Germinoma

Germinoma
Micrograph of a germinoma. H&E stain.
Classification and external resources
ICD-O	9060-9061, M9064/3
MeSH	D018237
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A germinoma is a type of germ cell tumor, which is not differentiated upon examination. It may be benign or malignant.

The term germinoma most often refers to a tumor in the brain that has a histology identical to two other tumors: dysgerminoma in the ovary and seminoma in the testis. Since 1994, MeSH has defined germinoma as "a malignant neoplasm of the germinal tissue of the gonads; mediastinum; or pineal region" and within its scope included both dysgerminoma and seminoma. Collectively, these are the seminomatous or germinomatous tumors.

Germinomas are thought to originate from an error of development, when certain primordial germ cells fail to migrate properly. Germinomas lack histologic differentiation, whereas nongerminomatous germ cell tumors display a variety of differentiation. Like other germ cell tumors, germinomas can undergo malignant transformation.

The tumor is uniform in appearance, consisting of large, round cells with vesicular nuclei and clear or finely granular cytoplasm that is eosinophilic.

On gross examination, the external surface is smooth and bosselated (knobby), and the interior is soft, fleshy and either cream-coloured, gray, pink or tan. Microscopic examination typically reveals uniform cells that resemble primordial germ cells. Typically, the stroma contains lymphocytes and about 20% of patients have sarcoid-like granulomas.

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