Sirenomelia: a review of embryogenic theories and discussion of the differences from caudal regression syndrome

Sirenomelia or mermaid syndrome with a cleft lip in a Tanzanian newborn: a case report

BACKGROUND

Sirenomelia or sirenomelia sequence, also known as mermaid syndrome, is a rare congenital anomaly involving the caudal region of the body. The syndrome is characterized by partial or complete fusion of lower extremities, renal agenesis, absent urinary tract, ambiguous external genitalia, imperforate anus, and single umbilical artery. Sirenomelia is often associated with several visceral congenital malformations, rendering it invariably incompatible with extrauterine life.

CASE PRESENTATION

We present the case of 22-year-old Black African woman who delivered a term newborn by caesarean section at a gestation age of 37 weeks due to obstructed labor with fetal distress. The newborn was a fresh stillbirth weighing 2100 g and had fusion of the lower extremities, a single upper limb, ambiguous genitalia, imperforate anus, and a cleft lip. The mother had made only two prenatal visits, at which she was found to be normotensive and normoglycemic. She was not screened for routine fetomaternal infections and missed supplementation for folic acid during the critical first trimester. She did not undergo any obstetric ultrasonography. The parents of the newborn were not close relatives and there was no family history of consanguinity. Further genetic testing was not performed due to lack of laboratory capacity, and post mortem examination was not permitted due to cultural taboo and restrictions relating to handling of deceased newborns.

CONCLUSION

Sirenomelia is a rare congenital malformation with very poor prognosis. Specific interventions during pre-conception and early prenatal care are critical in the prevention of specific congenital anomalies. Early obstetric ultrasonography is invaluable for diagnosis of sirenomelia as well as counseling for possible termination of pregnancy.

Sirenomelia in Twin Pregnancy: A Case Report

Sirenomelia is a rare congenital disorder that was once thought to be a severe case of caudal regression but is now thought to be entirely separate. It is often referred to as the "mermaid syndrome" because it causes the lower limbs to atrophy to varying degrees, giving the impression of a mermaid's tail or fin. The syndrome is often viewed as fatal due to the accompanying visceral deformities. Our case was a live born, delivered at term by caesarean section, to a 30-year-old third gravida having twin pregnancy. Examination of the baby revealed caudal dysgenesis with fusion of lower limbs, non-identifiable external genitalia and anus. The infant survived for 11 hours after birth. We report this case due to their rarity and term live birth. While sirenomelia is uncommon, the absence of distinct lower limbs on ultrasonography in the presence of oligo or anhydramnios may prompt consideration of the diagnosis of sirenomelia.

Caudal regression syndrome without maternal diabetes mellitus

Caudal regression is a rare complex disorder impacting the formation of the caudal segment of the spine and spinal cord. We report a preterm newborn baby who was referred to us due to respiratory distress syndrome and bilateral knee contracture. A clinical examination and a radiographic skeletal survey revealed a short spinal cord with complete agenesis of the lumbar, sacrum and coccygeal spine, and hypoplastic iliac bones with bilateral knee contractures. The mother did not have diabetes. The long-term outcome is not well-known in our set-up.

Neurogenic Bladder-Induced Stone in a Pelvic Kidney of a Caudal Regression Syndrome Patient: Management of a Complex Case

Percutaneous nephrolithotomy (PCNL) is a difficult treatment for treating kidney stones, especially when there are orthopedic or skeletal abnormalities. Here, in a 19-year-old male, we describe a two-step PCNL with a case of caudal regression syndrome (CRS) and a pelvic kidney, with an extremely deformed neurogenic bladder on intermittent catheterization. Our conclusion is that PCNL may be done safely with minimum morbidity in patients with caudal regression syndrome by utilizing adult equipment for heavy stone burdens, allowing full and rapid stone removal.

Multimodality Imaging Evaluation of Fetal Spine Anomalies with Postnatal Correlation

Congenital anomalies of the spine are associated with substantial morbidity in the perinatal period and may affect the rest of the patient's life. Accurate early diagnosis of spinal abnormalities during fetal imaging allows prenatal, perinatal, and postnatal treatment planning, which can substantially affect functional outcomes. The most common and clinically relevant congenital anomalies of the spine fall into three broad categories: spinal dysraphism, segmentation and fusion anomalies of the vertebral column, and sacrococcygeal teratomas. Spinal dysraphism is further categorized into one of two subtypes: open spinal dysraphism and closed spinal dysraphism. The latter category is further subdivided into those with and without subcutaneous masses. Open spinal dysraphism is an emergency and must be closed at birth because of the risk of infection. In utero closure is also offered at some fetal centers. Sacrococcygeal teratomas are the most common fetal pelvic masses and the prognosis is variable. Finally, vertebral body anomalies are categorized into formation (butterfly and hemivertebrae) and segmentation (block vertebrae) anomalies. Although appropriate evaluation of the fetal spine begins with US, which is the initial screening modality of choice, MRI is increasingly important as a problem-solving tool, especially given the recent advances in fetal MRI, its availability, and the complexity of fetal interventions. Online supplemental material is available for this article. ^©RSNA, 2021.

Caudal Regression Syndrome

Caudal Regression Syndrome (CRS) or Caudal dysgenesis syndrome (CDS) is characterized by maldevelopment of the caudal half of the body with variable involvement of the gastrointestinal, genitourinary, skeletal, and nervous systems. CRS affects 1–3 newborn infants per 100,000 live births. The prevalence in infants of diabetic mothers is reported at 1 in 350 live births which includes all the variants. A related condition is sirenomelia sequence or mermaid syndrome or symmelia and is characterized by fusion of the legs and a variable combination of the other abnormalities. The Currarino triad is a related anomaly that includes anorectal atresia, coccygeal and partial sacral agenesis, and a pre-sacral lesion such as anterior meningocele, lipoma or dermoid cyst. A multidisciplinary management approach is needed that includes rehabilitative services, and patients need a staged surgical approach.

Caudal Regression Syndrome-A Review Focusing on Genetic Associations

Caudal regression syndrome (CRS) represents a spectrum of clinical phenotypes with varying degrees of malformation of the lower body with involvement of structures deriving from all 3 layers of the trilaminar embryo. We review areas of active investigation in the diagnosis, etiology, epidemiology, and treatment of the disease with a focus on underlying genetics. CRS pathobiology is complex and multifactorial with a significant contribution from environmental factors as evidenced in twin studies. Contemporary genomic and genetic investigations in both human primary tissue and murine in vitro and in vivo models implicate various genes associated with caudal differentiation and neural cell migration in embryogenesis. A large number of identified targets center around the metabolic regulation of retinoic acid and its derivatives. Dysregulation of retinoic acid homeostasis has been associated with abnormal embryonic cell migration, differentiation, and organogenesis with resulting malformations and agenesis in both a laboratory and a clinical setting. There appears to be a significant overlap in potential genetic targets with CRS and other developmental syndromes with similar presentations, such as VACTERL (vertebral defects, anal atresia, cardiac defects, tracheo-esophageal fistula, renal anomalies, and limb abnormalities) association. CRS represents a spectrum of caudal developmental abnormalities with treatment options limited to mild and moderate expressions of disease. Continued research is necessary to further clarify mechanisms of disease pathobiology and complex polygenetic and environmental interaction. Despite this, progress has been made in identifying genetic targets and downstream effectors contributing to preclinical and clinical progression.

First-trimester sonographic diagnosis of sirenomelia: A multicenter series of 12 cases and review of the literature

OBJECTIVE

To determine the key sonographic features for the diagnosis of sirenomelia in the first trimester of pregnancy.

METHODS

Cases of sirenomelia from several prenatal diagnosis centers were retrospectively identified and reviewed. The diagnosis was established through the detection of fused lower limbs. Additional sonographic findings were also noted.

RESULTS

A total of 12 cases were collected. The most striking sonographic finding was the detection of malformed lower limbs, which appeared to be fused and in an atypical position. Nuchal translucency thickness was mildly increased in three cases (25%). An abdominal cyst, representing the dilated blind-ending bowel, was noted in seven cases (58%). Color flow imaging detected a single umbilical artery in six cases (50%) and the associated intra-abdominal vascular anomalies in three cases (25%). No cases of aneuploidy were detected. The pregnancy was terminated in nine cases (75%) and intrauterine demise occurred in the remaining three cases (25%).

CONCLUSIONS

The sonographic detection of abnormal lower limbs or an intra-abdominal cyst located laterally during the first-trimester scan may be warning signs of sirenomelia. This should prompt a detailed examination of the fetal lower body and intra-abdominal anatomy, including the main abdominal vessels, in order to look for additional confirmatory findings.

Tale of a mermaid

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.

Sirenomelia associated with Hypoplastic Left Heart in a Newborn

Sirenomelia, also known as “mermaid malformation/syndrome,” is a rare, serious congenital anomaly characterized by variable degrees of fusion of the lower limbs and associated with severe malformations of vertebral, genitourinary, cardiovascular system and single umbilical artery. The first pregnancy of a 25-year-old woman resulted in one twin born by Cesarian section at 32 weeks’ gestation, who was referred to our hospital with cyanosis, a congenital anomaly and respiratory distress. On physical examination, there was no urogenital region and anal fissure and gender was indeterminate. The arms were in adduction and wrist in flexion position with four fingers on the right hand and two fingers on the left hand. There was a single lower extremity with a webbed single foot and two toes consistent with sirenomelia type IV radiologically. Abdominal ultrasonography showed urogenital system agenesis and echocardiography detected hypoplastic left heart. However, the patient died 4 hours after birth. The other twin was followed for 1 week for nutrition and respiratory support and was then discharged without any problems.

Late Second Trimester Diagnosis of Sirenomelia

Sirenomelia is an uncommon complex congenital anomaly associated with fusion of the lower limbs and abnormalities of the urinary and gastrointestinal tract. Most cases of sirenomelia are not diagnosed in utero due to the complexity of the anomalies coupled with anhydramnios. With a male predominance of approximately 3:1, amniocentesis or noninvasive prenatal screening is the only way to confirm the chromosomes and gender of fetuses diagnosed with sirenomelia in utero. Few cases have been reported surviving past the neonatal period and a majority die in utero.