The fetal presacral pseudo-mass: a normal sonographic variant.

Abstract

We examined 416 consecutive third trimester intrauterine gestations over a 4-month period and discovered 26 hypoechoic masses in the fetal presacral space (6.3% incidence). These masses varied in diameter from 15 to 30 mm (mean, 21.5 mm). All neonates were normal on follow-up examination, without evidence of any masses or neurologic deficits. The fetal rectosigmoid colon frequently is identified in the third trimester and may reach 2 to 3 cm at term. Because the prevalence of meconium-filled rectum (6.3%) exceeds that of a presacral teratoma (0.0025%), this normal anatomic variant should be considered the most common cause of a third trimester presacral "mass."