Departamento de Obstetricia y Ginecología, Facultad de Medicina, Universidad de Concepción.Servicio de Obstetricia y Ginecología, Hospital Guillermo Grant Benavente, Concepción, Chile.

Synonyms: Human Tail, True Human Tail.

Definition: Human fetal tails are divided into two groups¹:

-True vestigial tails: which contain normal skin, connective tissue, muscle, vessels and nerves.

-Pseudotails: which represent a variety of caudal appendages and protrusions.

Case report

After an uncontrolled pregnancy, a 26-year-old primigravida was admitted in our center in advanced labor. Her prior history was unremarkable. She gave birth to a term baby girl, who weighted 3690 grams and measured 50 cm. Scored 8-9-9-9 in Apgar tests. She was classified in the 85^th centile for gestational age. Her physical examination revealed a long vermiform cutaneous appendage. It measured 10 cm and its width was 6 mm. It was located on the lumbar-sacral region, in the superior vertex of the intergluteal fold., slightly to the right of the sagittal line. The appendage was covered by normal skin and its consistence was soft and tender.

The post-birth sonography performed showed no other anomalies with absence of communication between the caudal appendage and the neural tube and its components.

Also it was noticed that the sacral curvature was normal. The appendage was removed surgically during the neonatal period with no incidents.

No osseous or cartilage structures were contained inside the appendage. There skin covering it was normal and it contained mainly fatty tissue, with normal vessels, muscular tissue and nerves.

The neurological follow-up has been normal so far (18 months).

Incidence: Unknown. Considered sporadic.

Pathogenesis & Etiology: remnant of embryonic tail. Fetal tail is a normal feature during embryonic development that should regress by the 8^th week. Its persistence has been described beyond the 8^th week.

Embryology: During the 5^th-6^th week, the human embryo has a tail with 10 to 12 vertebrae. Then, it starts to regress, reducing the number of vertebrae by fusion, leaving the vestigial coccyx. By this process, at 8 weeks, it disappears, although the exact moment varies². The persistent tail probably arises from the most distal non-vertebrate remnant of the embryonic tail^2,3,4.

Prenatal Diagnosis: Reported in a few cases ^3,5,6,7.

Associated anomalies: spina bifida (20%), meningocele, lipomeningocele, chondrodysplasia, cleft palate, cutaneous hemangiomas, syndactyly and oligodactyly ^8,9.

Differential diagnosis: Spina bifida, caudal regression sequence and sacrococcygeal teratomas.

Recurrence: never described.

Management: If diagnosed prenatally, no alteration of management is advisable as, to date, no morbidity or mortality related events have been described in these cases. After birth, a thorough examination, which includes CT-scan or MRI is suggested in order to rule out subtle anomalies prior to surgical removal of the tail.

Discussion:

The birth of a baby with a tail is indeed a disturbing happening for the medical team as well as for parents.

Several 19^th century medical reports and popular tales mentioned human tails. In was believed that the embryo, during its development passed through the form of inferior animals. In fact, most malformations were thought to be errors in the transition between inferior species and humans¹⁰. In particular, Darwin describes a case to support his theory related with human evolution in "The descent of Man‹¹.

There are many reports of this anomaly. Some report that tribes in Paraguay, Borneo and Philippines, have individuals with tails¹².

Bartels et al. in 1884 reviewed cases reported to that date finding 116. Of the 68 cases in which the sex was mentioned, 52 were male and only 16 were female infants¹³. In a similar report, Lu et al. reviewed cases between 1960 and 1997 finding only 59. He reported an association with spina bifida was 20%⁹.

When we compare this "human tail†with the tail of other vertebrates, the difference is evident. This tails do not contain vertebral structures. In fact, there is only one case reported in medical literature in which the human tail had vertebral remnants¹⁴.

References:

1. Dao A, Netsky M. Human Tails and pseudotails. Human Pathol 1984; 15: 449.
2. Ledley F. Evolution and the human tail. N Engl J Med 1982; 306:1212-15.
3. Zimmer EZ, Bronshtein M. Early sonographic findings suggestive of the human fetal tail. Prenat Diagn 1996 Apr;16(4):360-2.
4. Hughes AF, Freeman RB. Comparative remarks on the development of the tail cord among higher vertebrates. J Embryol Exp Morphol. 1974; 32: 355-63.
5. Abbot JF, Davis GH, Endicott B, Pfleghaar  K, Wapner RJ. Prenatal diagnosis of vestigial tail. J Ultrasound Med 1992; 11:53-5.
6. Grange G, Tantau J, Pannier E, Aubry M-C, Viot G, Fallet-Bianco C, Terrace G, Cabrol D. Prenatal diagnosis of fetal tail and postabortum anatomical description. Ultrasound Obstet Gynecol 2001; 18: 531-3.
7. Efrat Z, Perri T, Meizner I, Chen R, Ben-Rafael Z, Dekel A. Early sonographic detection of a human tail: a case report.  Ultrasound Obstet Gynecol 2001; 18: 534-5.
8. Warkany J. Congenital malformations. Chicago: Year Book, 1971:925-7.
9. Lu FL, Wang PJ, Teng RJ, Yau KI. The human tail. Pediatr Neurol 1998 Sep;19(3):230-3.
10. Gould GM, Pyle WL. Anomalies and curiosities of medicine. Philadelphia: WB Saunders, 1897:277-80.
11. Darwin C. The descent of man, and selection in relation to sex. Vol. I. New York: D Appleton1871: 28, 372.
12. Forbin V. Etrange anomalie chez une tribu des Philippines. Presse Med. 1926; 23:108-9.
13. Bartels M. Die geschwäntzen Menschen. Arch. Anthrop., 1884: V.15, p.45.
14. Kabra NS, Srinivasan G, Udani RH. True tail in a neonate. Indian Pediatr 1999 Jul;36(7):712-3.