Auditory and Vestibular System Findings in Patients with Vascular Loops in the Internal Auditory Canal

Many anatomic studies have shown that a loop of the anterior inferior cerebellar artery is frequently found in the cerebellopontine angle and internal auditory canal. The concept of vascular cross-compression has been extended to the eighth cranial nerve, and patients with symptoms of hearing loss, tinnitus, and vertigo have been treated surgically by separating the vascular loop from the nerve. Previous reports have emphasized vascular anatomy, surgical approaches, and treatment results. Our study provides details of audiometric and vestibular system test results in a series of ten patients with prominent vascular loops in the internal auditory canal diagnosed by computerized tomography after subarachnoid space air injection (pneumo-CT). All patients had a unilateral (or asymmetric) hearing loss on the side of the lesion, and no vascular loops were detected on the contralateral sides. Hearing losses ranged from mild to profound. Audiometric findings were generally of a cochlear type, and most patients had excellent speech discrimination. Spontaneous nystagmus was detected in all patients during neurotologic testing, and half of the patients had normal caloric test results. The variability of audiometric and vestibular system test results is probably a reflection of anatomic variations of the vascular loop and its branches. Auditory and vestibular symptoms may be due to a complex interaction between the eighth cranial nerve and the vascular loop, in which the loop compresses the nerve and the nerve compromises circulation to the inner ear. Although symptoms from vascular loops and eighth nerve tumors are similar, the findings of a cochlear type of hearing loss, excellent speech discrimination, and normal caloric test results should raise the suspicion of a vascular loop. Pneumo-CT is effective in diagnosing and differentiating a vascular loop from a tumor.