A tale of two "tails:" A curiosity revisited.

A human tail or a caudal appendage is a rare condition with preconceived notions and stigmata. They could be either true tails or "pseudotails" based on their embryology. Clinically, they are considered as a marker of occult spinal dysraphism. We report two such cases with tethering of cord, one of which was associated with a lipomeningomyelocele. These patients are in need of meticulous evaluation and appropriate management.

Introduction

Caudal appendage or “the human tail” is a curious and rare condition, which was initially thought to be an evidence of man's descent from or relation to other animals. It has even been made a subject of superstitious beliefs, especially in Asia. Although such malformations might not have a deeper connection to the neurospinal axis, they are frequently considered to be cutaneous signatures of occult spinal dysraphisms and malformations of the spinal cord.[1] There are several reports of “human tails” causing tethered cord syndrome.[23] We report two cases of “human tail” or caudal appendages associated with tethering. We briefly discuss their modes of presentation and management strategies along with their embryology.

Case Reports

Case 1

An 11-month-old boy born to nonconsanguineous married parents presented with a tail-like appendage arising from midline of the lower back since birth. The appendage had gradually increased in size with growth of the child. The appendage was arising from zenith of a sessile swelling in the lower lumbosacral region. The swelling was noncompressible, nonfluctuant, nonreducible, without any impulse on coughing [Figure 1a and b]. There were no neurological deficits, and growth and development were age appropriate. Magnetic resonance imaging (MRI) showed that the cord was ending at S4 level with a portion extending into the subcutaneous fatty tissue suggestive of lipomeningomyelocele [Figure 1c–e]. There was a syrinx in the terminal spinal cord. The child underwent excision of the appendage, subcutaneous lipoma, and lipomeningomyelocele along with detethering of the cord and dural reconstruction. The child made an uneventful recovery and was asymptomatic after 1 year of surgery.

Figure 1

(a-c) T2-weighted image sagittal, T1-weighted image axial, and T2-weighted image axial: Spinal cord extending up to lower sacral region ending with a lipoma which is continuous with subcutaneous lipoma. There is associated syrinx of the spinal cord. (d and e) the clinical photograph of the lesion

Case 2

An 18-month-old girl, the second born out of a nonconsanguineous marriage, presented with an elongated tail-like projection from the midline lower back. On palpation, the projection was soft to firm in consistency and was nonfluctuating, noncompressible, and covered with normal skin [Figure 2a–c]. Neurological examination was normal with age appropriate development. MRI showed spina bifida below S1. Spinal cord was low lying up to L4-L5 level with protrusion of meninges in the subcutaneous plane. She underwent excision of the appendage along with detethering of the cord [Figure 2d]. Histopathological examination showed skin with sweat glands and hair follicles and underlying lipomatous tissue with nodules of adipocytes. Portions of thickened meninges with plump arachnoid cells were seen partially surrounding the lipoma along with cluster of skeletal muscle fibers and occasional dorsal root ganglion and nerve fibers. The child recovered uneventfully.

Figure 2

(a-c) Clinical photograph of the sacral appendage, (d) intraoperative photograph showing the fibrous band continuous with the appendage causing tethering of the spinal cord

Discussion

Embryogenesis

At 5–6 weeks, human embryo has a tail with 10–12 vertebrae. This regresses by fusion of vertebrae, leaving the vestigial coccyx. The embryonic tail disappears by the 8th week; persistence may lead to formation of a true tail. However, the current concept of the embryology of this malformation is that the tail structure is a form of congenital dermal sinus tract resulting from premature or incomplete disjunction of the somatic and neuroectoderm during primary neurulation.[4] This theory is consistent with the more common cases of human tail. Other possibility is that this disorder may be caused due to disorder of secondary neurulation. As secondary neurulation with formation of tail bud begins prior to completion of primary neurulation, a disorder of the secondary neural tube or notochord could possibly affect closure of the neuropore and result in spinal cord lipoma and abnormal tail bud regression. An early disorder may result in spinal lipoma and tethering and later ones may cause persistence of tail bud without spinal anomalies.[5] In cases where such lesions are associated with lipomeningomyelocele, it has its origin in secondary neurulation and lipomeningomyelocele from primary neurulation.

The caudal appendages or “tails” have been classified as true tails or pseudotails. The “true persistent vestigial tails” are vertebrate, caudal, midline protrusion capable of spontaneous or reflex motion, consisting of skin covering a combination of muscle, adipose and connective tissue with normal blood vessels and nerves. The “pseudotails” are caudal protrusion composed of other normal and abnormal tissues.[6] This classification system has embryological importance without clinical significance.

The classification by Lu et al. of human tails with or without tethered cord appears to be more practical and clinically relevant.[2] They proposed that the caudal appendages are “true tails” when it is a benign condition, a prolongation beyond the coccygeal or midgluteal region, and not associated with any underlying malformation. It needs only simple excision. In contrast, the caudal appendages occurring with spina bifida occulta or spinal dysraphism are “pseudotails.” These appendages are only a cutaneous sign of underlying spinal dysraphism since the skin and nerve system are related by their similar ectodermal origin. Preoperative evaluation and complex surgical intervention are usually necessary.[2] Occasionally, congenital heart disease, anal and vaginal atresia, and horseshoe kidney are reported to be associated with such disorders,[7] and careful preoperative evaluation is required.

Various lengths of caudal appendage ranging from 1 to 20 cm have been reported to arise at various levels at the upper lumbar region to coccyx.[5] Associated abnormalities of the skin, including hypertrichosis, hyperpigmentation, dermal sinus tracts, and hemangiomas, are reported.[8] Lu et al. had reviewed 59 cases in literature on human tails from 1960 to 1997. Nearly half had an associated spinal dysraphism. Of the 16 cases where imaging was available, it revealed a tethered spinal cord in 81%. Rarely, the cutaneous appendages itself may be having continuity with intraspinal lipoma causing tethering of the cord.[239] A case of “bony human tail” causing tethered cord has also been reported.[10] Hence, caudal appendages and its association with tethering should always be kept in mind before considering surgery. Both our cases were “pseudotails” and were associated with underlying spinal cord anomalies. Our first case had lipomeningomyelocele, and the second case had only tethered cord.

If the cutaneous appendage and the spinal abnormality or tethering are at different planes or if the appendage is off midline, careful preoperative evaluation has to be performed before excluding the connection between the two. The MRI images especially the sagittal views might give a false impression, and hence, during surgery, it is of utmost importance to carefully dissect and try to locate any tract which might connect the appendage with the intraspinal lipoma or tethering.[5]

Conclusion

We reported two cases of pseudotails, where the caudal appendages were visually appearing like human tails and were associated with tethered cord. The associated social stigma and the possibility of development of new deficits as it grows make it vital to identify these cases early and intervene appropriately.

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Conflicts of interest

There are no conflicts of interest.