Crossed fused renal ectopia is a rare congenital anomaly. It involves both kidneys being located on the same side of the body, often fused together into a single mass. This happens when one kidney crosses the midline during development and merges with the kidney on the opposite side.
Understanding Cross Fused Renal Ectopia
“Ectopia” refers to a kidney in an abnormal position, while “fusion” indicates the two kidneys have joined. Instead of one kidney on each side of the spine, both kidneys reside on a single side, typically in the lower abdomen or pelvis. This developmental anomaly occurs during the 4th to 8th week of fetal life, a period when the kidneys normally ascend to their final position in the upper abdomen.
The estimated incidence of crossed fused renal ectopia is approximately 1 in 1,000 births, with some reports suggesting a range of 1 in 2,000 to 1 in 7,500 autopsies. The condition is observed more frequently in males, with a male-to-female ratio of about 2:1 or 3:2.
There are various patterns of fusion that can occur, resulting in different shapes of the combined kidney mass. These include:
Inferior crossed fusion, where the upper pole of the crossed kidney fuses with the lower pole of the normally positioned kidney.
Sigmoid (S-shaped) kidney.
Lump kidney.
Disc kidney.
L-shaped kidney.
Superiorly crossed fused kidneys.
Identifying the Condition
Crossed fused renal ectopia is often discovered incidentally, as it frequently presents without noticeable symptoms. Prenatal ultrasound can detect the condition in some cases, with up to 79% of diagnoses made antenatally. The International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM) code Q63.1 is used for conditions such as lobulated, fused, and horseshoe kidney, which includes fused kidneys.
Ultrasound is a common initial screening tool, often revealing an empty renal fossa on one side and both kidneys on the other. Further confirmation and detailed anatomical assessment can be achieved with computed tomography (CT) scans, which illustrate the kidney’s ectopic location and the collecting system. Magnetic resonance imaging (MRI) and intravenous pyelography (IVP) are additional diagnostic tools that can provide further information about the kidney structure and drainage. Dimercaptosuccinic acid (DMSA) scans can also confirm the diagnosis and assess renal function.
Potential Health Implications
While many individuals with crossed fused renal ectopia remain asymptomatic, the unusual anatomy can predispose them to certain health issues. One common complication is hydronephrosis, which is the swelling of a kidney due to a buildup of urine, often caused by abnormal ureteric drainage or obstruction. Up to 50% of ectopic kidneys may experience at least partial blockage.
The altered urinary flow can also increase the risk of kidney stones, classified under ICD-10-CM code N20.0 for calculus of the kidney. Urinary tract infections (UTIs), identified by ICD-10-CM code N39.0 for urinary tract infection, site unspecified, are another frequent concern due to potential urine stagnation and reflux. The abnormal location of the fused kidneys can also make them more susceptible to trauma.
Beyond urinary system issues, crossed fused renal ectopia can sometimes be associated with other congenital anomalies. These may include abnormalities affecting the skeletal system, cardiovascular system, or gastrointestinal tract. The presence of these additional malformations can sometimes lead to a higher risk of health problems.
Management and Outlook
For individuals with asymptomatic crossed fused renal ectopia and no associated complications, active intervention is usually not required. Instead, regular monitoring through periodic imaging studies and urine tests is often sufficient to track the condition and detect any potential issues early.
Surgical intervention becomes necessary when complications arise, such as significant ureteral obstruction, recurrent kidney stones, or persistent urinary tract infections that do not respond to conservative management. Procedures might include correcting ureteral obstructions, removing stones, or addressing vesicoureteral reflux. The complex blood supply of crossed fused kidneys necessitates careful preoperative assessment, often including angiography, before any surgical procedure.
Despite the potential for complications, the general outlook for individuals with crossed fused renal ectopia is favorable. Most individuals can lead normal lives, especially with appropriate monitoring and timely management of any arising issues.