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Cerebellopontine angle

The cerebellopontine angle (CPA) is a triangular space located at the junction of the cerebellum, pons, and medulla in the posterior cranial fossa. This critical region is bordered by the petrous part of the temporal bone laterally, the cerebellum posteriorly, and the pons and medulla medially. The CPA is an important anatomical and clinical region, as it contains several cranial nerves and vascular structures, and is a common site for the development of tumors, most notably vestibular schwannomas. Its anatomical complexity makes it significant in neurosurgery, radiology, and neuro-otology.

Synonyms

  • CPA (abbreviation)

  • Angle of cerebellopontine cistern

  • Pontocerebellar angle

Anatomy (Key Structures)

  • Borders:

    • Medial: Pons and medulla

    • Lateral: Petrous part of temporal bone

    • Posterior: Cerebellum

  • Cistern:

    • Contains cerebrospinal fluid (CSF); called the CPA cistern

  • Cranial Nerves:

    • CN V (Trigeminal nerve)

    • CN VII (Facial nerve)

    • CN VIII (Vestibulocochlear nerve)

    • Sometimes CN IX, X, and XI may pass nearby

  • Other Structures:

    • Flocculus of the cerebellum

    • Choroid plexus

    • Arteries and veins

Arterial Supply

  • Anterior inferior cerebellar artery (AICA): Primary artery to the CPA region; courses through the angle

  • Branches of the basilar artery

  • Small perforators to nerves and brainstem

Venous Drainage

  • Superior petrosal vein

  • Transverse pontine vein

  • Petrosal sinuses (superior and inferior petrosal sinuses)

Function

  • Conduit for cranial nerves and vascular structures between brainstem, cerebellum, and periphery

  • Site for transmission of auditory and vestibular signals (via CN VIII)

  • Facial movement and sensation (via CN VII and V)

  • Important for surgical access to certain posterior fossa lesions

MRI Appearance

  • Normal CPA:

    • Appears as a CSF-filled space at the junction of the pons, cerebellum, and petrous bone

    • Cranial nerves (VII, VIII) may be visible as thin linear structures within the cistern

  • Common MRI Sequences:

    • T1: CPA appears hypointense (dark, like CSF)

    • T2: CPA appears hyperintense (bright, like CSF)

    • FIESTA/CISS (high-resolution T2): Best for visualizing nerves and small lesions

    • Pathologies (e.g., vestibular schwannoma) seen as mass lesions in this region

CT Appearance

  • Normal CPA:

    • CPA seen as a low-density space (CSF) adjacent to the pons and cerebellum

    • Petrous bone forms a dense lateral boundary

    • Cranial nerves usually not visible unless thickened by pathology

  • Uses of CT:

    • Better for evaluating bony anatomy (petrous temporal bone)

    • Detects calcification or bone involvement in mass lesions

    • Masses (e.g., tumors) may present as soft tissue density in the cistern, with possible bone erosion if aggressive

MRI images

cerebellopontine angle MRI 3T coronal image

MRI images

cerebellopontine angle MRI 3T axial image

MRI images

cerebellopontine angle MRI 3T sagittal image

CT image

cerebellopontine angle ct image