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Metastases, CPA-IAC


KEY FACTS

Terminology

  • Definition: Cerebellopontine angle-internal auditory canal (CPA-IAC) metastases refers to systemic or CNS neoplasia affecting area of CPA-IAC

Imaging

  • 4 major sites: Leptomeningeal (pia-arachnoid), dura, flocculus, and choroid plexus

  • T1WI C+ MR

    • Leptomeningeal metastases : Diffuse thickening and enhancement of cranial nerves in IAC

    • Dural metastases : Thickened enhancing dura; may be diffuse or focal

    • Floccular metastases : Enhancing floccular mass extends into CPA cistern

    • Choroid plexus metastases : Enhancing nodular lesion along normal course of choroid plexus

    • Focal, enhancing brain metastases may be present

  • FLAIR MR

    • Parenchymal brain metastases usually high signal

Top Differential Diagnoses

  • Bilateral vestibular schwannoma (neurofibromatosis type 2, NF2)

  • Sarcoidosis

  • Meningitis

  • Ramsay Hunt syndrome

Clinical Issues

  • Rapidly progressive unilateral or bilateral facial nerve paralysis and sensorineural hearing loss

  • Patient with past history of treated malignancy

Diagnostic Checklist

  • If trying to diagnose bilateral “vestibular schwannoma” in adult as NF2, probably CPA metastases instead

  • Rapidly progressive 7th and 8th cranial nerve palsies + CPA mass suggest metastatic focus

    • Vestibular schwannoma rarely causes CN7 palsy

In 4 major types of cerebellopontine angle-internal auditory canal (CPA-IAC) area metastases, along the posterolateral margin of the IAC, thickened dural metastases
are visible. Within the IAC, metastatic leptomeningeal (pia-arachnoid)
involvement is present. Choroid plexus
and floccular
metastases are also depicted.

Axial T1WI C+ MR shows bilateral leptomeningeal breast carcinoma metastases
within the IACs. Left-sided disease is more subtle than the right.

Axial T2WI MR demonstrates right IAC leptomeningeal metastatic foci as thickening of the branches of CN7 and CN8
within the IAC.

Axial T2WI MR reveals left IAC metastatic disease as subtle thickening of the branches of CN7 and CN8
within the IAC. In an adult patient with suspected bilateral vestibular schwannoma, consider metastatic disease rather than neurofibromatosis type 2.

TERMINOLOGY

Abbreviations

  • Metastases (mets)

Synonyms

  • Leptomeningeal carcinomatosis, meningeal carcinomatosis, carcinomatous meningitis

    • All of the above terms are misnomers for the following reasons

      • –

        Neoplasms are not always carcinomas

      • –

        Pachymeninges (dura) and leptomeninges (pia + arachnoid) are often both involved

      • –

        Usually does not contain inflammatory component

        • □

          -itis suffix makes no sense

Definitions

  • CPA-IAC metastases: Systemic or central nervous system (CNS) neoplasia affecting area of CPA-IAC

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