Sirenomelia, also known as Mermaid Syndrome, is one of the rarest congenital anomalies that can affect a fetus during the early stages of development. This remarkable medical condition is characterized by the fusion of the lower limbs to varying degrees, giving the body an appearance resembling a mermaid’s tail, hence its name. However, the syndrome involves more than just physical abnormalities, as it may also be associated with severe malformations of several internal organs, particularly the kidneys, urinary system, and reproductive organs.Despite its rarity, Sirenomelia has attracted significant medical attention due to the complexity of its potential causes, the severity of some cases, and the challenges it presents in diagnosis and treatment. Therefore, Dalili Medical highlights the key aspects of Sirenomelia in this article, including its definition, possible causes, major symptoms, diagnostic methods, available treatment options, and its impact on the lives of affected individuals and their chances of survival.

1. 1. What Is Sirenomelia?

   Sirenomelia, also known as Mermaid Syndrome, is a rare congenital disorder characterized by the fusion of the fetus’s lower limbs to varying degrees. It may be accompanied by several congenital abnormalities affecting the kidneys, urinary and reproductive systems, as well as other organs.

   2. Why Is It Called Mermaid Syndrome?

   The name of this syndrome comes from the distinctive appearance of the fused lower limbs, which may resemble a mermaid’s tail. This characteristic explains the association between the condition and the mythical creature.

   3. Is Sirenomelia a Genetic Disorder?

   In most cases, Sirenomelia is not considered a hereditary disorder that is directly passed from parents to their children. The exact cause remains unknown; however, some theories suggest that it may be associated with abnormalities in blood vessel development and blood flow during the early stages of fetal development.

   4. Can Sirenomelia Be Detected During Pregnancy?

   Yes, Sirenomelia can be detected in many cases during pregnancy using ultrasound imaging. Detailed examinations can also help assess the degree of lower-limb fusion and identify associated congenital abnormalities. This contributes to determining the severity of the condition and developing an appropriate medical care plan.

   5. Which Organs Can Be Affected by Sirenomelia?

   Sirenomelia may be associated with multiple congenital abnormalities, which vary from one case to another. The most commonly affected organs and systems include:

   • The kidneys and urinary system.

   • The reproductive organs.

   • The intestines and rectum.

   • The spine and pelvis.

   • The heart in some cases.

   The nature and severity of these abnormalities directly influence the newborn’s health and chances of survival.

   6. Can a Child with Sirenomelia Survive?

   Survival depends on the severity of the associated abnormalities and the extent to which vital organs are affected. Cases involving the absence of both kidneys or severe impairment of kidney function are among the most critical, as they may lead to life-threatening complications.

   Nevertheless, some individuals with Sirenomelia have survived with specialized medical care, particularly when the associated abnormalities are less severe.

   7. Can the Legs Be Surgically Separated in Cases of Sirenomelia?

   Surgical intervention may be possible in selected cases. However, the feasibility of separating the lower limbs depends on the degree of fusion, the anatomical arrangement of the bones, blood vessels, and nerves, and the presence of other congenital abnormalities.

   Therefore, any decision regarding surgery requires a thorough assessment by a multidisciplinary medical team, as surgical separation is neither feasible nor appropriate for every patient.

   8. Does Sirenomelia Affect Future Fertility?

   Sirenomelia may affect future fertility, depending on the nature of the associated congenital abnormalities and the extent to which they affect the reproductive system.

   Some individuals may have abnormalities of the reproductive organs or urinary system that could affect fertility. However, this outcome cannot be generalized to all cases, as the potential effects vary according to the type and severity of the abnormalities.

   9. Can Sirenomelia Be Prevented?

   Currently, there is no established method for preventing Sirenomelia, as researchers have not identified a single definitive cause that explains its occurrence in all cases.

   Nevertheless, receiving appropriate medical care before and during pregnancy, managing chronic maternal conditions, and attending regular prenatal checkups are important measures for promoting maternal and fetal health and detecting potential congenital abnormalities early.

   10. Is Sirenomelia the Same as Sacral Agenesis?

   No. These are two distinct congenital conditions, although they may share certain features.

   Sirenomelia is characterized by fusion of the lower limbs to varying degrees and may be accompanied by abnormalities affecting several internal organs.

   Sacral agenesis, on the other hand, is a condition characterized by the partial or complete absence of the sacrum, the lower portion of the spine.

   Although some abnormalities associated with these conditions may overlap, they differ in their anatomical characteristics and underlying developmental mechanisms.

   What Are the Potential Causes of Sirenomelia?

   Sirenomelia is a rare congenital anomaly whose exact cause has not yet been definitively established. However, researchers have proposed several scientific hypotheses that may help explain how it develops. These include abnormalities in blood vessel formation and early embryonic development, as well as investigations into the potential role of certain maternal health factors.

   1. The Vascular Steal Phenomenon

   The vascular steal phenomenon is one of the leading proposed explanations for the development of Sirenomelia. According to this hypothesis, an abnormality may occur in the formation of fetal blood vessels, involving a single abnormal umbilical artery that connects to the aorta at a higher-than-usual location.

   This abnormal vascular arrangement may divert a substantial portion of the blood flow toward the placenta, potentially reducing the supply of blood, oxygen, and nutrients to the lower part of the fetus’s body. As a result, the development of tissues and organs in this region may be disrupted during the early stages of pregnancy.

2. This abnormality may be associated with congenital malformations affecting:

   • The lower limbs and their associated bones.

   • The kidneys and urinary system.

   • The reproductive organs and lower portions of the intestines.

   Although this hypothesis is supported by anatomical and vascular observations in some affected individuals, it does not necessarily explain every case. The precise mechanisms underlying Sirenomelia remain the subject of ongoing scientific research.

   2. Disruption of Early Embryonic Development

   Another theory suggests that Sirenomelia may result from a disruption during the very early stages of embryonic development, when the tissues that will form the lower part of the body begin to differentiate and grow.

   This disruption may affect the formation of the lower-limb buds and the development of the pelvic bones and lower vertebrae, as well as the development of certain internal organs. This may explain why affected infants can present with multiple congenital abnormalities rather than isolated fusion of the legs.

   However, further research is needed to identify the precise mechanisms responsible for the development of this syndrome.

   3. Is There a Relationship Between Maternal Diabetes, Genetic Factors, and Sirenomelia?

   Maternal diabetes: Some studies have identified an association between maternal diabetes and an increased risk of certain congenital abnormalities. Diabetes has also been reported in some mothers of infants with Sirenomelia. However, this association does not establish that diabetes is the direct cause of the syndrome, nor does it mean that all cases are linked to maternal diabetes.

   Genetic factors: No consistent, established inheritance pattern has been identified to explain most cases of Sirenomelia. The syndrome may occur in infants without a similar family history, suggesting that inherited genetic factors alone do not account for its development.

   Medications and chemical substances: Some animal studies have shown that exposure to certain substances during embryonic development can produce abnormalities resembling some features of Sirenomelia. However, the available evidence in humans is insufficient to establish that these substances directly cause the syndrome.

   Other factors during pregnancy: Researchers continue to investigate the potential roles of environmental factors and disturbances that may occur during fetal development. To date, however, no single factor has been established as responsible for all cases.

   Symptoms of Sirenomelia (Mermaid Syndrome)

   Sirenomelia is characterized by a range of congenital abnormalities that develop during fetal growth. Its manifestations vary from one case to another, depending on the severity of the condition and the extent to which internal organs are affected.

   Although fusion of the lower limbs is the most distinctive feature of the syndrome, it may also be accompanied by abnormalities affecting the urinary, reproductive, and digestive systems, as well as the bones, lungs, and other organs.

   First: Primary Symptoms and Signs

   - Fusion of the lower limbs: This is the hallmark of the syndrome. The fusion may be partial or complete, making the legs appear as a single limb. Underdevelopment or deformities of the leg bones may also occur.

   - Foot abnormalities: These may include the presence of one foot, two incompletely developed feet, or feet positioned in abnormal anatomical orientations, depending on the severity of the malformation.

   - Kidney and urinary tract abnormalities: The fetus may have underdeveloped kidneys or an absence of one or both kidneys, along with other urinary tract abnormalities. These defects may interfere with urine production and kidney function.

   - Low amniotic fluid levels: The volume of amniotic fluid surrounding the fetus may decrease because of severely impaired kidney function or the absence of both kidneys. This can adversely affect lung development, particularly during the early stages of pregnancy.

   - Reproductive organ abnormalities: These may include incomplete development or absence of certain external reproductive structures and may also involve abnormalities of the internal reproductive organs.

   - Anal and rectal abnormalities: These may include an absent or imperforate anus or incomplete development of the rectum, potentially affecting normal digestive function after birth.

   Second: Other Possible Abnormalities and Symptoms

   In addition to the primary features, Sirenomelia may be accompanied by other congenital abnormalities, including:

   • Incomplete development of the pelvic bones or the lower portion of the spine.

   • Underdeveloped lungs, particularly in cases involving severely reduced amniotic fluid levels.

   • Congenital heart defects of varying severity.

   • Abnormalities of the skeletal system or certain abdominal organs.

   • Abnormalities in blood vessel development.

   • Upper-limb abnormalities in some cases.

   The severity of these abnormalities varies from one fetus to another. Their presence and the extent to which they affect organ function are important factors in determining the severity of the condition and predicting its outcome.

   Third: How Do the Signs of Sirenomelia Appear During Pregnancy?

   Sirenomelia does not usually cause specific symptoms in the mother that can be relied upon to diagnose the condition, as the primary abnormalities affect the fetus.

   Therefore, detection of the syndrome relies mainly on medical examinations performed during pregnancy, particularly prenatal imaging and ultrasound assessments.

3. Ultrasound imaging may reveal the following signs:

   • Fusion of the lower limbs or obvious abnormalities in their development.

   • Failure to visualize the kidneys or bladder normally.

   • Reduced levels of amniotic fluid surrounding the fetus.

   • Associated abnormalities of the pelvis or spine.

   • Signs of impaired development of certain internal organs.

   Physicians may encounter difficulties assessing some fetal organs during the later stages of pregnancy, particularly when amniotic fluid levels are severely reduced. In such cases, additional examinations may be necessary, depending on the clinical circumstances.

   Fourth: Can Sirenomelia Be Fatal?

   Sirenomelia is a congenital anomaly that can be life-threatening, particularly in severe cases involving the absence of both kidneys or significant impairment of kidney function. These abnormalities may lead to a severe reduction in amniotic fluid, which can interfere with lung development and cause severe respiratory failure after birth.

   Such complications may result in fetal death before delivery or the death of the newborn shortly after birth. Nevertheless, rare cases of survival have been documented. Survival depends on the extent to which the kidneys, lungs, and other vital organs are affected, as well as the availability of specialized medical care.

   Types of Sirenomelia (Mermaid Syndrome)

   Sirenomelia can be classified according to the nature of the skeletal abnormalities affecting the lower limbs. It can also be categorized based on the number of feet present. These classification systems help describe the anatomical differences between cases and assess the severity of the malformations.

   1. Classification According to Skeletal Abnormalities

   An anatomical classification system includes seven types, determined by the presence, absence, and degree of fusion of the femur, tibia, and fibula bones.

   Type	Description of skeletal abnormalities
   Type I	Both femurs, tibias, and fibulas are present, with fusion of the soft tissues.
   Type II	Both femurs and tibias are present, but only one fibula is present.
   Type III	Both femurs and tibias are present, but both fibulas are absent.
   Type IV	Partial fusion of the femurs, with fusion of the fibulas.
   Type V	Partial fusion of the femurs, with both fibulas absent.
   Type VI	One femur and one tibia are present.
   Type VII	Only one femur is present, while the tibia and fibula are absent.

   Accurate classification depends on anatomical examination and medical imaging, particularly radiographs, which help clarify the number, shape, and degree of fusion of the bones. Some descriptive details may vary in rare cases.

   2. Classification According to the Number of Feet

   This classification is based on the external appearance of the lower limbs and the number of visible feet. It includes three main forms:

   - Sympus dipus — Two feet: The fetus has two feet despite fusion of the lower limbs or significant abnormalities in their development.

   - Sympus monopus — One foot: The fused lower limb terminates in a single foot.

   - Sympus apus — No feet: Neither foot is clearly present or fully developed.

   This classification differs from the skeletal classification described above. It focuses on external appearance and the number of feet, whereas the first classification is based on the anatomical structure of the bones.

   Diagnosis of Sirenomelia (Mermaid Syndrome)

   The diagnosis of Sirenomelia relies on identifying congenital abnormalities affecting the lower limbs and evaluating the fetus’s internal organs and blood vessels. Prenatal diagnosis is important for determining the extent of the malformations and assessing the severity of the condition.

   1. Diagnostic Methods

   First: Ultrasound Imaging

   Ultrasound is the primary method used to detect Sirenomelia during pregnancy. It helps assess fetal development and identify several characteristic findings, including:

   • Fusion of the lower limbs or severe abnormalities in their development.

   • Abnormalities of the thigh, lower-leg, and foot bones.

   • Reduced amniotic fluid levels (oligohydramnios), which may progress to its complete absence.

   • Failure to visualize the kidneys or suspicion of severe kidney abnormalities.

   • Associated abnormalities of the pelvis or spine.

   Second: Color Doppler Ultrasound

   Color Doppler imaging helps assess blood flow through the fetus’s blood vessels. It may reveal the presence of a single umbilical artery or abnormal patterns of vascular branching, including vessels connected to the abdominal aorta.

   When these findings are consistent with other anatomical abnormalities, they may support a suspected diagnosis of Sirenomelia.

   Third: Fetal Magnetic Resonance Imaging (Fetal MRI)

   Fetal MRI may be used when additional anatomical information is needed, particularly when certain organs cannot be clearly evaluated using ultrasound.

   Depending on the stage of pregnancy and the clinical circumstances, MRI can help clarify associated malformations and provide a more detailed assessment of the fetus’s internal organs.

   Ultrasound imaging may reveal the following signs:

4. Fusion of the lower limbs or obvious abnormalities in their formation.

5. Failure to visualize the kidneys or bladder normally.

6. Reduced levels of amniotic fluid surrounding the fetus.

7. Associated abnormalities of the pelvis or spine.

8. Signs of impaired development of certain internal organs.

9. Physicians may encounter difficulties evaluating some fetal organs during the later stages of pregnancy, particularly when amniotic fluid levels are severely reduced. In such cases, additional examinations may be required, depending on the clinical circumstances.

   Fourth: Can Sirenomelia Be Fatal?

   Sirenomelia is a congenital anomaly that can be life-threatening, particularly in severe cases involving the absence of both kidneys or significant impairment of their function. These abnormalities may lead to a severe reduction in amniotic fluid, which can interfere with lung development and result in severe respiratory failure after birth.

   These complications may cause fetal death before delivery or the death of the newborn shortly after birth. However, rare cases of survival have been documented. Survival depends on the extent to which the kidneys, lungs, and other vital organs are affected, as well as the availability of specialized medical care.

   Types of Sirenomelia (Mermaid Syndrome)

   Sirenomelia is classified according to the nature of the skeletal abnormalities affecting the lower limbs. It can also be classified according to the number of feet present. These classification systems help describe the anatomical differences between cases and assess the severity of the malformations.

   1. Classification According to Skeletal Abnormalities

   An anatomical classification system comprises seven types, determined by the presence, absence, and degree of fusion of the femur, tibia, and fibula bones.

   Type	Description of Skeletal Abnormalities
   Type I	Both femurs, tibias, and fibulas are present, with fusion of the soft tissues.
   Type II	Both femurs and tibias are present, but only one fibula is present.
   Type III	Both femurs and tibias are present, but both fibulas are absent.
   Type IV	Partial fusion of the femurs, with fusion of the fibulas.
   Type V	Partial fusion of the femurs, with both fibulas absent.
   Type VI	One femur and one tibia are present.
   Type VII	Only one femur is present, while the tibia and fibula are absent.

   Accurate classification depends on anatomical examination and medical imaging, particularly radiographs, which help determine the number, shape, and degree of fusion of the bones. Some descriptive details may vary in rare cases.

   2. Classification According to the Number of Feet

   This classification is based on the external appearance of the lower limbs and the number of visible feet. It includes three main forms:

   - Sympus dipus — Two feet: Two feet are present, despite fusion of the lower limbs or significant abnormalities in their development.

   - Sympus monopus — One foot: The fused lower limb terminates in a single foot.

   - Sympus apus — No feet: Neither foot is clearly present or fully developed.

   This classification differs from the skeletal classification described above. It focuses on external appearance and the number of feet, whereas the first classification is based on the anatomical structure of the bones.

   Diagnosis of Sirenomelia (Mermaid Syndrome)

   The diagnosis of Sirenomelia relies on identifying congenital abnormalities affecting the lower limbs and evaluating the fetus’s internal organs and blood vessels. Prenatal diagnosis is important for determining the extent of the malformations and assessing the severity of the condition.

   1. Diagnostic Methods

   First: Ultrasound Imaging

   Ultrasound is the primary method used to detect Sirenomelia during pregnancy. It helps assess fetal development and identify several characteristic findings, including:

10. Fusion of the lower limbs or severe abnormalities in their formation.

11. Abnormalities of the thigh, lower-leg, and foot bones.

12. Reduced amniotic fluid levels (oligohydramnios), which may progress to its complete absence.

13. Failure to visualize the kidneys or suspicion of severe kidney abnormalities.

14. Second: Color Doppler Ultrasound

    Color Doppler imaging helps evaluate blood flow through the fetus’s blood vessels. It may reveal the presence of a single umbilical artery or abnormal patterns of vascular branching, including vessels connected to the abdominal aorta.

    When these findings are consistent with other anatomical abnormalities, they may support a suspected diagnosis of Sirenomelia.

    Third: Fetal Magnetic Resonance Imaging (Fetal MRI)

    Fetal MRI may be used when additional anatomical information is needed, particularly if certain organs cannot be clearly evaluated using ultrasound.

    Depending on the stage of pregnancy and the clinical circumstances, MRI can help clarify associated malformations and provide a more detailed assessment of the fetus’s internal organs.

15. Associated abnormalities of the pelvis or spine.

2. Key Diagnostic Signs

Signs that help diagnose sirenomelia syndrome include:

• Fusion of the lower limbs (Sirenomelia): The hallmark anatomical feature of the syndrome.

• Kidney anomalies: May include complete absence of the kidneys in severe cases.

• Vascular disorders: Such as the presence of a single umbilical artery or an abnormal vascular pattern.

• Associated anomalies: In the lower spine, pelvis, anus, and the reproductive and gastrointestinal systems.

• Oligohydramnios (low amniotic fluid): Especially in the presence of severe renal impairment or renal agenesis.

A diagnosis is not based on a single sign in isolation; rather, the anatomical and vascular imaging of the fetus is evaluated comprehensively.

3. Differential Diagnosis

Diagnosing sirenomelia requires distinguishing it from other congenital anomalies that may share similar features, most notably:

• Caudal Regression Syndrome: A congenital disorder affecting the development of the lower part of the spine and body, which may be accompanied by anomalies in the pelvis, lower limbs, and urinary system.

• Bilateral Renal Agenesis: A condition where both kidneys are absent from embryonic development, which may be accompanied by severe oligohydramnios, but is not necessarily characterized by lower limb fusion.

• Other congenital lower limb anomalies: Certain limb formation disorders may be associated with defects in the spine or urinary system, necessitating a detailed anatomical evaluation to differentiate them from sirenomelia.

Surgical Treatment of Sirenomelia

Sirenomelia, or mermaid syndrome, is a rare congenital condition characterized by varying degrees of lower limb fusion, and may be accompanied by anomalies of the bones, pelvis, kidneys, urinary tract, gastrointestinal tract, and reproductive organs.

Surgical treatment depends on the nature of the child's existing anomalies, the functional capacity of the kidneys and internal organs, and the structure of bones, blood vessels, and nerves. Not every child requires all the procedures listed below; instead, a specialized multidisciplinary team formulates a customized treatment plan.

1. Lower-Limb Separation Surgery

• Medical Name: Lower-limb separation / Sirenomelia separation

This surgery aims to separate the fused lower limbs when bone, tissue, and vascular anatomy permit, while preserving viable tissue and achieving the best possible motor function.

Potential surgical approaches include:

• Single-stage separation: Separating the fused tissues in a single operation, along with tissue remodeling and wound closure, if anatomy permits.

• Staged separation: Performing multiple successive procedures rather than separating the limbs completely all at once to minimize surgical risks and improve wound healing rates.

• Separation with soft tissue reconstruction: Used when fusion is primarily limited to the skin and underlying subcutaneous tissues.

• Separation with bony deformity correction: May require additional procedures to correct bone alignment or address contractures, if feasible.

In general, surgery involves preoperative anatomical evaluation, identifying fused tissues, careful separation while protecting nerves and blood vessels, assessing blood supply to each limb, and closing wounds using appropriate techniques such as skin flaps or grafts.

Postoperatively, the child requires monitoring of wound healing and limb function, followed by an appropriate rehabilitation program.

Successful cases of lower limb separation in children with sirenomelia have been published; however, outcomes vary widely from case to case, and normal anatomical or functional legs cannot be guaranteed.

2. Tissue Expansion Before Limb Separation

• Medical Name: Tissue expansion

This technique is used when the available skin quantity is insufficient to cover the raw areas resulting from limb separation.

It is typically performed in stages:

1. Placing a tissue expander under the skin at a site determined by the surgeon.

2. Gradually expanding the device over a treatment plan lasting several weeks or months.

3. Performing a subsequent procedure to separate the limbs and utilize the newly generated expanded skin to cover the exposed areas.

This method helps provide additional skin and may reduce the need to harvest skin from other parts of the body. However, it may require multiple surgeries and can be associated with complications such as infection, expander exposure, or insufficient skin yield to cover the wounds. Tissue expansion has been utilized in select published sirenomelia cases.

3. Local Flaps, Z-Plasty, and Perineal Reconstruction

• Medical Name: Local flaps, Z-plasty, Perineal reconstruction

These surgeries aim to cover wounds resulting from limb separation, reduce skin tension, and reconstruct the perineum (the region between the lower limbs, genitalia, and anus).

Possible techniques include:

• Z-plasty: Rearranging the skin to reduce tension, improve scar direction, and enhance tissue elasticity.

• Local skin flaps: Transferring adjacent tissue to cover areas that cannot be closed directly.

• Rhomboid/Quad flaps: Can be used in selected cases to reconstruct perineal tissues.

• Skin grafting: Transferring a layer of skin from another site to cover wounds when surrounding tissue is insufficient.

The child may require additional surgeries to reconstruct external genitalia based on actual anatomy and functional needs as they grow.

It is important to distinguish between skin and external tissue reconstruction versus the creation of an absent internal organ; surgery does not guarantee the formation of fully normal genitalia.

4. Orthopedic Reconstruction and Lower Limb Correction

• Medical Name: Orthopedic reconstruction

If bones are present but malaligned or twisted, an orthopedic surgeon may recommend corrective procedures to improve limb position and function.

Possible options include:

• Corrective osteotomy: Cutting and repositioning bone to correct alignment axes.

• Bone fixation: Utilizing internal fixation devices, wires, or external fixators depending on the nature of the deformity.

• Joint reconstruction: When hip or knee joint structures permit a functional benefit.

• Foot deformity correction: To improve foot position and weight-bearing if present and correctable.

• Contracture management: To improve range of motion in indicated cases.

These procedures do not imply that every fused limb can be transformed into a normal leg; outcomes depend on bone count and shape, joint presence, and the integrity of muscles, nerves, and blood vessels.

5. Amputation and Prosthetic Rehabilitation

• Medical Name: Amputation and prosthetic rehabilitation

In some cases, the lower limbs are severely malformed, or the potential for achieving functional limbs is extremely limited. Under such circumstances, the medical team may discuss partial amputation or amputation at an appropriate level, combined with tissue separation and reconstruction.

This decision is not made simply because the legs are fused, but following a careful evaluation of limb salvage feasibility, expected function, surgical risks, and available alternatives.

A published case described a female infant who underwent tissue expansion prior to tissue separation, followed by a through-knee amputation utilizing a vascularized flap to cover the perineal region. Following rehabilitation, she was able to walk using short prostheses.

This case illustrates that prosthetic rehabilitation can provide significant functional capacity for certain children, though it is not a suitable option for all cases.

6. Gastrointestinal and Anal Reconstruction

• Medical Name: Pediatric gastrointestinal reconstruction

The child may require gastrointestinal surgery if suffering from intestinal obstruction, absent anal opening, rectal or colonic anomalies, or abnormal connections (fistulae) between the bowel and urinary tract.

Potential operations include:

• Colostomy: Creating an opening in the abdominal wall to divert stool into an external bag, which may be temporary or long-term.

• Ileostomy: Creating an opening to drain small bowel contents when medically indicated.

• Exploratory laparotomy and bowel atresia repair: Treating obstruction or non-functional bowel segments, reconnecting viable ends where possible.

• Imperforate anus repair: Establishing an appropriate passage for stool, which may require multiple surgical stages.

• Fistula repair: Treating abnormal connections between the gut and urinary tract or other organs when feasible.

• Stoma closure: Reconnecting the bowel and closing the opening in a subsequent procedure after verifying repair integrity and bowel readiness.

Gastrointestinal corrections may be necessary before considering limb separation, particularly if an obstruction threatens the child's life or prevents normal stool passage.

7. Renal and Urologic Reconstruction

• Medical Name: Pediatric urologic reconstruction

Kidney function is one of the most critical determinants of survival in children with sirenomelia, as the syndrome may be associated with unilateral or bilateral renal agenesis or severe urinary tract anomalies.

Treatment options vary according to present organs and functional capacity, and may include:

• Surgical urinary diversion: Creating a pathway to drain urine when the natural tract is obstructed or incomplete.

• Ureterostomy: Bringing the ureter to the skin surface to drain urine if the ureter is present and this approach is suitable.

• Urinary tract obstruction repair: Treating blockages or reconstructing the urinary tract when possible.

• Bladder or bladder-neck reconstruction: In cases where tissue availability allows functional benefit.

• Nephrectomy: May be considered under specific circumstances, such as a non-salvageable kidney causing complications, per specialist evaluation.

• Dialysis: May be required upon the onset of severe renal failure using peritoneal dialysis or hemodialysis depending on the child's condition.

• Kidney transplantation: A rare, long-term option for some survivors with end-stage renal failure, following evaluation of transplant suitability and management of associated comorbidities.

Medical reports have documented rare cases of sirenomelia surviving for years and receiving advanced renal therapies, including kidney transplantation. However, it must be emphasized that kidney transplantation is not suitable for every child with the syndrome, and its success requires appropriate medical conditions.

Important Medical Notice: If a child presents with renal agenesis combined with severe pulmonary hypoplasia (underdeveloped lungs), the condition carries extremely high risk. Neither limb separation nor urologic reconstruction alone can address all risk factors.

8. Genital and Pelvic Reconstruction

• Medical Name: Genital and pelvic reconstruction

The child may require surgery to reconstruct the perineal region or treat pelvic and genital anomalies based on actual anatomical configurations.

Possible procedures include:

• Reconstruction of external skin and soft tissues in the perineal region.

• Creation or improvement of a urinary outlet if anatomical structure permits.

• Reconstruction of external genitalia in selected cases.

• Management of pelvic deformities affecting sitting, mobility, or organ function.

• Additional corrective procedures as the child grows, if clear functional needs arise.

No single operation suits all children; some organs may be incompletely formed or completely absent, limiting reconstructive potential.

9. Neurosurgical and Spinal Reconstruction

• Medical Name: Neurosurgical and spinal reconstruction

If sirenomelia is accompanied by defects of the spine, spinal cord, or nerves, the child may require a specialized evaluation by a pediatric neurosurgeon.

Procedures, when clearly indicated, may include:

• Repair of certain congenital neural tube defects.

• Relief of compression on nerves or the spinal cord.

• Treatment of associated malformations affecting limb movement or bladder and bowel control.

Not every child with sirenomelia requires these operations; decisions depend on neurological and imaging findings and the functional impact of the deformity.

10. Vascular Surgery

• Medical Name: Vascular surgery

Vascular surgery may be necessary in certain cases due to associated vascular malformations or the need to protect blood vessels during limb separation.

Possible procedures include:

• Preoperative evaluation of vascular pathways.

• Identification and preservation of vessels supplying each limb during separation.

• Repair of damaged vessels when possible.

• Interventions to restore blood flow in appropriate cases.

• Risk assessment regarding perfusion to the kidneys, bowel, and lower limbs.