Case 22 - Renal obstruction with UVJ stone

This patient has an obstructing right UVJ stone.  All but one of the findings associated with this diagnosis are present (delayed  nephrogram, hydronephrosis, hydroureter, ureteral stone). 

There is a delayed nephrogram.  What does this mean? Notice how the kidney on the right is in the cortical phase of enhancement.  The cortex is much brighter and distinct from the medulla.  Contrast has filtered into the glomeruli but not really passed into the tubules yet.  This is the first phase of renal enhancement. The kidney on the left is in the medullary phase of enhancement.   The cortex and medulla appear indistinct.  This represents contrast in the nephrons.  This is the second phase of renal enhancement.  The third phase of renal enhancement is contrast primarily in the collecting system.  This is called the excretory phase.  The right kidney is progressing through these phases slower than the left.  Hence, its nephrogram is delayed. A delayed nephrogram can be caused by increased intratubular pressure (from obstruction of the collecting system or venous return), from decreased arterial inflow (renal artery stenosis, vascular trauma, fibromuscular dysplasia), or from damage to the nephrons and glomeruli (ATN, glomerulonephritis).

There is no contrast in the right collecting system.  For this scan we gave 30cc of contrast 3 minutes before the scan and 120 cc of contrast 60 seconds before the scan.  By the time we scan the kidneys those 30 cc of contrast should filter into the collecting system.  The 120 cc of contrast should be in the nephrons.  Thus, the kidney should actually be in both the medullary and excretory phases of enhancement. On the left, there is some contrast in the renal pelvis and proximal ureter.  On the right there is no contrast in the renal collecting system.  This again demonstrates the delayed nephrogram on the right.

There is right sided hydronephrosis.  The renal pelvis is dilated and the distention extends into the calyces.  Dilated calyces indicates hydronephrosis.  This suggests obstruction.

There is a standing column of fluid in a dilated right ureter.  A focal area of ureteral dilatation can be due to peristalsis. However, in this case the entire right ureter is distended.  Compare it to the ureter on the left.  This dilation also suggests obstruction.  Renal obstruction can be secondary to stones, tumor (transitional cell carcinoma, bladder cancer, primary pelvic malignancies, metastasis), congenital bladder abnormalities (ureteroceles, ectopic ureteral insertion), or bladder outlet obstruction (neurogenic, prostate enlargement).

There is a radio-opaque stone at the right UVJ.  A similar density is seen on the left.  I think this is a phlebolith.  It appears a few mm lateral to be ureter.  However, the ureter is not opacified and is not easy to follow.  It would be appropriate to either re-scan in 5 minutes for better opacification of the left ureter or to simply say that there also may be a non obstructing left UVJ stone.  All stones except for Crixivan stones in HIV patients are radio-opaque.  However, obstruction can remain after a stone has passed (from the residual edema).

The only other finding often seen in renal obstruction is perinephric stranding.  Sometimes you will see a peri-pelivc fluid collection which represents a ruptured calyx.  This acts as a pressure relief valve resulting in decompression of the collecting system.  They usually heal spontaneously.

Did you notice the patient has has a cholecystectomy.  Follow the normal appendix. It courses very close to the ureter in some places.

Take home point

• The three phases of renal enhancement are cortical, medullary, and excretory.  Renal masses are optimally seen in the medullary phase.
• The findings in renal obstruction are hydronephrosis, delayed nephrogram, hydroureter, perinpehric stranding, and lack of contrast excretion. Any combination can be present.