Discussion:
Although the ovary is a common site for benign and malignant lesions, tumors of lipomatous origin are rare. (4) Usually, lipomas of other sites are found in the 4th and 5th decades of life, where etiology is still unclear. These tumors are usually asymptomatic, unilateral, growing more than 10 cm (2, 3). Some constitutional factors and obesity may be associated with the growth of the tumor (3).
The origin of this tumor in the internal genital tract of a female is rare and unclear (4). The adipose tissue in the ovary is not native, so different mechanisms have been suggested for the development of ovarian lipoma in literature. (2, 5) Embryonic misplacement of the fat cells and metaplasia of ovarian stromal cells into the fat cells are some of the important proposed mechanisms. (3). Most of the ovarian lipomas are part of mature teratoma, and treatment of which may vary from just the lipoma of the ovary. Teratomas are the most common fat-containing ovarian neoplasm that contains tissue from all three germinal layers (ectoderm, mesoderm, and endoderm) that include adipose tissues and other components like bone cartilage, skin adnexae, and others (6). However, our patient like in the case reported by Zwiesler et al had a well-circumscribed lesion of mature adipocytes on the right ovary, and tissues from other germ layers were not present even in the extensive sampling.(7) Hence, the diagnosis of a lipoma was considered over teratoma.
Malignant mixed Mullerian tumors (carcinosarcoma) can also have adipose tissues as its component but are malignant. Carcinosarcoma is a biphasic tumor with malignant carcinomatous components like endometrial carcinoma and sarcomatous components like liposarcoma and others (8). The absence of nuclear atypia, lipoblast, and atypical mitoses in the microscopic examination helps to exclude liposarcoma (3, 4). In our case, the tumor did not have any malignant microscopic features.
The microscopic appearance of ovarian lipoma is similar to the other lipomatous tumor arising in other parts of the body (3). Lipoma of the other sites, such as the pelvis, also has to be ruled out with the help of clinicoradiological correlation (5). The lipoma in our case was located on the right ovary.
It is also important to distinguish lipoma of the ovary from adipocytic infiltration from the stromal tissues of the ovaries. In the study done by Honore et al. (1979) in 8 cases of the adipocyte infiltration of the ovarian tumor, they were exclusively unilateral, non- capsulated, and were made of closely packed adipose cells (9). We differentiate our case to pure lipoma because of the pure encapsulation and lack of connection with the ovarian stroma.