Arachnoid granulations of the posterior temporal bone wall: imaging appearance and differential diagnosis.

Arachnoid granulations are rarely seen on high-resolution CT (HRCT) at the posterior temporal bone wall, where they appear as erosions, without bone spicules and often with a lobulated surface. Differential diagnosis includes endolymphatic sac tumor, paraganglioma, chordoma, and chondromatous and metastatic tumors. MR imaging can confirm the diagnosis because arachnoid granulations behave like CSF without gadolinium enhancement. This report aims to illustrate the appearance and differentiation of temporal bone arachnoid granulations on HRCT and MR imaging.