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The cerebellopontine angle (CPA) is a common location for intracranial tumors, most of which are extra-axial and arise from structures within or near the internal auditory canal (IAC) or adjacent meninges.

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The majority of CPA lesions are benign nerve sheath or meningeal tumors, but others may include cysts, vascular lesions, and rare malignant neoplasms.

Anatomy

Anatomical boundaries:

Anterior: Petrous temporal bone
Posterior: Cerebellum
Medial: Pons
Lateral: Internal auditory canal (IAC)

Contents:

CN VII (facial), CN VIII (vestibulocochlear)
CN V superiorly, CN IX–XI inferiorly
Flocculus of cerebellum, choroid plexus
Vessels: AICA, labyrinthine artery

Most Common CPA Tumors

Tumor Type	Frequency	Origin/Notes
‣	~75–85%	Arises from vestibular nerve (CN VIII); also called acoustic neuroma
‣	~10–15%	Arises from the dura near petrous ridge or tentorium
‣	~5–7%	Congenital inclusion cyst
‣	~1–2%	Non-neoplastic CSF-filled cyst
Other rare tumors	<5%	Includes facial nerve schwannoma, metastases, lipomas, hemangiomas, ependymoma, choroid plexus papilloma

Radiological features:

Feature	Vestibular Schwannoma	Meningioma	Epidermoid Cyst	Arachnoid Cyst
IAC Involvement	Yes	No	No	No
Enhancement	Strong	Strong + dural tail	None	None
DWI Restriction	No	No	Yes	No
Dural Tail	No	Yes	No	No
Calcification	Rare	Common (CT)	Rare	No
T2 Signal	Hyperintense	Iso/hyper	CSF-like	CSF-like

Tumor	Imaging features
‣	• MRI T1: Iso- to hypointense
• MRI T2: Hyperintense; may show cystic degeneration in large tumors
• Post-contrast: Strong, homogeneous enhancement (smaller); heterogeneous if larger with cystic changes
• “Ice cream cone” appearance on axial MRI (cone = IAC portion; scoop = CPA component)
‣	• MRI T1: Iso- to hypointense
• MRI T2: Iso- to hyperintense
• Post-contrast: Homogeneous enhancement
• Key Features:

◦ Dural tail sign
◦ Calcifications and hyperostosis on CT
◦ No IAC widening |

| Epidermoid Cyst | • MRI T1: Hypointense • MRI T2: Hyperintense, mimicking CSF • DWI: Bright (restricted diffusion) – key differentiator from arachnoid cyst • No enhancement post-contrast • Irregular margins, insinuates around structures | | Arachnoid Cyst | • MRI T1/T2: Follows CSF on all sequences • DWI: No restriction • No enhancement • Smooth margins, displaces structures | | ‣ | • May involve geniculate ganglion, labyrinthine/tympanic segments • Imaging: similar to vestibular schwannoma but with facial canal involvement | | Lipoma | • MRI T1: Bright (hyperintense) • Fat-suppressed sequences: Signal drop confirms diagnosis • No enhancement | | Metastases | • Often enhancing, can be multiple • Consider especially in known malignancy or atypical location |