Answer to Medical Challenge | Sudden Pain

Posted on March 25, 2013


**If you would like another chance to read the challenge before seeing the answer, click here.  Scroll down for the answer.  **


The correct answer is D) Nephrolithiasis.

Some of you chose the correct condition, but on the wrong side of the body.  Remember that the patient had pain on the left, and that when we read a CT scan, we are always “facing” the patient – that is, what’s on the right of the screen is actually the patient’s left.  In the axial CT images below, the patient’s feet would be projecting out of the screen towards you (i.e. you are looking at a slice of them from below).

Non-contrast CT scan is the gold standard for detecting kidney stones, though this patient received contrast because other causes of abdominal pain may have been ranked higher in the ordering physician’s differential.  I want to point out several findings in the patient’s scan that aid in diagnosis.

Hydronephrosis of the left renal pelvis.  Click to enlarge.

Hydronephrosis of the left renal pelvis. Click to enlarge.

Immediately apparent is hydronephrosis (literally, “water kidney”) – or dilatation of the renal collecting system – on the patient’s left (red arrow).  This results from obstruction of the free flow of urine somewhere distal to the swelling.  Also note that contrast has not illuminated the left renal pelvis the way it has on the right.  Finally, the left kidney itself appears to have a lower signal intensity (brightness) than the right.

In the other images (refer to original post), multiple other stones can be detected in the kidneys.  The last two images show the obstructing stone.

Obstructing left-sided nephrolith.  Click to enlarge.

Obstructing left-sided nephrolith. Click to enlarge.

On the above image, the stone is clearly seen at the point of obstruction (red arrow), and perhaps more subtly you will note the “wispyness” of the ureter and surrounding area, indicating acute inflammation in the area.


Nephrolithiasis technically refers to stones in the kidney – the acute pain from “passing” a kidney stone occurs as the stone passes through the muscular tubes that connect the kidneys to the bladder, called the ureters.  Thus, the term for this patient’s actual condition would be “ureterolithiasis” – but this term is not often used, especially in the emergency department.

Kidney stones, or renal calculi, are typically formed from dietary minerals (most often calcium) and/or organic compounds (oxalic acid, uric acid, etc.).  When urine becomes “supersaturated”, these compounds precipitate out of their suspension to form a solid, which acts as a nidus for further crystallization.  They are nearly twice as common in males, where they present in early life (20s-30s); females typically present for the first time somewhat later in life, as this patient did.  First-time stone “attacks” after the age of 50 are somewhat uncommon.  The majority of renal calculi pass spontaneously, but those larger than 6mm are significantly less likely to do so.

When a stone’s passage is intermittently obstructed in the ureters, their intermittent contractions cause sharp, unilateral (one-sided) abdominal or back pain that may radiate toward the groin – known as “renal colic”.  The pain can be quite exquisite, and patients typically cannot find a comfortable position, causing them to writhe in bed (or pace, if they prefer to stand).  Nausea and vomiting are not uncommon, and diarrhea may also occur.  Patients may have gross (visible) blood in the urine, or smaller amounts detectable only on urinalysis.

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Posted in: Medicine