Staging

Traditionally, ovarian cancer was staged surgically, based on the International Federation of Obstetrics and Gynecology (FIGO) classification system. However, current state-of-the-art imaging modalities have been shown to play a potential role in non-invasive preoperative staging.

Intraperitoneal dissemination is the most common route of ovarian cancer spread, rather than solid organ parenchymal metastases in many malignancies. Peritoneal implants usually occur on the surfaces of the viscera rather than as masses within the viscera (Fig. 5-10). These tumor implants can be miliary and isoattenuating relative to the viscera at CT, which makes their detection challenging.55 When visible on CT, the peritoneal implants manifest as nodular soft tissue thickening that can coalesce to form plaques that coat the viscera.55 The most commonly involved locations are the peritoneal reflections, such as cul-de-sac, paracolic gutters, as well as subdiaphrag-matic space, splenic hilum, porta hepatis, and locations along the falciform ligament. Other common locations include the ileocecal valve and the rectosigmoid junction. Diffuse infiltration of the omentum by tumor may occur and is called omental caking.22 The nodular soft tissue thickening may also grow along and scallops the surfaces of solid organs such as liver and spleen.55 The implants may enhance with administration of intravenous contrast material or may calcify. Some implants can be hypoattenuating and mimic loculated fluid.51 When deposited on bowel, the tumor implants can cause tethering of bowel loops and lead to bowel obstruction. In fact, intestinal and ureteral obstructions have been reported as the two most common forms of tumor-induced morbidity in patients with ovarian cancer.84

Lymph node metastases in ovarian cancer constitute an important adverse prognostic factor. The pathways of ovarian cancer nodal dissemination are related to ovarian lymphatic drainage. Most commonly, nodal metastasis in ovarian cancer

Ovarian Cancer Staging

Figure 5-10. A 56-year-old woman with ovarian cancer. A, Axial contrast enhanced CT of the abdomen demonstrates extensive peritoneal carcinomatosis involving the liver capsule (arrowheads) and subdiaphragmatic space (arrow). B, Sagittal T2-weighted MRI of the pelvis demonstrates plaque-like nodular soft tissue thickening along the peritoneal reflection in the pelvis (arrows) that cannot be separated from adjacent bowel surface.

Figure 5-10. A 56-year-old woman with ovarian cancer. A, Axial contrast enhanced CT of the abdomen demonstrates extensive peritoneal carcinomatosis involving the liver capsule (arrowheads) and subdiaphragmatic space (arrow). B, Sagittal T2-weighted MRI of the pelvis demonstrates plaque-like nodular soft tissue thickening along the peritoneal reflection in the pelvis (arrows) that cannot be separated from adjacent bowel surface.

ascends along the gonadal vessels to the retroperitoneum. Dissemination of disease also occurs along the broad ligament that may result in internal iliac, obturator, and external iliac adenopathy. Occasionally, tumor may reach the superficial and deep inguinal nodes via the round ligaments.22 For diagnosing nodal metastases in patients with ovarian cancer, nodes larger than 1 cm in the short axis are considered abnormal on imaging.55 However, using size and shape criteria, imaging is not accurate for diagnosing nodal metastases (reported sensitivity and specificity of 43% and 89% for CT and 38% and 84% for MRI), since a lymph node can be enlarged owing to benign etiology such as inflammation and hyperplasia, whereas a malignant lymph node harboring a small amount of metastasis may not be abnormally enlarged.49,85 Therefore, investigations are being carried out on the use of new lymphotrophic contrast agents, such as ultra-small iron oxide particles, to detect metastatic lymph nodes. These contrast agents are taken up by benign lymph nodes but not by metastatic lymph nodes. Therefore, benign lymph nodes demonstrate reduced signal intensity on MRI after administration of lymphotrophic contrast agents, whereas metastatic lymph nodes remain high in signal intensity. Preliminary results have shown that these contrast agents have great promise for the detection of nodal metastases.86,87 Distant metastasis is relatively rare at the time of diagnosis. The potential locations that may be involved include the liver, lung, pleura, adrenal gland, and spleen. CT and MRI are both commonly performed to evaluate liver parenchymal metastases. Thoracic metastases are typically preceded either by abdominal or pelvic disease or by a rise in tumor markers, and they are best detected with CT.55,88 Pleural effusion in a patient with ovarian cancer is a nonspecific finding and by itself can be benign or malignant. Pleural thickening or nodularity indicates a malignant nature. In the absence of these findings on imaging, thoracentesis may be indicated for a cytology diagnosis.22 Bone and brain metastases are very rare.22 It should be noted that peritoneal implants on the surface of solid organs such as liver indicate stage III disease with peritoneal spread and carry different staging and clinical implications than parenchymal metastases (stage IV disease with hematogenous spread). However, at times tumor implants may mimic parenchymal lesions on imaging, especially when they grow deep into the liver along the falciform ligament. State-of-the-art thin-section multidetector helical CT with multiplanar data review capability, in addition to MRI with its intrinsic multiplanar capability, are valuable in differentiating solid organ surface implants and parenchymal metastases.

Studies have shown that in the staging of ovarian cancer CT and MRI are of equal accuracy and are more accurate than ultrasound.49,89 The overall accuracy of CT for predicting stage is 73% to 77%.50,52,89 Accuracy is lower for stages I or II disease at around 55%, and for stage III or IV disease it is around 89%.50 Specifically in the depiction of peritoneal metastases with CT, the overall accuracy may be as high as 89% to 95%, although sensitivity for metastases 1 cm or smaller in maximum diameter (25% to 50%) was significantly lower than overall sensitivity (85% to 93%).90 In addition, implants on mesentery and small bowel are also difficult to detect with either CT or MRI, presumably because of partial-volume averaging and physiologic bowel motion.89 Although the overall staging accuracy of CT is only moderate, prediction of tumor resectability is excellent, with a positive predictive value for cancer nonresectability of up to 100%, and a negative predictive value up to 92%.50,89 The parameters on preoperative CT that were significantly associated with residual disease were ascites, omental cake, mesenteric disease, paracolic gutter deposits, diaphragmatic deposits, and pleural effusion.50

The accuracy of ovarian cancer staging by MRI has been reported to be similar to that of CT, at around 75% to 78% when contrast-enhanced images are obtained.89,91 Evaluation of pelvic cancer extent is better with MRI than with CT, owing to the superior soft tissue contrast and multiplanar imaging capabilities of MRI. However, there is no difference in the detection of abdominal disease with these two modali-ties.89 Similar to CT, MRI is highly accurate in predicting inoperable tumor and suboptimal debulking preoperatively in newly diagnosed ovarian cancer, with reported positive and negative predictive values higher than 90%.89,92 This suggests that imaging may help to select patients who might be more appropriately managed by neoadju-vant chemotherapy.92 For disease in the greater omentum and lesser sac, MRI is less accurate.85

Fused PET-CT is particularly helpful when implants are present on or near bowel loops.55 Metastatic lesions from ovarian cancer including peritoneal implants and metastatic lymph nodes are FDG-avid,55 although necrosis within a tumor and/or lymph node can appear as a photopenic area.55 Standardized uptake values (SUV) should be routinely measured and reported. It is generally accepted that a standardized uptake value of less than 2 to 3 indicates malignancy.

When thoracic metastases are present, increased uptake may be seen in the pleural effusions and thoracic adenopathy.55 However, one pitfall is that metastases from mucinous adenocarcinoma of the ovary may not be associated with increased metabolic activity and could be underdiagnosed by PET (Fig. 5-11). In the abdomen, FDG-PET was found to be more sensitive in the retroperitoneal than in the intra-peritoneal region.93 The data regarding combined FDG-PET/CT in the evaluation of ovarian malignancy are still emerging. In a study by Yoshida and colleagues94 on preoperative tumor staging, CT alone had an accuracy of 53%, whereas FDG-PET evaluated in conjunction with CT had an accuracy of 87%. Another study demonstrated that FDG-PET and CT had a relatively low sensitivity for the detection of peritoneal metastases, indicating that surgical staging should remain the gold standard. Nevertheless, FDG-PET had a higher specificity and may be useful for evaluating residual or recurrent disease after surgery.

Figure 5-11. A 22-year-old woman with metastatic mucinous adenocarcinoma of the ovary. A, Axial contrast-enhanced CT image of the thorax displayed in lung window demonstrates a lobulated nodule in the right lower lobe. Multiple additional nodules are present in the lungs (not shown). B, Axial FDG-PET image of the thorax shows a maximum standardized uptake value of only 1.0 in the right lower lobe nodule. Subsequent surgical pathology confirmed this nodule to be a metastasis from the ovarian mucinous adenocarcinoma. (We thank Dr. Pek Lan Khong at the Department of Diagnostic Radiology, University of Hong Kong for providing these images.)

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