Labyrinthine Artery Aneurysm as an IAC Mass

We present a case report of a labyrinthine artery aneurysm masquerading as an internal auditory canal tumor. A 72-year-old woman presented to the clinic with a 1-week history of sudden onset right facial paralysis, right facial pain, hearing loss, and vertigo. On examination, she was found to have a dense right-sided facial paralysis involving all branches of the facial nerve, left-beating horizontal nystagmus, and anacusis of the right ear. MR imaging of the brain with gadolinium contrast enhancement demonstrated a 6 × 7 mm peripherally enhancing lesion with lack of central uptake filling the right internal auditory canal. After exhaustive consideration of treatment options, the patient elected to proceed with resection of the internal auditory canal mass via a translabyrinthine approach to decompress the neural structures of the internal auditory canal in an attempt to recover neural function, particularly of the facial nerve. Intraoperatively, the internal auditory canal mass was resected with minimal difficulty, with intraoperative dissection notable for brisk bleeding at the medial base of the tumor just as the tumor was dissected off of its medial fibrous attachments. Final pathology of the resected mass revealed a blood vessel with mucinous degeneration of the medial layer of the vessel wall. Immunohistochemical staining demonstrated positive staining to human muscle actin throughout the vessel wall, confirming presence of smooth muscle cells within the tumor wall, and negative staining to S-100, militating against neural or nerve sheath origin as the composition of the tumor specimen.

This case represents the first reported case of a labyrinthine artery aneurysm within the internal auditory canal masquerading as a schwannoma of the intracanalicular vestibulocochlear or facial nerve. Recognition of the existence of this entity will allow surgeons and radiologists to include labyrinthine artery aneurysm within the differential diagnosis of similar clinical case presentations and allow surgeons to counsel such patients and approach treatment decisions in a more comprehensive fashion.