PICA Syndrome: Anatomical Correlation with Clinical Manifestations
The symptoms of PICA syndrome (lateral medullary or Wallenberg syndrome) directly result from infarction of the lateral medulla oblongata and inferior cerebellum, caused by occlusion of the posterior inferior cerebellar artery, which supplies these specific structures through its medullary branches and cerebellar territory. 1
Anatomical Supply of PICA
The posterior inferior cerebellar artery (PICA) is a branch of the fourth segment (V4) of the vertebral artery that provides critical vascular supply to two distinct regions 1:
- Lateral medulla oblongata - supplied by medullary branches of PICA
- Inferior cerebellar hemisphere - supplied by the distal PICA territory
- Additional structures - posterior spinal arteries and posterior meningeal connections 1, 2
Clinical Manifestations Explained by Anatomical Location
Vestibular and Cerebellar Symptoms
Vertigo, dizziness, nausea, and vomiting occur because PICA supplies the vestibular nuclei in the lateral medulla and the inferior cerebellar hemisphere 3, 4. When the distal PICA territory involving only the cerebellum is affected, patients present with rotatory dizziness intensified by motion, imbalance, and nystagmus 3.
Ataxia and imbalance result from infarction of the inferior cerebellar hemisphere and cerebellar peduncle connections in the lateral medulla 4. The cerebellar territory receives one point per hemisphere in the posterior circulation ASPECTS scoring system 1.
Cranial Nerve Deficits
Cranial nerve palsies manifest because the lateral medulla contains multiple cranial nerve nuclei supplied by PICA's medullary branches 1, 4. Common presentations include:
- Dysphagia and dysarthria from involvement of nucleus ambiguus
- Facial sensory loss from spinal trigeminal nucleus damage
- Horner's syndrome from descending sympathetic pathway involvement 4
Sensory Disturbances
Bilateral or crossed sensory deficits occur because the lateral medulla contains the spinothalamic tract (contralateral body pain/temperature sensation) and spinal trigeminal nucleus (ipsilateral facial sensation) 1. Perioral numbness specifically indicates involvement of these medullary sensory pathways 1.
Motor and Coordination Deficits
Hemiparesis or monoparesis can occur when infarction extends to involve motor pathways, though pure PICA territory infarcts typically spare the pyramidal tracts 1. Severe cases may progress to stupor or coma if cerebellar swelling causes brainstem compression 3.
Critical Anatomical Considerations
Collateral Circulation Potential
The PICA territory can receive collateral flow from the anterior inferior cerebellar artery (AICA) and posterior meningeal artery through pre-existing anastomotic channels 2. This collateral potential explains why some patients develop delayed symptoms or have variable presentations depending on the adequacy of compensatory blood flow 2.
Anatomical Variants
The AICA-PICA common trunk variant, where a single vessel supplies both territories, carries higher morbidity risk because occlusion affects a more extensive vascular territory 5. Recognition of such variants is crucial for understanding symptom severity and treatment planning 5.
Diagnostic Pitfalls
The most common diagnostic error is misattributing symptoms to benign labyrinthine disorders rather than recognizing cerebellar infarction 3. This misdiagnosis can delay critical stroke treatment including thrombolysis, potentially causing long-term neurological damage 4. MRA or CTA is recommended over ultrasound for evaluating posterior circulation symptoms 1.
Life-Threatening Progression
Recognition becomes crucial when cerebellar infarction progresses to cerebellar swelling with brainstem compression, leading to coma and death unless surgically decompressed 3. The pons receives 2 points, cerebellum 1 point per hemisphere, midbrain 2 points, and thalamus 1 point per hemisphere in PC-ASPECTS scoring to quantify infarct burden 1.