Neuroradiology

Germinoma

the commonest tumours of germ cell origin, representing approximately 0.5 - 2% of primary intracranial tumours. They are midline tumours and their sites of predilection include the pineal region, suprasellar cistern and posterior third ventricle. Suprasellar germinoma may represent a primary localization or metastatic disease from pineal lesions. Synchronous occurrence in the pineal gland and suprasellar cistern is frequent and pathognomonic of this type of tumour. Other rarer locations are thalami and basal ganglia. Histologically germinomas resemble ovarian dysgerminoma and testicular seminoma. They are of relatively low grade malignancy; however, they tend to infiltrate adjacent structures and have a propensity to spread throughout the ependyma, the ventricular system and subarachnoid spaces ( Fig.1). Germinomas are highly radiosensitive. They affect primarily children or young adults; there is a strong male predominance for pineal germinomas and no sex prevalence for the suprasellar variety.

Clinical manifestations include: diabetes insipidus as the earliest symptom, optic atrophy and visual field defects, pituitary hypofunction and diplopia in the suprasellar location. Hydrocephalus can be the presenting symptom for pineal lesions.

Imaging

Precontrast CT scan shows a relatively ill-defined, slightly hyperdense suprasellar or pineal mass, which enhances strongly following contrast administration. MRI nicely delineates the typically midline location of tumours: suprasellar lesions (Fig.2) are centred at or just behind the pituitary infundibulum, pineal germinomas surround the pineal gland.

The tumour appears as an infiltrating, homogeneous mass, with a signal intensity similar to grey matter in all pulse sequences; occasionally the signal is hyperintense on T1-weighted and hypointense on T2-weighted images. Marked contrast enhancement is the rule. Contrast-enhanced studies are essential to identify ependymal and subarachnoid spread. Suprasellar germinomas differ from craniopharyngiomas in their homogeneity and in the lack of cystic and calcific components. The double pineal/suprasellar location is virtually diagnostic. Pineal teratomas have mixed, heterogeneous signal and most have fat or calcific inclusions.

 

GS

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Fig.2

a. MR of the head, T1-weighted image following gadolinium injection. Medium-sized space-occupying lesion in the pineal region, with homogeneous enhancement. The quadrigeminal plate and aqueduct are not yet significantly compressed. b. MR of the spine of the same patient, T1-weighted sagittal image following gadolinium injection. Early subarachnoid seeding with multiple enhancing nodules at the level of the cauda equina. c, d. Same patient following radiotherapy; marked reduction and apparent disappearance of the primitive tumour (c) and of the drop metastases.
Germinoma, Fig.1 (a)
Germinoma, Fig.1 (b)
Germinoma, Fig.1 (c)
Germinoma, Fig.2 (a)
Germinoma, Fig.2 (b)
Germinoma, Fig.2 (c)
Germinoma, Fig.2 (d)