What is the best imaging modality, Ultrasound (US) or Computed Tomography (CT), to assess endometrial cancer?

Ultrasound vs CT for Endometrial Cancer Assessment

Transvaginal ultrasound (TVUS) is the best initial imaging modality for assessing endometrial cancer, while CT is primarily useful for evaluating extrauterine spread and nodal involvement in advanced disease staging. 1

Initial Imaging Approach

Transvaginal Ultrasound (TVUS)

• First-line imaging modality for endometrial cancer assessment 1
• Benefits:
  • Readily available and cost-effective 1
  • High negative predictive value (nearly 100%) when endometrial thickness ≤4mm in postmenopausal women 1
  • Can effectively assess myometrial invasion with reported accuracies of 68-69% 1
  • Combined transabdominal and transvaginal approach provides optimal assessment of enlarged uterus or uterine tumors 1
• Limitations:
  • Operator-dependent with variable accuracies (77-91%) 1
  • Less reliable in patients with high BMI, myomas, adenomyosis, bulky tumors, or retroverted uterus 1

Computed Tomography (CT)

• Not recommended as first-line imaging for local disease assessment 1
• Role in endometrial cancer:
  • Best for detecting para-aortic nodal involvement 1
  • Useful for evaluating extrauterine spread and distant metastases 1
  • Indicated when planning treatment for advanced disease 1
• Limitations:
  • Limited accuracy (58-61%) for myometrial invasion assessment 1
  • Poor visualization of the uterine-cervical margin 1
  • Insensitive for detecting small tumors, especially stage IA disease 1

Advanced Imaging Options

MRI

• Superior to both US and CT for local disease assessment 1
• Best tool for assessing cervical involvement with accuracy of 85-88% 1
• Accurately evaluates depth of myometrial invasion (88-89% accuracy) 1
• Recommended when:
  • Need to establish tumor origin (endocervical vs endometrial) 1
  • Assessment of local disease extent is critical 1
  • Preoperative risk stratification is needed 1
  • TVUS findings are equivocal or visualization is inadequate 1

PET/CT

• Useful for detecting distant metastases 1
• Consider for high-risk patients or suspected recurrence 2

Clinical Decision Algorithm

1. Initial Presentation:

   • Begin with transvaginal ultrasound for all patients with suspected endometrial cancer 1
   • Combine with transabdominal ultrasound if uterus is enlarged 1

2. Based on TVUS findings:

   • If endometrium ≤4mm in postmenopausal woman: Very low risk of cancer (NPV ~100%) 1
   • If endometrium >4mm or abnormal findings: Proceed with endometrial sampling 1, 3

3. For confirmed endometrial cancer:

   • Low-risk features on TVUS: May proceed directly to surgery 1
   • High-risk features or equivocal findings: Consider MRI for better local staging 1
   • Suspected advanced disease: Add CT abdomen/pelvis to evaluate extrauterine spread 1

4. Preoperative planning:

   • For high-grade tumors or suspected extrauterine disease: CT abdomen/pelvis 1
   • For assessment of myometrial invasion and cervical involvement: MRI preferred 1

Important Considerations

• Endometrial cancer staging is primarily surgical, but preoperative imaging guides treatment planning 1
• No imaging modality can replace surgical staging due to limitations in detecting small lymph node metastases 1
• Dual-energy CT shows promise for detecting deep myometrial invasion (sensitivity 100%, specificity 91%), but requires further validation 1
• High-frequency TVUS may approach MRI accuracy in experienced hands (84% vs 82% for myometrial invasion) 1

Common Pitfalls to Avoid

• Relying solely on CT for local disease assessment 1
• Assuming normal findings on TVUS exclude cancer in symptomatic patients 3
• Failing to consider patient factors (obesity, uterine position) that may limit TVUS accuracy 1
• Not correlating imaging findings with histological grade and other risk factors 1

In summary, TVUS should be the initial imaging modality for endometrial cancer assessment, with MRI reserved for better characterization of local disease extent and CT primarily used for evaluating extrauterine spread in advanced disease.