Certain biologic and clinical data assume clinical importance. The highest incidence is in the fifth and sixth decades of life, and the sexes are equally affected. Familial occurrence is a mark, usually, of von Recklinghausen disease. The earliest symptom reported by the 46 patients in the decades-old but instructive series of Ojemann and coworkers was loss of hearing (33 of 46 patients); headache (4 patients); disturbed sense of balance (3 patients); unsteadiness of gait (3 patients); and facial pain, tinnitus, and facial weakness, each in a single case. Some patients sought medical advice soon after the appearance of the initial symptom, some later, after other symptoms had occurred. One-third of the patients were troubled by vertigo associated with nausea, vomiting, and pressure in the ear. The vertiginous symptoms differed from those of Ménière disease in that discrete attacks separated by periods of normalcy were rare. The vertigo coincided more or less with hearing loss and tinnitus (most often a unilateral high-pitched ringing, sometimes a machinery-like roaring or hissing sound, like that of a steam kettle). Some of our patients ignored their deafness for many months or years; often the first indication of the tumor in such patients is a shift to the unaccustomed ear (usually right to left) in the use of the telephone. Others neglected these symptoms to a point where they presented with impaired mentation, imbalance, and sphincteric incontinence because of brainstem compression and secondary hydrocephalus.
The neurologic findings at the time of examination in the series mentioned above were as follows: eighth nerve involvement (auditory and vestibular; 45 of 46 patients), facial weakness including disturbance of taste (26 patients), sensory loss over the face (26 patients), gait abnormality (19 patients), and unilateral ataxia of the limbs (9 patients). Inequality of reflexes and 11thand 12th-nerve palsies were present in only a few patients. Signs of increased intracranial pressure appear late and have been present in fewer than 25 percent of our patients. These findings are comparable to those reported by House and Hitselberger many years ago and, more contemporarily, by Harner and Laws. With the shift in recent years to fairly routine investigation of unilateral hearing loss by cerebral imaging, it is common to find these tumors at a far earlier stage, if as an incidental finding on cerebral imaging, well before the tumor becomes symptomatic.
The contrast-enhanced CT will detect practically all vestibular schwannomas that are larger than 2.0 cm in diameter and project further than 1.5 cm into the cerebellopontine angle. Much smaller intracanalicular tumors (i.e., restricted to within the internal acoustic canal) can be detected reliably by MRI with gadolinium (Fig. 30-20). Specialized thin-slice MRI sequences such as steady-state free precession can accurately define anatomic relationships between the tumor and adjacent cranial nerves and vessels with high resolution.
Audiologic and vestibular evaluation includes the various tests described in Chap. 14, the brainstem auditory evoked response probably being the most sensitive to the presence of acoustic schwannoma. In combination, they permit localization of the deafness and vestibular disturbance to the cochlear and vestibular nerves rather than to their end organs. The CSF protein is raised in two-thirds of the patients (greater than 100 mg/dL in one-third); a clinically inevident acoustic schwannoma is one of the causes of an unexpectedly elevated CSF protein when a lumbar puncture is performed for other reasons.