Intracranial germ cell tumours

Intracranial germ cell tumours are a heterogeneous group with variable imaging appearances, biology, response to treatment and prognosis. 

The WHO classification of CNS tumours divides intracranial germ cell tumours into: 

Intracranial germ cell tumours make up approximately 0.4 to 1% of brain tumours in the western population, although the incidence is up to 8 times higher in the far east (as is the rate of testicular tumours) 1-2.

In general, males are more frequently affected than females, and this is most evident in non-germinomatous tumours of the pineal, where approximately 90% are found in males 2. Interestingly this is not the case in suprasellar tumours, which have a relatively even distribution. 

Overall peak in incidence around the time of puberty (10-19 years of age) 2, somewhat earlier for non-germinomatous germ cell and somewhat later for germinomas.

As is the case with other pineal region masses, intracranial germinomas tend to cause obstructive hydrocephalus due to compression of the aqueduct, and thus present with signs and symptoms of raised intracranial pressure.

Markers

Tumour markers are useful in aiding preoperative diagnosis and monitoring following treatment. The two main markers are alpha-fetoprotein (AFP) which is synthesised by the yolk sac, and human chorionic gonadotropin (HCG) which is synthesised by the chorioepithelium 3.

  • germinoma: usually neither AFP or HCG
  • embryonal carcinoma: variable
  • yolk sac tumour: AFP
  • choriocarcinoma: HCG
  • teratoma: variable, depending on tissues present

These tumours tend to cluster in the midline, with a predilection of the pineal and the suprasellar regions. Controversy persists as to whether multifocal lesions, found at the time of diagnosis in 5-10% of patients, represents synchronous tumours or spread 1.

  • pineal region: twice as common as all other sites
  • suprasellar region
    • next most common
    • suprasellar germinomas more common in women
  • floor of the third ventricle
  • basal ganglia: more likely germinoma
  • thalamus: more likely germinoma
  • fourth ventricle
CT

CT is usually the first investigation that reveals an abnormality. Except mature teratomas, which often demonstrate fat density, CT cannot reliably differentiate between different types of germ cell tumours, although as a general rule germinomas are more homogeneous in appearance than non-germinoma germ cell tumours 3

General features of intracranial germ cell tumours include: 

  • hyperdense compared to normal brain
  • vivid contrast enhancement 
  • calcification:  present in the majority of cases, usually representing engulfed normal pineal calcification, as well as sometimes tumour calcification 3

Features of individual histologies are discussed separately. 

MRI

MRI is the modality of choice for evaluation of pituitary region masses and pineal region masses. Similar to CT, it is difficult to distinguish histologies based on MRI appearance (again, except for the identification of fat in mature teratomas). 

General imaging features include 4

  • T1: isointense to grey matter
  • T2: isointense to grey matter
  • T1 C+
    • vivid contrast enhancement 
    • germinomas tend to be homogeneous
  • DWI: restriction is common especially for germinomas due to high cellularity
  • SWI: haemorrhage is common in non-germinomatous germ cell tumours

Features of individual histologies are discussed separately. 

In general, a biopsy is required as treatment and prognosis will vary with histology (whereas it is independent of location). Aggressive surgical debulking is of unproven benefit and carries significant morbidity given the usual locations of these tumours.

Germinomas are exquisitely radiosensitive, with cure achieved with radiation alone in 80-90% of patients 1-4.

Non-germinomatous tumours have much worse prognosis with survival rates ranging between 40-70% 1.

Teratoma prognosis depends on the degree of differentiation (mature vs. immature) and whether malignant transformation on a component is present (uncommon). In general, mature teratomas are indolent, whereas immature teratomas do poorly, with survival rates ranging between 50-70% 1.


Germ cell tumours
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Article Information

rID: 5956
Synonyms or Alternate Spellings:
  • Intracranial germ cell tumors
  • Intracranial germ cell tumour
  • Intracranial germ cell tumor

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Cases and Figures

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    Case 1: NG-GCT
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    Case 2: germinoma
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    Case 3: germinoma on CT
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