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.