Vestibular schwannoma:   

  • Background
    • Vestibular schwannomas (also known as acoustic schwannomas) are benign intracranial extra-axial tumors that arise from Schwann cell sheaths that invest the vestibular or cochlear nerve in cerebellopontine angle-internal auditory canal (CPA-IAC). Acoustic neuromas account for approximately 80% of tumors found within the CPA. The remaining 20% are principally meningiomas. In rare cases, a facial nerve neuroma, vascular tumor, lipoma, or metastatic lesion is found within the cerebellopontine angle.
    • Acoustic tumors, like other space-occupying lesions, produce symptoms by any of 4 recognizable mechanisms: (1) compression or distortion of the spinal fluid spaces, (2) displacement of the brain stem, (3) compression of vessels producing venous or arterial infarction, or (4) compression and/or attenuation of nerves.
    • Because the CPA is relatively empty, tumors can continue to grow until they reach 3-4 cm in size before they come in contact with important structures. Growth is often sufficiently slow that the facial nerve can accommodate to the stretching imposed by tumor growth without clinically apparent deterioration of function. Tumors that arise within the IAC may produce relatively early symptomatology in the form of unilateral sensorineural hearing loss or vestibular disturbance by compressing the cochlear nerve, vestibular nerve, or labyrinthine artery against the bony walls of the internal auditory canal.
  • Imaging findings
    • MRI
      • Gold standard for diagnosis is gadolinium enhanced T2 MRI of the brain and CPA-IAC.
      • MRI can detect masses as small at 2 mm.
      • T1WI: lesion will appear as an intermediate signal most commonly; a high signal foci will be present if there is a hemorrhagic lesion (which is rare).
      • T2WI: lesion will appear as a "filling defect" in high signal CSF of CPA-IAC cistern. Small lesions will appear as ovoid filling defect, where as larger lesions have an "ice cream on cone" shaped filling defect.
      • T1 C+: Focal, enhancing mass of CPA-IAC cistern.
      • Other MR findings: 0.5% associated arachnoid cyst.
    • CT with contrast
      • Well-delineated, enhancing mass of CPA-IAC cistern with no calcification.
      • Smaller intracanalicular lesions < 6 mm may be missed.