Previous studies classified metastatic tumors on the basis of ultrasound characteristics into solid, multilocular–solid or at least unilocular solid, and not purely unilocular or multilocular masses (6, 15, 11, 12). This classification is too broad and does not provide images for reference. In the present study, we classified metastatic tumors into three different types (A, B, and C) that provide more vivid ultrasonography characteristics for reference. Aside from the commonly described multilocular solid (Type A) and purely solid (Type B) tumors, we described herein a novel sonographic feature of solid ovarian metastasis morphology, that is, Type C, which is characterized by a solid tumor with one or several round or oval cysts that are plump with a smooth wall and superior transparency. The cyst lumens contained a clear, mucinous, or hemorrhagic fluid. The presumed pathological reason was glands, many of which are cystically dilated and punctuate the peripheral cellular component and more conspicuously the edematous central component. Guerriero et al. (6) reported a cystic component in 39% of solid metastatic ovarian cases, but they did not explain further these cases. Kiyokawa et al. (10) found a cystic component in a third of such tumors of Krukenberg. In the present study, we observed that this phenomenon did not only exist in Krukenberg but also in—but not limited to—SRCC. This sonographic characteristic was readily recognizable and present in 43.3% (62/143) of metastatic tumors. Furthermore, the SRCC metastatic tumors of the ovary featured Types B and C characteristics only regardless of their origin (stomach, colon, gall bladder, and appendix). Primary ovarian tumors with signet-ring cells are rare (8, 11, 10). The relatively large number of cases included in our study permitted a quite accurate analysis of the different parameters of each group. Nevertheless, a possible source of bias was the retrospective nature of this study.
Colorectal metastases are difficult to differentiate from primary ovarian cancer both via ultrasonography and microscopy (11). We confirmed this observation in our large study population: 69.0% of the colorectal metastases closely mimicked primary epithelial ovarian tumor morphologically, and we relied on immunohistochemistry to confirm their diagnosis. The bilaterality characteristics agreed fairly well with descriptions in pathology textbooks of metastatic tumors in the ovary. However, the detection rate of bilaterality by ultrasonography was low. Two possible reasons the metastatic tumors were not detected are as follows. First, the ovary was grossly normal, thereby rendering detection via imaging difficult. By contrast, the focal metastasis was identified by histologic examination and immunohistochemistry. This case mostly occurred in breast cancer metastasis, an observation consistent with the report of a previous study (9) that found six cases following breast cancer ovariectomy. Second, the contralateral mass was too huge and thus obstructed the smaller ones. The maximum bilateral diameter ratio ranged from 1.3 to 14.2 (3.4±2.4).
There is certain disadvantage in this work that it is a retrospective study that in a small patient population, even this is a ten-years data. Further study would make it clear how these findings would generalize to the larger population and what diagnostic guidelines could be derived from these results.