Low-grade epithelial ovarian cancer: what a radiologist should know

Abstract

Ovarian cancer accounts for the death of over 100,000 females every year and is the most lethal gynecological malignancy. Low-grade serous ovarian carcinoma (LGSOC) and high-grade serous ovarian carcinoma (HGSOC) have been found to represent two distinct entities based on their molecular differences, clinical course, and response to chemotherapy. Currently, all ovarian cancers are staged according to the revised staging system of the International Federation of Gynecology and Obstetrics (FIGO). Imaging plays an integral role in the diagnosis, staging, and follow-up of ovarian cancers. This review will be based on the two-tier grading system of epithelial ovarian cancers, with the main emphasis on serous ovarian cancer, and the role of imaging to characterize low-grade vs high-grade tumors and monitor disease recurrence during follow-up.

Figure 1.

Illustration of the current FIGO staging system for ovarian cancer. Stage I ovarian tumors are subdivided into three major subtypes. Stage IA (a) is for tumors found in one ovary (with an intact capsule) or fallopian tube. Stage IB is designated for tumors involving either both ovaries (with intact capsules) or fallopian tubes. Stage IC (b) include the findings in any of the previous two stages in addition to either intraoperative surgical spill (IC1), pre-operative capsule rapture (IC2) or malignant ascites/ peritoneal washing (IC3). Stage II involves tumors in one or both ovaries or fallopian tubes extending either to the surface of the uterus or the fallopian tube, which is Stage IIA (c) or to the pelvic intraperitoneal organs below the pelvic brim such as the rectum and urinary bladder, which is Stage IIB (d). Stage III ovarian tumor (e) spread to the abdominal area through peritoneal spread. Stage IIIA1 involves spread to the retroperitoneal lymph nodes and it is further subdivided, based on the size of the metastases in the lymph nodes, into Stage IIIA1(i) if it is <10 mm and Stage IIIA1(ii) if it is >10 mm. Patients with microscopic extrapelvic peritoneal spread (above the pelvic brim) are considered Stage IIIA2, regardless of the state of retroperitoneal lymph node involvement. While females with macroscopic extrapelvic peritoneal spread are staged according to the size of these metastases into Stage IIIB if <2 cm and IIIC if >2 cm, with or without positive retroperitoneal lymph nodes. Furthermore, tumor spread to the capsule of the liver or spleen is within the scope of Stage IIIC as long as the parenchyma is spared. Stage IV includes distant metastases, and it is further subdivided into two stages. Stage IVA (f) includes patients with malignant pleural effusion and a positive cytology, while Stage IVB encompasses metastases to visceral organs such as the liver, spleen, and intestine, including parenchymal or transmural extension, in addition to extra abdominal spread as supraclavicular and inguinal lymph nodes. FIGO, International Federation of Gynecology and Obstetrics.

Figure 2.

48-year-old female with low-grade serous ovarian carcinoma that presented with a back pain of 1 year duration. (a) and (b) Axial contrast-enhanced CT images of the pelvis demonstrate a complex cystic and solid mass (dotted white arrow) within the right adnexa measuring approximately 6 × 6 cm, with associated calcification (black arrowhead) in the mass. Diffuse largely calcified omental thickening (white arrows) is also noted, representing peritoneal carcinomatosis. (c) and (d) Axial contrast-enhanced CT images of the pelvis, 2 months after the patient underwent optimal tumor reductive surgery and started chemotherapy, depict residual calcified peritoneal implants in the gastrohepatic ligament region (black arrowhead), anterior to the gallbladder fossa (white arrowhead), and anterior to the spleen (white arrow). (e) and (f) Axial contrast-enhanced CT image (e) and Axial fused PET/CT image (f) of the pelvis, 4 months later, show small regression in the size of the previously noted calcified peritoneal implants anterior to the gallbladder fossa (white arrowhead) and anterior to the spleen (white arrow) without evidence of F-18 FDG avidity. No evidence of new metastatic disease. PET, positron emission tomography.

Figure 3.

45-year-old female with low-grade serous ovarian carcinoma that presented with vague abdominal pain. (a), and (b), Axial contrast-enhanced CT images of the pelvis demonstrate bilateral adnexal masses; large left adnexal mass (white arrow) with focal areas of calcifications (black arrowhead) and calcified right ovarian mass (black arrow). Calcified implants (white arrowhead) are also seen along the peritoneal lining representing peritoneal carcinomatosis.

Figure 4.

65-year-old female with recurrent LGSOC. The recurrent disease was treated with chemotherapy, hormonal therapy, and recently radiotherapy. (a) and (b) Follow-up axial contrast-enhanced CT images of the pelvis shows metastatic calcified peritoneal implants (black arrowheads). There is also a large mass of high attenuation (black arrow) within the pelvis. (c) and (d) Follow-up axial contrast-enhanced CT images of the pelvis, after 6 months, demonstrate a reduction in the size of the previously noted calcified implants (black arrowheads) in the pelvis. Implant identified anterior to the rectum (black arrowhead) is also significantly smaller in comparison to the prior study. (e) and (f) Follow-up axial T₂ weighted (e) and sagittal T₂ weighted (f) MR images of the pelvis, after 2 years, show disease progression with the metastatic implant (black arrows) in the left mesorectum appearing larger in size. LGSOC, low-grade serous ovarian carcinoma.

Figure 5.

34-year-old female with low-grade mucinous carcinoma of the ovary that presented with pelvic pressure. (a) and (b) Axial T₁ weighted Fat sat (a) and axial T₂ weighted (b) pelvic MR images show a complex multicystic, multiseptated right ovarian mass (white arrows) measuring approximately 14 × 9 cm. The mass is displacing surrounding structures and depicts varying regions of signal intensity consisting of hemorrhage components (black asterisks). The patient underwent optimal cytoreductive surgery and completed four cycles of chemotherapy. She had regular follow-up with no evidence of the disease. (c) and (d) Axial contrast-enhanced CT images of the pelvis obtained nearly 5 years later when the patient presented to the ER with acute abdominal pain. The images show stranding and nodularity within the right lower quadrant adjacent to the cecum (black arrowhead). Some haziness is also noted within the transverse mesocolon (white arrowhead). The findings are suggestive of a recurrent disease.

Figure 6.

34-year-old female with low-grade endometrioid adenocarcinoma involving the left ovary. (a) and (b) Pre-treatment axial T₁ weighted fat sat (a) and axial T₂ weighted (b) MR images of the pelvis shows a large mass (white arrows) within the left ovary, which has solid and cystic components and has some internal hemorrhage (white arrowhead). The patient underwent bilateral salpingo-oophorectomy and omentectomy. (b) Follow-up axial T₂ weighted MR image of the pelvis shows the uterus (U) with no pelvic mass lesions identified.