anterior inferior cerebellar artery

**Anatomy** - Origin: usually from the lower (proximal) basilar artery, just after the vertebrobasilar junction. Variants exist, such as a common trunk with PICA. - Course: runs near CN VII and CN VIII at the cerebellopontine angle, often looping into or near the internal auditory meatus. - Branches: the labyrinthine (internal auditory) artery arises from AICA in about 80% of people (otherwise from the basilar artery). It supplies the inner ear (cochlea and vestibular apparatus). Other branches go to the pons and cerebellum. - Territory: the anterior inferior cerebellum (including the flocculus), the middle cerebellar peduncle, the lateral (caudal) pons, and the inner ear.

**Lateral pontine syndrome (AICA syndrome)** - Ipsilateral findings: - Facial nucleus (CN VII): facial paralysis involving the whole face (LMN pattern), loss of taste in the anterior 2/3 of the tongue, decreased lacrimation and salivation. - Vestibulocochlear nuclei/labyrinth (CN VIII): vertigo, nystagmus, nausea/vomiting, tinnitus, sensorineural hearing loss. - Spinal trigeminal nucleus/tract (CN V): loss of pain and temperature sensation on the face. - Middle cerebellar peduncle and cerebellum: ataxia, dysmetria. - Descending sympathetic fibers: Horner syndrome (ptosis, miosis, anhidrosis). - Contralateral findings: loss of pain and temperature sensation in the body (spinothalamic tract).

**High-yield associations** - Lateral medullary (Wallenberg) syndrome from PICA occlusion is the key comparison. Both cause crossed sensory findings and Horner syndrome. The difference is that AICA syndrome adds facial paralysis and hearing loss, while PICA syndrome adds dysphagia and hoarseness (nucleus ambiguus) and spares CN VII and VIII. - Sudden unilateral hearing loss or isolated acute vertigo can be the only warning of impending AICA/basilar territory infarction. Hearing loss with vertigo suggests AICA ischemia over a benign peripheral cause. - Because the labyrinthine artery is an end artery, the inner ear is very sensitive to ischemia. - Facial nerve palsy in AICA stroke is peripheral (LMN) because the facial nucleus itself is involved. This contrasts with a supranuclear (UMN) lesion, which spares the forehead. - Cerebellopontine angle tumors (for example vestibular schwannoma) involve CN VII and VIII. AICA loops can also compress these nerves. - Mnemonic for pontine arteries: AICA supplies the lateral pons, the paramedian pontine branches of the basilar supply the medial pons, and the superior cerebellar artery (SCA) supplies the upper lateral pons and superior cerebellum.

**Clinical approach** - Diagnosis: MRI with diffusion-weighted imaging (CT often misses posterior fossa infarcts), plus vascular imaging (CTA/MRA) of the vertebrobasilar system. - Management: for acute ischemic stroke, IV thrombolysis within the time window and/or thrombectomy for basilar occlusion where indicated. Secondary prevention includes antiplatelets, statins, blood pressure control, and risk factor management. - Complications: cerebellar edema with brainstem compression or hydrocephalus can require decompressive surgery.