Hydronephrosis and aberrant renal artery

Images Evy Panos

A 32 year old man presents with right loin pain after a drinking binge. His friends have urged him to attend the Emergency Department because he always complains of  right loin pain after drinking in their company and they would like him to get to the bottom of it. He describes having right loin pain after heavy drinking for a number of years. This generally lasts from hours to days depending on how much he has drunk. At one point he describes stopping drinking for 6 weeks and was pain free during that time. He has a family history of renal colic. His renal function is normal.

A point of care renal ultrasound is performed

Longitudinal view of the right kidney shows hydronephrosis.

Transverse view of the right kidney

In the transverse view, the balloon shaped pelvis is over 7cm in diameter

Transverse view with colour Doppler. There is no flow with Colour Doppler within the anaechoic structure

Transverse view in slow motion. This is a slowed down sweep through the right kidney in the transverse plane. Note that the pelvic cystic structure is not entirely concave and communicates with the dilated calyces excluding a renal cyst. This is severe hydronephrosis.  The parenchyma is thin.

A CT with contrast was organised which showed a pelviureteric junction stenosis with cortical parenchymal thinning secondary to extrinsic compression by an ectopic inferior right renal artery

CT upper pole coronal view

Mid pole coronal view

lower pole coronal view

The patient was referred for a pyeloplasty with the pelviureteric anastamosis being placed anterior to the aberrant vessel.

Discussion 

Hydronephrosis from congenital PUJ obstruction has an incidence of around 1 in 1000-1500. The cause for this is most likely functional, resulting in neuromuscular incoordination of the ureteropelvic junction secondary to abnormalities in the smooth muscle of the pelvis and ureter. Physical obstruction of the ureter by compression from an aberrant renal vessel is observed but may not actually be the cause of the obstruction.

The renal arteries usually  arise from the aorta below the superior mesenteric artery at L1-L3. The right renal artery is longer, passing posterior to the IVC, right renal vein, head of pancreas and descending part of the duodenum to join with the aorta. Each renal artery divides into anterior and posterior divisions at or very close to the hilum of the kidney and then further divides into segmental arteries to supply the respective segments of the kidney.

Accessory or aberrant arteries are common (30% of the population). The term applies equally to an additional artery in the renal pedicle, or to a vessel entering the kidney directly at either pole, whether derived from the main renal artery, from the aorta or from a branch of the aorta

In this case, the hydronephrosis was so severe that it may have been difficult to differentiate it from other pathology. The following are some mimics of hydronephrosis.

Mimics of Hydronephrosis:

1. Extrarenal pelvis
2. Parapelvic cysts
3. Prominent renal vasculature and vascular malformations.

Extrarenal pelvis:

• Easy to confuse with hydronephrosis.
• Anatomical variant (10% of population)
• The renal pelvis is outside the renal sinus and therefore not surrounded by fat
• The pelvis is larger and more distensible
• Usually asymptomatic but stone formation and infection have been reported
• Unlike hydronephrosis it is not associated with dilated calyces, parenchymal thinning, hydroureter or enlarged kidney
• Tip : An easy way to differentiate an extra renal pelvis from hydronephrosis is to place the patient prone . In the prone position , hydronephrosis will remain, an  extrarenal pelvis will collapse

Parapelvic cysts: 

• Easy to confuse with hydronephrosis
• Describes cysts around the renal pelvis or renal sinus
• The cysts do not communicate with the collecting system
• Probably lymphatic in origin
• Mainly asymptomatic but may cause haematuria, hypertension, hydronephrosis or become infected
• Unlike hydronephrosis, it is not associated with dilated calyces, parenchymal thinning, hydroureter or enlarged kidney
• More spherical in shape than hydronephrosis
• Tip: In the transverse view the cyst does not appear connected with the calyceal system
• Differentiation with hydronephrosis is confirmed with a CT scan with contrast 

Prominent renal vasculature and vascular malformations

• Easy to differentiate from hydronephrosis with colour Doppler.  Vascular structures will demonstrate flow

References

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