Human tails are rare congenital anomalies typically noted in otherwise normal infants.  We present a two-day-old male born by vaginal delivery at full term to a 25-year-old G3P2 mother.  Both parents were of non-consanguineous, Hispanic ancestry. There were no known teratogenic exposures during the pregnancy.  Birth weight, length, and head circumference were all within the 50th to 75th percentiles. The patient was noted at delivery to have a caudal appendage and a malformation of the left arm and was transferred to a tertiary hospital for further evaluation. The caudal appendage consisted of a soft, flesh-colored, non-bony, 2 cm x 0.5 cm tail at the base of the spine. Ultrasound demonstrated a low-lying conus medullaris tip suggesting possible tethered cord. An MRI of the spine was planned for three months of age.  Physical examination of the left arm revealed an absent hand with five very short fingers, each approximately 0.5 cm in length.  The right arm and hand appeared normal.  X-rays of the left arm and hand showed a normal radius and ulna with no significant bone formation in the hand.  Echocardiogram was normal and renal ultrasound demonstrated unilateral grade I hydronephrosis. Tail-like appendages are commonly thought to be remnants of the embryonic tail.  In normal development, the tail regresses as the lower extremities grow.  Caudal appendages are generally non-syndromic, although they have been seen in conjunction with Goltz-Gorlin syndrome and FGFR2-related craniosynostosis.  Although most individuals with caudal appendages are normal save this extra tissue, there are multiple reports of individuals with spine and spinal cord anomalies as well as reports of co-occurrence with cleft palate, hemangiomas, camptodactyly, and hypodactyly. Specific cases of caudal appendage with limb anomalies include an infant with a tail measuring 4.4 cm at 2 weeks of age who was also noted to have hypophalangia of four toes of the right foot.  Additionally, an infant girl with a tail attached to the lumbar spine and again attached to the anterior abdominal wall has also been reported. This girl furthermore had ring constrictions of the left leg and malformations of the toes suggestive of amniotic bands. However, the majority of these patients do not show evidence of amniotic bands.  Our patient’s limb findings were suggestive of amniotic bands, though no other signs of bands such as constriction rings or amnion remnants were observed.  The case reported here extends the association of human tail with limb defects and the previously suggested causation of amniotic bands.  Limb formation, including development of the hand, is complete by 36 days post-conception while tail regression is complete by 56 days.  Rupture of the amnion prior to 56 days could theoretically explain this patient’s constellation of findings.  Although amniotic banding would not readily explain the persistence of a caudal appendage, a common etiology is suggested given the recurrence.

This poster (#265) will be presented at the ACMG Annual Meeting by Sara Halbach, a genetic counselor in the Department of Human Genetics, Thursday March 29: 10:30-11:30am. Stop by and learn more.