Conference 08 - 2015 Case: 03 20151110

Signalment:

3-year-old, neutered, herma-phrodite, Pug (Canis familiars)The dog was seen at an animal hospital clinic on 8/8/08 with a high temperature, anxious appearance, tense abdomen and painful in the lumbar area. CBC, Chemistry panel, urinalysis and radiographs of the spine, abdomen and thorax were within normal limits. It was treated for vertebral disk syndrome. No improvement was noted after initial treatment with dexamethasone. After 12 days post presentation the dogs condition deteriorated and was hospitalized. Abnormal physical findings included anorexia, knuckling of the rear legs, circling to the left, dilated right pupil, constricted left pupil, semi consciousness, protruding tongue, lateral recumbency and lack of response to stimuli. The dog became unconscious before death.

Gross Description:

The ventral surface of the brain has a large irregular mass destroying the pituitary gland, most of the thalamus and the optic chiasma. The mass extended along the base of the skull and measured approximately 7 X 1.5 X 3 cm. On longitudinal section, the brain has an approximately 1.3 cm in diameter, granular, greenish colored, irregular round mass primarily within the thalamus and third ventricle.

Histopathologic Description:

Brain and meninges: Within the meninges and extending into the gray and white matter is a poorly circumscribed, expansile, invasive, densely cellular neoplasm subdivided in lobules and packets by a fibrovascular stroma. The neoplasm is composed of two populations of pleomorphic cells and three patterns. One cell population consists of large polygonal cells arranged in pseudorosettes, occasionally around a central vascular core, and cords separated by fine fibrovascular stroma. These cells have distinct cell borders and moderate to abundant, wispy eosino-philic (hepatoid-like appearance), frequently vacuolated (signet ring-like appearance)

The primary cytoplasm. Occasionally hepatoid type cells have apical brush borders. The nuclei are large, vesicular, irregularly round, central or peripherally located with finely stippled chromatin and one or two nucleoli. The second population of cells is smaller (round and epithelial type) and they are scattered throughout the neoplasm. These cells have scant eosinophilic cytoplasm, indistinct cell borders and round nuclei with clumped chromatin. Mitotic figures range from 3-5 per 400X field in some areas. There is marked anisocytosis and anisokaryosis, and individual cell necrosis. There are extensive areas of necrosis characterized by cellular and eosinophilic debris, mild hemorrhage, degenerate neutrophils, plasma cells and MOTT cells interspersed between neoplastic cells. Within the adjacent gray and white matter, there is multifocal moderate gliosis with occasional glial nodules, satellitosis and scattered neuronal necrosis.

Morphologic Diagnosis:

Suprasellar germ cell tumor

Lab Results:

Immunohisto-chemistry stains for vimentin (VM) and cytokeratin (CK) are positive. Within the neoplasm, the small cell population constantly strongly stained with CK. On the other hand, the large cell population was mostly stained with (VM). Stains for NSE, S100 and GFAP are negative.

Condition:

Suprasellar germ cell tumor

Contributor Comment:

Germ cells give rise to spermatogonia in the testis and oogonia in the ovary. Gonadal germ cell tumors more commonly reported in domestic animals include seminomas, teratomas, embryonal carcinomas, and mixed germ cellsex cord stromal tumors. However, extragonadal tumors have been reported including the intracranial suprasellar germ cell tumor and mixed germ cell tumor in the eye and spinal cord of dogs.(2,6) Suprasellar germ cell tumors or germinomas are very rare neoplasms in man (children and adolescents) and young dogs presumed to arise from ectopic migration of germinal epithelium from the yolk sac (embryonic stages) and its persistence at these novel sites. A recent genetic study of intracranial germ cell tumor in man suggests that these tumors are derived from cells that retain, at least partially, an embryonic stem cell-like phenotype, which is a hallmark of primordial germ cells.(3) The preferred location of these tumors, as the name refers, is the pineal and hypothalamus region above the sella turcica. Microscopically, these tumors vary in cell morphology and patterns; primarily from large polygonal cells with hepatic like or vacuolated signet like appearances forming cords and pseudorosettes (similar to hormone-producing cells or gonadal teratomas) to small cells with small amounts of cytoplasm forming nests scattered throughout the neoplasm (similar to a neuroendocrine pattern or resembling seminomas).(8) Few foci of epithelial cells (cuboidal or squamous epithelial cells) can be seen within the tumor. Neoplastic cells are very pleomorphic making difficult to establish the difference between two or more populations of neoplastic cells. However, other authors described three populations of cells: round cells with a large round to ovoid nucleus and indistinct borders arranged in clusters, large hepatoid cells with distinct borders and compact or vacuolated cyto-plasm arranged in trabeculae and epithelial cells (columnar or cuboidal, occasional squamous cell differentiation) forming tubuloacinar structures.(2)

Immunohistochemically, these tumors express alphafetoprotein, vimentin and keratin. Alphafetoprotein is a positive marker for germ cell tumors in humans and dogs, and is produced by yolk sac tumors, enteric elements of teratomas and some embryonal carcinomas.(6) The diagnosis of the suprasellar germ cell tumor is based on three criteria: 1) midline suprasellar location, 2) presence within the tumor of several distinct cell types (histomorphology), and 3) positive staining for alphafetoprotein, VM and CK. Within the sellar region, the WHO classification of tumors from the nervous system of domestic animals has four tumors that include pituitary adenoma, pituitary carcinoma, craniopharyngioma and suprasellar germ cell tumor.(4)

The neoplasm was considered as a suprasellar germ cell tumor as a primary differential based on the pleomorphism of the neoplastic cells with different patterns and gross location. However, alphafetoprotein, which is an important marker for this type of tumor, was unavailable in the laboratory. In addition, this tumor was highly cellular and invasive with extensive areas of necrosis and frequent mitotic figures. Anaplastic meningioma was also considered as differential diagnosis since the microscopic location is associated with the meninges, the tumor has features of malignancy and the neoplastic cells are CK and VM positive. However, meningiomas are usually present in middle aged to older dogs. Furthermore, anaplastic astrocytoma and craniopharyngioma should also been considered since they share several histomorphological features with suprasellar germ cell tumor. Craniopharyngioma has areas resembling ameloblastoma and usually the mitotic rate is low.

JPC Diagnosis:

Cerebrum: Suprasellar germ cell tumor.

Conference Comment:

Overall the conference histologic description was similar to the contributors description. Many thought there were only two populations of cells, but some participants described three: 1) polygonal cells arranged in tubules, acini and/or rosettes, 2) polygonal cells arranged in small islands and cords, and 3) round to polygonal cells arranged in loose sheets, with the third population having multifocal areas of individual cell necrosis. The different cell populations were described as being haphazardly intermingled, making specific patterns difficult to discern. There was discussion regarding the presence of epithelial like cells, though some participants thought this population was not a prominent feature of the neoplasm. Participants also described deeply basophilic amorphous material and focally extensive areas of lytic necrosis. Immunohistochemical stains eval-uated included alpha-fetoprotein, vimentin and pancytokeratin; there was multifocal cytoplasmic immunoreactivity in each with the strongest positivity demonstrated with pancytokeratin.

The differential diagnosis list for neoplasms in the suprasellar region were discussed including craniopharyngioma. This tumor arises from remnants of Rathkes pouch.

Craniopharyngiomas are composed of polygonal to columnar cells arranged in solidly cellular areas but may also be seen arranged in cysts or tubules. These tumors generally have areas of squamous differentiation and ciliated cells lining cystic spaces, neither of which were present in the tumor in this case. They can have multifocal areas of necrosis, and cholesterol crystals may be seen. Pituitary adenoma and pituitary carcinoma were also discussed. Pituitary adenomas are composed of polygonal to spindle shaped cells which can be arranged in solidly cellular areas as well as a sinusoidal pattern, and they lack the characteristic of multiple cell types as seen in the tumor in this case. The nuclei in pituitary adenomas are vesiculate, similar to the tumor in this case, but the cells have a moderate to abundant amount of granular cytoplasm. Pituitary carcinomas are similar to adenomas but are more invasive with greater cellular atypia and higher mitotic rate.(4)

Grossly, suprasellar germ cell tumors are grey-white in color, located on midline and usually obscure the pituitary and compress overlying neuroparenchyma. Pituitary tumors are white to brown in color and can be quite large, also compressing the adjacent neuroparenchyma.(4) Craniopharyngiomas are also large tumors that grow along the ventral brain, but may extend dorsally into the neuroparenchyma.(5) Each of these is a reasonable gross differential diagnosis for a mass located in the most ventral region of the brain, on midline and caudal to the optic chiasm.

References:

1. Barnhart KF, Wojcieszyn J, Storts RW. Immunohistochemical staining patterns of canine meningiomas and correlation with published immunophenotypes. Vet Pathol. 2002; 39:311-321.

2. Ferreira AJA, Peleteiro MC, Carvalho T, Correia JMJ, Shulman FY and Summers BA. Mixed germ cell tumor of the spinal cord in a young dog. J Small Anim Pract. 2003; 44(2):81-84.

3. Hoei-Hansen CE, Sehested A, Juhler M, Y-FC Lau, Skakkebaek NE, Laursen H and Rajpert-De Meyts E. New evidence for the origin of intracranial germ cell tumors from primordial germ cells: expression of pluripotency and cell differentiation markers. J. Pathology. 2006; 209 (1):25-33.

4. Koestner A, Bilzer T, Fatzer R, Schulman FY, Summers BA, Van Winkle TJ. Histological Classification of Tumors of the Nervous System of Domestic Animals. 2nd series. Vol. V. Washington DC: Armed Forces Institute of Pathology; 1999:30-36.

5. Koestner A, Higgins RJ. Tumors of the nervous system. In: Meuten DJ, ed. Tumors Cytoplasm of the epithelial-like cells strongly positive for alpha fetoprotein. (anti-AFP, 200X) in Domestic Animals. 4th ed. Ames, IA: Blackwell Publishing Professional; 2002:623-626,728.

6. Patterson-Kane JC, Shulman FY, Santiago N, McKinney L and Davis CJ. Mixed germ cell tumor in the eye of a dog. Vet Pathol. 2001; 38(6):712-714.

7. Summers BA, Cummings and de Lahunta A. Tumors of the central nervous system. In: Summers BA, Cummings and de Lahunta A, eds. Veterinary Neuropathology. St. Louis, MO: Mosby; 1995:384- 385.

8. ACVP meeting, neuropathology mystery slides, case # 5. Presented by Dr. Amanda Fales-Williams (Iowa State University).