Where Is the Lower Pole of the Kidney?

The lower pole of the kidney is the rounded bottom tip of the organ, pointing downward and slightly toward the midline of the body. Because the kidneys sit in the retroperitoneal space along either side of the spine, the lower pole of each kidney typically rests around the level of the second or third lumbar vertebra, though the right kidney usually sits a bit lower than the left due to the liver pushing it down. This seemingly simple anatomical landmark turns out to be one of the most clinically important regions of the entire urinary system, influencing everything from how kidney stones drain to how surgeons plan transplant operations.

Where Exactly the Kidneys Sit and How the Lower Pole Fits In

Each kidney is roughly the size of a fist and shaped like a bean, oriented vertically with a slight tilt. The upper pole (the top end) nestles against the lower ribs, while the lower pole extends below the rib cage and is therefore somewhat more accessible to physical examination and more exposed to trauma. A CT-based study looking at kidney positioning found that the uppermost border of scanned kidneys sat at the T10 vertebral level or below, with the majority of upper kidney borders appearing around T12. The lowest kidney border in that study reached as far down as L2 in one patient.

The kidneys are not perfectly vertical. They are tilted so the upper poles lean slightly inward toward the spine and the lower poles angle slightly outward and forward. This tilt matters for imaging, surgery, and stone management because the lower pole’s orientation determines gravity’s effect on anything sitting inside it. A stone lodged in a lower-pole calyx, for example, has to travel upward before it can exit into the renal pelvis and then the ureter, which is one reason lower-pole stones are notoriously stubborn.

The right kidney’s lower pole tends to be a fraction lower than the left because the liver occupies a large amount of space on the right side of the abdomen, pushing the right kidney downward. This asymmetry is normal and generally not clinically meaningful on its own, but it does come into play during imaging when clinicians need to decide how far down to scan. The study on CT scan optimization noted that starting scans too high wastes radiation on tissue above the kidney, while the lower border rarely drops past L2.¹

Anatomy Inside the Lower Pole

Understanding the lower pole goes deeper than just pointing to the bottom of the kidney on a diagram. Inside, the kidney is divided into segments that each drain through their own minor calyces (small cup-shaped chambers that collect urine). These minor calyces merge into major calyces, which in turn funnel into the renal pelvis and then the ureter. The lower pole has its own group of calyces, and the channel connecting these lower calyces to the renal pelvis is called the lower-pole infundibulum.

The geometry of this lower-pole infundibulum is not the same in every person. A post-mortem anatomical study found that infundibular length was under 3 cm in about 39% of kidneys and over 3 cm in the remaining 61%. The angle between the lower infundibulum and the renal pelvis (often called the infundibulopelvic angle) was less than 70 degrees in roughly 43% and greater than 70 degrees in about 57% of cases.² These numbers are not just academic trivia. As we will see, the length and angle of the lower-pole infundibulum directly predict whether kidney stones in that area will clear after treatment.

The overall layout of the collecting system also varies quite a bit. That same study classified the pelvicalyceal systems and found a range of configurations: about a third had two major calyceal groups, roughly a quarter had three, and about a fifth had more than three.² A narrative review of collecting system anatomy emphasized that variations in calyx position, infundibular diameter, and the angle between the lower infundibulum and the pelvis are all relevant to planning endourological procedures.³

Blood Supply to the Lower Pole

The kidney typically receives its blood from a single renal artery branching off the aorta. That main artery divides into segmental branches inside the kidney, each supplying a specific territory. The lower pole gets its share through one of these segmental branches. But a meaningful number of people also have accessory renal arteries, extra vessels that enter the kidney outside the main hilum, and the lower pole is one of the most common places these extra arteries land.

A systematic review and meta-analysis of anatomical studies across Africa found that among people who had accessory renal arteries, about 42% of those extra vessels entered through the inferior (lower) pole of the kidney, making it the single most common entry point for accessory arteries. About 39% entered through the hilum, and roughly 21% entered through the upper pole.⁴ A cross-sectional CT study from Sudan reported a somewhat different breakdown: among participants with accessory vessels, lower polar and hilar arteries each accounted for about 29%, with upper polar arteries at about 42%.⁵ The discrepancy between these studies reflects the fact that accessory artery patterns differ by population, but the consistent takeaway is that the lower pole is a frequent site for extra arterial supply.

This matters most in surgery and transplantation. A lower polar artery is not just feeding a portion of the kidney’s filtering tissue; it also contributes to the blood supply of the proximal ureter, the tube that carries urine from the kidney to the bladder. Accidentally cutting or failing to reconnect a lower polar artery during a transplant can starve the ureter of blood, causing it to die and the surgical connection to fail.⁶ Transplant surgeons therefore pay close attention to whether a donor kidney has a lower polar artery and plan their anastomosis technique accordingly.

Why Lower-Pole Kidney Stones Are a Particular Problem

Kidney stones can form anywhere inside the collecting system, but stones that settle in the lower-pole calyces are among the most difficult to clear. The reason is straightforward: gravity works against you. The lower pole is the lowest point of the kidney, and the only exit route for a stone fragment is upward through the infundibulum and into the renal pelvis. If that infundibulum is long, narrow, or steeply angled, fragments sit at the bottom like marbles in a cup with no easy way out.

A study evaluating shock wave lithotripsy for lower-pole stones found that the geometry of the lower-pole infundibulum strongly predicted whether patients ended up stone-free. When the infundibular length was 30 mm or less, the infundibular width was 5 mm or more, and the infundibulopelvic angle was 45 degrees or greater, every single patient in the study cleared their stones. Meanwhile, patients with unfavorable geometry (a long, narrow infundibulum with a steep angle) had dramatically lower clearance rates. Among failures, only 18% had a favorable angle compared to 73% of successes.⁷

More recent work looking at retrograde intrarenal surgery (where a flexible scope is passed up through the ureter to reach the kidney) tells a similar story. A single-center analysis found that patients with a very acute infundibulopelvic angle (less than 30 degrees) had residual stones 96% of the time after the procedure, compared to about 29% of patients whose angle was greater than 30 degrees. On multivariate analysis, the angle and stone size were the only two factors that independently predicted whether stones would remain.⁸ In practical terms, if you are told you have a lower-pole kidney stone, the anatomy of your specific lower pole may matter as much as the size of the stone when it comes to predicting whether treatment will work.

Surgical Approaches to the Lower Pole

When stones or tumors in the lower pole require surgery, the location creates distinct challenges and tradeoffs. For large kidney stones, percutaneous nephrolithotomy (PCNL) involves creating a small tunnel through the back into the kidney. Surgeons can puncture through the lower pole or through the upper pole to reach the stone, and each route has different risk profiles. A randomized controlled trial comparing upper-pole versus lower-pole puncture for PCNL found that lower-pole access had a somewhat higher residual stone rate (about 23% versus 20% for upper-pole access), but the upper-pole approach came with significantly more chest complications, roughly 11% compared to about 5% with lower-pole access.⁹ The lower pole’s position below the ribs makes it easier to access without risking the lung lining, which is why lower-pole puncture has historically been the default approach.

For kidney tumors, the story is slightly different. Robot-assisted partial nephrectomy, where only the tumor and a margin of normal tissue are removed rather than the whole kidney, can be performed on tumors at either pole. A study comparing outcomes for lower-pole versus upper-pole tumors found that lower-pole operations were actually faster, with operative times averaging about 165 minutes compared to 179 minutes for upper-pole tumors. The robotic portion of the surgery was also shorter for lower-pole cases. Despite the time difference, the rates of achieving the surgical “trifecta” (negative margins, no major complications, and minimal loss of kidney function) were similar between the two groups.¹⁰ The lower pole’s accessibility works in the surgeon’s favor here.

Rare complications can still arise. A case report described a pseudoaneurysm (a contained rupture in an artery wall) that developed at a lower-pole vessel after a clampless laparoscopic partial nephrectomy. The surgical complexity of the tumor and its proximity to the renal sinus were thought to be contributing factors.¹¹ The lower pole’s rich vascular supply, including the possibility of accessory arteries described earlier, means surgeons must be meticulous about controlling bleeding in this region.

Horseshoe Kidney and the Lower Pole

The lower pole plays a starring role in one of the most common congenital kidney anomalies. In a horseshoe kidney, the two kidneys are fused together by a bridge of tissue called the isthmus, and in over 90% of cases this fusion occurs at the lower poles. The condition affects roughly 1 in 400 to 600 people.¹² The remaining cases show fusion at the upper poles, creating what is sometimes called an inverted horseshoe kidney, but that arrangement is far less common.

The reason lower-pole fusion predominates has to do with how the kidneys develop. During fetal life, the kidneys form low in the pelvis and gradually ascend to their final position in the upper abdomen. As they ascend, the lower poles are the last parts to clear each other before the kidneys separate to their respective sides. If the lower poles make contact before they finish migrating, they fuse. The isthmus typically sits in front of the aorta and inferior vena cava, usually around the level of the fourth or fifth lumbar vertebra, which is lower than where a normal kidney’s lower pole would rest.

People with horseshoe kidneys may go their entire lives without knowing about the anomaly. It is often discovered incidentally on imaging done for an unrelated reason. However, the altered anatomy does create a higher risk for certain complications, including kidney stones (because the drainage angle of the collecting system is distorted by the fusion), ureteropelvic junction obstruction, and a higher susceptibility to trauma because the fused isthmus lies across the spine and can be compressed against the vertebral column during blunt abdominal injury.

When the Lower Pole Moves Out of Place

In most people, the kidneys are held in position by surrounding fat, connective tissue, and the pressure of neighboring organs. But in some individuals, a kidney can drop significantly when they stand up, a condition called nephroptosis (sometimes colloquially known as a “floating kidney”). The classic diagnostic criterion is a drop of more than two vertebral bodies between lying down and standing up. When the kidney descends, the lower pole swings forward and downward, and the ureter and hilar vessels can kink.

Symptomatic nephroptosis causes flank pain, often worsened by standing or physical activity and relieved by lying down. The suspected mechanism involves intermittent obstruction or reduced blood flow as the kidney shifts, either because the ureter kinks and blocks urine drainage or because the hilar vessels stretch and restrict blood flow. Direct stretching of nerve fibers around the kidney may also contribute to the pain.¹³ The condition is more common in thin women and can be difficult to diagnose because standard imaging is usually performed while the patient is lying flat, which is when the kidney returns to a normal position. Upright imaging or nuclear medicine scans performed in both positions can reveal the difference.

The Lower Pole in Kidney Transplantation

When a kidney is transplanted, the organ is placed in the recipient’s pelvis rather than in the original location high in the abdomen. The lower pole takes on added importance during this process because of its relationship to the ureter’s blood supply. The ureter receives blood from several sources along its length, but the portion nearest the kidney depends heavily on branches from the renal artery, particularly from any lower polar artery that may be present.

If a donor kidney has a lower polar artery and that vessel is not properly reconnected during the transplant, the proximal ureter can lose its blood supply. This can lead to ureteral necrosis, where the tissue dies, causing the connection between the transplanted kidney and the bladder to break down. This is one of the more serious urological complications of transplantation, potentially requiring additional surgery to repair. For this reason, transplant teams routinely assess the donor kidney’s vascular anatomy with CT angiography before the operation and have developed specific techniques for managing lower polar arteries, including direct anastomosis to the recipient’s iliac artery or reconstruction on a shared patch of aortic wall.⁶

The frequency of accessory lower polar arteries makes this a practical concern rather than a rare edge case. As the meta-analysis noted earlier found, over 40% of accessory renal arteries in one large pooled analysis entered through the lower pole.⁴ A transplant surgeon who ignores a lower polar artery is taking a real gamble with the ureter’s viability. This is one of those areas where understanding a simple anatomical landmark, the bottom of the kidney, has consequences that cascade through surgical planning in ways most people would never guess.

How Imaging Identifies the Lower Pole

For patients and non-specialists, the lower pole shows up clearly on several common imaging modalities. On ultrasound, the lower pole of the right kidney can often be seen through the liver as an acoustic window, while the left lower pole is typically visualized through the spleen or from a posterior approach. The lower pole is the part of the kidney that dips below the costal margin, making it the easiest portion to see on a bedside ultrasound.

On CT scans, the kidneys and their poles are visible in exquisite detail. The study on CT scan optimization found that protocols could be adjusted to start scanning at a lower vertebral level than traditionally used, since the upper border of most kidneys was at T12 or below, and the lower border rarely extended past L2.¹ This has practical value: tightening the scan range reduces the amount of radiation a patient receives without missing any kidney tissue. For the lower pole specifically, the key measurements that clinicians extract from CT include the infundibular length, infundibular width, and infundibulopelvic angle, all of which feed directly into treatment planning for lower-pole stones.

On an intravenous urogram or CT urogram (where contrast dye highlights the collecting system), the lower-pole calyces are the lowest group of urine-filled chambers visible on the image. Their orientation, number, and the angle at which they drain upward toward the renal pelvis can all be assessed. Radiologists routinely note these features in their reports when a patient is being evaluated for stones or surgical planning, because, as the evidence consistently shows, the geometry of the lower pole is one of the strongest predictors of treatment success for stones in that location.