What are the urgent indications for a computed tomography (CT) scan in obstetrics and gynecology?

Urgent Indications for CT Scan in Obstetrics and Gynecology

CT scans in obstetrics and gynecology are indicated primarily for life-threatening conditions, failed conventional medical treatment, or when ultrasound and MRI are inconclusive or unavailable. 1

Obstetric Emergencies

Trauma in Pregnancy

• Polytrauma assessment in pregnant patients with high-velocity trauma 1
• Suspected intra-abdominal hemorrhage and unstable pelvic fractures 1
• Persistent hemorrhage after empiric embolization 1

Postpartum Complications

• Failed conventional medical treatment for postpartum hemorrhage 1
• Suspected vascular complications following delivery 1
• Suspected surgical complications in the postpartum period 1

Gynecologic Emergencies

Acute Pelvic Pain

• Poorly localized pain with suspected gynecologic and non-gynecologic etiologies 2
• Nonspecific clinical presentation with broad differential diagnosis 2
• Equivocal or nondiagnostic ultrasound evaluation, particularly with concern for appendicitis 2

Specific Gynecologic Conditions

• Ovarian torsion when ultrasound is inconclusive (CT findings include enlarged, featureless, hypoenhancing ovary with swirling vascular pedicle) 2, 1
• Tubo-ovarian abscess (CT shows complex cystic mass with thick enhancing walls) 2, 1
• Degenerating or torsed uterine fibroids (diminished contrast enhancement of fibroids with 86% sensitivity) 2
• Pelvic inflammatory disease with suspected complications 2
• Suspected ovarian vein thrombosis 1
• Ruptured ectopic pregnancy with hemodynamic instability when ultrasound is inconclusive 3

Non-Gynecologic Causes of Pelvic Pain

• Suspected appendicitis after inconclusive ultrasound 1
• Suspected diverticulitis 1
• Small bowel obstruction (after initial evaluation with conventional radiography) 1
• Mesenteric ischemia (CT angiography preferred) 2, 1

Important Considerations

Contrast Enhancement

• Contrast-enhanced CT is preferred for most urgent indications as it:
  • Has higher sensitivity (89% vs 70%) than ultrasound for urgent diagnoses 2
  • Provides 88% overall accuracy compared with surgical diagnosis 2
  • Is essential for detecting active extravasation in hemorrhage (97% accuracy) 1
  • Improves visualization of vascular complications and abscess formation 2

Radiation Safety in Pregnancy

• Avoid CT scans in pregnancy whenever possible
• Use non-ionizing imaging modalities (ultrasound and MRI) as preferred alternatives 1
• When CT is necessary in pregnancy:
  • Use proper abdominal shielding to minimize fetal exposure 1
  • Keep cumulative ionizing radiation exposure less than 50 mGy 1
  • Obtain informed consent after discussing risks and benefits 1

Common Pitfalls

• Overreliance on CT for initial evaluation of gynecologic conditions when ultrasound would be more appropriate
• Failure to use IV contrast when evaluating for vascular complications or abscess formation
• Misinterpretation of normal postpartum changes as pathology on CT 1
• Limited accuracy of CT for adnexal mass characterization compared to ultrasound or MRI 2

Imaging Algorithm for Acute Pelvic Pain

1. First-line imaging: Transvaginal ultrasound for suspected gynecologic etiology
2. Second-line imaging:
   • CT with IV contrast if:
     • Ultrasound is inconclusive
     • Non-gynecologic etiology is suspected
     • Patient is hemodynamically unstable
     • Widespread disease is suspected
   • MRI if:
     • Patient is pregnant and ultrasound is inconclusive
     • Detailed soft tissue characterization is needed
     • Radiation exposure is a significant concern

CT remains a valuable tool in the emergency setting for obstetric and gynecologic conditions, particularly when ultrasound is inconclusive or when rapid assessment of multiple organ systems is needed 4, 5.