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PICA (posterior cerebellar artery syndrome). 


Timothy C. Hain, MD Page last modified: May 27, 2015

The PICA syndrome is also known as "lateral medullary syndrome", or "Wallenberg's syndrome", after Wallenberg's description in 1895. This is the most common brainstem stroke. It is typified by vertigo, ipsilateral hemiataxia, dysarthria, ptosis and miosis. Most patients with this stroke recover very well and often resume their previous activities (Nelles et al, 1998). Patients often have a Horner's syndrome (unilateral ptosis, miosis and facial anhidrosis).

medullary infarct contrapulsion
Medullary infarct from left vertebral artery dissection (L dorsolateral medulla) associated with "contrapulsion". For vertical saccades upward or downward, eyes always move to the right, which is contralateral to the side of the stroke (on the left). This is contrapulsion (see below). We know it is not due to the head being tilted, because in that case, the eyes would not always go the same direction.


There also may be saccadic dysmetria (overshoot), saccadic pulsion (pulling of the eye during vertical saccades toward the side of lesion -- called ipsipulsion). Rarely, the eyes go towards the opposite side of the lesion (called contrapulsion). (Kaski et al, 2012). Because the eyes can go either way, ipsi or contra, the localizing significance of pulsion is not teriffic.

Prognosis is generally quite good with full or near full recovery expected at 6 months. Diagnosis is generally via MRI (see below). CT-angiography with 3D reconstruction has gotten good enough in recent years to be helpful too.

ABR testing is often abnormal in persons with central Horner's syndrome (Faught and Oh, 1985), but as the lesion in Wallenberg syndrome is usually below the auditory connections, Horners due to Wallenbergs are not generally associated with abnormal ABR.

cerebral blood vessals wallenberg
Arrangment of PICA as a branch of the vertebral artery Inferior cerebellar territory stroke following a vertebral artery dissection (right side of picture)


PICA may arise from the vertebral artery (the usual case), or as a separate branch of the basilar artery. Because of the far more common origin from the vertebral artery, most "PICA" syndrome strokes actually are due to vertebral artery occlusion (Kim 2003). Cardiac embolism causes only 5% of these strokes, while dissection causes 15% (Kim, 2003).

PICA is the most common site of occlusion from propagating thrombus or embolism caused by injury to the third section of the vertebral artery, and Wallenberg's syndrome is the most common stroke caused by chiropractic manipulation (Caplan, 1986).

See also: Brainstem Strokes



We thank Dr. Dusan Pavlocic for helping correct a reference on this page.


Copyright August 3, 2016 , Timothy C. Hain, M.D. All rights reserved. Last saved on August 3, 2016