The human circulatory system is characterized by anatomical variability, and the kidneys frequently display differences in their blood supply. An accessory renal artery is a common example of this variation, representing an extra blood vessel that supplies blood to the kidney in addition to the main artery. This additional presence is a congenital feature, established before birth.
Defining the Anatomical Variation
The typical kidney receives its blood supply from a single main renal artery branching directly from the abdominal aorta. An accessory renal artery is a separate vessel that also originates from the aorta, or occasionally from another major artery, and enters the kidney independently. This variation is common, with reports suggesting that between 21% and 42% of the population possess at least one accessory renal artery.
These additional vessels are remnants from kidney development during embryonic life. As the kidneys ascend from the pelvis to their final position, they are sequentially supplied by temporary blood vessels that usually degenerate. An accessory renal artery forms when one of these temporary embryonic vessels fails to regress completely. The accessory vessel often supplies a specific area of the kidney, most frequently entering the upper or lower pole.
Functional Impact and Diagnosis
In most individuals, an accessory renal artery causes no health issues and remains asymptomatic. However, the vessel’s presence can become clinically significant if its structure or course creates a functional problem. One potential issue arises if the vessel develops a narrowing, known as stenosis, which reduces blood flow to the kidney tissue it supplies. This reduced blood flow (ischemia) can activate the renin-angiotensin-aldosterone system, leading to renovascular hypertension.
Studies indicate that people with accessory renal arteries may have higher blood pressure compared to those without this variation, possibly due to the overactivation of the blood pressure regulation system. Another functional concern occurs when an accessory artery supplying the lower pole crosses over the ureter. This positioning can compress the ureter, obstructing urine flow and leading to hydronephrosis, the swelling of the kidney due to fluid backup.
Because accessory renal arteries are often silent, they are usually discovered incidentally during medical imaging for an unrelated reason. Specialized imaging techniques map the kidney’s vascular structure in detail. Computed Tomography Angiography (CTA) and Magnetic Resonance Angiography (MRA) are reliable methods for visualizing these extra vessels and identifying any associated narrowing or stenosis. Doppler ultrasound can also assess blood flow velocity through these vessels.
Management During Surgical Procedures
The presence of an accessory renal artery introduces complexity during any surgical procedure involving the kidney. This is particularly true in kidney transplantation, where the donor kidney must be connected to the recipient’s circulatory system. Historically, a kidney with multiple arteries was sometimes considered less suitable for donation, but improved surgical techniques now allow these organs to be used successfully.
Surgeons face the challenge of establishing blood flow through both the main and accessory arteries to prevent damage to the donated kidney. Techniques involve either reconstructing the accessory artery with the main artery outside the body into a single opening, or performing separate connections, known as anastomoses, for each vessel in the recipient. For very small accessory arteries, the surgeon may decide to sacrifice the vessel by tying it off, but this decision must be weighed against the risk of losing function in the segment of the kidney it supplies.
Accessory arteries are often “end-arteries,” meaning they are the sole source of blood for the specific section of the kidney they supply, with no backup from other vessels. If an accessory artery is unintentionally damaged or ligated during procedures like a partial nephrectomy or pyeloplasty, the result can be segmental ischemia. This loss of blood supply can cause the affected part of the kidney to die, emphasizing the necessity of detailed pre-operative imaging to map the complete vascular anatomy.