Sirenomelia Apus with Vestigial tail
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《美国医学杂志》
Department of Neonatology, Seth GS Medical College & King Edward Memorial Hospital, Parel, Mumbai, India
Abstract
Sirenomelia is an exceptionally rare congenital malformation characterized by complete or near complete fusion of lower limbs. A newborn with clinical features of sirenomelia including fused lower limbs in medial position, absent fibula, anal atresia, complete absence of urogenital system (bilateral renal agenesis, absent ureters, urinary bladder, absent internal and external genitalia), a single umbilical artery and a vestigial tail is reported. Association of vestigial tail with sirenomelia is not described in the literature.
Keywords: Sirenomelia; Vestigial tail
Sirenomelia is exceptionally rare congenital malformation with frequency of 1.5 to 4.2 per 1,00,000 births and is characterized by a single fused lower limb. Due to its close resemblance to the mermaid of Greek and Roman mythology, sirenomelia has fascinated scientists for centuries.
Case history
A full term, severely growth retarded baby weighing 1340 gm, was born to a 20 year old primigravida, with non-consanguineous marriage. Antenatally she was diagnosed to have severe oligohydromnios. The baby had severe birth asphyxia (Apgar 3, 2,2 at 1, 5 and 10 minutes respectively) and despite all resuscitative attempts baby died after 20 minutes.
Physical examination revealed potter facies, single umbilical artery and a well developed upper half of the body. In the lower half there was complete fusion of both the thighs and legs and there were no feet. There were no external genitalia or anal opening. There was a small soft tissue projection at the tip of the coccyx suggestive of vestigial tail. This caudal appendage was 4 cm long, 1.5 cm in diameter and had soft fibrous consistency. Figure1
Necrogram of the baby revealed, hypoplastic sacral segments, deformed pelvic bones, a single femur with two ossification centers at the lower end suggestive of fusion of the two femora and a single bony tag replacing leg bones. The vestigial tail did not show any bony or cartilaginous structure. The abdominal cavity revealed a diffuse stippled calcification all over the abdomen suggestive of meconium peritonitis. Chest skiagram and rest of the skeleton survey were unremarkable. Figure2
On autopsy there were single umbilical artery, hypoplastic lungs, anal atresia, and complete absence of urogenital system (bilateral renal agenesis, absent ureters and urinary bladder, absent internal and external genitalia). The vestigial tail contained fibrous and adipose tissue with normal skin covering.
Discussion
Sirenomelia is an anomalous development of the caudal region of the body. Complete or near complete fusion of the lower limbs is the most striking feature and the major diagnostic feature for sirenomelia.[1] Depending on the degree of fusion of lower limb and feet, sirenomelia can be classified into three types: a) Simpus Apus (Sirenomelus): No feet, one tibia, one femur b) Simpus Unipus (Uromelus): One foot, two femur, two tibia, two fibula c) Simpus Dipus (Simelus): Two feet and two fused legs (flipper like)-this is popularly known as mermaid. [1],[2] The present case was simpus apus.
The sirenomelia sequence cases have many visceral anomalies like imperforate anus, renal agenesis, heart defects and neural tube defects. The genitalia may vary from completely absent internal and external genitalia (as in our case) to almost near normal genitalia. Single umbilical artery is common but not a constant finding.[1],[3] Association of vestigial tail with Sirenomelia has not been described in the literature. The present case had 4 cm long true tail arising at the tip of the coccyx. Most of the cases are still born or die soon after birth due to severe visceral anomalies though two case reports have documented survivors.[3]
The etiology of sirenomelia sequence is uncertain, as no specific teratogens have been associated with the malformation in human. Duhamel et al considered sirenomelia as a manifestation of the caudal regression syndrome and, maternal diabetes mellitus, genetic predisposition and vascular hypoperfusion as possible causative factors.[4] A critical review of the literature mentioned only 0.5%-3.7% of cases of sirenomelia occurring in offspring of diabetic mothers,[1],[5] Absence of familial cases and discordance in monozygotic twin made a genetic mechanism unlikely.[5] Exposure to etretinate (a synthetic vitamin A analogue) or ochratoxin A (a fungal toxin) during organogenesis in the experimental animals have produced defects similar to sirenomelia.[6],[7] However no such teratogen has been proven in humans. In the present case antenatal period was uneventful and there was no history of any medical / surgical illness or drug intake during pregnancy. There was no family history of malformations in the present case.
Harrison classified human tail on embryological ground.[8] Human embryo shows appearance of tail bud in the late fourth week, tail complete with as many as 10 to 12 caudal vertebrae during the sixth week (14 to 16 mm) and disappearance of all the evidences of the tail bud by eighth week.[9]. A true tail represents vestigial remnants of an embryonic tail, and it contains adipose and connective tissue, striated muscle, blood vessels and nerves which are covered with intact skin but does not contain bone, cartilage, notochord, or spine elements. [10],[11] On the other hand, 'pseudotails' are varied lesions with only a superficial resemblance to a true vestigial tail and represents prominent sacrum, elongated coccyx, or underlying lipoma or teratoma. [8],[11] The present case had fibrous and adipose tissue suggestive of a True tail.
In the human embryo, the period between 24 to 36 days is the most vulnerable period for lower limb defects.[9] Association of a true tail in the sirenomelia might represent an insult to the embryo, after the appearance of tail bud (late fourth week). The association of neural tube defects and sirenomelia, described in the past, could indicate disturbances in the embryonal development before the closure of the neural tube, presumably prior to 4th week.[12] The rare association of true tail with sirenomelia indicates the timing and pathogenesis of wide spectrum of sirenomelia anamoliex.
References
1. Buyse ML. Birth Defects Encyclopedia, 1st edn. Massachusetts 02142, USA; Blackwell Scientific Publication, 1990: 1541-1542.
2. Jones KL. Smith's Recognizable Patterns of Human Malformations. 4 th edition. Philadelphia, W.B.Saunders Company, 1988: 574.
3. Murphy JJ, Fraser GC, Blair GK. Sirenomelia: case of the surviving mermaid. J Ped Surg 1992; 27: 1265-1268.
4. Duhamel B. From the mermaid to anal imperforation: the syndrome of caudal regression. Arch Dis Child 1964; 36: 152-155
5. Perez-Aytes A, Montero L, Gomez J, Paya A. Single aberrant umbilical artery in a fetus with severe caudal defects: Sirenomelia or caudal dysgenesis. Am J Med Genet 1997; 69: 409-412
6. Von Lennep E, Elkhazen, De Pierreux. A case of partial Sirenomelia and possible vitamin A teratogenesis. Prenatal Diagnosis 1985; 5: 35-40.
7. Wei X, Sulik KK. Pathogenesis of caudal dysgenesis/sirenomelia induced by ochratoxin A in chick embryos. Teratology 1996; 53: 378-391.
8. Harrison RG. On the occurrence of tail in man. Bull John Hopkins Hosp 1901; 12: 96-101.
9. Moore KL. The Developing Human: Clinically Oriented Embryology . 2nd edn Philadelphia; W.B. Saunders, 1997: 70-73.
10. Ledley FD. Evolution and the human tail; a case report. NEJM 306 (20): 1212-1215.
11. Kabra NS, Srinivasan G, Udani RH. True tail in a neonate. Indian Pediatr 1999; 36: 712-713.
12. O'Rahilly R, Muller F. Interpretation of some median anomaly as illustrated by cyclopia and symmelia. Teratology 1989; 40: 409-411.(Parikh Tushar B, Nanavati)
Abstract
Sirenomelia is an exceptionally rare congenital malformation characterized by complete or near complete fusion of lower limbs. A newborn with clinical features of sirenomelia including fused lower limbs in medial position, absent fibula, anal atresia, complete absence of urogenital system (bilateral renal agenesis, absent ureters, urinary bladder, absent internal and external genitalia), a single umbilical artery and a vestigial tail is reported. Association of vestigial tail with sirenomelia is not described in the literature.
Keywords: Sirenomelia; Vestigial tail
Sirenomelia is exceptionally rare congenital malformation with frequency of 1.5 to 4.2 per 1,00,000 births and is characterized by a single fused lower limb. Due to its close resemblance to the mermaid of Greek and Roman mythology, sirenomelia has fascinated scientists for centuries.
Case history
A full term, severely growth retarded baby weighing 1340 gm, was born to a 20 year old primigravida, with non-consanguineous marriage. Antenatally she was diagnosed to have severe oligohydromnios. The baby had severe birth asphyxia (Apgar 3, 2,2 at 1, 5 and 10 minutes respectively) and despite all resuscitative attempts baby died after 20 minutes.
Physical examination revealed potter facies, single umbilical artery and a well developed upper half of the body. In the lower half there was complete fusion of both the thighs and legs and there were no feet. There were no external genitalia or anal opening. There was a small soft tissue projection at the tip of the coccyx suggestive of vestigial tail. This caudal appendage was 4 cm long, 1.5 cm in diameter and had soft fibrous consistency. Figure1
Necrogram of the baby revealed, hypoplastic sacral segments, deformed pelvic bones, a single femur with two ossification centers at the lower end suggestive of fusion of the two femora and a single bony tag replacing leg bones. The vestigial tail did not show any bony or cartilaginous structure. The abdominal cavity revealed a diffuse stippled calcification all over the abdomen suggestive of meconium peritonitis. Chest skiagram and rest of the skeleton survey were unremarkable. Figure2
On autopsy there were single umbilical artery, hypoplastic lungs, anal atresia, and complete absence of urogenital system (bilateral renal agenesis, absent ureters and urinary bladder, absent internal and external genitalia). The vestigial tail contained fibrous and adipose tissue with normal skin covering.
Discussion
Sirenomelia is an anomalous development of the caudal region of the body. Complete or near complete fusion of the lower limbs is the most striking feature and the major diagnostic feature for sirenomelia.[1] Depending on the degree of fusion of lower limb and feet, sirenomelia can be classified into three types: a) Simpus Apus (Sirenomelus): No feet, one tibia, one femur b) Simpus Unipus (Uromelus): One foot, two femur, two tibia, two fibula c) Simpus Dipus (Simelus): Two feet and two fused legs (flipper like)-this is popularly known as mermaid. [1],[2] The present case was simpus apus.
The sirenomelia sequence cases have many visceral anomalies like imperforate anus, renal agenesis, heart defects and neural tube defects. The genitalia may vary from completely absent internal and external genitalia (as in our case) to almost near normal genitalia. Single umbilical artery is common but not a constant finding.[1],[3] Association of vestigial tail with Sirenomelia has not been described in the literature. The present case had 4 cm long true tail arising at the tip of the coccyx. Most of the cases are still born or die soon after birth due to severe visceral anomalies though two case reports have documented survivors.[3]
The etiology of sirenomelia sequence is uncertain, as no specific teratogens have been associated with the malformation in human. Duhamel et al considered sirenomelia as a manifestation of the caudal regression syndrome and, maternal diabetes mellitus, genetic predisposition and vascular hypoperfusion as possible causative factors.[4] A critical review of the literature mentioned only 0.5%-3.7% of cases of sirenomelia occurring in offspring of diabetic mothers,[1],[5] Absence of familial cases and discordance in monozygotic twin made a genetic mechanism unlikely.[5] Exposure to etretinate (a synthetic vitamin A analogue) or ochratoxin A (a fungal toxin) during organogenesis in the experimental animals have produced defects similar to sirenomelia.[6],[7] However no such teratogen has been proven in humans. In the present case antenatal period was uneventful and there was no history of any medical / surgical illness or drug intake during pregnancy. There was no family history of malformations in the present case.
Harrison classified human tail on embryological ground.[8] Human embryo shows appearance of tail bud in the late fourth week, tail complete with as many as 10 to 12 caudal vertebrae during the sixth week (14 to 16 mm) and disappearance of all the evidences of the tail bud by eighth week.[9]. A true tail represents vestigial remnants of an embryonic tail, and it contains adipose and connective tissue, striated muscle, blood vessels and nerves which are covered with intact skin but does not contain bone, cartilage, notochord, or spine elements. [10],[11] On the other hand, 'pseudotails' are varied lesions with only a superficial resemblance to a true vestigial tail and represents prominent sacrum, elongated coccyx, or underlying lipoma or teratoma. [8],[11] The present case had fibrous and adipose tissue suggestive of a True tail.
In the human embryo, the period between 24 to 36 days is the most vulnerable period for lower limb defects.[9] Association of a true tail in the sirenomelia might represent an insult to the embryo, after the appearance of tail bud (late fourth week). The association of neural tube defects and sirenomelia, described in the past, could indicate disturbances in the embryonal development before the closure of the neural tube, presumably prior to 4th week.[12] The rare association of true tail with sirenomelia indicates the timing and pathogenesis of wide spectrum of sirenomelia anamoliex.
References
1. Buyse ML. Birth Defects Encyclopedia, 1st edn. Massachusetts 02142, USA; Blackwell Scientific Publication, 1990: 1541-1542.
2. Jones KL. Smith's Recognizable Patterns of Human Malformations. 4 th edition. Philadelphia, W.B.Saunders Company, 1988: 574.
3. Murphy JJ, Fraser GC, Blair GK. Sirenomelia: case of the surviving mermaid. J Ped Surg 1992; 27: 1265-1268.
4. Duhamel B. From the mermaid to anal imperforation: the syndrome of caudal regression. Arch Dis Child 1964; 36: 152-155
5. Perez-Aytes A, Montero L, Gomez J, Paya A. Single aberrant umbilical artery in a fetus with severe caudal defects: Sirenomelia or caudal dysgenesis. Am J Med Genet 1997; 69: 409-412
6. Von Lennep E, Elkhazen, De Pierreux. A case of partial Sirenomelia and possible vitamin A teratogenesis. Prenatal Diagnosis 1985; 5: 35-40.
7. Wei X, Sulik KK. Pathogenesis of caudal dysgenesis/sirenomelia induced by ochratoxin A in chick embryos. Teratology 1996; 53: 378-391.
8. Harrison RG. On the occurrence of tail in man. Bull John Hopkins Hosp 1901; 12: 96-101.
9. Moore KL. The Developing Human: Clinically Oriented Embryology . 2nd edn Philadelphia; W.B. Saunders, 1997: 70-73.
10. Ledley FD. Evolution and the human tail; a case report. NEJM 306 (20): 1212-1215.
11. Kabra NS, Srinivasan G, Udani RH. True tail in a neonate. Indian Pediatr 1999; 36: 712-713.
12. O'Rahilly R, Muller F. Interpretation of some median anomaly as illustrated by cyclopia and symmelia. Teratology 1989; 40: 409-411.(Parikh Tushar B, Nanavati)