Ultrasound and the IOTA system
Ultrasonography is the primary modality in oncogynecology. For differential diagnosis, the IOTA (International Ovarian Tumour Analysis) system is applied, dividing ultrasound features into two groups:
- B-features (benign): unilocular cyst, acoustic shadows, absence of blood flow, solid component less than 7 mm, or multilocular tumor up to 100 mm.
- M-features (malignant): irregular solid tumor, ascites, more than 4 papillary structures, intense blood flow, and multilocular-solid lesions measuring 100 mm or more.
If only features of a single group are detected, the prediction has high accuracy. When B- and M-features are combined or absent, the mass is considered indeterminate, and an MRI is ordered. Color Doppler mapping (CDM) is also used: malignant nodes frequently demonstrate neovascularization (vessels lacking smooth muscle walls).
Computed tomography and staging
Computed tomography is used for preoperative FIGO staging and determining the extent of cytoreductive surgery.
- Stage I (tumor limited to ovaries/fallopian tubes): CT visualizes altered ovaries. If capsule rupture occurs or malignant cells are found in ascites (Stage IC), the tumor appears as a cystic-solid mass with irregular contours and thick septations.
- Stage II (pelvic extension): CT shows effacement of the fat plane between the uterus and the tumor. A distance of less than 3 mm between the pelvic wall, rectum, or urinary bladder and the tumor mass indicates invasion into these structures.
- Stage III (peritoneal spread outside the pelvis and lymph node involvement): enlarged retroperitoneal lymph nodes (10 mm or greater) are identified. A characteristic feature is omental caking (omental cake). Small peritoneal implants are not visualized on CT.
- Stage IV (distant metastases): pleural effusion or metastases to the liver parenchyma and supradiaphragmatic lymph nodes.
The role of MRI and PET/CT
MRI is a problem-solving modality with an overall diagnostic accuracy of 93%. The protocol strictly includes standard T1- and T2-weighted images, diffusion-weighted imaging (DWI), and dynamic contrast-enhanced MRI. Diagnosis is established if at least one major criterion (size greater than 4 cm, cyst with a solid component, septal or wall thickness >3 mm, necrosis) and one minor criterion (pelvic organ involvement, omental spread, ascites, lymphadenopathy) are present.
Peritoneal metastases and omental caking are best visualized on delayed contrast-enhanced MR scans (strictly at 5 minutes) and show restricted diffusion on DWI. Waiting longer than 5 minutes is unacceptable, otherwise, the ascites will take up contrast and obscure small implants.
PET/CT is not used for primary staging, but it is critical for diagnosing recurrences. The method detects complex hidden implants (e.g., in the small bowel mesentery) when tumor markers are rising while conventional CT and MRI yield negative results.
Morphology and routes of spread
The morphological pattern of epithelial cancer is variable: it can present as multilocular cysts with solid areas or lobulated papillary formations. Serous carcinomas often contain coarse amorphous calcifications, while mucinous carcinomas feature high-density cyst contents (proteinaceous fluid).
The most common pathway of metastasis is intraperitoneal dissemination. Implants settle in the rectouterine pouch (cul-de-sac), paracolic gutters, intestinal surfaces, omentum, and beneath the diaphragm. Ascitic fluid outlines these nodes, making them easier to spot. Notably, the CT appearance of gastrointestinal metastases to the ovary is identical to primary ovarian cancer, so the stomach and colon must always be thoroughly evaluated.
For rapid estimation of FIGO stages: I — strictly in the ovaries, II — extended into the pelvis, III — disseminated across the peritoneum (omentum) and lymph nodes, IV — spread beyond the abdomen (liver, pleura).
Class and exam questions
Does the presence of ascites affect the stage of ovarian cancer?
Ascites by itself does not alter the stage. It affects staging (shifting to stage IC3) only if malignant cells are cytologically detected in the ascitic fluid.
Why is it prohibited to acquire delayed MRI scans later than 5 minutes?
After 5 minutes, the contrast agent begins to penetrate the ascitic fluid. It starts to enhance on scans, masking small peritoneal implants.
Which CT findings make a tumor unresectable?
Surgically challenging (difficult to resect) lesions include subcapsular liver metastases, implants along the diaphragm, in the porta hepatis, gallbladder fossa, and small bowel mesentery.
What else to study on this topic
- MRI criteria for malignancy of adnexal masses
- Features of malignant tumor neovascularization on ultrasound
- Nuances of ovarian cancer staging according to the FIGO classification
- Differential diagnosis of primary cancer and ovarian metastases
- Diffusion restriction on DWI in peritoneal carcinomatosis
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