Learning objectives
Neoplasms of the posterior fossa in adults form a heterogeneous group of tumors that manifest either within the cerebellum,
the fourth ventricle or the cisternalspaces.
The objectives of this work are:
- To get the diagnosis of these tumors and precise their location: intra VS extra axial.
- To discuss the differential ones.
- Toillustrate different masses with specific MRI features and correlate them with the histopathological study.
Background
The posterior fossa is the deepest of three of cranial fossae.
It’s 1/8 of all the intra-cranial space.
It contains the most complex anatomy where we can find pathways regulating consciousness,
vital autonomic functions and motor activities.
It is the infra-tentorial compartment of the brain that extends from the tentorium to foramen magnum.
Its essential limits are: (figure 1)
- In front: dorsum sellae and the clival part of the occipital bone.
- Behind: the lower portion of the squamosal part of the occipital bone....
Findings and procedure details
MRI protocolincludes:
- T1 Weighted MPRAGE sequences obtained in the axial plan.
- Axial FLAIR,
T2 spin echo and gradient echo.
- Diffusion Weighted Imaging (DWI) in axial plan.
- Injection of Gadolinium is required.
- Perfusion and spectroscopy are performed according to the kind of lesions on 3 Tesla MRI.
Posterior fossa tumors in adults were divided depending on the location:
Extra-axial lesions,
mainly in cerebellopontine angle: schwannoma,
meningioma,
archnoïd and epidermoïd cysts.
Intra-axial lesions:
- Cerebellum: metastasis,
hemangioblastoma,
pilocystic astrocytoma,
and medulloblastoma.
-...
Conclusion
Many tumors may occur in the posterior fossa in adults,
regrouped according to their location.
Extra-axial tumors are more frequent in adults; metastasis and hemangioblstoma are most common intra-axial ones.
MRI is the best modality to diagnose,
precise location,
determinate extension and characterize these masses.
With advanced techniques such as spectrosopy,
we can expect specific diagnosis and predict histology.
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