Comparison of Imaging Modalities
To select the optimal treatment plan, it is critically important to choose the appropriate diagnostic imaging modality:
- MRI is the preferred modality. It accurately determines tumor localization (exophytic or endocervical), distance to the internal os, and the length of the intact cervical portion (which is essential for fertility-sparing trachelectomy).
- Contrast-enhanced CT is primarily used for assessing advanced disease, planning radiation therapy, and detecting enlarged lymph nodes. It is inferior to magnetic resonance imaging in pelvic soft tissue detail.
- FDG-PET/CT is indispensable in staging advanced disease to search for distant metastases and lymphatic involvement. In early stages (I–IIa), routine application of this modality is considered impractical.
MRI features of early stages (FIGO I–II)
Assessment is performed primarily using T2-weighted images (T2WI), where the pathological lesion shows intermediate or high signal intensity against the background of low signal intensity of the fibrocervical stroma.
- Stage I (tumor confined to the cervix). In stage Ia, changes are diagnosed only microscopically, and imaging is not indicated except when preparing for fertility-sparing surgery. In Ib, a distinct mass is visualized. The stromal ring remains intact, completely ruling out parametrial spread.
- Stage II (extension beyond the uterus).
- In IIa, the tumor extends to the upper 2/3 of the vagina: tomograms show disruption of the low signal of the vaginal wall.
- In IIb, parametrial invasion is diagnosed. Destruction of the stromal ring is noted, along with the appearance of spiculated strands between the cervix and parametrial adipose tissue, up to encasement of the uterine vessels.
MRI features of advanced stages (FIGO III–IV)
In advanced stages, the tumor extends far beyond the primary site, requiring careful evaluation of neighboring structures and urinary outflow tracts.
- Stage III. Variant IIIa is characterized by extension to the lower third of the vagina. Variant IIIb is assigned if the tumor masses approach the pelvic sidewall or iliac vessels closer than 3 mm. This stage also includes the development of hydronephrosis (or a non-functioning kidney) due to ureteral compression.
- Stage IV. Substage IVa involves direct invasion into the bladder or rectal mucosa. Perivesical and perirectal fat planes disappear on scans. Substage IVb reveals distant metastases. Notably, involvement of inguinal or para-aortic nodes (above the renal hila) is classified as stage IVb, whereas metastases solely within pelvic drainage basins do not affect staging.
Role of PET/CT in metastatic assessment
Standard CT and MRI rely solely on lymph node size criteria, which inevitably leads to missing micrometastases. Fluorodeoxyglucose PET has a sensitivity of up to 100% in detecting lymphatic dissemination.
Starting from stage IIb, performing a PET/CT can drastically alter management strategy. The maximum standardized uptake value (SUVmax) of the primary lesion and pelvic lymph nodes serves as a powerful prognostic biomarker, allowing prediction of the risk of local recurrence and overall survival. In established recurrence, it is used in conjunction with MRI to determine indications for pelvic exenteration.
Briefly: answers to topical questions
What are the main differences in the capabilities of MRI, CT, and transvaginal ultrasound in evaluating pelvic soft tissues?
- Transvaginal ultrasound (Transvaginal US) — has low soft tissue contrast and limited utility for detecting cervical cancer, determining the depth of stromal invasion, or assessing parametrial spread.
- Contrast-enhanced CT (Contrast-enhanced CT) — may be useful for local staging, but is primarily used in advanced disease to evaluate lymph nodes and search for distant metastases.
- MRI (MRI) — is the modality of choice for locoregional staging, allowing precise determination of tumor size, localization, depth of stromal invasion, and local spread.
FIGO MRI ladder: I — cervix only (tumor bright against dark stroma); II — parametrial extension (dark ring breached); III — renal obstruction (hydronephrosis) or pelvic sidewall (<3 mm); IV — fat plane obliterated between bowel/bladder.
Class and exam questions
Is bullous edema a sign of bladder invasion (stage IVa)?
No, bullous edema alone does not confirm stage IVa. Visualization of obliterated fat planes and disrupted mucosal signal intensity is required, which is then confirmed by biopsy.
Do pelvic lymph node metastases affect the FIGO stage?
No, pelvic lymph node involvement does not change the FIGO stage. However, metastases to para-aortic or inguinal lymph nodes upstage the disease to stage IVb.
Why is MRI usually not ordered in stage Ia?
In stage Ia, the depth of invasion is less than 5 mm; such microscopic changes are not visualized on MRI, except when planning a trachelectomy.
What else to study on this topic
- CT semiotics of advanced cancer: assessment of hydronephrosis and lymphadenopathy
- Prognostic significance of the SUVmax biomarker in PET/CT
- Imaging diagnostics of ovarian cancer: ultrasound, CT patterns of ascites and peritoneal dissemination
- Criteria for unresectable pelvic disease and indications for neoadjuvant chemotherapy
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