Imaging of stone disease in pregnancy.

Renal colic is the most frequent non-obstetric cause for abdominal pain and subsequent hospitalization during pregnancy. Intervention is necessary in patients who do not respond to conservative treatment. Ultrasound (US) is widely used as the first-line diagnostic test in pregnant women with nephrolithiasis, despite it is highly nonspecific and may be unable to differentiate between ureteral obstruction secondary to calculi and physiologic hydronephrosis. Magnetic resonance imaging (MRI) should be considered as a second-line test, when US fails to establish a diagnosis and there are continued symptoms despite conservative management. Moreover, MRI is able to differentiate physiologic from pathologic dilatation. In fact in the cases of obstruction secondary to calculi, there is renal enlargement and perinephric edema, not seen with physiological dilatation. In the latter, there is smooth tapering of the middle third of the ureter because of the mass effect between the uterus and adjacent retroperitoneal musculature. When the stone is lodged in the lower ureter, a standing column of dilated ureter is seen below this physiological constriction. MRI is also helpful in demonstrating complications such as pyelonephritis. In the unresolved cases, Computed tomography remains a reliable technique for depicting obstructing urinary tract calculi in pregnant women, but it involves ionizing radiation. Nephrolithiasis during pregnancy requires a collaboration between urologists, obstetricians, and radiologists.