A 12 year old male woke up in the middle of the night with left mid abdominal pain. This was followed by nausea and persistent vomiting, with severe left flank pain.
Initial evaluation at an outside emergency department included this study:
CT images show severe left hydronephrosis without hydroureter, suggesting proximal obstruction. Additionally the fluid in the perinephric space is suspicious for forniceal (or calyceal) rupture, due to increased pressure in the renal collecting system resulting from obstruction of outflow.
Ultrasound images demonstrated similar findings, with severe hydronephrosis, and thinned but viable renal cortex.
To unequivically say that a kidney is obstructed, a functional study depicting urine excretion is needed. (Although in this case the anatomic images are strongly suggestive.) Nonetheless this patient underwent a renogram with Tc99m MAG3.
These posterior MAG3 images show accumulation of radiotracer in a dilated left renal collecting system, with minimal excretion. Compare this with the normal sized right renal collecting system with prompt excretion. Results can also be quantified, with the amount of radiotracer activity in each kidney over 30 minutes displayed in the graph below.
There was also no drainage from the left kidney after administration of furosemide. These findings confirm a left ureteropelvic junction (or UPJ) renal obstruction.
This case is a classic example of Dietl’s crisis, i.e. an attack of abdominal/flank pain resulting from renal obstruction, which may be associated with chills, nausea, and vomiting. This has been reported as an under-recognized cause of abdominal pain in pediatric patients. Alagiri M, et al. Int Brazil J Urol 2006;32:451-3.
Ureteropelvic junction obstruction may be congenital or acquired, with the congenital form one of the most common causes of hydronephrosis in infants and young children. The underlying etiology of obstruction may be due to intrinsic narrowing (abnormal muscle fibers or collagen, sequelae of ischemia, urothelial fold) or extrinsic compression (fibrous band, crossing vessel) at the junction of the renal pelvis with the ureter. CTA has been advocated for identification and characterization of crossing vessels, which may decrease the success rate of surgical correction if performed endoscopically (endopyelotomy), but this is not routinely performed at all centers. Mitsumori A, et al. Radiographics 2000;20:1383-93.
Tc99m Mercaptoacetyltriglycine or MAG3 has a relatively high first pass extraction from the blood stream (40-50%) and is excreted primarily by secretion in the renal tubules (>95%). These properties make it an excellent radiotracer for evaluating the excretory urinary tract (renal pelvis, ureters, bladder).