Cryptic cerebellopontine angle neuroglial cyst presenting with hemifacial spasm.

Hemifacial spasm (HFS) is commonly caused by a vascular loop compressing the Root Exit Zone (REZ) of the facial nerve. We report a case of HFS caused by a vascular loop that was abnormally displaced by a neuroglial cyst not seen in Magnetic Resonance Imaging (MRI). Microvascular decompression (MVD) was planned and the patient underwent a key-hole retromastoid posterior fossa exposure. A cystic lesion was found in the cerebellopontine angle (CPA), located around the seventh and eighth cranial nerves extending from the porous acousticus to the brainstem REZ of the facial nerve. The cyst wall was partially excised revealing the region of the neurovascular conflict. MVD of the facial nerve was performed with immediate postoperative complete resolution of the patient's symptoms.