Kidney transplantation is the definitive treatment for patients with end-stage renal disease, offering an improved quality of life compared to long-term dialysis. While most procedures involve transplanting a single, mature kidney, “en bloc” transplantation expands the donor organ pool. This specialized method involves surgically removing and implanting both kidneys simultaneously from a single donor as one cohesive unit. The en bloc approach is primarily utilized when the donor is a very young child whose organs are too small for a standard single-kidney procedure.
Understanding the En Bloc Anatomical Unit
The term “en bloc” is a French phrase meaning “in a block” or “as a whole,” describing the physical components of the transplanted graft. In this procedure, the two donor kidneys remain connected to their native blood supply, including a continuous segment of the donor’s abdominal aorta and inferior vena cava. This differs from a standard single-kidney transplant, where the renal artery and vein are separated from the main vessels before implantation. The resulting composite graft features the two kidneys attached by this central vascular trunk. Keeping the main vessels intact avoids the technically demanding task of individually connecting the minuscule renal arteries and veins of a small pediatric donor.
Indications for En Bloc Transplantation
The primary rationale for choosing the en bloc method is to facilitate the use of kidneys from very small pediatric donors, typically weighing less than 20 kilograms or under five years of age. The individual blood vessels of these young donors are delicate and small, making conventional single-kidney transplantation technically challenging and prone to vascular complications. Transplanting both kidneys together provides a larger, more robust connection point for the recipient’s circulatory system.
Nephron Mass and Function
The en bloc technique ensures the recipient receives an adequate total mass of filtering tissue, known as nephron mass. This is particularly important when the recipient is an adult or older child. A single kidney from a very small donor may not possess enough filtering capacity to support an adult body size, potentially leading to hyperfiltration injury. By implanting both organs, the total functional capacity is sufficient to meet the recipient’s metabolic demands. This strategy addresses the persistent organ shortage by utilizing organs that might otherwise be discarded due to their size. The en bloc approach offers a safer, more reliable option for the smallest available organs, solving the size mismatch between a tiny donor and a typically larger recipient.
Key Steps of the Surgical Procedure
Graft Preparation (Back Table)
The transplantation process begins with a meticulous preparation of the graft on the “back table.” The donor’s aorta and vena cava are carefully trimmed, and their upper ends are oversewn to close them off. All small branching vessels from the aortic and caval segments, such as the lumbar arteries, are ligated to prevent any leaks after the blood flow is restored. This bench work transforms the two kidneys and their central vessels into the final composite unit ready for implantation.
Implantation and Vascular Connection
The recipient operation involves placing the entire en bloc graft into the iliac fossa, usually in the lower right side of the abdomen, in an extraperitoneal position. The primary step is the vascular connection, where the surgeon performs only one arterial and one venous anastomosis to the recipient’s large iliac vessels, despite the presence of two kidneys. The donor aorta segment is sewn end-to-side to the recipient’s external iliac artery, and the donor vena cava segment is similarly connected to the recipient’s external iliac vein. This single vascular connection greatly simplifies the most technically challenging part of the procedure, as the surgeon is working with larger, more substantial vessels.
Urinary System Connection
Once blood flow is established, the final step involves connecting the urinary system. Since the two kidneys each have their own ureter, both must be implanted separately into the recipient’s bladder. This dual ureteral implantation is a unique and delicate feature of the en bloc technique, typically requiring two separate ureteroneocystostomies to ensure proper urine drainage from both transplanted kidneys.
Specific Post-Operative Management and Results
The post-operative period following an en bloc transplant requires specialized management due to the small vessel size and the dual ureteral connections. Initial function of the transplanted organs may be slower or delayed compared to a standard adult-to-adult transplant, necessitating close monitoring of urine output and blood chemistry. Color Doppler ultrasound studies are performed frequently to assess blood flow and check for any signs of vascular compromise in the graft.
Early Risks and Complications
One significant early risk is vascular thrombosis—a blood clot forming in the small donor vessels—which can lead to immediate graft failure. This risk is elevated in the first few months after surgery due to the narrow caliber of the pediatric vessels. Aggressive management with anti-coagulation and careful fluid balance is often required to maintain vessel patency. The dual ureteral implantations also introduce a higher chance of urologic complications, such as ureteral strictures or urine leaks, which can occur in a notable percentage of cases.
Long-Term Outcomes
Despite the increased technical complexity and early complication rates, the long-term outcomes for en bloc kidney transplantation are highly favorable. Studies have shown that after the initial high-risk period, the graft and patient survival rates are comparable to those achieved with standard adult deceased donor transplants. The transplanted kidneys from the pediatric donor will also grow in size and function over time, eventually providing excellent long-term renal function for the recipient.