Abnormalities of the kidney and /or urinary tract are more common in male than female patients.

The autopsy incidence of renal ectopia is 5.9%.

In renal ectopia,the affected kidney is abnormal in position, either lower or higher than the normal site. The anomaly results from abnormal caudal-to-cranial ascent of the kidney. Initially,the kidneys lie close together in the pelvis, anterior to the sacrum and with the hila directed anteriorly. Withgrowth, the kidneys gradually ascend to lie in the abdomen and separate away from the midline. They attain their adult position adjacent to the adrenal gland by the ninth week. As the kidneys ascend, they rotate.Underascent is more common than overascent. Hence, ectopic kidneys are most often found in the pelvis or lower abdomen.The overascended kidney or intrathoracic kidney lies cranial to its normal expected position. The affected kidney remains subdiaphragmatic in location.However, its high position may lead to focal eventration of the diaphragm overlying the kidney, and may mimic a supradiaphragmatic renal position. Pelvic kidneys are usually relatively small and irregular in shape, have a variable degree of rotation, and may fuse to form a discoid or pancake kidney. The length of the ureter is appropriate to the position of the kidney, an important point in differentiation between true ectopia and nephrotosis .During ascent, the ureteric bud may cross the midline and encounter the contralateral kidney. This is knownas crossed ectopia. (The renal tissue in crossed ectopia is usually fused, and known as crossed-fused ectopia)

In most cases, the fusion is between the lower pole of the orthotopic kidney and the upper pole of the ectopic kidney.

It is more common for the left kidney to cross the midline to lie on the right side.

Blood supply to the ectopic kidneys usually arises from the major adjacent blood vessels, and they are often supplied by multiple vessels. As the kidneys ascend from the pelvis to abdomen, they receive blood supply from vessels that are close to them. While in the pelvis, they receive blood supply from the common iliac arteries.When they reach a higher level, they receive new branches from the aorta. The inferior branches undergo evolution and disappear.

Many renal anomalies are incidental findings.

Ectopia kidneys are prone to trauma, particularly if they are located arterior to the spine. As in our patient, an ectopic kidney may present as a palpable abdominal or pelvic mass. The patient may present with signs and symptoms of urinary tract obstruction due to passage of the ureter anterior to the lower pole in renal ectopia. The ectopic kidney is associated with an increased incidence of stone formation as a result of stasis caused by the altered geometry of urinary drainage.

Patients with crossed-fused renal ectopia are usually asymptomatic. However, they may have increased susceptibility to develop complications seen in other forms of ectopic kidneys .

Imaging is useful in the detection of renal ectopia and its complications.

These patients are prone to infections because of coexisting urinary tract anomalies such as duplicated ureter, ureter opening anomalies, and urinary stasis. Assessment of renal parenchymal damage resulting from acute or chronic renal infection is the primary indication for radionuclide imaging with Tc-99m DMSA. I

Renal ultrasonography, intravenous pyelography, computerized tomography, and renal scintigraphy (technetium-based tests) are the imaging methods used for diagnosis.

Demonstration of crossed renal ectopia is important because it is a predisposing factor for obstruction, infection, and neoplasia of the urinary system.