What are the indications for computed tomography (CT) scans in obstetrics and gynecology?

Indications for CT Scan in Obstetrics and Gynecology

CT scans should be performed in obstetrics and gynecology only when the benefits clearly outweigh the risks, with ultrasound and MRI being preferred first-line imaging modalities due to their lack of ionizing radiation. 1, 2

Obstetric Indications

Trauma in Pregnancy

• Thoracic, abdominal, and pelvic CT scan (with or without contrast) is indicated in pregnant trauma patients when clinically necessary 1
• The risk/benefit balance should guide the decision, but maternal well-being takes priority
• CT is particularly valuable for:
  • Polytrauma assessment
  • Suspected intra-abdominal hemorrhage
  • Suspected surgical complications

Postpartum Hemorrhage

• CT with IV contrast is indicated in hemodynamically stable patients when:
  • Conventional medical treatment has been unsuccessful 1
  • Intra-abdominal hemorrhage is suspected
  • Postsurgical complications are suspected
  • Need to identify surgical causes of PPH (uterine rupture, genital tract laceration)

CT Angiography (CTA) in Postpartum Hemorrhage

• Indicated for persistent hemorrhage after empiric embolization 1
• Multiphasic CT (including noncontrast, arterial, and portal venous phases) has 97% accuracy for detecting active extravasation 1
• Enables comprehensive evaluation of abdominopelvic vasculature

Acute Abdominal/Pelvic Pain in Pregnancy

• CT with IV contrast is appropriate when:
  • Nongynecological etiology is suspected 1
  • Ultrasound findings are normal but symptoms persist
  • Timely intervention is necessary to decrease risk to mother and fetus

Gynecologic Indications

Acute Abdominal/Pelvic Pain

• CT abdomen and pelvis with contrast media is indicated for: 1
  • Suspected appendicitis (after inconclusive ultrasound)
  • Suspected diverticulitis
  • Suspected abscess
  • Small bowel obstruction (after initial evaluation with conventional radiography)
  • Mesenteric ischemia (CT angiography preferred)

Gynecologic Malignancies

• CT has limited role in initial local staging of endometrial cancer due to poor soft tissue contrast 1
• CT is useful for:
  • Detecting extrauterine metastases
  • Planning surgical approach (minimally invasive vs. laparotomy)
  • Evaluating treatment response
  • Surveillance for recurrence

Radiation Safety Considerations

Fetal Radiation Risk

• Fetal radiation exposure >50mGy is associated with doubled relative risk of childhood cancer 1, 2
• Exposure >100mGy increases risk of mental retardation 1
• Exposure >150mGy increases risk of malformations 1
• A threshold of 200-500mGy may be considered for pregnancy termination discussions 1

Risk Minimization

• Single CT scan typically delivers radiation below thresholds for major complications 2
• Use low-dose protocols when possible
• Shield areas not being imaged
• Consider alternative imaging when appropriate:
  • Ultrasound as first-line imaging in pregnancy 2, 3
  • MRI as second-line when ultrasound is inconclusive 2, 3

Common Pitfalls and Caveats

1. Overreliance on CT in pregnancy: Always attempt ultrasound first for most obstetric indications 2, 3

2. Contrast considerations:

   • Iodinated contrast appears safe in pregnancy 3
   • Gadolinium (for MRI) is contraindicated in pregnancy 2, 3

3. Misinterpreting normal postpartum findings:

   • Hypodense edema at cesarean incision site can be misinterpreted as dehiscence in first postpartum week 1
   • Dilated tortuous hypertrophic uterine arteries can mimic extravasation 1

4. Limited value in certain conditions:

   • CT has poor sensitivity for detecting myometrial invasion in endometrial cancer (58-61% accuracy vs. 88-89% for MRI) 1
   • CT cannot reliably distinguish vascular uterine abnormalities from normal postpartum changes 1

5. Radiation anxiety: Healthcare providers should be prepared to address patient concerns about radiation exposure with accurate information about actual risks 4

By carefully weighing the benefits against the risks and using appropriate protocols, CT scans can be valuable diagnostic tools in obstetrics and gynecology when used judiciously.