Conjoined twins are monozygotic twins who remain physically joined after incomplete separation of a single fertilized egg between 13 and 17 days following conception. This rare condition occurs in approximately one out of every 200,000 births, and a significant percentage of these pregnancies do not survive to term. For those who do, surgical separation is a massive undertaking, representing one of the most complex procedures in medicine. This specialized surgery requires the coordinated effort of dozens of highly trained medical professionals working across multiple disciplines in a pediatric specialty center. The success of the procedure hinges entirely on the shared anatomy and the meticulous, months-long preparation conducted before the twins enter the operating room.
Classification and Feasibility Assessment
The decision to attempt separation is based on which anatomical structures the twins share. Conjoined twins are classified by the site of their connection, using the Greek suffix “pagus” to indicate the point of fusion. The most common type is thoracopagus, where the twins are joined at the chest, often involving a shared heart, pericardium, or diaphragm.
Omphalopagus twins are joined at the abdomen, frequently sharing liver tissue, parts of the gastrointestinal tract, and sometimes the lower sternum. Craniopagus twins are fused at the head, which is one of the rarest and most complicated forms due to the potential sharing of brain tissue and major blood vessels. Separation viability is greatly diminished if the twins share a single heart or another vital organ that cannot be successfully divided and reconstructed for two individuals.
A comprehensive assessment using various imaging modalities determines if separation is possible and what the prognosis might be. If the anatomical connection involves organs that can be individually reconstructed or if the shared organ, like the liver, can be safely divided, a surgical path is considered. Historically, only about 5% to 25% of conjoined twins survive long-term, though this figure improves to around 60% for those who undergo successful separation surgery.
Detailed Preoperative Planning
Preparation for conjoined twin separation can span several months and involves a multidisciplinary team including pediatric surgeons, plastic surgeons, cardiologists, neurosurgeons, and anesthesiologists. The process begins with postnatal imaging, which acts as the roadmap for the procedure. Advanced techniques like Computed Tomography (CT) scans, Magnetic Resonance Imaging (MRI), and CT angiography map out shared organs, skeletal structures, and blood vessel connections with precision.
The imaging data is used to create patient-specific three-dimensional (3D) models, often printed to life-size scale. These 3D models allow the surgical team to physically explore the complex anatomy and practice the planned division points for shared tissues, such as the liver or the lining of the heart. The models also help with spatial planning, ensuring the operating room setup and the positioning of the twins are optimized for the lengthy procedure.
In some cases, preliminary surgeries are performed months before the final separation to prepare the twins’ bodies. Plastic surgeons may implant tissue expanders beneath the skin surrounding the connection site. These devices are slowly filled with saline over weeks to stretch the skin, creating the necessary soft tissue to cover the surgical defects left on each twin after separation. The team also uses virtual reality (VR) and augmented reality (AR) simulations to rehearse the procedure, anticipate complications, and refine the surgical plan before the first incision.
The Surgical Separation Process
The actual separation surgery is a marathon event, often lasting between 11 and 24 hours, involving a large team of specialists working in orchestrated shifts. Anesthesia management is particularly challenging, as two separate teams of anesthesiologists must monitor and manage two patients with intertwined physiologies. Everything in the operating room, from monitoring lines to medication pumps, must be clearly color-coded to prevent confusion.
The procedure begins with the skin incision, following a pre-planned line designed to maximize the skin available for final closure on both twins. Surgeons then carefully separate the soft tissues, muscle, and bone structures connecting the infants. The most delicate part of the operation involves dividing shared organs and blood vessels.
When a shared organ like the liver is present, the surgical team uses advanced techniques to divide the tissue and ensure adequate blood supply remains for both halves. For twins sharing a complex vascular connection, such as a major blood vessel, this division requires meticulous micro-surgical techniques and immediate reconstruction to create two independent circulatory systems. Once the physical separation is complete, the twins are moved onto two separate operating tables.
Immediate Post-Surgical Care and Reconstruction
Once separated, the focus shifts to stabilizing each infant and addressing the large anatomical defects left by the procedure. Each twin requires extensive reconstruction to close the body wall, often performed by the plastic surgery team using the skin and soft tissue gained from the earlier tissue expansion process. In situations where tissue is insufficient, surgeons may use materials like biological mesh or dermal substitutes to close the chest or abdominal wall defects.
The separated infants are transferred to the Neonatal or Pediatric Intensive Care Unit (ICU) for intensive monitoring. The first few days are fraught with risk, as the twins must adapt to independent circulation and organ function. This adaptation can lead to fluid shifts, changes in blood pressure, and potential organ failure. The recovery period often involves managing infections and ensuring the reconstructed body areas heal properly.
The initial separation is frequently only the first step, with many twins requiring subsequent, staged reconstructive surgeries. Longer-term care involves physical, occupational, and speech therapy to help the children overcome developmental delays and adapt to their individual bodies. Continuous follow-up is necessary to monitor their growth, address any resulting physical limitations, and help them achieve developmental milestones.