Intimal hyperplasia of the infant parasellar carotid artery: a potential developmental factor in atherosclerosis and SIDS.

Intimal cushions that project into the lumen of arteries are precursors of atherosclerotic plaque formation. The "carotid siphon, " although frequently affected by atherosclerosis, was never analyzed for the occurrence of neonatal intimal hyperplasia. This study provides a topographic and morphometric analysis of intimal cushions in the parasellar internal carotid artery (pICA) of the human infant. A total of 35 specimens were studied in detail, using both standard histological techniques and a new method of computer-aided 3D reconstruction. Intimal hyperplasia occurred at 3 characteristic locations of the pICA: (1) the convex side of the posterior knee (C5 cushion), (2) the bottom of the horizontal segment (C4 cushion), and (3) the concave side of the anterior knee (C3 cushion). The extension of the cushions and the degrees to which they occluded the vessel lumens were measured. The complex shape of the pICA required 3D computer models for exact topographical descriptions and precise measurements. Our results suggest that the occurrence and degree of intimal hyperplasia are related to shape changes of the pICA during postnatal development. We predict that individuals who retain the relatively straight course of the fetal pICA throughout their lives are less prone to develop atherosclerotic lesions at this portion of the carotid artery. A possible contribution of neonatal intimal cushions to the origin of sudden infant death syndrome is discussed.