Also known as dysgerminoma, or extra-gonadal seminoma, germinomas arise from germ cells, and therefore demonstrate no differentiation. They form soft friable tumours, which in the brain typically arise in the the midline, relating to the third ventricle:

– pineal gland – 80 – 90% – where they “engulf” normal pineal tissue, and associated calcification, in contrast to pineocytomas, and pineoblastomas which “explode” the pineal calcification.
– suprasellar mass – 50% – filling and expanding the infundibular recess and supraoptic recess
– thalamus & basal ganglia – 5 – 10%

Typically germinomas are tumours of young patients (peak age 10 – 12 years) with 90% of patients being younger than 20. Gender ratios are interestingly different depending on location. When of the pineal region, then M:F 10:1 whereas in the suprasellar region, they are more frequent in females. Overall, due to the pineal region being most common, germinomas are seen more frequently in males M:F ~ 2:1.
For more discussion on germinomas, and additional images of this same case, please visit here.

Credit: Dr Frank Gaillard