Germinoma pathophysiology

Histology
The term germinoma most often has referred to a tumor in the brain that has a histology identical to two other tumors: dysgerminoma in the ovary and seminoma in the testis. Increasingly, the term refers to any tumor with this histology, regardless of where it occurs in the body.

MeSH defines germinoma as "a malignant neoplasm of the germinal tissue of the gonads; mediastinum; or pineal region" and within its scope includes both dysgerminoma and seminoma. Collectively, these are the seminomatous or germinomatous tumors.

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.

Ovary (dysgerminoma)
Dysgerminoma is the most common type of malignant germ cell ovarian cancer. Dysgerminoma usually occurs in adolescence and early adult life; about 5% occur in pre-pubertal children. Dysgerminoma is extremely rare after age 50. Dysgerminoma occurs in both ovaries in 10% of patients and, in a further 10%, there is microscopic tumor in the other ovary.

Abnormal gonads (due to gonadal dysgenesis and androgen insensitivity syndrome) have a high risk of developing a dysgerminoma. Most dysgerminomas are associated with elevated serum lactic dehydrogenase (LDH), which is sometimes used as a tumor marker.

Metastases are most often present in the lymph nodes.

Intracranial germinoma
Intracranial germinoma occurs in 0.7 per million children. As with other germ cell tumors (GCTs) occurring outside the gonads, the most common location of intracranial germinoma is on or near the midline, often in the pineal or suprasellar areas; in 5-10% of patients with germinoma in either area, the tumor is in both areas. Like other (GCTs), germinomas can occur in other areas of the brain. Within the brain, this tumor is most common in the hypothalamic or epiphysial regions. In the thalamus and basal ganglia, germinoma is the most common GCT.