MRI is useful for characterizing masses in the cerebellopontine angle (CPA) and internal auditory meatus (IAM) based on imaging characteristics. The most common CPA masses are vestibular schwannomas (80%) and meningiomas (10%), while epidermoid cysts account for about 5% of cases. Different types of CPA masses can be distinguished on MRI by their enhancement patterns on T1-weighted and T2-weighted sequences and early versus delayed post-gadolinium images.

1. MRI OF CPA AND IAM

3. CPA
Pathology
• CPA masses can be divided
into four groups, based on
imaging characteristics
ECHO:
• Enhancing mass
• mass with CSF
intensity/density
• mass with High T1 signal
on MRI
• Other masses
• Enhancing mass
• Vest schwannoma: 1st
(~80%)
• Meningioma: 2nd
(~10%)
• Trigeminal or facial
schwannoma
• Ependymoma
• Mets: breast, lung,
malignant melanoma

4. Vestibular Schwannoma

5. Meningioma

6. • CSF density mass
• Epidermoid cyst: 3rd (~5%)
• Arachnoid cyst
• High T1 signal mass
• hemorrhagic vest schwannoma
• thrombosed berry aneurysm
• CPA lipoma
• ruptured intracranial dermoid cyst
• Other masses present at CPA
• primary melanocytic neoplasm
• Endolymphatic sac tumour
• cholesterol granuloma
• paraganglioma
• petrous apicitis
• Chondrosarcoma
• Lymphoma
• Ependymoma
• Brainstem glioma

7. Epidermoid cyst

8. T1-weighted T2-weighted Early post-
gadolinium T1-
weighted
(10-15 min)
Delayed post-
gadolinium T1-
weighted
(30-50 min)
Granulation tissue Intermediate signal Intermediate signal Enhancement Enhancement
Cholesterol
granuloma
High signal Intermediate signal No enhancement No enhancement
Scar tissue fibrosis Intermediate signal Intermediate signal No enhancement Low enhancement
Inflammatory tissue Intermediate signal Intermediate signal Enhancement Enhancement
Cholesteatoma Intermediate signal Intermediate signal No enhancement No enhancement
Fluid Low signal High signal No enhancement No enhancement