Step I Qbank Conundrum

[5150man]

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So it's been a long day studying the renal system and I'm sure this question will make sense in the morning but I can't figure it out now.

The question is a male infant has bilateral hydronephrosis with a dilated ureter from 3 cm above insertion into bladder to the renal pelvis.
The cause of the obstruction is a ureteropelvic junction obstruction.
My question is how would an obstruction cause dilation distal to the obstruction?
It has been a long day and the kidney is truly an amazing organ.

 

[mpp]

The dilation is proximal to the obstruction, from the renal pelvis down until the ureteropelvic junction (which occurs 3 cm above the insertion into the bladder).

 

[Mossjoh]

No..the ureteropelvic junction is the junction of the ureter and renal pelvis...

 

[5150man]

I'm sorry but I still don't get it. The urine goes from the renal pelvis, through the ureteropelvic junction, into the ureter, and then into the bladder. The only way I see this making sense is if the infant's ureter is only 3 cm. long. Is that the case? That seems awful short to me but it's been awhile since I've been an infant.

 

[Mossjoh]

I don't get it either. The dilation should be proximal to the UPJ...so in the renal pelvis and the kidney.

I'm speaking from experience here...I had a 3x5mm calcium oxalate stone in my right UPJ and blocking flow. It causes a right hydronephrosis of the kidney as well as dilation of the renal pelvis. The ureter distal to the stone was not dilated. (As would be expected) I have the CT scan to prove it. 😛

Mossjoh (don't worry, I'm better now)

 

[Idiopathic]

Doesnt peristaltic activity in obstruction cause dilation distal to the obstruction? Isnt this one way to tell bowel obstruction on plain film of the abdomen, when you see dilated bowel distal to obstruction? I always thought it was.

 

[Mossjoh]

I thought you normally see dilation proximal to the obstruction due to increased pressure....