Journal of Postgraduate Medicine
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Year : 2006  |  Volume : 52  |  Issue : 3  |  Page : 219-220  

Sirenomelia: MRI appearance

S Sawhney1, R Jain1, N Meka2,  
1 Departments of Radiology, Obstetrics, Sultan Qaboos University Hospital, PO Box 38, Sultan Qaboos University, Muscat PC 123, Oman
2 Departments of Gynecology, Sultan Qaboos University Hospital, PO Box 38, Sultan Qaboos University, Muscat PC 123, Oman

Correspondence Address:
S Sawhney
Departments of Radiology, Obstetrics, Sultan Qaboos University Hospital, PO Box 38, Sultan Qaboos University, Muscat PC 123

How to cite this article:
Sawhney S, Jain R, Meka N. Sirenomelia: MRI appearance.J Postgrad Med 2006;52:219-220

How to cite this URL:
Sawhney S, Jain R, Meka N. Sirenomelia: MRI appearance. J Postgrad Med [serial online] 2006 [cited 2023 Sep 25 ];52:219-220
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Full Text

Sirenomelia is an extremely rare congenital anomaly with a reported incidence of up to 1 in 100,000 live births. More than 300 cases have been reported in the world literature. In the vast majority of cases, the associated anomalies, especially renal agenesis are incompatible with life, though there have been very few survivors, even with hypoplastic kidneys.[1]

 Case Report

A 26-year-old woman (consanguineous marriage) delivered a stillborn baby at 31 weeks gestation. She had not undergone an antenatal ultrasound examination. All her laboratory investigations were normal. The baby had discolored skin, folded ears, low lying nipples, low back mass and fused lower limbs. No genitalia were identified. A single cloacal opening was seen on the lower back. Clinical photograph [Figure 1] and MRI study [Figure 2][Figure 3][Figure 4] were performed on the stillborn baby.

In this patient MRI demonstrated the characteristic features of this rare anomaly, viz., fused lower limbs, medially rotated acetabuli and femoral heads, single midline fibula, single cloacal opening, abrupt conical termination of aorta at D12 level and hypoplastic kidneys. The unusual feature of this case was the presence of a well-defined identifiable sacrum.


Sirenomelia is a condition characterized by fusion of the pelvic girdle and lower extremities into a single conical structure, and is considered a part of the spectrum of the caudal regression syndrome. The lower extremity is always inverted and externally rotated, so that the knee is situated posteriorly, and the toes points posteriorly.[2] In these children, the coccyx is absent and sacrum is partially or wholly absent.[3] The fused lower extremities may have a normal number of bones, partial fusion of bones, or no bones at all. The etiology of sirenomelia is uncertain. In addition to defective mesodermal embryogenesis, a vitelline artery steal syndrome has been proposed by some authors.[4] It is presumed that a large artery, likely to be a derivative of the vitelline artery arises from the aorta high in the abdominal cavity, beyond which the aorta and its branches are hypoplastic. This results in a 'vitelline artery steal', which diverts blood and nutrients away from the caudal portion of the embryo to the placenta. Maternal diabetes mellitus shows a possible weak association with sirenomelia.[5] There is an apparent overlap between in the phenotypic manifestations of sirenomelia and the VACTERL complex (vertebral, anal, cardiovascular, tracheal, esophageal, renal and limb), with at least three of the components of VACTERL shown in all cases of sirenomelia, in addition to the lower limb deformities, with more severe involvement of the gastrointestinal and genitourinary systems.[6] Antenatal sonographic screening maybe helpful in detecting fetal genitourinary anomalies associated with sirenomelia, however, oligohydramnios can often prevent optimal assessment.


1Smith DW, Jones KL. Recognisable patterns of human malformation. Genetic, embryologic and clinical aspects. 2nd ed. Saunders: Philadelphia; 1976. p. 486-7.
2Naidich TP, Mc Lone DG, Harwood-Nash DC. Spinal dysraphism. In : Newton TH, Potts EG, editors. Mordern neuroradiology. Vol 1. Computed tomography of the spine and spinal cord. Clavadel Press: CA; 1993.
3Hendry DW, Kohler HG. Sirenomelia ("Mermaid"). J Obstet Gynaecol 1956;63:865-70.
4Stevenson RE, Jones KL, Phelan MC, Jones MC, Barr M, Clericuzio C, et al . Vascular steal: The pathogenetic mechanism producing sirenomelia and associated defects of the viscera and soft tissues. Pediatrics 1986;78:451-7.
5Schuler I, Salzano FM. Patterns in multi-malformed babies and the question of the relationship between sirenomelia and VACERL. Am J Med Genet 1994;49:29-35.
6Duncan PA, Shapiro LR. Interrelationships of the hemifacial microsomia-VATER, VATER, and sirenomelia phenotypes. Am J Med Gen 1993;47:75-84.

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