NeuroradiologyCerebellopontine angle tumour
In its narrow sense the definition of a cerebellopontine angle (CPA)
tumour is limited to a mass that primarily arises in the cistern. The most common of these extra-axial tumours are:
acoustic schwannoma (75% of all lesions in this location), trigeminal nerve schwannoma,
meningioma and
epidermoid tumour.
Paragangliomas, lipoma (see
lipoma CNS),
dermoid tumour and haemangiomas originating in the CPA itself are uncommon. In a broader sense tumours that arise in the adjacent brain and skull and extend secondarily into the CPA can be included in the definition. This group comprises
ependymoma and
choroid plexus papilloma, extending from the fourth
ventricle through the lateral foramina; paraganglioma arising in the jugular foramen; exophytic cerebellar and brain stem glioma; chordoma from the clivus; and osteocartilagineous tumours from the skull base and
temporal bone.
In children medulloblastoma can occasionally be extra-axial in the CPA.
Metastases account for 1-2% of CPA masses in adults; they usually involve the cranial nerves and leptomeningeal structures. A particular type of secondary lesion affecting the trigeminal nerve is perineural spread of head and neck malignancy, along the neural branch through the foramen ovale.
Contrast-enhanced MR is the imaging modality of choice for the study of CPA tumours; it is useful for distinguishing intra- from extra-axial lesions, cystic from solid portions that enhance. The morphology and MR signal behaviour of the tumours, as well as the age can suggest the diagnosis.
CT is superior in demonstrating calcification and bone abnormalities such as erosion or hyperostosis.
NC