Ultrasonography should be the first-line (see ultrasound in appendicitis). Second line should be MRI or CT. MRI is likely the best second choice if rapidly available. Consultation with the radiologist may be appropriate to determine the optimal imaging modality.
Ultrasound should be first line and sensitivity for ureteral stones is reported to be greater than 30% in pregnancy (see imaging in ureterolithiasis). Low-dose CT coupled with high accuracy make CT the second line imaging modality. MRI urography should also be considered as a second line test (discuss this with radiology). Remember symptomatic treatment and observation is an option but missing an appendicitis or misdiagnosis of a placental abruption as ureteral stone could be fatal.
Compression US of the lower extremities is recommended as the initial imaging study for suspected cases of PE in pregnancy. If a DVT is present then treat. If no DVT then move onto CT of the chest. CT pulmonary angiography should be second line, rather than ventilation-perfusion scintigraphy. The radiation dose to the fetus is similar for the 2 studies and ventilation-perfusion scan is indeterminate in up to 25% of pregnant patients (Oops now more radiation).
If mama dies baby dies, therefore fetal radiation exposure should not be a factor. If CT is indicated – SCAN AWAY.
Patel SJ, Reede DL, Katz DS, Subramaniam R, Amorosa JK. Imaging the pregnant patient for nonobstetric conditions: algorithms and radiation dose considerations.Radiographics. 2007 Nov-Dec;27(6):1705-22.
Chen MM, Coakley FV, Kaimal A, Laros RK Jr. Guidelines for computed tomography and magnetic resonance imaging use during pregnancy and lactation. Obstet Gynecol. 2008 Aug;112(2 Pt 1):333-40.