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Year : 2009  |  Volume : 52  |  Issue : 4  |  Page : 579-580

1 Department of Pathology and Obstretics, M.S. Ramaiah Medical College, Bangalore, Karnataka, India
2 Department of Gynaecology, M.S. Ramaiah Medical College, Bangalore, Karnataka, India

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Date of Web Publication1-Oct-2009

How to cite this article:
Gouri MS, Kumari KM, Rao SG, Devi U. Sirenomelia. Indian J Pathol Microbiol 2009;52:579-80

How to cite this URL:
Gouri MS, Kumari KM, Rao SG, Devi U. Sirenomelia. Indian J Pathol Microbiol [serial online] 2009 [cited 2023 Sep 30];52:579-80. Available from:


Sirenomelia is a rare congenital anomaly characterized by fused or single lower limb and severe visceral anomalies with an incidence of 1.5-4.2 per 100,000 births. [1] We report a similar case of sirenomelia in a 23-week fetus.

A 28-year-old female with 23 weeks of gestation was admitted to the hospital and on ultrasound scan was diagnosed to have oligohydramnios, a fetus with severe intrauterine growth retardation and absence of fetal kidneys. Pregnancy was terminated and the fetus was submitted for autopsy along with placenta. Since only a single limb was seen, the fetus was subjected to radiological examination which revealed a single femur and tibia, sacral agenesis and absence of pelvic bones, hemivertebrae in the lower thoracic and lumbar region [Figure 1] and [Figure 2].

The fetus weighed 450 g with flexion deformity (valgus) at right wrist joint and absence of right thumb. There was a single lower limb which was ill formed and measured 10 cm in length, with no development of muscles around the tibia, and the foot was absent. The tibial end appeared club-shaped. No external genitalia were seen. There was no anal opening (imperforate anus). On autopsy brain, thymus, heart and lungs were unremarkable. The intestine ended in a blind loop filled with meconium. The testes were seen bilaterally in the pelvic region. There was absence of both kidneys, ureters, urinary bladder, seminal vesicles and urethra. Umbilical cord revealed a single umbilical artery. Placenta was unremarkable.

The primary defect in sirenomelia apparently dates back to the primitive streak stage during the third week of embryonic life. A derangement in gastrulation disturbs the migration and differentiation of mesoderm which is responsible for the array of defects in caudal dysplasia. [2] There are several hypotheses to explain the pathogenesis of sirenomelia. Dissection of the abdominal vasculature in 11 cases of sirenomelia has demonstrated a pattern of vascular abnormalities that explains the defects usually found in this condition. The common feature is the presence of a single large artery, arising high in the abdominal cavity, which assumes the function of the umbilical arteries and diverts nutrients from the caudal end of the embryo distal to the level of its origin. The steal vessel derives from the vitelline artery complex, an early embryonic vascular network that supplies the yolk sac. Arteries below the level of the steal vessels are underdeveloped and tissues dependent upon them for nutrient supply fail to develop, are malformed or arrest in some incomplete stage. [3] Absence of chromosomal abnormalities and familial inheritance has been noted in almost all cases. [4]

The classification of sirenomelia infants on the presence or absence of bones within the lower limb from Type I to Type VII was made by Stocker and Heifetz. [5] Our case fitted into Type III with absent fibula.

Banerjee et al. [4] had reported two cases of sirenomelia with right thumb being hypoplastic and blind intestinal loop without anal opening. In our case also there was complete absence of right thumb, fibula, anal opening and external genitalia. The intestines ended in a blind loop filled with meconium. Sirenomelia is invariably fatal. Prenatal diagnosis is very important. It has been diagnosed antenatally as early as 13 weeks. Third trimester ultrasonographic diagnosis is usually impaired by severe oligohydramnios related to bilateral renal agenesis, whereas during the second trimester the amount of amniotic fluid is sufficient to allow diagnosis. Early antenatal sonographic diagnosis is important in view of dismal prognosis and allows for earlier, less traumatic termination of pregnancy.

   References Top

1.Mysorekar VV, Rao SG, Sundari N. Sirenomelia: A case report. Indian J Pathol Microbiol 2007;50:359-61.  Back to cited text no. 1  [PUBMED]    
2.Chen C, Shih SL, Jan SW, Lin YN. Sirenomelia with an uncommon osseous fusion associated with a neural tube defect. Pediatr Radiol 1998;28:293-6 .  Back to cited text no. 2      
3.Stevenson RE, Jones KL, Phelan MC, Jones MC, Barr M Jr, Clericuzio C, et al. Vascular steal: The pathogenetic mechanism producing sirenomelia and associated defects of the viscera and soft tissue. Pediatrics 1986;78:451-7.  Back to cited text no. 3      
4.Banerjee A, Faridi MM, Banerjee TK, Mandal RN, Aggarwal A. Sirenomelia. Indian J Pediatr 2003;70:589-91.  Back to cited text no. 4      
5.Stocker JT, Heifetz SA. Sirenomelia: A morphological study of 33 cases and review of literature. Perspect Pediatr Pathol 1987;10:7-50.  Back to cited text no. 5      

Correspondence Address:
Mangala S.R. Gouri
No 12, 1st Main 13th cross road, Hanumaiah layout Sanjaynagar, Bangalore-560 094
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0377-4929.56124

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  [Figure 1], [Figure 2]

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