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Year : 2019  |  Volume : 62  |  Issue : 4  |  Page : 611-613
Tale of a mermaid

1 Department of Histopathology, Post Graduate Institute of Medical Education and Research, Chandigarh, India
2 Department of Radiodiagnosis and Imaging, Post Graduate Institute of Medical Education and Research, Chandigarh, India
3 Department of Obstetrics and Gynecology, Post Graduate Institute of Medical Education and Research, Chandigarh, India

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Date of Web Publication14-Oct-2019


Sirenomelia is a rare congenital anomaly characterized by the presence of a median single lower appendage. The affected fetus is popularly referred to as a “Mermaid baby,” due to the uncanny resemblance to the fictious fable character. The manifestation is a result of the merger of the lower limbs with variable fusion or complete absence of bones. Sirenomelia is universally fatal due to the associated lethal anomalies involving the internal organs, which are usually part of the VACTER or VACTERL complex. However, this sirenomelia-afflicted fetus is unique in being associated with VACTERL as well as congenital hydrocephalus.

Keywords: Hydrocephalus, mermaid, sirenomelia

How to cite this article:
Vasisht P, Madakshira MG, Kakkar N, Singla V, Jain V. Tale of a mermaid. Indian J Pathol Microbiol 2019;62:611-3

How to cite this URL:
Vasisht P, Madakshira MG, Kakkar N, Singla V, Jain V. Tale of a mermaid. Indian J Pathol Microbiol [serial online] 2019 [cited 2023 Jun 7];62:611-3. Available from:

   Introduction Top

Sirenomelia is a rare fatal congenital abnormality characterized by the presence of a single lower limb in place of the usually paired limbs.[1] The presence of a single limb resembles the appendage of the fictious “Mermaid” character, for which these babies are commonly referred to as mermaid babies.[1] It has been hypothesized to be a result of the fusion of the two para-medial limb buds. However, no consensuses have been arrived in terms of the nosology, with the absence of a specific International Classification of Diseases (ICD) code.[2] The reason for this is the association of the condition with many syndromes, such as caudal dysgenesis, VACTERL, or VACTERL-H.[2] The prenatal diagnosis of this condition is challenging due to the frequent association with oligohydramnios secondary to bilateral renal dysgenesis or agenesis.[1] We discuss a case of sirenomelia with a rare association with hydrocephalus.

   Case History Top

The fetus was a product of the nonconsanguious marriage. The mother was a booked case with a history of two previous abortions, the cause of which was not known. There was no history of gestational diabetes. The ultrasonography done at 16 weeks revealed the presence of sirenomelia with hydrocephalus, dilated stomach, hydronephrotic right kidney, nonvisualized left kidney, single umbilical artery (SUA), and oilgohydraminos. Following counseling, the lady underwent termination of pregnancy. A fetal autopsy was performed after taking due consent.

The fetus at autopsy weighed 165 g with anthropometric indicators showing an increased head circumference of 18 cm against a mean of 13 cm for gestational age. The fetus had an enlarged head with a single lower limb [Figure 1]. The kidigram [Figure 2] done showed fusion of the distal end of both femurs and complete fusion of both tibias along the entire length. The fibula was not visualized. The radiological picture was that of type-V sirenomelia as per the classification proposed by Stocker and Heifetz.
Figure 1: Fetus with sirenomelia in the form of single caudal appendage

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Figure 2: Kidigram shows a fusion in the lower end of the femur with a single fused tibia and absent fibula, corresponding to type V sirenomelia

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The brain was delivered following the flower-petal technique. The brain was soft with the absence of sulci or gyral patterns. On sagittal incision, there was marked bilateral dilatation of lateral ventricles with thinning of the cortex. The abdominal organs were dissected in-toto. There was the presence of hypoplastic lungs with absent left kidney and dysplastic right kidney. The ureters and urinary bladder were absent. An ano-rectal malformation in the form of absent anal opening was also seen. The internal genitalia was not developed, nor was the external genitalia identifiable [Figure 3]. A final postmortem diagnosis of sirenomelia as part of the VACTERL-H association was made.
Figure 3: Two halves of the brain following sagittal cut, with the presence of dilated lateral ventricle and thinned out cortex

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   Discussion Top

Siren as per Greek mythology were dangerous aquatic creatures, who used to menace the sailors at sea.[3] Over the course of time, they were romanticized in fables as cute mermaids.[3] The sirenomelia malformation is, however, a fatal and severe malformation, which is characterized by the presence of a single lower limb as a result of the variable fusion of legs.[4] Sirenomelia has been likened to be a sequence rather than a syndrome having such wide variety of phenotypic manifestations and associations with visceral and genitourinary abnormalities.[1] The presence of concomitant visceral abnormalities makes the condition incompatible with life resulting in the perinatal death of the fetus.[5] The condition has a reported incidence varying between 1.1 and 4.2 among 100,000 births, with no reported ethnic variation.[2] The prenatal diagnosis can be made by ultrasonography, which can be challenging as these fetuses have concomitant oligohydramnios.[6] The best time for ultrasonographic assessment is between 8 and 16 weeks of gestation, when the amniotic fluid is derived from maternal production, making visualization of the limbs easier.[6]

The classification proposed of sirenomelia by Stocker and Heifetz remains the most widely used based on dysmorphogenetic rationale.[7] The classification includes seven types from type I to type VII [Table 1]. Type I is the mildest form with merging of only the superficial tissue with preservation of all the limb bones. Type VII is the most severe form with the presence of a single bone and absence of any resemblance to legs or feet. The genesis of sirenomelia phenotype is secondary to merging of early hindlimb fields.[4] The developing lower limbs lie on the lateral body walls. Hence, the limbs tend to approximate and merge with each other following failure of development of the midline structures – such as the cloaca, urogenital sinus, the somites, and neural tubes.[8] Considering this hypothesis, sirenomelia may be a secondary defect, rather than a primary congenital abnormality. During the normal development, the limb buds rotate medially resulting in positioning the original ventral surface dorsally. The early fusion of the limbs is also indicated by the presence of 180° mal-rotated limbs at presentation, with the soles facing anteriorly and fibula taking a medial position.[4]
Table 1: Classification of sirenomelia

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Sirenomelia has been reported to be part of the VACTER or VACTERL association.[9] This association has been described as a constellation of nonrandom abnormalities which should include at least three of following defects: segmentation defects of costo-vertebral [V], anal stenosis or atresia [A], defects of cardiovascular system [C], esophageal defects and/or trachea–esophageal fistula [TE], renal dysgenesis or agenesis [R], and limb abnormalities [L].[9] Briaid Evans extended the association to include hydrocephaly leading to the designation of VACTERL-H.[9] This is possibly the second case in the literature reporting sirenomelia in association with VACTERL-H.[10] Central nervous system anomalies have been reported in as many as 10% of sirenomelia fetus. These anomalies include cebocephaly, alobar holoprosencephaly, lumbar spina bifida, craniorachischisis, anencephaly, hydrocephalus, meningomyelocoele, and meningocoele.[11],[12]

Sirenomelia has been also characterized by the presence of a SUA, which has been considered as pathognomonic by some authors.[4] The SUA is derived from the vitelline plexus indicating a possible persistence of the vitelline artery.[13] The SUA is seen to arise high in the abdominal aorta, just below the celiac artery. The aorta also shows considerable narrowing below the origin of SUA indicating a reduced supply to the kidneys, intestines, genitalia, and lower limbs. This abnormal vasculature has prompted some authors to propose a vascular steal phenomenon, in which the blood is diverted to the placenta instead of the lower half of the body.[4] This deficient blood supply results in reduced nutrient and oxygen supply to the caudal mesoderm, resulting in agenesis of the structures including merging of the limb buds.[14] Another proposed hypothesis to explain sirenomelia is a probable defect during blastogenesis. This theory propounds that the abnormality is secondary to a defect of blastogenesis in the last phase of gastrulation at about third week of gestation.[4] The variable phenotypic presentation may be a reflection of the time of initiation of the defect and the duration of the defective event. Some of the genes indicated for being responsible for sirenomelia have been those coding for the enzyme Cyp26a1, which degrades retinoic acid, and gene, which codes for bone morphogenic protein signaling. It has been demonstrated that mice with a mutation in these genes develop a phenotype similar to sirenomelia indicating a possible role in humans as well.[1]

Sirenomelia, a rare severe and fatal congenital anomaly, still remains a fascinating entity whose nosology remains blur and is a challenge for the clinician who is faced with the daunting task of counseling the unfortunate parents about the cause and possible precautions while planning the next pregnancy.

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Conflicts of interest

There are no conflicts of interest.

   References Top

Boer LL, Morava E, Klein WM, Schepens-Franke AN, Oostra RJ. Sirenomelia: A multi-systemic polytopic field defect with ongoing controversies. Birth defects Res 2017;109:791-804.  Back to cited text no. 1
Orioli IM, Amar E, Arteaga-Vazquez J, Bakker MK, Bianca S, Botto LD, et al. Sirenomelia: An epidemiologic study in a large dataset from the international clearinghouse of birth defects surveillance and research, and literature review. Am J Med Genet C Semin Med Genet 2011;157C: 358-73.  Back to cited text no. 2
Romano S, Esposito V, Fonda C, Russo A, Grassi R. Beyond the myth: The mermaid syndrome from Homerus to Andersen. A tribute to Hans Christian Andersen's bicentennial of birth. Eur J Radiol 2006;58:252-9.  Back to cited text no. 3
Garrido-Allepuz C, Haro E, Gonzalez-Lamuno D, Martinez-Frias ML, Bertocchini F, Ros MA. A clinical and experimental overview of sirenomelia: Insight into the mechanisms of congenital limb malformations. Dis Model Mech 2011;4:289-99.  Back to cited text no. 4
Kinjo Y, Masamoto H, Nitta H, Kinjo T, Tamaki T, Yoshimi N, et al. Fetal Sirenomelia associated with an abdominal cyst originating from a saccular cloaca. Case Rep Obstet Gynecol 2018;2018:7513287. doi: 10.1155/2018/7513287.  Back to cited text no. 5
Singh C, Lodha P, Arora D, Prabhu Sharma A, Kaul A. Diagnosis of sirenomelia in the first trimester. J Clin Ultrasound 2014;42:355-9.  Back to cited text no. 6
Stocker JT, Heifetz SA. Sirenomelia. A morphological study of 33 cases and review of the literature. Perspect Pediatr Pathol 1987;10:7-50.  Back to cited text no. 7
Isik Kaygusuz E, Kurek Eken M, Sivrikoz ON, Cetiner H. Sirenomelia: A review of embryogenic theories and discussion of the differences from caudal regression syndrome. J Matern Fetal Neonatal Med 2016;29:949-53.  Back to cited text no. 8
Lhuaire M, Jestin A, Boulagnon C, Loock M, Doco-Fenzy M, Gaillard D, et al. Sirenomelia: A new type, showing VACTERL association with Thomas syndrome and a review of literature. Birth Defects Res A Clin Mol Teratol 2013;97:123-32.  Back to cited text no. 9
Onyeije CI, Sherer DM, Handwerker S, Shah L. Prenatal diagnosis of sirenomelia with bilateral hydrocephalus: Report of a previously undocumented form of VACTERL-H association. Am J Perinatol 1998;15:193-7.  Back to cited text no. 10
Chikkannaiah P, Mahadevan A, Gosavi M, Kangle R, Shankar SK. Sirenomelia with associated systemic anomalies: An autopsy pathologic illustration of a series of four cases. Pathol Pract 2014;210:444-9.  Back to cited text no. 11
Islam N, Mandal B, Das RN, Bera G, Mukherjee S, Chatterjee U. Sirenomelia associated with discoid adrenal and lumbar meningocoele: An autopsy report. Pathol Pract 2017;213:1450-3.  Back to cited text no. 12
Thottungal AD, Charles AK, Dickinson JE, Bower C. Caudal dysgenesis and sirenomelia-single centre experience suggests common pathogenic basis. Am J Med Genet Part A 2010;152:2578-87.  Back to cited text no. 13
Duesterhoeft SM, Ernst LM, Siebert JR, Kapur RP. Five cases of caudal regression with an aberrant abdominal umbilical artery: Further support for a caudal regression–sirenomelia spectrum. Am J Med Genet Part A 2007;143:3175-84.  Back to cited text no. 14

Correspondence Address:
Manoj G Madakshira
Department of Histopathology, Post Graduate of Medical Education and Research, Chandigarh - 160 012
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/IJPM.IJPM_668_18

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This article has been cited by
P. V. Hryhorieva
Bulletin of Problems Biology and Medicine. 2021; 3(1): 26
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