What is the top of the basilar syndrome?
Occlusion of the rostral basilar artery, usually embolic, often results in the Top of the basilar syndrome caused by infarction of the midbrain, thalamus, and portions of the temporal and occipital lobes.
This syndrome should be suspected in a patient with sudden onset of unresponsiveness, confusion, amnesia, abnormal eye movement, and visual defect. The neurologic signs may be variable, but the most common include:
- Impairments of ocular movements —unilateral or bilateral vertical (upgaze, downgaze, or complete) gaze palsy, skew deviation, hyperconvergence or convergence spasms causing pseudo-VI nerve palsy, convergence-retraction nystagmus, and retraction of the upper eyelids.
- Abnormalities in pupils —small with incomplete light reactivity (diencephalic dysfunction), large or midposition and fixed (midbrain dysfunction), ectopic pupils (corectopia), oval pupils.
- Alterations of consciousness and behavior —stupor, somnolence, apathy, lack of attention, memory deficits, agitated delirium.
- Defects in vision —homonymous hemianopsia, cortical blindness, Balint’s syndrome (impaired visual form discrimination and color dysnomia), and abnormal color vision.
- Motor weakness, sensory deficits, and reflex abnormalities are usually variable and subtle and due to the involvement of long tracts at the infarcted region.
This syndrome may be reversible in patients who are younger and do not have significant risks for cerebrovascular disease.