Imaging of the Non-Obstetric Acute Abdomen in Pregnancy
Introduction
Radiologic evaluation of acute abdominal pain in the pregnant patient poses unique challenges owing to implications of radiation dose to the fetus as well as physiologic alterations to maternal anatomy. Furthermore, differentiating between obstetric and non-obstetric etiologies adds another layer of complexity. The main objective of this review is for the reader to augment their understanding and increase comfort in the imaging evaluation of non-obstetric etiologies of acute abdominal pain in pregnancy.
Section snippets
Appendicitis
The incidence of acute appendicitis is lower than age-matched nonpregnant patients; however, it remains the most common non-obstetric cause of abdominal pain in pregnancy which requires surgical intervention.1,2 While morbidity for laparoscopic appendectomy is similar between pregnant and nonpregnant patients, risk for perforation is higher in pregnancy. Risk of fetal loss must also be considered, which can range from 7% to 10% in simple cases and up to 24% after perforation.3
Urolithiasis
The incidence of symptomatic urolithiasis during pregnancy is relatively rare and similar to the nonpregnant women of child-bearing age, occurring in approximately 1500-3000 pregnancies and typically during the second or third trimester. As many as 70%-80% of ureteral stones pass spontaneously during pregnancy.6,7 Progression to ureteral obstruction however may lead to significant maternal morbidity including obstructive pyonephrosis, sepsis, and premature labor.8 Physiologic dilatation of the
Pyelonephritis
Although the pathogenesis of pyelonephritis is identical to non-gravid patients, several physiological changes in pregnancy confer increased risk in the pregnant patient, such as smooth muscle relaxation from increased progesterone and subsequent ureteral dilatation which facilitate the ascent of bacteria from the lower urinary tract.12 Although the incidence of bacteruria is approximately the same between pregnant and nonpregnant patients, the incidence of recurrent bacteruria is more common
Acute Biliary Disease (Cholecystitis and Choledocholithiasis)
Risk factors for gallstone formation in the pregnant patient are increased owing to decreased gallbladder motility and increased cholesterol concentration in bile.16 The incidence of symptomatic disease such as cholecystitis is only observed in 1.2% of patients with cholelithiasis.17 Despite the uncommon occurrence of acute biliary disease, it remains the second most common cause of abdominal surgery in the pregnant patient.
Bowel Disease
Acute bowel diseases, including obstruction and inflammatory bowel disease are overall rare in the pregnant patient. Risk of small bowel obstruction in pregnant patients increases as the uterus enlarges into the upper abdomen during the second and third trimesters. Risk of volvulus is also increased in the pregnant patient. The severity of inflammatory bowel disease in pregnancy is partially determined by disease activity at conception. While Crohn's disease patients experience a similar
Trauma
Trauma is the leading non-obstetric cause of maternal death, with blunt trauma leading to fetal death in approximately 3%-38% of cases.
Conclusion
Imaging evaluation of the non-obstetric acute abdomen in pregnant patients presents the challenge of avoiding or reducing fetal exposure to ionizing radiation. The use of ultrasound therefore plays a key role in screening and diagnosis in the pregnant patient. The use of MRI remains a second line modality for most indications; however, sensitivity and specificity of MRI can be augmented by a preceding ultrasound study, even if ultrasound is inconclusive. CT remains the front-line study in the
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