|Chris Herget, AuD|
By Chris Herget, Au.D
First reported by neurosurgeon Walter Dandy in 1925 , vascular loops are anatomical abnormalities that arise from branches of the basilar artery (98%) or from the vertebral artery (2%) . Small veins develop off of these two arteries and form around the vestibulocochlear nerve (VIII cranial nerve), compressing it. Grocoske et al  suggested that when the vascular loop comes in contact with the nerve, it causes “ectopic excitation”, causing nervous hyperfunction.
Janetta first proposed that vascular loops located at the patients cerebellopontine angle (CPA) might interfere with the eighth cranial nerve resulting in symptoms of vertigo, tinnitus and auditory neural loss . After evaluating 47 patients with these symptoms, Grocoske et al found 31.9% patients had vascular loops located at their CPA, 36.2% had loops that projected into their porus acusticus with extension as much as 50% into the internal auditory canal, and 12.8% had vascular loops that extended completely through their inner auditory canal . After studying 667 patients with vascular loops, McDermott et al classified the loops based on their nerve trajectory. They found 62% were located in the patients CPA (Degree I), 30% were located in their porus acusticus (Degree II), and 8% were located completely in their internal auditory canal (Degree III) . Lee et al also had similar results, finding the distribution of vascular loops by location varied considerably, but Degree III is consistently a minority location .
Due to the pressure and strain vascular loops put on the vestibulocochlear nerve, vestibular paroxysmia (VP), and disabling positional vertigo (DPV) may occur . VP and DPV are only caused by a vascular loop compressing the nerve and symptoms of these particular syndromes include episodes of vertigo (with and without nausea) as well as sensations of tinnitus and hearing loss with changes in head and body position . Usually, patients experience a worsening of symptoms during physical activity, including rapid head movement .
Although the dizziness brought on by vascular compression of the eighth cranial nerve may mimic symptoms related to other balance disorders, VP and DPV are characterized as their own syndromes. Unlike other balance disorders like Meniere’s disease, vestibular neuritis, and benign paroxysmal positional vertigo, VP and DPV typically appear as a constant feeling of dizziness, which is not fatigable, are not associated with fluctuating hearing loss, and typically does not respond to vestibular suppressing medications .
Moller et al (1986) studied 21 patients with suspected DPV, whose main complaint was constant, non-fatigable dizziness. Other, more subtle symptoms included hissing or pulsatile tinnitus (47.6%), facial numbness (15%) and facial twitching (5%). Audiologic tests included an auditory brainstem response (ABR), audiometric evaluation and vestibular testing. Due to the nonspecific symptoms of DPV, the ABR was used to help identify the most effected side. Even though 47.6% of the patients had hearing loss, and 81% had abnormal vestibular testing, 90% of the patients tested had abnormal ABR results (increased interwave latency between waves I and III). Although increased interwave latencies between waves I and III can be indicative of an acoustic neuroma, verification of a vascular loop can and was done during surgery.
Although unilateral pulsatile tinnitus is typically associated with vascular loops, many researchers; including McDermott et al , Grocoske et al , and Lee et al , found that there is no clear relationship or correlation between tinnitus and the presence of a loop. Although McDermott et al  did find a correlation between unilateral hearing loss and the presence of a vascular loop; tinnitus and vertigo were not associated in his study. Based on this research, patient reported symptoms (particularly pulsatile tinnitus and vertigo) may not be the most reliable source for identification of vascular loops. Makins, et al found no significant difference in the presence of vascular loops, between patients that were reporting audiologic symptoms (including pulsatile tinnitus, unilateral hearing loss and vertigo) and patients with healthy ears . This being said, vascular loops may still be present in patients without reported audiologic symptoms so effective identification is needed in order to proceed with the evaluation, care and follow up of the patient.