Osseous metaplasia in ovarian tumours: a case with serous cystadenoma

In a recent paper in the Journal of Clinical Pathology, Godbole et al¹ reported a case of osseous metaplasia in a benign ovarian cyst in association with cloacal anomaly. These authors stated that only four published cases with osseous metaplasia in ovarian tumours exist, three in the literature,²,³,⁴ and the one they presented. The former three cases were associated with papillary serous carcinoma, thecoma and endometrioma in a supernumerary ovary, respectively. According to their data, Godbole etal concluded that osseous metaplasia is more common in anatomically abnormal ovarian tissue in women of reproductive age. However, a thorough search we made in the literature revealed that to date, the total number of cases with osseous metaplasia in an ovarian tumour reported in the literature has reached 10,¹,²,³,⁴,⁵,⁶,⁷,⁸,⁹,¹⁰ (one of them⁵ was actually added after the report of Godbole et al, whereas one more case is described herein).

Our case concerns a 37‐year‐old woman who was subjected to hysterectomy with the right adnexa, owing to multiple leiomyomas. The right ovary measured 7 cm in diameter, and presented an osseous lesion that was hard in consistency and 3 cm in diameter. Histologic examination, after decalcification, showed a serous cystadenoma with extensive, circumferential osseous metaplasia of its wall (fig 1). The cyst wall was lined by a single layer of flattened or cuboidal cells, whereas the osseous tissue consisted of mature lamellar bone. The ovary was searched thoroughly to exclude the possibility of an underlying teratoma. The rest of the pathology of the present specimen revealed only the aforementioned uterine leiomyomas. This is the first reported case where osseous metaplasia has occurred in a benign ovarian serous cystadenoma.

Figure 1 The cyst wall is lined a single layer of cells and contains abundant osseous tissue. Ovarian stroma is seen on the right part of the picture. Original magnification, ×25.

Bone formation in the ovary, with the exception of developing in the setting of a mature cystic teratoma or a heterologous mixed mesodermal tumour, is exceedingly uncommon. Excluding the previous cases, so far, the ovarian neoplasms most commonly associated with osseous metaplasia are mucinous cystadenomas (three cases),⁶,⁷,⁸ followed by serous cystadenocarcinomas (two cases).²,⁹ A minority only seems to occur in anatomically abnormal ovaries (two cases). The most plausible explanation for bone formation in an ovarian neoplasm is a metaplastic process of the multipotential stromal cell. No prognostic significance has been attributed to this unusual phenomenon.