The normal angiographic sylvian point on the lateral cerebral angiogram.

The angiographic sylvian point (ASP) is one of the most useful landmarks on cerebral angiograms for detecting retrosylvian masses. Although it is suggested to be the halfway point on the clinoparietal line (CPL), its exact normal position has not been defined. The lateral carotid angiograms of 100 consecutive patients from 22 to 65 years of age were used to study the normal ASP in relation to the CPL. Patients with severe neurological deficits or angiographic evidence of hydrocephalus, severe vascular disease or mass lesions were eliminated from this study. In our 100 normals, the normal ASP was within 8 mm above and below the CPL, and in the majority (82%) it was located behind the midpoint of the CPL. It was not situated more than 14.4 mm posterior and never more than 3.1 mm anterior to the midpoint. Application of these normal relationships facilitates detection of small, deep retrosylvian masses occupying the medial portions of the parietal, occipital and temporal lobes.