Anterior Inferior Cerebellar Artery–Neurovascular Conflict (AICA–NVC) Causing Pulsatile Tinnitus
- Background:
- Pulsatile tinnitus is a type of tinnitus that occurs due to blood flow changes causing disruption of the laminar flow, resulting in local turbulence that is audible, or increased bone conduction/disturbances in sound conduction that cause a loss of masking effect of external sounds, resulting in perceiving normal flow sounds more intensely.
- Redundant vascular loop around the vestibulocochlear nerve within the internal auditory canal causing compression is an unrecognized and underdiagnosed entity.
- Chronic neurovascular compression may lead to progressive nerve damage.
- Atherosclerotic changes due to aging and hypertension may result in worsening of the symptoms.
- Clinical Presentation:
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Patients may present with auditory and vestibular symptoms like hearing loss, tinnitus (including pulsatile and typewriter tinnitus), vertigo, headache, and hemifacial spasm.
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Audiometry test of our patient was normal.
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- Key Diagnostic Features:
- A single vessel loops around the vestibulocochlear and facial nerves at the cerebellopontine angle cistern, which may extend into the internal auditory canal. The culprit vessel commonly identified is the anterior inferior cerebellar artery (AICA).
- The neurovascular structures at the cerebellopontine angle are clearly depicted on 3D FIESTA/CISS MRI sequence. TOF MR angiogram can be used to study the course of the redundant vascular loop at the cerebellopontine angle, as it provides excellent visualization of arterial anatomy. These sequences help in classifying the types of looping.
- Classification of vascular loop of AICA (neurovascular conflict) based on anatomic location:
- Type I: Vascular loop within the cerebellopontine angle level
- Type II: Vascular loop proximal to the internal auditory canal extends to less than 50% of the canal
- Type III: Vascular loop distal to the internal auditory canal extends to more than 50% of the canal
- It can be further categorized according to the presence of vascular contact with the vestibulocochlear nerve as:
- No contact
- Contact without nerve angulation
- Contact with eighth cranial nerve angulation
- Differential Diagnoses:
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Though in symptomatic patients, the presence of a vascular loop is a straightforward diagnosis, other causes of pulsatile tinnitus should be excluded by imaging.
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The causes can be classified into arterial, arteriovenous, or venous origin. MRI along with contrast/TOF MR angiogram assists in differentiating them.
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Arterial causes: Aneurysm, dissection, atherosclerosis, anatomic variants like aberrant internal carotid artery, persistent stapedial artery, and vascular loops
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Arteriovenous causes: Arteriovenous malformations and glomus tumors
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Venous causes: Idiopathic intracranial hypertension, jugular bulb variants, and dural venous thrombosis
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Treatment:
- Symptomatic patients are commonly treated with voltage-gated sodium and potassium channel blockers. The symptoms of our patient resolved following treatment with carbamazepine.
- Microvascular decompression could be considered as the treatment option for refractory cases, especially in the type III category.
