- Email: [email protected]
The human tail
The Human Tail Frank L. Lu, MD, Pen-Jung Wang, MD, Ru-Jeng Teng, MD, and Kuo-Inn Tsou Yau, MD
before surgical management. The authors reviewed the available and more detailed reports in recent literature from 1960 to 1995 to further explore this topic [1-34]. An index case of lipoma that manifested with a human tail and was complicated by tethered spinal cord is presented.
Case Report The human tail is a congenital anomaly with a protruding lesion from the lumbosacrococcygeal region. A newborn with a tail-like structure over the coccygeal area observed since birth is presented. Lipoma accompanied by tethered spinal cord were found. In reviewing the literature from 1960 to 1997, 59 cases were described. Higher incidences of spinal dysraphism (49.15%) and tethered spinal cord (20.34%) compared with previous reports were evident. This fact plays an important role in understanding the disturbance of development and regression of human tails. A new classification according to whether the anomaly appears in combination with spinal dysraphism is proposed for clinical usage. Preoperative detailed image studies are needed to clarify the possibility of tethered spinal cord syndrome developing in the future and thus prevent it. Magnetic resonance imaging is the modality of choice if available. Long-term follow-up for possible sequelae after operation, especially in cases with spinal dysraphism, is necessary. © 1998 by Elsevier Science Inc. All rights reserved. Lu FL, Wang P-J, Teng R-J, Yau K-IT. The human tail. Pediatr Neurol 1998;19:230-233.
A female neonate had a tail-like structure evident since birth. The patient was born to a healthy mother (G2P1) after a normal delivery, with a birth weight of 3,750 gm at 39 weeks gestation. Only some medications for a common cold were taken during the first trimester. No similar lesion or any other neurologic disease was found in the family. Physically a 4.5-cm tail-like structure over the sacral area with its base surrounded by a soft tissue mass was noticed immediately after birth (Fig 1). Neurologic examination results were compatible with her age. Hemogram, blood chemistry, urinalysis, manometry, anal sphincter electromyography, and renal echography were all within normal limits. MRI was performed at 12 days of age and revealed spinal cord termination at about the upper margin of S1, compatible with tethered cord. Lipoma was considered present because of a bright signal lesion on the T1-weighted image at the level of L5-S1 involving the spinal cord and extending externally to the skin tag (Fig 2). At 4 months of age, the length of the tail-like structure increased to 6 cm. The growth rate of the tail was estimated to be about 4 mm per month. Under the base of the tail, at the level of L5-S1, a 3 3 1.5 cm2 lipoma was found. The conus of the spinal cord ended at the junction of L5-S1, and spina bifida was also visualized. Subtotal resection of the lipoma was performed smoothly, and the tethered cord was released. Dural graft insertion with lamina retransplantation was performed. No complications or neurologic deficits were noted during the operation or later in the follow-up of 1 year. Developmental milestones, reflexes, muscle tone, and urinary and anal sphincter function were all normal in this child. Pathologic study of the excised specimen revealed mature adipose tissue within the tail-like structure extending from its base. Normal skin and subcutaneous tissue were evident. No bone or cartilage tissue was found inside the structure.
Introduction Discussion The human tail is a protruding lesion from the lumbosacrococcygeal region. It has been reported since the late nineteenth century, but its etiology is still unclear. In 1984, Dao and Netsky [1] reviewed 33 cases of human tails from descriptions in the literature between 1859 and 1982. The classification of true tail and pseudotail then emerged. Later, in 1988, Dubrow et al. [2] reviewed reports of 24 true tails and 10 pseudotails from 1884 to 1985. The data were not in depth until recently, when more detailed image studies, computed tomography (CT) and magnetic resonance imaging (MRI), could be performed
From the Department of Pediatrics; National Taiwan University Hospital; Taipei, Taiwan, Republic of China.
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The authors reviewed the literature from 1960 to 1997; 35 articles (including this one) presented 59 cases of lumbosacrococcygeal appendage termed human tail [1-34]. More detailed description with plain radiography was available since 1960. The first available CT report of a human tail was from Ohara [16] in 1980. MRI study was first mentioned by Dubrow et al. [2] in 1988. The appendages were mostly evident from birth, and the incidence was equal in either sex (male/female 20:19 in the reports that documented the gender).
Communications should be addressed to: Dr. Lu; Department of Pediatrics; National Taiwan University Hospital; 7 Chung-Shan South Road; Taipei, Taiwan, 10016, ROC. Received January 5, 1998; accepted April 2, 1998.
© 1998 by Elsevier Science Inc. All rights reserved. PII S0887-8994(98)00046-0 ● 0887-8994/98/$19.00
Table 1.
Associated anomalies in human tail
Associated Anomaly
Figure 1. At birth, a 4.5-cm tail-like structure over the sacral area extended from the lipoma base.
In all the cases with a pathologic report available, mature adipose tissue was the main component of the tail structure. Collagenous tissue, small nerves, and vessels comprised the human tail. The presence of skeletal muscle and vertebra was occasionally reported. As in the authors’ case the lipoma formed the base of the tail structures in 16 cases (27.12%). Growing potential was mentioned in many reports. Movement of the tail was occasionally recognized.
Figure 2. MRI of the human tail demonstrating tethered cord with the spinal cord terminating at the upper margin of S1. A bright signal lipoma is demonstrated on T1-weighted image (TR 5 500, TE 5 17) at L5-S1, which extends to the human tail.
Spinal dysraphism Meningocele Spina bifida only Lipoma Tethered spinal cord Coccygeal vertebrae Syndactyly Hemangioma Cleft palate Crouzon syndrome Congenital tracheal stenosis Clubfoot Von Recklinghausen disease Omphalocele Hypoplasia of digits Tetralogy of Fallot
Incidence (%) 29/59 (49.15) 8/29 (27.59) 21/29 (72.41) 16/59 (27.12) 12/59 (20.34) 7/59 (11.86) 2/59 (3.39) 1/59 (1.69) 1/59 (1.69) 1/59 (1.69) 1/59 (1.69) 1/59 (1.69) 1/59 (1.69) 1/59 (1.69) 1/59 (1.69) 1/59 (1.69)
Spinal dysraphism is the most frequently associated anomaly in human tail. It may be myelomeningocele, meningocele, or spina bifida. Other anomalies include tethered spinal cord, lipoma, coccygeal vertebrae, and syndactyly (Table 1). Two case reports with a family history were published, one of a grandmother who also had a tail [1] and the other of a mother with a low spinal lipoma [28]. Interest was evoked in the nineteenth century because of a possible relationship and explanation of the human tail with evolutionary theories. To clarify this question, the embryologic approach is the most valuable tool. The associated embryogenesis of the human tail is first noted at the fourth week of gestation. The somites are formed, and the remaining primitive knot and streak composes a compact mass at the caudal end of the embryo that is called the tail bud or end bud. The continued uneven growth causes the tail bud to extend and curl beneath the hind gut. During the fifth and sixth weeks the trunk ends in a conspicuous tail containing 10-12 caudal vertebrae. The distal portion lacks bone and is composed of mesodermal elements. During the seventh and eighth weeks, the vertebrated portion retracts into the soft tissue. The nonvertebrated part projects temporarily and then undergoes regression caused by phagocytosis, with the debris-laden macrophages migrating back to the body [35], and it disappears completely at the end of the eighth week. Thus, the presence of human tail can be considered a disturbance in the development of the embryo but not a regression in the evolutionary process. The high incidence of human tail combined with spinal dysraphism noted recently may throw light on the problem. A high association with skin lesions such as subcutaneous tumors, skin dimples or sinuses, hemangiomas, hypertrichosis, and hyperpigmentation was observed in the patients with spinal dysraphism [14]. These associations
Lu et al: Human Tail 231
give a hint to the relationship between human tail and spinal dysraphism. Focal premature dysjunction of the neural tube may thus be an important factor in the disturbance of human tail development and regression. The unfused neural tube exposes the paraxial mesoderm to the dorsal aspect of the neural ectoderm and induces formation of fatty elements and lipoma. This event can be supported by the high incidence of lipoma (27.12%) in the authors’ series. The formation of fatty elements and lipoma may prevent the fusion of the neural tube thus tethering the cord because of attachment of the fatty elements with neural structures, resulting in tethered spinal cord syndrome. The different extents of the fusing tube may develop different features of the lumbosacrococcygeal area that may result in human tail. In 1884, Bartels first classified five types of caudal appendage based on the theory that regression of the tail may be arrested at any point. Harrison also believes that the appendage is a remnant of the unvertebrated mesodermal portion of the embryonic appendage. In 1901, he classified those cases with coccyx as human tails, and those without as caudal appendages. These classifications are not widely accepted by others. Dao and Netsky [1] reviewed a series of published cases and proposed the classification of true tail and pseudotail. True tail describes the most distal remnant of the embryonic tail that contains adipose and connective tissue, striated muscle, blood vessels, and nerves and is covered by skin. It was presumed that no bone, cartilage portion, or connection with the neurospinal axis can be found in the true human tail. Some authors described it as a benign condition that does not involve the spinal cord [20]. During the fifth and sixth week of development, however, the proximal tail does contain vertebrae. This embryonic finding challenges the presumption mentioned by Dao and Netsky [1]. As for the pseudotail, the varying lesions have in common a lumbosacral protrusion and a superficial resemblance to true tails that includes anomalous prolongation of coccygeal vertebrae, lipoma, teratoma, chondromegaly, and glioma. This classification remains obscure, and the distinction during clinical examination is many times inconclusive [25]. The incidence of associated spinal dysraphism and tethered spinal cord increased much after detailed studies became available, causing the classification between true and pseudotail to become even more confused; and almost all of the recent cases were classified as pseudotail. Thus this separation cannot be supported by the embryonic point of view nor by its usage in clinical differentiation. After reviewing the recent cases, the authors suggest a simplification of the classification according to whether the human tail occurs in association with spinal dysraphism. From the practical point of view, all cases must be investigated for spinal dysraphism because of its high association with human tail (49.15% in the authors’
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Table 2. Incidence of important associated anomalies in cases of human tail between different years
Associated Anomaly Spinal dysraphism Meningocele Spina bifida only Lipoma Tethered spinal cord
Incidence 1960-1979 1980-1997 (%) (%) 3/16 (18.75) 1/3 (33.33) 2/3 (66.67) 3/16 (18.75) 1/16 (6.25)
26/43 (60.47) 7/26 (26.92) 19/26 (73.08) 13/43 (30.23) 11/43 (25.58)
Total (%) 29/59 (49.15) 8/29 (27.59) 21/29 (72.41) 16/59 (27.12) 12/59 (20.34)
review). The incidence of tethered spinal cord syndrome is much higher if spinal dysraphism is present, and it is the main factor affecting the prognosis. Thus the cases with associated spinal dysraphism should especially receive long-term follow-up for neurologic development. The definition of true tail should be used only for the one that is actually caused by abnormal development and regression of the human tail. Pseudotail has no relationship to human tail development; it is a tissue that has been accidentally located in the lumbrosacrococcygeal area. A clear-cut distinction is impossible to make by clinical, imaging, or pathologic studies at present. Tethered spinal cord syndrome results from a pathologic condition related to spinal dysraphism [36]. This syndrome should always be considered in cases of human tail because the incidence was as high as 20.34% (12 of 59) during 1960-1997 and was especially evident in the recent years of 1980-1997 as 25.58% (11 of 43) in the authors’ review. Progressive motor and sensory dysfunction of lower extremities, muscle atrophy, decreased or hyperactive reflexes, urinary incontinence, spastic gait, or orthopedic deformities such as scoliosis are the clinical clues. Final confirmation is determined by detailed image studies and surgery. After 1980 the incidence of associated anomalies, such as spinal dysraphism, became higher because CT or MRI began to be performed as part of examination (Table 2). The incidence is probably underestimated because some reports did not perform any detailed image studies. In the early reports, plain radiography was the only available tool for examination, and only rare cases were found to have spinal dysraphism and tethered cord syndrome. Because of the concept at the time that this was a benign condition, deeper exploration during surgery was not always performed. The detailed structure may not even have been explicated. Recently, CT and MRI [37] have revealed more detailed information about the associated defects. According to the authors’ review, 13 of the 16 that were studied by CT or MRI (81%) had confirmed tethered spinal cord during surgery, whereas in the cases that received only plain radiography examination the diagnosis of tethered spinal cord could be missed. Detailed imaging should be performed in every case of human tail because of the possibility of spinal dysraphism. When available, MRI should be the modality of choice because of its
excellent resolution. The area of focus should include at least the lower thoracic to coccygeal regions. Although spinal dysraphism may have multifocal abnormalities, neurologic sequelae because of a cervical lesion have not ever been reported in association with human tails. Thus whole spine MRI study is not necessary under the consideration of cost and benefit, except for cases with symptoms or signs suggestive of cervical lesions. The clinical course becomes worse with the advance of age in patients with tethered spinal cord syndrome, especially after 2 years of age [38]. Early operation to relieve the tethered spinal cord will protect symptom-free patients from developing neurologic deficits. MRI study and careful exploration is the most important strategy in managing human tail to prevent further neurologic sequelae. Longterm follow-up of the neurologic status is also warranted. The authors are indebted to Dr. Ming-Ho Liao, Department of Pediatrics, Taiwan Provincial Hsin-Chu Hospital, for referring the case and Dr. Mung-Fae Kou, Department of Surgery, National Taiwan University Hospital, for provision of the neurosurgical management.
References [1] Dao AH, Netsky MG. Human tails and pseudotails. Hum Pathol 1984;15:449-53. [2] Dubrow TJ, Wackym PA, Lesavoy MA. Detailing the human tail. Ann Plast Surg 1988;20:340-4. [3] Rijsbosch JKC. Tail formation in man. Arch Chir Neerl 1960; 12:216-9. [4] Parsons RW. Human tails. Plast Reconstr Surg 1960;25:618-21. [5] Lundberg GD, Parsons RW. A case of human tail. Am J Dis Child 1962;104:72-3. [6] Jolly H. Baby with a tail. Arch Dis Child 1963;38:524-5. [7] Giroud A, Salet J, Pernet-Robert J. L’appendice caudal du nouveau-ne. Arch Fr Pediatr 1966;22:887. [8] Salisachs LG, Gubern AM. Phylogenie et ontogenie des teratomes sacrococcygeins et de l’appendice caudal. Ann Chir Infant 1968;9:125-46. [9] Gaur AC. Correspondence. J Indian Med Assoc 1969;52:398-9. [10] Odeku EL, Adeloye A. A case of human pseudo-tail. West Afr Med J 1970;19:115-6. [11] White JJ, Wexler HR. A baby with a tail. J Pediatr Surg 1973;8:883. [12] Itoh H, Koike M, Watanabe K. Two cases of caudal appendage (human tail). Jpn J Plast Reconstr Surg 1976;19:176. [13] Rijsbosch JK. Tail formation in man: Some historical notes on a case report. Arch Chir Neerl 1977;29:261-8. [14] Tavafoghi V, Ghandchi A, Hambrick GW, Udverhelyi GB. Cutaneous signs of spinal dysraphism: Report of a patient with a tail-like lipoma and review of 200 cases in the literature. Arch Dermatol 1978;114:573-7.
[15] Bar-Maor JA, Kesner KM, Kaftori JK. Human tails. J Bone Joint Surg 1980;62B:508-10. [16] Ohara Y. Human tail and other abnormalities of the lumbosacro-coccygeal region relating to tethered cord syndrome. Ann Plast Surg 1980;4:507-10. [17] Ledley FD. Evolution and the human tail: A case report. N Engl J Med 1982;306:1212-5. [18] Talwalker VC. Tale of a tail. N Engl J Med 1982;307:1089. [19] Brauchin AM, Mahler D, Hauben DJ, Rosenberg L. The human caudal appendage (human tail). Br J Plast Surg 1983;36:120-3. [20] Spiegelmann R, Schinder E, Mintz M, Blakstein A. The human tail: A benign stigma—Case report. J Neurosurg 1985;63:461-2. [21] Hoffman HJ, Taecholarn C, Hendrick EB, Humphreys RP. Management of lipomeningoceles: Experience at the Hospital for Sick Children, Toronto. J Neurosurg 1985;62:1-8. [22] Aso M, Kawaguchi T, Mihara M, Shimao S, Morimoto K, Sakinaga Y. Pseudotail associated with spinal dysraphism. Dermatologica 1987;174:45-8. [23] Sugamata A, Sato M, Ikeda J, Kinosita J, Tanihira S, Makino K. Two cases of a true human tail. Jpn J Plast Reconstr Surg 1988;31: 1072. [24] Gaskill SJ, Marlin AE. Neuroectodermal appendages: The human tail explained. Pediatr Neurosci 1989;15:95-9. [25] Belzberg AJ, Myles ST, Trevenen CL. The human tail and spinal dysraphism. J Pediatr Surg 1991;26:1243-5. [26] Ente G, Penzer PH, Kenigsberg K, Sherman J. The human tail. N Y State J Med 1991;91:506-7. [27] Yamatani K, Saitoh T, Oi M, Oka N, Endoh T, Takaku A. A case of human tail. No Shinkei Geka 1991;19:93-6. [28] Abbott JF, Davis GH, Endicott B, Pfleghaar K, Wapner RJ. Prenatal diagnosis of vestigial tail. J Ultrasound Med 1992;11:53-5. [29] Sagehashi N. An infant with Crouzon’s syndrome with a cartilaginous trachea and a human tail. J Craniomaxillofac Surg 1992; 20:21-3. [30] Chakrabortty S, Oi S, Yoshida Y, et al. Myelomeningocele and thick filum terminale with tethered cord appearing as a human tail: Case report. J Neurosurg 1993;78:966-9. [31] Matsuo T, Koga H, Moriyama T, Yamashita H, Imazato K, Kondo M. A case of true human tail accompanied with spinal lipoma. No Shinkei Geka 1993;21:925-9. [32] Matsumoto S, Yamamoto T, Okura K. Human tail associated with lipomeningocele— case report. Neurol Med Chir (Tokyo) 1994;34: 44-7. [33] Ohara K, Nakamura K. Human tail. Br J Plast Surg 1994;47: 288-9. [34] James HE, Canty TG. Human tail and associated spinal anomalies. Clin Pediatr 1995;34:286-8. [35] Fallon JF, Simandl BK. Evidence of a role for cell death in the disappearance of the embryonic human tail. Am J Anat 1978;52:398-9. [36] Matthias FR, Lausberg G. Diagnosis and therapeutic problems of restriction in cranial migration of spinal cord. Neuropaediatrie 1972; 3:339-47. [37] Raghavan N, Barkovich AJ, Edwards M, Norman D. MR imaging in the tethered spinal cord syndrome. AJR 1989;152:843-52. [38] Stolke D, Zumkeller M, Seifert V. Intraspinal lipomas in infancy and childhood causing a tethered cord syndrome. Neurosurg Rev 1988;11:59-65.
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before surgical management. The authors reviewed the available and more detailed reports in recent literature from 1960 to 1995 to further explore this topic [1-34]. An index case of lipoma that manifested with a human tail and was complicated by tethered spinal cord is presented.
Case Report The human tail is a congenital anomaly with a protruding lesion from the lumbosacrococcygeal region. A newborn with a tail-like structure over the coccygeal area observed since birth is presented. Lipoma accompanied by tethered spinal cord were found. In reviewing the literature from 1960 to 1997, 59 cases were described. Higher incidences of spinal dysraphism (49.15%) and tethered spinal cord (20.34%) compared with previous reports were evident. This fact plays an important role in understanding the disturbance of development and regression of human tails. A new classification according to whether the anomaly appears in combination with spinal dysraphism is proposed for clinical usage. Preoperative detailed image studies are needed to clarify the possibility of tethered spinal cord syndrome developing in the future and thus prevent it. Magnetic resonance imaging is the modality of choice if available. Long-term follow-up for possible sequelae after operation, especially in cases with spinal dysraphism, is necessary. © 1998 by Elsevier Science Inc. All rights reserved. Lu FL, Wang P-J, Teng R-J, Yau K-IT. The human tail. Pediatr Neurol 1998;19:230-233.
A female neonate had a tail-like structure evident since birth. The patient was born to a healthy mother (G2P1) after a normal delivery, with a birth weight of 3,750 gm at 39 weeks gestation. Only some medications for a common cold were taken during the first trimester. No similar lesion or any other neurologic disease was found in the family. Physically a 4.5-cm tail-like structure over the sacral area with its base surrounded by a soft tissue mass was noticed immediately after birth (Fig 1). Neurologic examination results were compatible with her age. Hemogram, blood chemistry, urinalysis, manometry, anal sphincter electromyography, and renal echography were all within normal limits. MRI was performed at 12 days of age and revealed spinal cord termination at about the upper margin of S1, compatible with tethered cord. Lipoma was considered present because of a bright signal lesion on the T1-weighted image at the level of L5-S1 involving the spinal cord and extending externally to the skin tag (Fig 2). At 4 months of age, the length of the tail-like structure increased to 6 cm. The growth rate of the tail was estimated to be about 4 mm per month. Under the base of the tail, at the level of L5-S1, a 3 3 1.5 cm2 lipoma was found. The conus of the spinal cord ended at the junction of L5-S1, and spina bifida was also visualized. Subtotal resection of the lipoma was performed smoothly, and the tethered cord was released. Dural graft insertion with lamina retransplantation was performed. No complications or neurologic deficits were noted during the operation or later in the follow-up of 1 year. Developmental milestones, reflexes, muscle tone, and urinary and anal sphincter function were all normal in this child. Pathologic study of the excised specimen revealed mature adipose tissue within the tail-like structure extending from its base. Normal skin and subcutaneous tissue were evident. No bone or cartilage tissue was found inside the structure.
Introduction Discussion The human tail is a protruding lesion from the lumbosacrococcygeal region. It has been reported since the late nineteenth century, but its etiology is still unclear. In 1984, Dao and Netsky [1] reviewed 33 cases of human tails from descriptions in the literature between 1859 and 1982. The classification of true tail and pseudotail then emerged. Later, in 1988, Dubrow et al. [2] reviewed reports of 24 true tails and 10 pseudotails from 1884 to 1985. The data were not in depth until recently, when more detailed image studies, computed tomography (CT) and magnetic resonance imaging (MRI), could be performed
From the Department of Pediatrics; National Taiwan University Hospital; Taipei, Taiwan, Republic of China.
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The authors reviewed the literature from 1960 to 1997; 35 articles (including this one) presented 59 cases of lumbosacrococcygeal appendage termed human tail [1-34]. More detailed description with plain radiography was available since 1960. The first available CT report of a human tail was from Ohara [16] in 1980. MRI study was first mentioned by Dubrow et al. [2] in 1988. The appendages were mostly evident from birth, and the incidence was equal in either sex (male/female 20:19 in the reports that documented the gender).
Communications should be addressed to: Dr. Lu; Department of Pediatrics; National Taiwan University Hospital; 7 Chung-Shan South Road; Taipei, Taiwan, 10016, ROC. Received January 5, 1998; accepted April 2, 1998.
© 1998 by Elsevier Science Inc. All rights reserved. PII S0887-8994(98)00046-0 ● 0887-8994/98/$19.00
Table 1.
Associated anomalies in human tail
Associated Anomaly
Figure 1. At birth, a 4.5-cm tail-like structure over the sacral area extended from the lipoma base.
In all the cases with a pathologic report available, mature adipose tissue was the main component of the tail structure. Collagenous tissue, small nerves, and vessels comprised the human tail. The presence of skeletal muscle and vertebra was occasionally reported. As in the authors’ case the lipoma formed the base of the tail structures in 16 cases (27.12%). Growing potential was mentioned in many reports. Movement of the tail was occasionally recognized.
Figure 2. MRI of the human tail demonstrating tethered cord with the spinal cord terminating at the upper margin of S1. A bright signal lipoma is demonstrated on T1-weighted image (TR 5 500, TE 5 17) at L5-S1, which extends to the human tail.
Spinal dysraphism Meningocele Spina bifida only Lipoma Tethered spinal cord Coccygeal vertebrae Syndactyly Hemangioma Cleft palate Crouzon syndrome Congenital tracheal stenosis Clubfoot Von Recklinghausen disease Omphalocele Hypoplasia of digits Tetralogy of Fallot
Incidence (%) 29/59 (49.15) 8/29 (27.59) 21/29 (72.41) 16/59 (27.12) 12/59 (20.34) 7/59 (11.86) 2/59 (3.39) 1/59 (1.69) 1/59 (1.69) 1/59 (1.69) 1/59 (1.69) 1/59 (1.69) 1/59 (1.69) 1/59 (1.69) 1/59 (1.69) 1/59 (1.69)
Spinal dysraphism is the most frequently associated anomaly in human tail. It may be myelomeningocele, meningocele, or spina bifida. Other anomalies include tethered spinal cord, lipoma, coccygeal vertebrae, and syndactyly (Table 1). Two case reports with a family history were published, one of a grandmother who also had a tail [1] and the other of a mother with a low spinal lipoma [28]. Interest was evoked in the nineteenth century because of a possible relationship and explanation of the human tail with evolutionary theories. To clarify this question, the embryologic approach is the most valuable tool. The associated embryogenesis of the human tail is first noted at the fourth week of gestation. The somites are formed, and the remaining primitive knot and streak composes a compact mass at the caudal end of the embryo that is called the tail bud or end bud. The continued uneven growth causes the tail bud to extend and curl beneath the hind gut. During the fifth and sixth weeks the trunk ends in a conspicuous tail containing 10-12 caudal vertebrae. The distal portion lacks bone and is composed of mesodermal elements. During the seventh and eighth weeks, the vertebrated portion retracts into the soft tissue. The nonvertebrated part projects temporarily and then undergoes regression caused by phagocytosis, with the debris-laden macrophages migrating back to the body [35], and it disappears completely at the end of the eighth week. Thus, the presence of human tail can be considered a disturbance in the development of the embryo but not a regression in the evolutionary process. The high incidence of human tail combined with spinal dysraphism noted recently may throw light on the problem. A high association with skin lesions such as subcutaneous tumors, skin dimples or sinuses, hemangiomas, hypertrichosis, and hyperpigmentation was observed in the patients with spinal dysraphism [14]. These associations
Lu et al: Human Tail 231
give a hint to the relationship between human tail and spinal dysraphism. Focal premature dysjunction of the neural tube may thus be an important factor in the disturbance of human tail development and regression. The unfused neural tube exposes the paraxial mesoderm to the dorsal aspect of the neural ectoderm and induces formation of fatty elements and lipoma. This event can be supported by the high incidence of lipoma (27.12%) in the authors’ series. The formation of fatty elements and lipoma may prevent the fusion of the neural tube thus tethering the cord because of attachment of the fatty elements with neural structures, resulting in tethered spinal cord syndrome. The different extents of the fusing tube may develop different features of the lumbosacrococcygeal area that may result in human tail. In 1884, Bartels first classified five types of caudal appendage based on the theory that regression of the tail may be arrested at any point. Harrison also believes that the appendage is a remnant of the unvertebrated mesodermal portion of the embryonic appendage. In 1901, he classified those cases with coccyx as human tails, and those without as caudal appendages. These classifications are not widely accepted by others. Dao and Netsky [1] reviewed a series of published cases and proposed the classification of true tail and pseudotail. True tail describes the most distal remnant of the embryonic tail that contains adipose and connective tissue, striated muscle, blood vessels, and nerves and is covered by skin. It was presumed that no bone, cartilage portion, or connection with the neurospinal axis can be found in the true human tail. Some authors described it as a benign condition that does not involve the spinal cord [20]. During the fifth and sixth week of development, however, the proximal tail does contain vertebrae. This embryonic finding challenges the presumption mentioned by Dao and Netsky [1]. As for the pseudotail, the varying lesions have in common a lumbosacral protrusion and a superficial resemblance to true tails that includes anomalous prolongation of coccygeal vertebrae, lipoma, teratoma, chondromegaly, and glioma. This classification remains obscure, and the distinction during clinical examination is many times inconclusive [25]. The incidence of associated spinal dysraphism and tethered spinal cord increased much after detailed studies became available, causing the classification between true and pseudotail to become even more confused; and almost all of the recent cases were classified as pseudotail. Thus this separation cannot be supported by the embryonic point of view nor by its usage in clinical differentiation. After reviewing the recent cases, the authors suggest a simplification of the classification according to whether the human tail occurs in association with spinal dysraphism. From the practical point of view, all cases must be investigated for spinal dysraphism because of its high association with human tail (49.15% in the authors’
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Table 2. Incidence of important associated anomalies in cases of human tail between different years
Associated Anomaly Spinal dysraphism Meningocele Spina bifida only Lipoma Tethered spinal cord
Incidence 1960-1979 1980-1997 (%) (%) 3/16 (18.75) 1/3 (33.33) 2/3 (66.67) 3/16 (18.75) 1/16 (6.25)
26/43 (60.47) 7/26 (26.92) 19/26 (73.08) 13/43 (30.23) 11/43 (25.58)
Total (%) 29/59 (49.15) 8/29 (27.59) 21/29 (72.41) 16/59 (27.12) 12/59 (20.34)
review). The incidence of tethered spinal cord syndrome is much higher if spinal dysraphism is present, and it is the main factor affecting the prognosis. Thus the cases with associated spinal dysraphism should especially receive long-term follow-up for neurologic development. The definition of true tail should be used only for the one that is actually caused by abnormal development and regression of the human tail. Pseudotail has no relationship to human tail development; it is a tissue that has been accidentally located in the lumbrosacrococcygeal area. A clear-cut distinction is impossible to make by clinical, imaging, or pathologic studies at present. Tethered spinal cord syndrome results from a pathologic condition related to spinal dysraphism [36]. This syndrome should always be considered in cases of human tail because the incidence was as high as 20.34% (12 of 59) during 1960-1997 and was especially evident in the recent years of 1980-1997 as 25.58% (11 of 43) in the authors’ review. Progressive motor and sensory dysfunction of lower extremities, muscle atrophy, decreased or hyperactive reflexes, urinary incontinence, spastic gait, or orthopedic deformities such as scoliosis are the clinical clues. Final confirmation is determined by detailed image studies and surgery. After 1980 the incidence of associated anomalies, such as spinal dysraphism, became higher because CT or MRI began to be performed as part of examination (Table 2). The incidence is probably underestimated because some reports did not perform any detailed image studies. In the early reports, plain radiography was the only available tool for examination, and only rare cases were found to have spinal dysraphism and tethered cord syndrome. Because of the concept at the time that this was a benign condition, deeper exploration during surgery was not always performed. The detailed structure may not even have been explicated. Recently, CT and MRI [37] have revealed more detailed information about the associated defects. According to the authors’ review, 13 of the 16 that were studied by CT or MRI (81%) had confirmed tethered spinal cord during surgery, whereas in the cases that received only plain radiography examination the diagnosis of tethered spinal cord could be missed. Detailed imaging should be performed in every case of human tail because of the possibility of spinal dysraphism. When available, MRI should be the modality of choice because of its
excellent resolution. The area of focus should include at least the lower thoracic to coccygeal regions. Although spinal dysraphism may have multifocal abnormalities, neurologic sequelae because of a cervical lesion have not ever been reported in association with human tails. Thus whole spine MRI study is not necessary under the consideration of cost and benefit, except for cases with symptoms or signs suggestive of cervical lesions. The clinical course becomes worse with the advance of age in patients with tethered spinal cord syndrome, especially after 2 years of age [38]. Early operation to relieve the tethered spinal cord will protect symptom-free patients from developing neurologic deficits. MRI study and careful exploration is the most important strategy in managing human tail to prevent further neurologic sequelae. Longterm follow-up of the neurologic status is also warranted. The authors are indebted to Dr. Ming-Ho Liao, Department of Pediatrics, Taiwan Provincial Hsin-Chu Hospital, for referring the case and Dr. Mung-Fae Kou, Department of Surgery, National Taiwan University Hospital, for provision of the neurosurgical management.
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