Teaching Case

A 10-year-old male patient presented to the pediatrics department with complaints of intermittent left flank pain since 5 years. Developmental history was normal. No significant family history was found. Physical examination was done which was within normal limits. Blood investigation was found to be normal.

B-mode ultrasonography of abdomen was done for this patient in supine position using curvilinear probe in transverse and sagittal planes. Ultrasound revealed ectopic right kidney and non-visualization of left kidney. CT urography was done on this patient for further evaluation.

On CT urography, the right kidney was normal in size shape and contour and located in the right renal fossa. The left kidney was found to be in ectopic location in right renal fossa fused to the right kidney along the hilar margin (Figure 1). The renal pelvis of the fused collecting system was found to be directed anteriorly. Single ureter was seen draining the fused kidneys opening into the urinary bladder at VUJ on right side (Figures 2 and 3). A single renal artery arising from right common iliac artery at L3 vertebral level was seen supplying the fused kidneys (Figure 4) and a single renal vein draining the fused kidneys. High bifurcation of the aorta at L3 vertebral level was also noted.

An undescended right testis was also noted in subcutaneous plane of right inguinal region close to superficial inguinal ring (Figure 5).

Crossed fused kidney ectopia is an uncommon congenital malformation in which one kidney migrates abnormally to the opposite side and fuses with the other kidney during development. The fused kidneys are almost always drained by two separate collecting systems and two ureters [1].

Normally the kidney reaches its appropriate position at L2 level at the end of the 2nd month.

In crossed fused renal ectopia there is abnormal renal ascent in embryogenesis with fusion of the kidneys.

It is thought to occur in the first trimester due to abnormal development of the ureteric bud and metanephric blastema between 4 and 8 weeks gestation [2].

Skeletal abnormalities, anorectal and genital abnormalities for e.g. undescended testes may be associated with this condition [3].

Literature has reported cases of renal ectopia with fused kidneys with two separate collecting systems.

Crossed fused renal ectopia has always been classically categorised into six types which are: type 1, inferior crossed fused ectopia; type 2, sigmoid or S-shaped kidney; type 3, unilateral lump kidney; type 4, unilateral disc kidney; type 5, L-shaped kidney; and type 6, superior crossed fused ectopia [4].

As per this classification system, two ureters drain both the kidneys separately into the urinary bladder at its orthotopic position.

However, in our case, a single collecting system is seen draining the fused kidneys with a single ureter opening into the bladder at the VUJ which is a very rare entity with very few case reports. Also in our case, associated anomalies were seen in form of undescended testes and high bifurcation of aorta.

To the best of our knowledge no case of cross fused ectopic kidney with single ureter and undescended testes has been reported before in world literature. This paper highlights the role of imaging in a rare case of cross-fused renal ectopia with a single collecting system with normal function.

All patient data have been completely anonymized throughout the entire manuscript and related files.