Cerebellopontine Angle Tumors

Electrophysiologic Test
• ABR is the most sensitive and specific for detection of a vestibular schwannoma • The most common findings is to have all wave, but have interaural difference in the latency of wave V, with a delay of more than 0.2msec • 40~60% with vestibular schwannoma • The other is wave I present, but the rest is abscent. 10~20% with schwannoma
• • • • • Heel-shin Finger-to-nose test Romberg test Tandem gait Fine motor movement
Audiometry
• • • • • PTA Speech discrimination Acoustic reflex threshold Acoustic-reflex decay ABR
Vestibular Schwannomas
• Difficult to determine the incidence, clinically silent vestibular schwannomas • 7 cases per 10,000 MRI for nonotologic reason • 0.7~1.2 of 100,000
Faical Numbness
• 4% • More often with larger tumor > 2cm • Most frequently begins in the maxillary division of CN5 • Corneal reflex will be absent prior to development of facial hypesthesia • Facial weakness, rare
• 40 % extends into IAC • Labyrinthine a.
• CN 7 and CN 8, encased in glial tissue throughout intracranial course • Schwann cells surround nerves beginning in the IAC, near porus. • The glial-schwann junction is also known as the Obersteiner-Redlich zone • Scarpa ganglion located the midportion of ICA
Tumor biology
• Arise from vestibular segment • Equal frequency between sup and inf vestibular nerve • Japan, 85% from inf. portion • From Schwann cells, most within the IAC • Most lateral to the Scarpa ganglion
Imaging Studies
• MRI is the gold standard • Gadolinium is preferentially taken up into the vestibular schwannoma, brightly on T1 and T2
Treatment
• Observation • Surgery
Internal Acoustic Canal
Bill bar
Ant. sup Facial n. Post. sup Superior vestibular n.
Transverse Crest Ant. Inf Post. inf Cochlear n. Inferior vestibular n.
Neurotologic Examination
• The sensation of the posterior portion of the bony ear canal can be determined by palpation during otoscopic exam • Hitselberger sign, decreased sensation in EAC • Sensory branch of CN 7 is more sensitive to pressure than motor portion • Small tumor can be present with facial weakness
Manifestations
• Symptom is related to the tumor size and growth • Intracanalicular tumors: hearing loss, tinnitus, vestibular dysfunction, including vertigo • With extension to CPA, CN 5 involved, midfacial hypesthesia • With further brainstem compression, hydrocephalus occurs. • Cerebellar involvement may occur in late course
Hearing Loss
• 85% with unilateral hearing loss • Loss of speech discrimination out of proportion to hearing loss is most common • Vestibular schwannoma with occur in 1~2.5% with sudden SNHL
• Scarpa ganglion with the greatest density of Schwann cells • Vestibular schwannomas is not all acoustic neuroma. • Misnomer. It is not neuromas. • The most appropriate term is vestibular schwannoma. • Cochlear schwannomas with propensity for invasion into the cochlea
Ocular Symptoms
• • • • Rare Decreased corneal reflex Diplopia, visual blurring, nystagmus Nystagmus tends to beat toward intact side • Visual blurring is usually secondary to papilledema, which is secondary to IICP
• CN 5: superiorly • CN 9, 10, 11: inferiorly • In this space:
– Foramen of Luschka, lateral aperture of the fourth ventricle – Ant. inf. cerebelar artery 2nd most common, often precedes hearing loss • 66% of vestibular schwannoma • Typically high-pitched ringing sound
Vestibular Symptoms
• Often present • Commonly described as only vague, transient lightheadedness, exacerbated by positional change • 36~50%, dysequilibrium • 27%, whirling vertigo, primarily accompanies smaller tumors
Cerebellopontine Angle Tumors
Introduction
• 10% of all intracranial tumors • Vestibular schwannomas (acoustic neuromas), 78% of CPA tumor
Anatomy
• CPA is an irregularly shaped space in the posterior fossa • • • • • Ant: temporal bone Post: cerebellum Medial: inf. olive Sup: pons and cerebellar peduncle Inf: cerebellar tonsil
• High-frequency SNHL is the most common pattern (65%) • It may be either gradual slope or and abrupt configuration • 5% with normal hearing • Acoustic reflex threshold of 500, 1K, 2K, 4K • Decay test of 500 and 1K
Vestibular Testing
• 70~90% of VS with abnormal ENG • 50% of small tumor with normal ENG • Caloric testing may miss inferior vestibular nerve • 98% of superior VS with reduced caloric response • 60% of inferior VS with reduced caloric response