Stroke Location: Pons (Locked-In Syndrome)
The stroke location is B - Pons, specifically involving the ventral pons causing locked-in syndrome, characterized by quadriplegia and anarthria with preserved consciousness, hearing, normal respiration, and ability to communicate through vertical eye movements and blinking. 1
Clinical Presentation and Anatomical Correlation
The clinical scenario describes classic locked-in syndrome, which results from damage to the ventral pons and caudal midbrain 2. The key features that localize this to the pons include:
- Sudden loss of speech (anarthria) and inability to move (quadriplegia) due to disruption of the corticospinal and corticobulbar tracts in the ventral pons 1
- Preserved consciousness and hearing because the reticular activating system and auditory pathways remain intact 1
- Normal respiration as the respiratory centers in the medulla remain functional 1
- Communication through eye movements - specifically vertical eye movements and blinking are preserved, which is pathognomonic for ventral pontine lesions 1, 3
Why Not the Other Options
Left anterior cerebellum (Option A) would present with ipsilateral ataxia, dysmetria, and coordination problems, but would not cause the complete motor paralysis with preserved vertical eye movements seen here 4.
Basal ganglia (Option C) lesions typically cause movement disorders like hemiparesis, rigidity, or chorea, but do not produce locked-in syndrome with preserved vertical gaze 4.
Midbrain (Option D) lesions can affect vertical gaze and cause pupillary abnormalities, but the preservation of vertical eye movements in this case argues against midbrain involvement 2.
Vascular Etiology
The basilar artery supplies the pons, and mid-basilar occlusions specifically produce locked-in syndrome 1. This typically occurs from basilar artery thrombosis or occlusion 3, 5.
Diagnostic Approach
The American Heart Association recommends testing for vertical eye movements and blinking in patients with apparent unresponsiveness to diagnose locked-in syndrome 1. Urgent vascular imaging (CTA or MRA from aortic arch to vertex) is essential for posterior circulation evaluation 4, 1.
Clinical Subtypes
There are three types of locked-in syndrome 3, 2:
- Classical LIS: Total immobility with preserved vertical eye movements, blinking, and consciousness (as described in this case) 3
- Partial LIS: Some residual motor function remains 2
- Total LIS: Complete paralysis including eye movements, rendering communication impossible 2
Common Pitfall
The critical pitfall is mistaking locked-in syndrome for coma or unresponsiveness 1. Always test for vertical eye movements and blinking in apparently unresponsive patients, as consciousness is fully preserved despite complete motor paralysis 1, 6.