Signalment:  

8-year-old, intact, female Great Dane (Canis familiaris).This dog had intermittent abdominal pain for the last 4 weeks. An exploratory laparotomy revealed the presence of a 9 cm diameter mass coming from the left ovary.

Gross Description:  

Not reported.

Histopathologic Description:

Ovary: Sections are largely effaced by sheets of neoplastic round cells that exhibit mild to moderate anisocytosis and anisokaryosis. Rarely, these sheets are separated by a fine stroma. Neoplastic cells completely efface the architecture and have round euchromatic nuclei with single prominent nucleoli. Mitotic figures are present in moderate numbers (2-4 per 40x HPF). Neoplastic cells (17-25 μm) have moderate amounts of amphophilic cytoplasm and large round nuclei (12-17 μm) with 1-2 prominent nucleoli. Rare aggregates of 2-5 small lymphocytes are present amid the neoplastic cells. Immunohistochemistry: Approximately 50% of the neoplastic cells stain positively for vimentin and negatively for CD18, synaptophysin and pancytokeratin.

Morphologic Diagnosis:  

Ovary: Dysgerminoma.

Condition:  

Dysgerminoma

Contributor Comment:  

The primary ovarian neoplasms are classified into 3 categories according to their histogenic origin: tumors of the surface coelomic epithelium, tumors of the gonadal stroma, and tumors of germ cells. Germ cell neoplasms of the ovary include dysgerminomas and teratomas.(2,4) Dysgerminomas are rare neoplasms that are considered to be the counterpart of the more common seminoma of the testicle in gross and microscopic features. They are extremely rare in all species but most cases have been reported in the bitch and mare.(1,2) They are usually unilateral and have a low potential for local and distant metastasis. The neoplastic cells stain positively for vimentin and alkaline phosphatase and negatively for cytokeratin.(1) The differential diagnosis in the current case included lymphoma, neuroendocrine carcinoma, pheochromocytoma and histiocytic sarcoma. The diagnosis of dysgerminoma was confirmed using immunohistochemsitry, wherein, the neoplastic cells stained positively for vimentin and stained negatively for CD18, pancytokeratin, and synaptophysin.

JPC Diagnosis:  

Ovary: Dysgerminoma.

Conference Comment:  

In addition to the morphologic features described by the contributor, conference participants noted frequent individual cell necrosis among the neoplastic cells. Moreover, many sections contain abundant hemorrhage; in the absence of evidence for chronicity (e.g. hemosiderin-laden macrophages), participants interpreted the finding as likely representing acute, surgical induced hemorrhage associated with ovariectomy. The moderator also commented that reproductive tissues are very sensitive to surgical manipulation and susceptible to hemorrhage. The conference moderator further reminded participants that it is not uncommon to find two or more different neoplasms in a single gonad.

Conference participants reviewed the primary ovarian tumors of domestic species, among which the dysgerminoma is rare. As classified by the World Health Organization, these are summarized below:(3,4) Neoplasm

Primary Ovarian Tumors of Domestic animals
Category	Notes
Tumors of the surface coelomic epithelium	Papillary adenoma; papillary cystadenoma	Common only in the bitch; arise from the coelomic mesothelium forming surface epithelium or subsurface epithelial structures (SES); form papillary projections covered by ciliated cuboidal to columnar cells, with or without glandular or cystic cavity formation
	Papillary adenocarcinoma	Common only in the bitch; malignant counterpart of papillary adenomas; larger and extends through ovarian bursa; fronds may dislodge and cause metastatic implantations (carcinomatosis) and ascites)
	Rete adenoma	Rare; reported only in the bitch; arise from the tubular network of rete; differentiate from papillary adenomas by location in the tubal extremity of the ovarian medulla (vs. surface epithelium for the latter)
Mesenchymal tumors	Hemangioma	Most common ovarian tumor of the sow; rare in the cow, mare, and bitch
	Leiomyoma	Rare; reported in the bitch, queen, and sow; arise from smooth muscle of the mesovarium
Sex cord-stromal (gonadostromal) tumors	Granulosa (granulosatheca) cell tumor; thecoma (theca cell tumor); interstitial cell tumor (luteoma, lipid cell tumor, steroid cell tumor)	Most common ovarian tumor of the cow and mare; slightly less common than epithelial tumors of the ovary in the bitch; infrequent in the queen; arise from granulosa and theca interna cells (and their luteinized counterparts); may produce estrogens or androgens; produce inhibin in the mare with contralateral ovarian atrophy; rarely metastasize; distinctive Call-Exner bodies are present histologically
Germ cell tumors	Dysgerminoma	Uncommon; arise from germ cells before differentiation; may metastasize or spread locally but biological behavior largely unknown due to low incidence in domestic species; histologically indistinguishable from the much more common testicular seminoma
	Teratoma	Rare; arise from totipotential germ cells that have undergone somatic differentiation; consist of two or more of the three embryonic layers (i.e. endoderm, mesoderm, ectoderm); usually well-differentiated and benign
	Embryonal carcinoma	Arise from embryonic multipotential cells capable of further differentiation; variable histologic pattern

References:

1. Chandra AMS, Woodard JC, Merritt AM: Dysgerminoma in an Arabian filly. Vet Pathol 35:308-311, 1998
2. Jackson ML, Mills JHL, Fowler JD: Ovarian dysgerminoma in a bitch. Can Vet J 26:285-287, 1985
3. Kennedy PC, Cullen JM, Edwards JF, Goldschmidt MH, Larsen S, Munson L, Nielsen S: Histological Classification of Tumors of the Genital System of Domestic Animals, 2nd series, vol. IV, ed. Schulman YF, pp. 24-28. Armed Forces Institute of Pathology (in cooperation with the ARP and the WHO Collaborating Center for Worldwide Reference on Comparative Oncology), Washington, DC, 20306
4. Schlafer DH, Miller RB: Female genital system. In: Jubb, Kennedy, and Palmer's Pathology of Domestic Animals, ed. Maxie MG, 5th ed., vol. 3, pp. 450-454. Saunders Elsevier, Philadelphia, PA, 2007

Click the slide to view.

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3-1. Dysgerminoma, ovary

3-2. Dysgerminoma, ovary

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