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 .
 ureteropelvic junction obstruction is usually intrinsic and is most common in children . 
 aberrant renal arteries are present in about 30% of individuals . 
 aberrant renal arteries to the inferior pole cross anteriorly to the ureter and may cause hydronephrosis . to the best of our knowledge , although there are some papers about aberrant renal arteries producing ureteropelvic junction obstruction , there is no report of a case which is diagnosed by the new modalities , such as computed tomography angiogram ( cta ) or magnetic resonance angiogram ( mra ) . 
 we describe a 36-year - old woman with right hydronephrosis . 
 kidney ultrasonogram and excretory urogram revealed right hydronephrosis . 
 cta and mra clearly displayed an aberrant renal artery and hydronephrosis . 
 the patient underwent surgical exploration . 
 for the evaluation of hydronephrosis by an aberrant renal artery , use of cta and mra is advocated . 
INTRODUCTION
CASE
DISCUSSION