Congenital arachnoid cyst mimicking meningocele

The subject of this report is a rare case of a 5-year-old girl who developed an arachnoid cyst with a bony and dural defect in the parietal convexity. She had no history of head trauma or infection. Surgical exploration revealed the bulging lesion to consist of cerebrospinal fluid-containing spongy subcutaneous tissue and to extend into the bony and dural defect. The arachnoid cyst cavity was found beneath the subcutaneous lesion and was not connected to the adjacent subarachnoid space. Histologically, the subcutaneous tissue contained a complex of sinusoidal channels formed by an abundance of migrating arachnoidal cells, thus mimicking meningocele.