The case is from a 118-week old Wistar rat. Both ovaries were normal at necropsy.

Click on the images below for a larger view.
Fig. 1: H&E, x2.5	Fig. 2: H&E, x5
Fig. 3: H&E, x10	Fig. 4: H&E, x20

The alteration is characterized by multifocal nodular lesions in the ovary, which are surrounded by a cystic space of variable size. The nodules consist of highly cellular aggregates of tubular structures or cords, lined by a cuboidal to columnar epithelium. The basophilic cells show a high nuclear:cytoplasmic ratio. Although stromal cells are not prominent, a few luteinized cells can be recognized. The histogenic origin of this lesion is the surface epithelium of the ovary.

General comment: Since the lesion was without cellular atypia and the diameter of the largest nodule was smaller or equal to the size of a corpus luteum, it was considered to represent a hyperplasia rather than a tumor. The RITA-data base panel decision was 8:3 for hyperplasia : adenoma.

Cystadenoma was considered as an alternative diagnosis by several contributing participants. Although stromal cells are not prominent in the present case, a few luteinized cells could be recognized. In addition, the growth pattern is tubular and not papillary.

Hyperplasia, cystic-papillary the lesion was without cellular atypia and the diameter of the largest nodule was smaller or equal to the size of a corpus luteum.

Granulosa cell tumor shows a different cellular morphology (round to oval) and no tubular growth pattern.

Dysgerminoma-germ cell tumor the present lesion shows only well-differentiated cells in organized structures.

Click on the images below for a larger view.
Fig. 5: H&E, x20	Fig. 6: H&E, x20
Fig. 7: H&E, x40

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