A 29 y/o F 20 weeks pregnant presents with fever, dysuria, and left flank pain. She has some CVA tenderness on the right. WBC is elevated to 15. UA shows both blood and leukocytes in the urine. You are concerned about pyelonephritis vs. and infected stone. What are the risks of imaging this patient?
Pregnant patients have hydronephrosis on ultrasound at baseline so this may make diagnosis difficult. The positive predictive value of ultrasound is 77% for stones.
MRI has a PPV of 80% for nephrolithiasis .
CT has a PPV of 96% and is still the preferred imaging modality. If necessary it can be done with contrast if there is suspicion for abscess as iodinated contrast has not been shown to be harmful to fetal development. The dose of radiation for this scan is about 0.7 rads. No adverse deterministic effects on fetal development have been observed up to levels of 10 rads and most routine abdominal imaging is less than 5 rads.
Remember this is an excellent opportunity to use shared decision making and should be documented appropriately in the chart.