic patients present with headaches, seizures, and focal neurological deficits. The adjacent calvarial bone may show remodeling and scalloping. Magnetic resonance imaging (MRI) stands superior in soft-tissue contrast and multiplanar imaging in excluding other lesions from the arachnoid cyst. Arachnoid cysts follow CSF signals in all pulse sequences with no gadolinium enhancement. Intraorbital extension of the intracranial arachnoid cyst (intraorbital meningocele) is rarely reported in the literature and occurs through the small bony defect. We report a case of a 20-year-old male presenting with proptosis who was detected to have an arachnoid cyst in the middle cranial fossa with intraorbital extension through a small bony defect in the lateral wall of orbit with the resultant orbital cyst.