Several risk factors related with the sirenomelia malformation are maternal diabetes, retinoic acid, exposure to heavy metals and teratogens, genetic factors, monozygotic twins, male gender, and mother’s age <20 years or >40 years [1,3-12,18]. There is a strong relationship between sirenomelia and maternal diabetes; the relative risk ratio is 1/200-250, and this ratio was found to be 22% among the fetuses with anomaly [8,10,11,16-18]. The male/ female ratio is 2.7-3 [5,6,16-18]. In the present case, none of the known risk factors except for male gender was detected.

The most characteristic finding of sirenomelia is the fusion of lower extremities [1-14,18]. The disease has a wide diversity ranging from the mildest form that is fusion, in which all the lower extremity bones exist, to the most severe type, in which there is only rudimentary bone. Significant efforts have been made in order to classify sirenomelia. However, the classification that is most widely used nowadays is the one developed by Stocker and Heifetz, which has been used since 1987 (Table I). This classification was developed based on the presence of the skeletal elements in the thigh and leg. In Type I, which is the mildest form, all the bones are present and fusion is observed only in superficial tissues. In Type VII, which is the most severe form, there is a single bone and the legs and feet are not present [1,7,8]. Although there was no radiological finding available, the present case was found to correspond to Type IV or sympos monopus in terms of macroscopic appearance.

Table I: Classification of Sirenomelia by Stocker and Heifetz

The visceral organ malformations seen in sirenomelia include various grades of renal and urethral dysplasia. Absence of one or both kidneys (frequently the total renal agenesis), cystic malformations in kidneys, absence of the bladder, and urethral atresia can be seen [1,6-8,12,13,16,18]. In addition to the renal agenesis, the present case also had absence of the ureter, urethra, and rectum. Ectopic renal tissues may be seen at various points of pelvis because of the anomalies in the migration of metanephritic tissue. The most important genital anomalies are the external genital organ malformations. Either the external genital structures are absent or they are located at a different position and the gonads are generally not affected. In the present case, the penis was in the anal region and not at its normal position. However, contrary to the literature, there was a single testis. Gastrointestinal anomalies are frequently seen and some of these are the blind-ended colon, rectal atresia, and imperforate anus [1,5-7,12,18]. An imperforate anus was observed in the present case. The venous malformations seen in this disorder include a dual venous structure (an umbilical artery and an umbilical vein) instead of a triple venous structure (two umbilical arteries and an umbilical vein) [1,5-8,10,12,13,18]. In the present case, there was a dual venous structure consisting of an umbilical artery and an umbilical vein.

The differential diagnosis includes bilateral renal agenesis, kidney malformations, single umbilical artery, megacystis, VACTERL/VATER (vertebral defects, anal atresia, cardiac defects, tracheo-esophageal fistula, renal anomalies and limb abnormalities) association, and caudal regression syndrome (CRS). Although sirenomelia may be regarded as a severe form of the latter, the two entities represent distinct nosologic conditions and should receive individual genetic counseling [21].

CRS is a broad term that refers to a heterogenous constellation of congenital caudal anomalies affecting the caudal spine and spinal cord, the hindgut, the urogenital system, and the lower limbs [16,17,19-21]. In fact, while CRS is hypothesized to arise from a primary defect of the caudal mesoderm that interferes with the formation of the notochord, the primary mechanism leading to sirenomelia is the diversion of blood flow away from the caudal portion of the embryo through a single vitelline artery [21]. As a result, fetuses with caudal regression show two umbilical arteries, two hypoplastic lower extremities, and non-fatal kidney findings with imperforate or normal anus, while sirenomelic fetuses have renal agenesis or dysgenesis, a single aberrant umbilical artery, fused sub-extremities, and imperforate anus [20-21]. We diagnosed our patient with sirenomelia due to the presence of single umbilical artery, a single testis, imperforate anus, fused lower extremities, cleft palate, cleft lip, total renal agenesis, and absence of the bladder, ureter, urethra and rectum.

The other anomalies that might be seen in sirenomelia include sacral agenesis, absence of gallbladder and spleen, omphalocele, lordosis, malformed vertebra-hemivertebra, and central nervous system (CNS) anomalies, as well as less frequently observed ones such as cleft palate, upper thoracic and cervical vertebra anomalies, pulmonary hypoplasia, and cardiac anomalies [1,6-8,12,13,16-19]. In the literature, adrenomegaly has been detected in the case of a baby with a diabetic mother [15]. In the present case, there were sunken nasal bridge, fallen ears, cleft palate, and cleft lip. Ultrasonography (USG) performed in the antenatal period (end of the first trimester) is very important in the diagnosis of sirenomelia. If possible, 3D USG should be preferred over 2D USG. This is because the skeletal anomalies can be better detected using 3D USG [3,13]. The absence of fetus movements; adorsal, lumbal, or sacral vertebral gap; short craniocaudal length, and lower extremities with an abnormal appearance can be detected with USG. Oligohydramnios is the finding that is easiest to detect [3,16]. In the present case, the pregnant woman was not followed-up on a regular basis and she applied to the emergency unit with complaints of vaginal bleeding, inguinal pain, and nausea. No cardiac or fetal activity was observed, the amniotic fluid volume was significantly low (oligohydramnios), and the internal os was closed. Revision curettage was performed. It was therefore not possible to make an early diagnosis using USG images and the diagnosis was made based on the pathological examination.

In surviving sirenomelia cases, treatment can be provided with a multidisciplinary approach. The conjoined legs can be surgically separated. During the preparation for surgery, subcutaneous tissue expanders such as balloons can be placed and the skin stretched and prepared for enlargement by filling the balloons with saltwater. The enlarged skin is used during surgical separation [6,8,11].

In conclusion, the diagnosis of sirenomelia can be made using ultrasonography performed at the end of the first trimester. Among the ultrasonographic findings, oligohydramnios and lower extremity defects can be useful in the diagnosis. The pregnancy may be terminated in cases of a fetus with a severe anomaly that is inconsistent with survival.

CONFLICT of INTEREST
The authors report no conflicts of interest.