From the Guidelines
A Type I vascular loop impinging upon the right cranial nerves VII (facial) and VIII (vestibulocochlear) complex can cause significant neurological symptoms, and management should prioritize conservative approaches, with microvascular decompression surgery considered if symptoms significantly impact quality of life. This condition, known as neurovascular compression syndrome, typically presents with hemifacial spasm, vertigo, tinnitus, and/or hearing loss on the affected side. According to the most recent study 1, vascular loops in contact with CN VIII are a normal variant, but may contribute to otological symptoms due to neurovascular compression.
Symptoms and Diagnosis
The symptoms of neurovascular compression syndrome can vary, but often include:
- Hemifacial spasm
- Vertigo
- Tinnitus
- Hearing loss Diagnosis can be made using MRI head and internal auditory canal without IV contrast, which can detect neurovascular loops in patients with pulsatile tinnitus 1. Heavily T2-weighted thin-section sequences of MRI head can also detect the neurovascular loops in patients with pulsatile tinnitus 1.
Management
Management depends on symptom severity, with initial conservative approaches including:
- Anticonvulsants like carbamazepine (200-400 mg twice daily) or gabapentin (300-600 mg three times daily) for pain or spasm
- Vestibular suppressants such as meclizine (25 mg every 4-6 hours as needed) for vertigo symptoms If conservative management fails and symptoms significantly impact quality of life, microvascular decompression surgery should be considered 1. This procedure involves placing a cushioning material between the blood vessel and nerve to relieve compression.
Anatomical Basis
The anatomical basis for these symptoms involves pulsatile compression of these cranial nerves by the aberrant vascular loop, typically from the anterior inferior cerebellar artery, causing demyelination at the root entry/exit zone and resulting in ephaptic transmission or hyperexcitability of the affected nerves. Regular follow-up with neurology and neurosurgery is essential to monitor symptom progression and treatment efficacy. As noted in 1, MRI can be helpful for detection and evaluation of the extension of the glomus jugulare in the internal jugular vein, and can detect mass lesions in the IAC and posterior fossa.
From the Research
Implications of a Type I Vascular Loop
The implications of a type I vascular loop impinging upon the right seventh (VII) and eighth (VIII) cranial nerve complex can be significant, leading to various audio-vestibular symptoms and hemifacial spasm.
- A vascular loop in the internal auditory canal can cause compression of the vestibulocochlear nerve, resulting in symptoms such as vertigo, tinnitus, and hemifacial spasm 2.
- The loop characteristics, including depth of penetration, largest diameter of the vessel, and number of contacts between the vessel and nerve, can help predict whether a vascular impingement is responsible for a symptom 2.
- Compression of the facial nerve by a vascular loop can cause hemifacial spasm, while compression of the cochlear or vestibular nerve may cause audio-vestibular symptoms 2, 3.
Audio-Vestibular Symptoms
Audio-vestibular symptoms associated with a type I vascular loop include:
- Vertigo: a sensation of spinning or loss of balance 2, 4, 3
- Tinnitus: ringing or other sounds in the ear 2, 4, 3
- Asymmetric sensorineural hearing loss (SNHL) 2
- Hyperacusis: increased sensitivity to sound 3
Treatment Options
Treatment options for a type I vascular loop impinging upon the VII and VIII cranial nerve complex include:
- Microvascular decompression: a surgical procedure to relieve compression of the nerve by the vascular loop 4, 5
- Nervus intermedius sectioning: a surgical procedure to cut the nervus intermedius nerve to relieve symptoms of geniculate neuralgia 5
- Medical management: carbamazepine is a effective drug for treating vestibular paroxysmia, a condition characterized by short attacks of rotational vertigo and other audio-vestibular symptoms 3