Cerebellopontine angle (CPA) masses are relatively common. Although a diverse range of pathologies may be seen in this region, the most common by far is vestibular schwannoma.
Pathology
Cerebellopontine angle masses can be divided into four groups, based on imaging characteristics:
- enhancing mass
- mass with high T1 signal on MRI
- mass with CSF intensity/density
- other masses
Alternatively, a quick mnemonic to remember the common entities affecting the cerebellopontine angle is AMEN or SAME.
Enhancing mass
- vestibular schwannoma: most common by far (~80%)
- meningioma: second most common (~10%)
- trigeminal schwannoma
- facial nerve schwannoma
- ependymoma
- metastasis, e.g. breast, lung, malignant melanoma
High T1 signal mass
- hemorrhagic vestibular schwannoma
- neurenteric cyst: usually prepontine, but fluid may be proteinaceous and high on T1
- thrombosed berry aneurysm: often will have a calcified rim and hemosiderin staining
- white epidermoid: rare; restricts on DWI
- cerebellopontine angle lipoma: usually has the facial nerve and vestibulocochlear nerve coursing through it; saturates on fat suppressed sequences
- ruptured intracranial dermoid cyst: often multiple droplets with original midline lesion still often seen
CSF density mass
- epidermoid cyst: third most common (~5%)
- arachnoid cyst
Other masses
Many other masses can present at or around the cerebellopontine angle. They include:
- primary melanocytic neoplasm
- neurosarcoidosis
- cholesterol granuloma
- paraganglioma
- petrous apicitis
- chondrosarcoma
- chordoma
- endolymphatic sac tumor
- pituitary adenoma
- brainstem glioma
- choroid plexus papilloma
- lymphoma
- hemangioblastoma
- ependymoma
- medulloblastoma
- dysembryoplastic neuroepithelial tumor
- ganglioglioma (rare 3)
- mass mimics
- calcified choroid plexus from the fourth ventricle protruding through the lateral foramen of Luschke: Bochdalek's flower basket
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