The correct answer is A. The patient's symptoms are consistent with an infected and obstructing ureteral stone, especially in light of his past stone history and probable dehydration from his hiking trip. Colicky flank pain radiating to the groin typically marks the presence of a midureteral obstruction. An obstruction in the presence of an infection is a medical emergency because of the very high possibility of septic shock, therefore a quick diagnosis is needed. The best imaging study for nephrolithiasis is a non-contrast CT scan which can visualize all types of stones and then accurately locate them. It can also tell us whether the patient has hydronephrosis, hence, disclosing whether the patient has an obstruction. Once the diagnosis is made, a urologist will most likely need to put in a ureteral stent to correct the obstruction.
A DMSA renal scan (choice B) is a radionucleotide study that evaluates renal function and does not give much information about a renal obstruction. It also takes 4-24 hours to obtain optimal images.
An IVP (choice C) is incorrect because of the patient's renal insufficiency at the time of presentation. The elevated creatinine is a contraindication to IV contrast. In any other cases of noninfected nephrolithiasis with a normal creatinine, an IVP would be appropriate.
A KUB (choice D) would not be able to demonstrate the presence of a renal obstruction. It can be helpful in verifying the presence of kidney stones. However, uric acid stones are radiolucent and would not be seen on a plain film.
A renal ultrasound (choice E) is incorrect because an ultrasound cannot visualize the presence of ureteral stones. It can tell us whether the patient has hydronephrosis, but nothing more.
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