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A KUB (kidneys, ureters and bladder) plain film
23%
3/13
Intravenous pyelogram
15%
2/13
Transvaginal ultrasound
0%
0/13
Noncontrast CT scan
62%
8/13
Exploratory laparoscopy
Select Answer to see Preferred Response
The clinical presentation is most likely consistent with nephrolithiasis. The most appropriate next step is to obtain a noncontrast helical CT scan to evaluate for renal stones. The patient above endorses symptoms commonly found with renal stones such as colic pain (depending on where the stone is located), dysuria, urgency, nausea and vomiting. Additionally, this patient has a history of gastric bypass surgery, which increases the risk of stone formation. The patient also shows hematuria without signs of infection on urinalysis. A noncontrast helical CT scan has high sensitivity and specificity for detecting all types of renal stones and can rule out other etiology for abdominal pain (Illustration A). Portis et al. describes that noncontrast helical CT scans have high sensitivity (95-100%) and specificity (94 to 96%) in identifying all stones types. Another advantage of this imaging modality is that measuring Hounsfield density of calculi allows one to differentiate between cysteine and uric acid stones as well as subtyping calcium containing stones. In contrast, plain films sensitivity is 45-59% and specificity is 71-77%. Plain films may not detect stones that are purely uric acid or cysteine. Asplin et al. has found that patients who have undergone modern bariatric surgery demonstrate a higher level of hyperoxaluria, which increases the risk of renal oxalate stone formation. This is likely due to the increase absorption of oxalate absorption after surgery. Illustration A: The image depicts a non-contrast CT of the abdomen and pelvis. A calculus is seen on the left ureter. Incorrect Answers: Answer 1: A plain film will detect large radiopaque stones, but may miss radiolucent stones such as uric acid or smaller size stones. Answer 2: An intravenous pyelogram has higher sensitivity and specificity for detecting stones than a plain film and can show the degree of obstruction. However, this modality has fallen out of favor due to risk of contrast reaction and radiation exposure. Answer 3: A transvaginal ultrasound may be useful if there is suspicion for ectopic pregnancies or adnexal lesions and masses. However, the patient is not pregnant, has no signs of pelvic inflammatory disease, and the clinical presentation is more consistent with renal stones. Answer 5: Exploratory laporoscopy is an invasive procedure and some type of imaging would be useful for guidance before subjecting the patient to unnecessary risk and complication.
3.0
(8)
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