Marked segmental thinning of the umbilical cord vessels.

Marked segmental thinning of the umbilical cord vessels is an infrequent finding of undetermined origin and significance. We identified this lesion in 17 (1.5%) of 1100 consecutively examined placentas and reviewed the clinical records of both mothers and infants to determine its clinicopathologic significance. In each case, the tunica media vasorum (later referred to as media) was virtually absent in at least one cord level in an area usually less than 30% of the vessel circumference. The vein was affected in 13 (76%) cases, and one or both arteries were affected in four (24%) cases. The lesion faced the cord surface in nine (53%) cases. Similar changes were seen in the stem vessels of all the placentas. Five (30%) of the 17 mothers had infants with severe congenital anomalies, including anencephaly (n = 2), genitourinary tract abnormalities (n = 2), and conjoint twins (n = 1). Complications in other pregnancies included meconium-stained amniotic fluid (n = 4), variable decelerations or bradycardia during labor (n = 4), twinning (n = 3), and nuchal cord (n = 3). While the origin of this lesion is not known, it most likely represents a form of dysplasia of the media. Marked segmental thinning may be associated with increased congenital anomalies and perinatal problems.