The prevalence of "incidental" acoustic neuroma.

OBJECTIVE: To estimate the prevalence of "incidental" acoustic neuromas (ANs) in the population at large. DESIGN: An intracranial magnetic resonance imaging (MRI) database of 46 414 patients presenting to the University of California, San Francisco (UCSF), without known audiovestibular complaints was searched retrospectively from July 1995 to February 2003. Seventy percent of these MRIs included gadolinium, and none was specifically targeted through the internal auditory canal. A medical chart review of 688 patients with acoustic neuromas presenting to UCSF between 1980 and 1999 was searched for sex distribution. SETTING: Tertiary care university medical center. RESULTS: Eight patients with incidental AN were discovered. This figure suggests that undiagnosed ANs may be present in at least 0.02% of the population. Three patients were found to have audiovestibular symptoms on inquiry after diagnosis. Audiometry revealed asymmetry at 4 kHz in only 3 of 7 patients, with an otherwise symmetric audiogram in the remaining patients. Tumor size in this population ranged from 3 to 28 mm. Incidental ANs were more common in men, but ANs were more common in women overall. CONCLUSIONS: The prevalence of incidental AN appears to be roughly 2 in 10,000 people. This figure indicates that AN may be less prevalent than suggested in previously reported temporal bone studies and more prevalent than suggested by epidemiologic studies.

Chronic pachymeningitis presenting as asymmetric sensorineural hearing loss.

OBJECTIVE: The objective of this study was to characterize the auditory dysfunction associated with chronic pachymeningitis (inflammation of the dura mater). STUDY DESIGN AND SETTING: We conducted a university-based retrospective review. RESULTS: Three patients were identified who were diagnosed with chronic pachymeningitis after being referred for asymmetric sensorineural hearing loss. All patients were found to have other neurologic symptoms and signs during careful neurotologic evaluation. Two varieties of chronic pachymeningitis exist: a hypertrophic mass lesion and a linear dural thickening. Although the hypertrophic variety could be easily detectable by noncontrast magnetic resonance imaging (MRI), the linear form is only visible with the use of gadolinium enhancement. CONCLUSION: Chronic pachymeningitis is a rare form of sensorineural hearing loss that could portend an underlying disease of greater concern. Extensive evaluation is needed to exclude identifiable causes of chronic pachymeningitis, including infectious, neoplastic, and autoimmune diseases. SIGNIFICANCE: The clinician should be aware that the evaluation of a patient with asymmetric sensorineural hearing loss involves more than simply ruling out an acoustic neuroma. Fast-spin echo MRI techniques without the use of gadolinium contrast could miss a number of potentially treatable diseases such as chronic pachymeningitis. Patients with asymmetric sensorineural hearing loss should be carefully evaluated for other neurologic findings, and imaging with enhanced MRI is recommended.

Distal anterior inferior cerebellar artery syndrome after acoustic neuroma surgery.

OBJECTIVE: To define a clinicopathologic syndrome associated with persistent cerebellar dysfunction after acoustic neuroma (AN) excision. STUDY DESIGN: Case series derived from radiographic and clinical chart review. SETTING: Tertiary referral center. PATIENTS: In 12 patients with AN, persistent cerebellar dysfunction developed after AN removal. Each case demonstrated abnormality in the ipsilateral cerebellar peduncle on postoperative magnetic resonance imaging. MAIN OUTCOME MEASURES: Cerebellar function and ambulatory status over the first postoperative year. RESULTS: On magnetic resonance imaging scans, the extent of cerebellar peduncle infarcts was variable. It ranged from focal brain injury (<1 cm) involving only one third of the peduncle to diffuse defects (>2 cm) spanning the full thickness of the peduncle. Peduncular infarcts were associated with large tumor size (average 3.8 cm, range 2.0-5.5 cm diameter). The long-term functional outcomes (>1 yr) varied. Dysmetria was unchanged or improved in over half of the patients (6 of 11 patients). Gait recovered to normal or to preoperative levels in 5 patients. In the 6 patients with persistent impaired mobility, 2 had mild gait disturbance, 3 required regular use of a cane, and 1 has been dependent on a walker. One patient had sustained mild motor weakness. Three of 11 patients remained dependent on others for activities of daily living. CONCLUSIONS: Peduncle injury most likely stems from interruption of distal branches of the anterior inferior cerebellar artery (AICA). These small vessels are intimately related to the capsule of the tumor and may supply both the neoplasm and the brain parenchyma. It has long been recognized that interruption of the proximal segment of the AICA results in severe injury to the pons, with devastating neurologic sequelae. A limited AICA syndrome caused by loss of its distal ramifications seems a more plausible explanation for peduncular infarction than either venous insufficiency or direct surgical trauma.

The value of enhanced magnetic resonance imaging in the evaluation of endocochlear disease.

BACKGROUND: Gadolinium-enhanced magnetic resonance imaging (GdMRI) is routinely used in the evaluation and management of suspected retrocochlear pathology such as vestibular schwannoma. However, its value in the evaluation and diagnosis of cochlear pathology associated with sensorineural hearing loss (SNHL) has been less clear. STUDY DESIGN: Retrospective review of case histories and imaging studies of patients with SNHL and cochlear enhancement on GdMRI diagnosed between 1998 and 2000. RESULTS: Five patients with SNHL who required gadolinium administration to establish the diagnosis of endocochlear disease were identified. Diagnosed lesions included an intralabyrinthine schwannoma, intracochlear hemorrhage, radiation-induced ischemic change, autoimmune labyrinthitis, and meningogenic labyrinthitis. In these illustrative cases, the GdMRI demonstrated intrinsic high signal or contrast enhancement within the cochlea and labyrinth in the absence of a retrocochlear mass. In one patient with meningogenic labyrinthitis, cochlear enhancement on MRI led to prompt cochlear implantation before the potential development of cochlear ossification. CONCLUSION: Our experience suggests that GdMRI plays a crucial role in the diagnosis of cochlear pathology associated with sensorineural hearing loss and may directly impact patient management.