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Nontraumatic Abdominal Emergencies in Pregnant Patients
Key Points
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Normal physiological changes of pregnancy often interfere with clinical evaluation of pathological causes of abdominal pain.
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Imaging, particularly ultrasound, and increasingly magnetic resonance, plays a critical role in evaluation of abdominal pain in pregnancy.
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Various processes can lead to abdominal pain, with management strategies ranging from medical therapy to emergent surgeries.
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Familiarity with the imaging appearance of these processes is crucial in directing timely and effective care.
Introduction
Abdominal pain is a common symptom in pregnancy that results from a variety of causes ranging from normal physiological changes to serious conditions that require prompt diagnosis and treatment. Vague abdominal pain, nausea, and vomiting are frequent complaints during a normal pregnancy. Furthermore, physiologic leukocytosis, displacement of bowel and the appendix by the gravid uterus, and loss of guarding in the case of peritonitis can limit the typical clinical clues for surgical causes of abdominal pain. Therefore, imaging plays a crucial role in identifying potential surgical causes of abdominal pain and directing timely and effective care.
In the pregnant patient, imaging modalities that do not expose the patient to ionizing radiation are strongly preferred, specifically ultrasound and magnetic resonance imaging (MRI). Ultrasound is by far the most used imaging technique in pregnancy, especially for evaluating fetal health and obstetric complications. It is also typically the first-line technique for evaluating suspected gallbladder and renal pathologies. However, normal physiological changes in pregnancy, along with gravid uterus and bowel gas, can potentially limit its use for evaluating deeper structures such as the bowel and appendix. MRI without intravenous contrast has been increasingly used in evaluation of abdominal pain in pregnancy due to lack of ionizing radiation, superb resolution of anatomical details, and the ability to depict various causes of abdominal pain in pregnancy, especially in the evaluation of suspected appendicitis. Gadolinium-based intravenous contrast is avoided in pregnancy, as it crosses the placenta and is associated with adverse fetal outcomes.
The causes of abdominal pain in pregnancy can be divided into four main categories: gastrointestinal, hepatobiliary, genitourinary, and obstetric causes. In the following sections, we discuss the common causes of abdominal pain and review the spectrum of imaging findings in each category ( Table 6.1 ).
Table 6.1
Typical Imaging Findings of the Common Causes of Nontraumatic Abdominal Pain During Pregnancy
| Category | Imaging Findings |
|---|---|
| Gastrointestinal | |
| Acute appendicitis | Appendiceal distention, wall thickening, fluid-filled appendix, surrounding soft tissue stranding, free fluid, appendicolith |
| Inflammatory bowel disease | Bowel wall thickening, submucosal edema, perienteric stranding, terminal ileal involvement, penetrating disease |
| Small bowel obstruction | Dilated fluid-filled small bowel loops with a transition point |
| Diverticulitis | Diverticula, colonic wall thickening, surrounding fat stranding |
| Epiploic appendagitis | Edema and fat stranding surrounding a fat-intensity mass adjacent to the colon |
| Hepatobiliary | |
| Cholelithiasis | Gallstones, typically with posterior acoustic shadowing on US |
| Acute cholecystitis | Gallbladder distention and wall thickening, pericholecystic fluid, gallstones |
| Acute pancreatitis | Focal or diffuse pancreatic edema, restricted diffusion, surrounding fat stranding |
| HELLP syndrome | Hepatomegaly, hepatic necrosis and intra- and extrahepatic hematoma |
| Genitourinary | |
| Nephrolithiasis | Echogenic foci with shadowing and twinkle artifact (ultrasound) or T2 hypointense calculus (MRI) |
| Acute pyelonephritis | Imaging is frequently normal, ultrasound may show collecting system debris or reduced vascularity in uncomplicated cases, abscess |
| Ovarian torsion | Asymmetrically enlarged ovary, peripheralization of follicles, stromal edema, twisted vascular pedicle |
| Leiomyoma degeneration | Edema (increased T2 signal on MRI), hemorrhage (increased T1 signal on MRI) |
| Pelvic inflammatory disease | Hydrosalpinx, tubo-ovarian abscess |
| Endometriosis | T1-hyperintense and T2-hypointense masses typically involving the adnexa, hemoperitoneum |
| Obstetric | |
| Ectopic pregnancy | Lack of intrauterine gestational sac, adnexal mass, free fluid in the pelvis |
| Uterine rupture | Focal myometrial defect, extrusion of the pregnancy products, hemoperitoneum |
HELLP , Hemolysis, elevated liver enzymes, and low platelet count; US , ultrasound; MRI , magnetic resonance imaging.
Gastrointestinal Pathologies
Acute Appendicitis
Appendicitis is the most common nonobstetric cause of emergency surgery in the pregnant patient, complicating approximately 1 per 1000 pregnancies. Early diagnosis of appendicitis is of paramount importance, as delayed diagnosis can lead to serious maternal and fetal complications, including up to 36% fetal loss in the case of perforation.
Although ultrasound may be used in the initial evaluation of suspected appendicitis, it is limited by a high nonvisualization rate. MRI has emerged as the preferred modality due to its nonionizing nature and high sensitivity and specificity of 94% and 97%, respectively. The MRI protocol can be optimized for safe and fast examination, which also allows for evaluation of other potential causes of abdominal pain. MRI findings of acute appendicitis include appendiceal distension (≥8 mm), wall thickening, fluid-filled appendix, surrounding soft tissue stranding/free fluid, and presence of appendicolith ( Fig. 6.1 ). The normal appendix can be greater than 8 mm in diameter, and therefore size should be used in conjunction with other features to suggest appendicitis.
The appendix may not always be visualized on MRI, but the lack of an abnormal appendix and inflammatory change in the right lower quadrant has a high negative predictive value and should be interpreted as negative rather than indeterminate.
Inflammatory Bowel Disease
Inflammatory bowel disease affects women of childbearing age, and pregnancy itself may be a risk factor in disease exacerbations. The presenting symptoms include abdominal pain, diarrhea, and potentially fever. MRI findings of active inflammation include bowel wall thickening, submucosal edema, and perienteric stranding, most frequently involving the distal and terminal ileum. MRI can also show potential complications such as bowel obstruction, fistulization, abscess formation, and perforation ( Fig. 6.2 ).
Small Bowel Obstruction
Small bowel obstruction in pregnancy has similar etiologies to that in nonpregnant patients, most frequently due to adhesions from prior surgery. Other etiologies include hernias, intussusception, and volvulus, particularly in patients with prior gastric bypass surgeries. The clinical presentation of early small bowel obstruction can be subtle or masked by physiologic findings and symptoms of pregnancy. Although computed tomography in general is the preferred modality for the diagnosis of small bowel obstruction, MRI without contrast should be strongly considered in the pregnant patient with suspected small bowel obstruction if the patient is clinically stable. In small bowel obstruction, MRI shows dilated fluid-filled loops of small bowel upstream of the transition point and depicts potential complications such as closed-loop configuration, peritonitis, or perforation ( Fig. 6.3 ).
Diverticulitis
Diverticulitis is relatively rare in younger patients and presents with similar symptoms to nonpregnant patients, namely left lower quadrant pain and fever. MRI shows colonic wall thickening and surrounding fat stranding and also depicts potential complications such as perforation and abscess formation ( Fig. 6.4 ).
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