Prenatal diagnosis of fetal tail and postabortum anatomical description

Fetal ultrasound examination at 13 weeks of gestation demonstrated a homoge neously echogenic protrusion, or tail, 7 mm in length, in the sacral region . At 15 weeks, the ultrasound appearance was consistent with a regression o f the tail and by 21 weeks it bad completely disappeared. Severe intrauteri ne growth restriction with reduced uterine blood flow was diagnosed at 21 w eeks and intrauterine death occurred at 24 weeks of gestation. Postmortem e xamination revealed a 4-mm caudal appendage which contained no vertebrae on radiography. The appendage was located under and behind the last sacral ve rtebra suggesting a true vestigial tail with a delayed process of regressio n.