====== Intracranial germ cell tumor epidemiology ======

[[Intracranial germinoma]]s comprise 0.5-2.0 % of all central nervous system (CNS) tumors and 50-60 % of CNS germ cell tumors. 

They most frequently originate in the [[pineal gland]] and the [[suprasellar region]]. 

Intracranial germinomas (IGs) comprise 1.3% of all primary intracranial brain tumors in adolescents and young adults, and, among them, only 5–10% develop in other brain regions, which are known as ectopic germinomas (EGs).

These tumors may originate from any midline or paramedian structure of the brain. EGs in the basal ganglia or thalamus are the most common
((Kim DI, Yoon PH, Ryu YH, Jeon P, Hwang GJ. MRI of germinomas arising from the 
basal ganglia and thalamus. Neuroradiology. 1998 Aug;40(8):507-11. PubMed PMID:
9763338.
)).
There have been only a few EGs reported in the corpus callosum 
((Yonezawa H, Shinsato Y, Obara S, Oyoshi T, Hirano H, Kitajima S, Arita K.
Germinoma with syncytiotrophoblastic giant cells arising in the corpus callosum. 
Neurol Med Chir (Tokyo). 2010;50(7):588-91. PubMed PMID: 20671388.
))
((Tajima S, Koda K. Germinoma with an extensive rhabdoid cell component centered
at the corpus callosum. Med Mol Morphol. 2015 May 27. [Epub ahead of print]
PubMed PMID: 26012485.
))
, medulla oblongata 
((Okuno S, Hisanaga M, Chitoku S, Sakaki T, Tsunoda S. [Germinoma with
granulomatous reaction arising from the corona radiata; case report and review of
articles]. No Shinkei Geka. 1992 Jul;20(7):775-80. Japanese. PubMed PMID:
1630569.
))
, and cerebellum 
((Nakase H, Ohnishi H, Touho H, Karasawa J, Tsunoda S. Cerebellar primary
germ-cell tumor in a young boy. Brain Dev. 1994 Sep-Oct;16(5):396-8. PubMed PMID:
7892960.
))
, all of which showed no other lesion locations simultaneously.

Their origin within the optic nerve or chiasm is extremely rare
((Chaudhry NS, Ahmad FU, Whittington E, Schatz N, Morcos JJ. Primary intrinsic
chiasmal germinoma. J Neuroophthalmol. 2015 Jun;35(2):171-4. doi:
10.1097/WNO.0000000000000201. PubMed PMID: 25621861.)).

Loco-regional extension of suprasellar GCT to the optic nerve is not uncommon; however, infiltration of the tumor into the retina is only reported in the literature by Abu Arja et al., . Early detection of [[optic pathway]] involvement and proper delineation of the irradiation field may prevent GCT infiltration of the retina with subsequent [[vision loss]]
((Abu Arja MH, Stalling M, Governale LS, Pierson CR, Rusin JA, Palmer JD, Finlay
JL, Olshefski R, Boué DR. Germinoma Involving the Retina: An Unusual Presentation
of Recurrent Intracranial Mixed Germ Cell Tumor. World Neurosurg. 2019 Jan 7.
pii: S1878-8750(19)30002-6. doi: 10.1016/j.wneu.2018.12.143. [Epub ahead of
print] PubMed PMID: 30630044.
)).

===== References =====