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Clinical Observations |
1 Department of Radiology, Research Institute and Hospital, National Cancer
Center, 809 Madu 1-dong, Ilsan-gu, Koyang, Kyonggi, Korea.
2 Department of Gynecologic Oncology, Research Institute and Hospital, National
Cancer Center, Koyang, Kyonggi, Korea.
3 Department of Pathology, Research Institute and Hospital, National Cancer
Center, Koyang, Kyonggi, Korea.
Received June 3, 2005;
accepted after revision October 21, 2005.
Address correspondence to H. J. Choi.
Abstract
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CONCLUSION. On contrast-enhanced CT scans, ovarian metastatic lesions from stomach cancer appear more solid than, more frequently have dense enhancement of the solid portion, and are smaller than ovarian metastatic lesions from colon cancer.
Keywords: cancer • CT • metastasis • oncologic imaging • ovary • pelvic imaging
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A number of studies have highlighted the CT and MRI findings of Krukenberg tumors [13-19]. Most of these investigations showed that differentiation between metastatic and primary tumors on the basis of imaging findings is almost impossible [17-20]. Some authors, however, reported findings suggestive of Krukenberg tumors [13-16]. CT showed that Krukenberg tumors were solid ovarian tumors containing well-demarcated intramural cysts that have apparently strong contrast enhancement [14]. In a previous study we found that on CT scans, ovarian metastatic lesions from colon cancer had smooth margins and were more cystic than primary malignant ovarian tumors [13]. To our knowledge, however, there has been no CT documentation of differentiation between ovarian metastasis from stomach cancer and that from colon cancer. In this study, we investigated whether CT can be used to differentiate ovarian metastasis from stomach cancer and ovarian metastasis from colon cancer.
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Our institutional review board did not require its approval for this study.
CT Image Acquisition
All CT data were obtained with a 4-MDCT scanner (Mx 8000, Philips Medical
Systems). Preoperative CT scans were obtained in a single institution an
average of 22 days before surgery (range, 2-50 days). Patients received IV
contrast material (iopromide; Ultravist 300, Schering) in an antecubital vein
via mechanical injector; 140 mL of the agent was administered at a rate of 2.3
mL/s. Scanning began 70 or 80 seconds after the start of IV injection of
contrast material and covered the region from the diaphragm to the lower
pelvis. Scanning parameters included a detector array of 4 x 1.25 mm,
beam pitch of 1.35, section thickness of 3.2 mm, and a reconstruction
increment of 3 mm.
Image Interpretation
CT images were interpreted retrospectively by consensus of two radiologists
unaware of the histologic results. The radiologists had three and four years
of experience in gynecologic imaging, including CT. All CT images were
randomized before interpretation to decrease selection bias.
The following characteristics of each ovarian mass were recorded: laterality, size (longest diameter in axial scan), margin (smooth versus irregular), shape (oval versus nonoval), mass characteristics (cystic; mainly cystic, i.e., more than two-thirds of the mass; mainly solid, i.e., more than two thirds of the mass; solid), enhancement of the solid portion (none; mild, i.e., less than that of the junctional zone of the myometrium; moderate, i.e., equal to or more than that of the outer myometrium; and dense, i.e., equal to or more than that of the outer myometrium), amount of ascites (none; mild, i.e., few collections of fluid and largest dimension generally less than 3 cm; moderate, i.e., multiple collections and smallest dimension more than 3 cm; and severe, i.e., generalized fluid, floating bowel), peritoneal seeding (peritoneal carcinomatosis, including omental, mesenteric, peritoneal, and serosal deposits; perihepatic, perisplenic, gastrohepatic, and gastrosplenic ligaments), abdominal and retroperitoneal lymph node enlargement (> 1 cm in the largest short axis diameter), and presence of metastasis to abdominal solid organs.
Statistical Analysis
The Fisher's exact test was used to correlate statistical association
between binary dependent variables of the pathologic features of the ovarian
masses to variables of interest, including laterality, margin, shape, mass
characteristics, enhancement of the solid portion, amount of ascites, presence
of peritoneal seeding, lymph node enlargement, and presence of metastasis.
Odds ratio (or relative risk) and 95% CI were reported for each variable. We
used the independent samples t-test to compare tumor sizes and
patient ages between the two diseases. A p value less than 0.05 was
considered significant.
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Imaging Findings
The frequencies of imaging findings and their corresponding p
values are presented in Table
1. Mass characteristics of the two tumor types were distinct.
Ovarian metastatic lesions from stomach cancer (Figs.
1A,
1B, and
2) were more solid in nature
(cystic, 0% [0/13]; mainly cystic, 30.8% [4/13]; mainly solid, 15.4% [2/13];
solid, 53.8% [7/13]) than those from colon cancer (Figs.
3 and
4) (cystic, 6.5% [2/31]; mainly
cystic, 83.9% [26/31]; mainly solid, 6.5% [2/31]; solid, 3.2% [1/31])
(p < 0.001). The enhancement patterns of solid portions of the
masses were discrete (p = 0.013). Ovarian metastatic lesions from
stomach cancer displayed more prominent enhancement (none, 0% [0/13]; mild,
30.8% [4/13]; moderate, 15.4% [2/13]; dense, 53.8% [6/13]) than those from
colon cancer (none, 0% [0/29]; mild, 6.9% [2/29]; moderate, 82.8% [24/29];
dense, 10.3% [3/29]) (p = 0.01).
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Applying the imaging characteristics that masses with a mainly solid or solid nature and dense enhancement of the solid portion were ovarian metastasis from stomach cancer and that masses without these findings were from colon cancer, we accurately differentiated the origin of ovarian metastasis in 32 (72.7%) of 44 cases. The ovarian metastatic lesions from colon cancer were larger than ovarian metastatic lesions from stomach cancer (p = 0.006). In addition, patients in the former group were older than those in the latter group (p = 0.007). No differences were evident between the two patient groups in laterality, shape, margin, amount of ascites, peritoneal seeding, abdominal retroperitoneal lymph node enlargement, and presence of metastasis.
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Misinterpretation of a metastatic ovarian tumor as a primary tumor may have adverse consequences for the patient, such as unnecessary surgery or inappropriate chemotherapy or radiation therapy. Therefore whenever adnexal masses are encountered, especially those with bilateral or smooth margins, ovarian metastasis is highly suspected. It has been proposed that an initial search be performed for a primary site in the gastrointestinal tract [13-20]. Accordingly for the management of ovarian neoplasms, differentiation between primary and secondary neoplasms is one of the principal roles of the radiologist. In our study, ovarian metastatic lesions were found without known primary cancer in two (6.5%) of the patients. In addition, although it is easy to find the primary site when the histologic type clearly indicates primary disease, in many instances the pathologic findings are ambiguous. In such cases, clinicians attempt to identify the primary disease according to the order of the likelihood of ovarian metastasis.
The results of our study strongly suggest that specific CT findings are useful for differentiation of ovarian metastasis from stomach cancer and from colon cancer. Our CT results showed that mass characteristics, laterality, enhancement pattern of the solid portion, and size are valuable parameters for differentiating ovarian metastasis from stomach cancer and from colon cancer. Specifically, 69.2% of ovarian metastatic lesions from stomach cancer were mainly solid or solid in appearance on CT scans, whereas only 9.7% of ovarian metastatic lesions from colon cancer displayed these patterns. These different imaging findings may arise from variations in primary sites and, consequently, in histologic type. The histologic type of all ovarian metastatic lesions from stomach cancer with a solid or mainly solid appearance was signet ring cell carcinoma, and 90.0% (9/10) of the ovarian metastatic lesions from stomach cancer that were of the signet ring cell type had a solid or mainly solid appearance. Ovarian metastasis from stomach cancer that had a histologic type other than signet ring cell carcinoma (adenosquamous cell carcinoma [n = 2], tubular adenoma [n = 1]) had a mainly cystic appearance. The histologic types of ovarian metastasis from colon cancer included tubular adenocarcinoma (n = 19) and mucinous adenocarcinoma (n = 12), 84.2% (16/19) and 96.7% (11/12) of the lesions displayed a cystic or mainly cystic appearance.
Histopathologically, metastatic colorectal cancer often simulates primary adenocarcinoma of the ovary [4, 22-25]. Metastatic colorectal adenocarcinoma forms large, complex glands and cysts that contain necrotic debris [25]. Although it is characteristic of metastatic colorectal adenocarcinoma, extensive necrosis also can occur in primary ovarian carcinoma [4]. We postulate that the more cystic nature of ovarian metastatic lesions from colon cancer compared with lesions from stomach cancer is attributable to this pathologic feature. This finding is consistent with our previous results [13]. Furthermore, the cystic nature of metastatic lesions from colon cancer may interfere with correct differentiation of primary malignant tumors and metastatic ovarian tumors from colon cancer. Thus, on the basis of the data obtained, we suggest that thorough preoperative examination of the stomach is required when ovarian masses display a mainly solid or solid appearance on CT scans. The sensitivity and specificity for differentiation were 69% and 90%. Although there is large overlap between the characteristics of these two tumors, we propose that this finding can serve supplementary roles.
Dense enhancement of the solid portion on a CT scan was present in 46.2% (6/13) of ovarian metastatic lesions from stomach cancer compared with only 10.3% (3/29) of ovarian metastatic lesions from colon cancer. Unfortunately, radiologic-pathologic correlation of the solid portion with dense enhancement was not performed because of the retrospective nature of the study. Although there is overlap for this finding, we propose that these parameters serve a supplementary role in differentiation of subtypes of ovarian metastatic lesions from stomach and colon cancers.
Ovarian metastatic lesions from stomach cancer were larger (5.6 ± 2.1 cm) than those from colon cancer (9.1 ± 4.6 cm) (p = 0.007). We postulate that the more cystic nature is partly responsible for the larger size of ovarian metastatic lesions from colon cancer.
In our study, patients with ovarian metastasis from colon cancer were older than those with metastasis from stomach cancer. Specifically, 37.5% (3/8) of the patients with ovarian metastasis from stomach cancer were younger than 40 years, whereas none of the patients in the other group were younger than 40 years. This finding may be attributable to an increase in the percentage of young patients with stomach cancer and the more aggressive nature of this disease in younger patients [26, 27].
There were limitations to our study. First, the number of cases was not large. The rare incidence of the disease entity provides little opportunity for comprehensive observation. Furthermore, ovarian metastasis is often viewed as a late presentation of cancer, and patients often are treated with palliative measures, which frequently do not include comprehensive assessment of disease extension.
A second limitation was that although they were unaware of the pathologic features of the ovarian masses, the radiologists who reviewed the images may have deduced the pathologic characteristics of the mass on the basis of clues such as evidence of stomach or colon resection or the presence of a mass. In our study, ovarian metastasis and primary cancer were found simultaneously in 17 (54.8%) of the patients, and ovarian metastasis was found after operations for primary cancer in 12 (38.7%) of the patients. The primary cancer or clues of a previous operation were detected on the CT scans of 27 (93.5%) of the patients. Finally, primary malignant tumors of the ovary were not included in this study. This factor might have given rise to selection bias.
In conclusion, our findings imply that CT is useful in differentiation between ovarian metastasis from stomach cancer and ovarian metastasis from colon cancer. Mass characteristics, dense enhancement of the solid portion, and size are valuable CT parameters for differentiation.
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