ureteropelvic junction ( upj ) obstruction is the most common form of upper urinary tract obstruction in children . the variations in renal arterial supply are best understood when embryology of the renal vasculature is considered . multiple renal arteries have been reported to occur in approximately 30% of cases , with a preponderance on the left side . with respect to the presence of multiple renal arteries , by a study of sampaio et al . , an inferior  accessory  or  aberrant  artery was found to cross anteriorly to the upj in 6.8% of the cases . in few specimens did this inferior accessory artery pass close to the upj . therefore , the presence of an anomalous vessel crossing the upj and causing obstruction is a very rare finding . we describe a 36-year - old woman with hydronephrosis due to upj obstruction by an aberrant renal artery and review the literature in brief . a 36-year - old woman was admitted to our hospital with intermittent right flank pain for 4 years . the pain was most often experienced during the later hours of the day , especially after ingestion of large quantities of fluid . she had been treated at a local clinic in the past for urinary tract infection with right flank pain and weakness . physical examination revealed blood pressure of 110/80 mmhg and the presence of costovertebral - angle tenderness . urinalysis were within normal limits ( wbc 0 - 1/hpf , rbc 0 - 1/hpf ) . biochemical analysis revealed blood urea nitrogen level of 11.0 mg / dl and serum creatinine level of 0.8 mg / dl . kidney ultrasonogram showed a marked dilatation of the right pelvocalyceal system and right proximal ureter . excretory urogram revealed a marked right hydronephrosis with dilated calyces due to ureteropelvic junction obstruction ( figure 1 ) . computed tomography angiogram ( cta ) clearly displayed the aberrant renal artery which originated from the aorta below the normal right renal artery ( figure 2 ) . a source image of magnetic resonance angiogram ( mra ) also showed a severe hydronephrosis of the right kidney and smooth obstruction of the right ureteropelvic junction due to extrinsic compression by an aberrant renal artery which originated from the aorta , crossing anteriorly to the ureteropelvic junction ( figure 3 ) . after furosemide infusion , the delayed right kidney excretion was somewhat improved ( figure 5 ) . the patient underwent surgical exploration via an anterior approach which revealed a slightly ptotic , mobile , right kidney which was normal in size , with a marked hydronephrotic pelvis froman aberrant renal artery and vein crossing the ureteropelvic junction , proceeding to the lower pole and compressing the ureteropelvic junction against the lower pole of the kidney . a dismembered pyeloplasty was performed , with the pelvis anastomosed to the ureter in front of the aberrant renal artery . this is partly attributable to the more widespread use of angiography and other imaging modalities in recent years . some knowledge of the embryology of the renal vessels is necessary to understand the frequent anomalies that may occur . with complicated development of the kidneys , through the three stages of pronephros , mesonephros and metanephros , and the migration of the definitive kidney ( metanephros ) from the pelvic region to the region of the posterior abdominal wall ( in the lumbar area ) , the renal blood supply undergoes successive changes in its upward migration . since arterial degeneration begins at the cephalic pole of the metanephros , the segmental branch to the lower renal pole is the one most likely to remain as an accessory artery . the association between lower polar aberrant vessels and a dilated renal pelvis was appreciated and this , acting in the nature of a physical obstruction to the urine flow , seemed to provide a logical explanation for the condition . however , it has been suggested that the obstruction may result from a neuromuscular incoordination of the ureteropelvic junction and the vascular obstruction is a secondary rather than a primary event . however , the work of johnson who studied the manometric pressures in such cases , and the electron microscopic evidence presented by notley appear to favor mechanical obstruction . the symptom of vascular ureteropelvic junction obstruction may include colicky mid - abdominal pain , nausea and vomiting . however , our patient did not present such symptoms or signs , except an abdominal pain . older modalities , such as intravenous urography and angiography , have essentially been replaced by endoluminal ultrasonography and cta . a significant advantage of the technique is that it can quantify the number and location of vessels and aid in directing an incision away from vessels . the image can be reconstructed three - dimensionally in longitudinal fashion , providing accurate information about vessels as small as 1 mm in diameter . mr imaging , including mr urography and angiography , is an effective diagnostic method to evaluate various renal diseases . mr angiography can rapidly and accurately depict renovascular diseases without using contrast medium and ionizing radiation . a source image of mra shows renal parenchyme as well as a dilated pelvocalyceal system . in the present case , the source image of mra clearly displayed the relationship between hydronephrosis and an aberrant renal artery . on the other hand , the number , location , morphology and size of the aberrant renal vessels were accurately depicted by cta . therefore , cta and mra are considered to be more non - invasive and more powerful diagnostic methods to evaluate an aberrant renal artery than conventional angiography or ct . currently , the most widely accepted surgical procedure is dismembered pyeloplasty , with the anastomosis performed anterior to the obstructing vessel .