Endometrial Cancer – MR Staging

Stephanie Nougaret¹, Doenja Lambregts², Annemarie Bruining², Margriet de Haan²

Dept. of Radiology, ¹Montpellier Cancer Centre, France and ²the Netherlands Cancer Institute

Publication date: 22-05-2024

Introduction

Endometrial cancer is the fifth most common cancer in women and, along with cervical cancer, accounts for 0.7% of all cancer-related deaths. MRI plays a crucial role in the local staging of endometrial cancer, guiding surgical treatment and identifying candidates for fertility-preserving strategies. The main risk factors assessed on imaging are depth of myometrial invasion, cervical/bladder/rectal invasion, and lymph node involvement.

Contents

  • MR Reporting Checklist
  • MR Anatomy
  • Staging Endometrial Cancer
  • Non-Tumor (Benign) MRI Findings
  • Lymph Node Detections
  • MR Protocol & Sequence Planning
  • Pitfalls
  • Fertility Preservation
  • FIGO Staging (2023)
  • Best Practices for Clinical Accuracy
  • References

MR Reporting Checklist

  • Tumor size (longest diameter, all planes)
  • Myometrial invasion: none, <50% (Stage IA), ≥50% (Stage IB)
  • Cervical stromal invasion (Stage II)
  • Serosal/adnexal invasion (Stage IIIA)
  • Vaginal/parametrial involvement (Stage IIIB)
  • Lymph node status: pelvic (IIIC1), para-aortic (IIIC2)
  • Bladder/rectal mucosal invasion (Stage IVA)
  • Distant metastases (Stage IVB): list sites
  • Benign mimics (fibroids, adenomyosis, etc.)
  • Diagnostic uncertainties and recommended further tests
Include also benign conditions (endometriosis, leiomyoma), anatomical variants, total uterine size (impacts surgical approach), and fertility preservation eligibility.

MR Anatomy

  • T2-weighted MRI best displays uterine anatomy.
  • Three layers (reproductive age):
    • Endometrium (high signal)
    • Junctional zone (low signal)
    • Myometrium (relatively high signal)
  • Postmenopausal: zonal anatomy less visible; uterus shrinks more than cervix.
  • Uterine position: varies (anteflexion, retroflexion, anteversion, retroversion).

Staging Endometrial Cancer

Tumor Size:
  • Typically hyperintense or hypointense (age-dependent) on T2W.
  • Measure longest diameter in the best plane (sagittal or axial).
  • Normal endometrial thickness varies:
    • Premenopausal: ≤16 mm
    • Postmenopausal (no bleeding): <11 mm
    • Postmenopausal (bleeding/tamoxifen): <5 mm
Atypical Enhancement Patterns: Most tumors are hypovascular, but some (e.g., sarcomatoid) are hypervascular or enhance similarly to myometrium.
Myometrial Invasion:
  • Use sagittal and perpendicular axial planes.
  • Measure ratio of tumor invasion to full myometrial thickness.
  • <50%: superficial; >50%: deep (higher risk).
  • Absence of invasion is key for fertility sparing.
  • DWI and contrast-enhanced images aid delineation.
  • Pitfall (expansion vs invasion): Expansion may mimic invasion; an intact junctional zone rules out invasion.
Cervical Stromal Invasion: Seen as disruption of low signal on T2W or enhancement on CE images. Distinguish from tumor protrusion into the cervical canal (not true invasion).
Extrauterine Extension: Rare; seen as direct invasion of bladder, rectum, or beyond serosa. Presence indicates advanced disease and affects surgical planning.
Lymph Node Staging:
  • Regional nodes: pelvic and para-aortic up to renal veins
  • Distant nodes: above renal veins, inguinal
  • Sentinel node mapping and/or lymphadenectomy usually performed during surgery.
Hematogenous Metastases: Most often peritoneum or lung (e.g., ascites, omental cake).
FIGO Staging MRI Findings (2023):
  • Stage I: Tumor confined to the uterus
    • IA: Tumor limited to the endometrium or invades less than half (<50%) of the myometrium.MRI: Tumor does not breach the inner half of the myometrium; junctional zone may remain partially preserved.
    • IB: Tumor invades one half or more (≥50%) of the myometrium.MRI: Tumor extends into the outer half of the myometrium, with loss of the normal low-signal intensity of the junctional zone.
  • Stage II: Cervical stromal invasion, but not extending beyond the uterus.
  • Stage III (Locally Advanced Disease):
    • IIIA: Tumor invades the serosa of the corpus uteri and/or adnexa (ovaries/fallopian tubes).MRI: Disruption of the uterine serosa by tumor, or direct invasion into the ovaries/fallopian tubes.
    • IIIB: Vaginal and/or parametrial involvement.MRI: Tumor signal extends into the vagina or parametrial tissues.
    • IIIC: Lymph node involvement.
      • IIIC1: Pelvic lymph node metastases
      • IIIC2: Para-aortic lymph node metastases (with or without pelvic node involvement)
      MRI: Enlarged, round, or irregular lymph nodes in the pelvic or para-aortic regions.
  • Stage IV (Metastatic Disease):
    • IVA: Invasion of bladder and/or rectal mucosa.MRI: Tumor breaches the bladder or rectal wall, often with loss of fat planes.
    • IVB: Distant metastases (including intra-abdominal, intra-abdominal organs, inguinal lymph nodes, lung, liver, bone, etc.).MRI/CT: Lesions in distant organs (e.g., liver, lung, bone), omental caking, ascites, or involvement of inguinal nodes.

Non-Tumor (Benign) MRI Findings

MRI for endometrial cancer staging may also reveal non-tumor (benign) conditions that impact clinical management, surgical planning, or patient counseling:

  • Endometrial Polyps: Focal, well-defined, intracavitary masses often with a central fibrous core; may mimic tumor but lack myometrial invasion.
  • Leiomyomas (Fibroids): Well-circumscribed, low T2 signal masses within myometrium; may distort uterine anatomy or mimic serosal invasion when subserosal.
  • Adenomyosis: Thickened junctional zone (>12mm), small myometrial cysts, ill-defined low T2 signal areas within myometrium.
  • Endometriosis: Ovarian endometriomas (T1 hyperintense, T2 shading), deep infiltrating lesions in pelvic ligaments or rectovaginal septum.
  • Cysts and Hydrosalpinx: Thin-walled fluid-filled adnexal cysts or tubular structures (hydrosalpinx).
  • Congenital Uterine Anomalies: Septate, bicornuate, didelphys uterus, etc., identified by abnormal uterine contour or cavity division.
  • Other Pelvic Masses: Ovarian cysts, paraovarian cysts, benign lymphadenopathy.

Accurate identification and reporting of these findings is essential, as benign conditions may alter surgical approach, mimic malignancy, or explain patient symptoms.

Lymph Node Detections

MRI evaluation of lymph nodes is crucial for accurate staging of endometrial cancer, impacting treatment planning and prognosis. Lymph node status distinguishes between Stage IIIC1 (pelvic nodes) and Stage IIIC2 (para-aortic nodes), and distant (M) stage if above the renal veins or inguinal.

  • Pelvic Lymph Nodes (IIIC1): Includes nodes along the iliac vessels, obturator, presacral, and parametrial regions.MRI: Enlarged (>10 mm short axis), round, irregular borders, loss of fatty hilum, or heterogeneous signal/contrast enhancement.
  • Para-aortic Lymph Nodes (IIIC2): Nodes along the aorta up to the renal veins.MRI: Similar criteria as pelvic, but location is above bifurcation and below renal veins.
  • Distant (M-stage) Nodes: Nodes above renal veins or inguinal.These are considered distant metastases (Stage IVB), not regional.
  • Imaging Features Suggestive of Metastatic Involvement:
    • Short axis diameter >10 mm (pelvic) or >8 mm (inguinal)
    • Round shape rather than ovoid
    • Irregular margins or extracapsular spread
    • Central necrosis or cystic change
    • Abnormal contrast enhancement
  • Pitfall: Small lymph nodes (<10 mm) can still harbor metastases. PET-CT or surgical sentinel node mapping may be considered for higher sensitivity.

Accurate identification and characterization of lymph nodes on MRI is essential for assigning FIGO stage and guiding multidisciplinary management.

MR Protocol & Sequence Planning

  • Field strength: 1.5T or higher, pelvic phased-array coil
  • Patient: supine, fasting (4–6 hr), empty bladder, antiperistaltic agents (Buscopan/Glucagon)
  • Saturation bands: anterior & posterior fat
  • Contrast-enhanced images: after 2.5 min; DCE preferred for fertility cases
  • Sequence planning:
    • Axial: perpendicular to uterine cavity
    • Coronal: parallel to uterine cavity
DCE Phases:
  • Early (30–60s): sub-endometrial enhancement (fertility sparing eligibility)
  • Equilibrium (120–180s): myometrial invasion
  • Delayed (4–5min): cervical stromal invasion

Pitfalls

  • Uterine anatomy/position variations: Plan sequences based on uterine flexion/version.
  • Bladder filling: alters uterine position during MRI.
  • Technician training: essential for correct plane planning; radiologist supervision recommended.

Fertility Preservation

  • Hormonal therapy in select patients only.
  • Criteria: Tumor confined to endometrium (intact sub-endometrial line on early DCE).
  • DCE imaging is mandatory in young patients considered for fertility preservation.
  • Fusion of T2W and DWI can aid exclusion of myometrial invasion.

FIGO Staging (2023)

  • Imaging, especially MRI, is now integrated into staging and treatment planning.
  • 2023 system incorporates molecular profiles (POLEmut, MMRd, p53abn, NSMP) which can modify stage and adjuvant therapy recommendations.
  • See complete FIGO guidelines for latest details.

Best Practices for Clinical Accuracy

  • Clinical Content Validation: All staging, reporting, and criteria must be based on the latest international guidelines (e.g., FIGO 2023, ESGO/ESTRO/ESP). Content should be reviewed by a board-certified radiologist and gynecologic oncologist.
  • Image Agent Accuracy: If using an AI model, it must be validated on large, diverse datasets. Always provide confidence scores and state that results are for assistance only.
  • Checklist & Workflow: Use structured reporting checklists with mandatory fields. Implement logic checks (e.g., cannot be Stage IB with no myometrial invasion).
  • Pitfalls and Differential Diagnosis: Explicitly list common diagnostic pitfalls and show how to distinguish benign conditions from malignancy.
  • Lymph Node and Metastasis Detection: Use standardized size and morphology criteria. Highlight that small nodes can harbor metastases and recommend further action if needed.
  • Staging Details: Clearly distinguish all substages and consider including decision trees or flowcharts.
  • Continuous Updates: Monitor for guideline updates and allow users to report errors.
  • Disclaimers: Prominently display that the app is an adjunct, not a replacement for expert review.

Final Recommendations

  • Peer review all medical logic and UI by domain experts.
  • Provide clear user guidance for ambiguous or rare findings.
  • Log user feedback and diagnostic discrepancies for continuous improvement.

References

For educational and clinical guidance purposes. Always refer to the latest protocols and multidisciplinary team input for patient management.