Diagnosis of acoustic neuroma with computed tomography

Multicystic Acoustic Neuroma

A rare case of a multicystic acoustic neuroma is reported. At computed tomography (CT) and magnetic resonance imaging (MRI) the tumor was found to cause hydrocephalus, and displacement of the brainstem. The multicystic character was revealed on CT, while MRI only showed the mass lesion and the common signal intensities for an acoustic neuroma. The differential diagnosis of a multicystic lesion in the cerebellopontine angle is discussed.

Imaging review of the temporal bone: part I. Anatomy and inflammatory and neoplastic processes

From a clinical-radiologic standpoint, there are a limited number of structures and disease entities in the temporal bone with which one must be familiar in order to proficiently interpret a computed tomographic or magnetic resonance imaging study of the temporal bone. It is helpful to examine the region in an organized and systematic fashion, going through the same checklist of key structures each time. This is the first of a two-part review that provides a practical approach to understanding temporal bone anatomy, localizing a pathologic process with a focus on inflammatory and neoplastic processes, identifying pertinent positives and negatives, and formulating a differential diagnosis.

Auditory Brainstem Response versus Magnetic Resonance Imaging for the Evaluation of Asymmetric Sensorineural Hearing Loss

OBJECTIVES/HYPOTHESIS

Auditory brainstem response (ABR) testing and magnetic resonance imaging (MRI) are compared for the evaluation of patients with asymmetric sensorineural hearing loss (SNHL). MRI with gadolinium administration is the current gold standard for identifying retrocochlear lesions causing asymmetric SNHL. The study seeks to determine the sensitivity and specificity of ABR in screening for possible retrocochlear pathology. Most important among SNHL etiologies are neoplastic lesions such as vestibular schwannomas, cerebellopontine angle (CPA) tumors, as well as multiple sclerosis, stroke, or other rare nonneoplastic causes. The study results will allow the author to recommend a screening algorithm for patients with asymmetric SNHL.

STUDY DESIGN

The study is a multi-institutional, institutional review board approved, prospective, nonrandomized comparison of ABR and MRI for the evaluation of patients with asymmetric SNHL.

METHODS

Three hundred twelve patients (between the ages of 18 and 87) with asymmetric SNHL completed the study. Asymmetric SNHL was defined as 15 dB or greater asymmetry in two or more frequencies or 15% or more asymmetry in speech discrimination scores (SDS). These patients prospectively underwent both ABR and MRI. The ABR and MRI were interpreted independently in a blinded fashion. In addition to the ABR and MRI results, a variety of clinical and demographic data were collected.

RESULTS

Thirty-one (9.94%) patients of the study population of 312 were found on MRI to have lesions causing their SNHL. Of the 31 patients with causative lesions on MRI there were 24 vestibular schwannomas, 2 glomus jugulare tumors, 2 ectatic basilar arteries with brainstem compression, 1 petrous apex cholesterol granuloma, 1 case of possible demyelinating disease, and 1 parietal lobe mass. Twenty-two of the 31 patients had abnormal ABRs, whereas 9 patients (7 with small vestibular schwannomas) had normal ABRs. This gives an overall false-negative rate for ABR of 29%. The false-positive rate was found to be 76.84%. Sensitivity of ABR as a screening test was 71%, and specificity was 74%.

CONCLUSIONS

Ten percent of patients with asymmetric SNHL (by this study's criteria) are likely to have causative lesions found on MRI. Although the recently reported annual incidence of vestibular schwannoma in the general population is 0.00124%, for patients with asymmetric SNHL in this study, the incidence was 7.7% (nearly 4 orders of magnitude higher). ABR has been demonstrated to have low sensitivity and specificity in the evaluation of these patients and cannot be relied on as a screening test for patients with asymmetric SNHL. Keeping the use of MRI conditional on the results of ABR will annually result in missed or delayed diagnosis of causative lesions in 29 patients per 1,000 screened. The author recommends abandoning ABR as a screening test for asymmetric SNHL and adoption of a focused MRI protocol as the screening test of choice (within certain guidelines).

Imaging of acoustic neuromas. 1992

Diagnosis of acoustic neuromas has been simplified considerably by computed tomography (CT) and magnetic resonance imaging (MRI). Either enhanced method will visualize almost every acoustic neuroma. MRI is more sensitive inside the internal auditory canal. Currently, a gadolinium-enhanced MRI scan is considered an accurate indicator of whether or not an individual has an acoustic neuroma, although there have been false-positive enhanced MRI scans recently reported.

Calcified vestibular schwannoma in the cerebellopontine angle

Although vestibular schwannoma is a common tumor in the cerebellopontine angle, calcified vestibular schwannoma is rare. A 59-year-old woman with sudden onset epileptic seizures, was referred to Hokkaido Neurosurgical Memorial Hospital. Neurological examination revealed left Bruns nystagmus, left deafness and left cerebellar ataxia. Brain MRI revealed a mass, about 3cm in diameter, in the left cerebellopontine angle. The mass showed heterogeneous intensity on T1- and T2-weighted and fluid-attenuated inversion recovery (FLAIR) images. Hydrocephalus was seen. On CT scan, the tumor was calcified. Preoperatively, vestibular schwannoma, meningioma, cavernous hemangioma, or thrombosed giant aneurysm were considered as differential diagnoses. The pathological diagnosis was schwannoma. For a calcified mass in the cerebellopontine angle, vestibular schwannoma should be considered in the differential diagnosis to plan appropriate treatment strategies.

Natural history of acoustic neuromas

OBJECTIVES/HYPOTHESIS

1) Develop a computerized technique to accurately compare acoustic neuroma size on routine computed tomography and magnetic resonance imaging (MRI) scans; 2) use this technique to determine the growth pattern in a large series of patients with acoustic neuroma who were conservatively managed; 3) describe the natural history of patients with acoustic neuromas who did not receive surgical intervention and those who underwent subtotal resection; 4) correlate the size and growth rate of acoustic neuromas to clinical presentation and auditory and vestibular testing; and 5) recommend guidelines for the management of patients with acoustic neuromas.

STUDY DESIGN

A retrospective study from 1974 to 1999 of patients with unilateral acoustic neuromas who had conservative treatment by serial imaging studies (80 patients) or subtotal resection (49 patients).

METHODS

All patient charts were evaluated for presenting symptoms, reasons for the type of management given, and clinical outcome. Charts were also reviewed with respect to serial audiological assessment, electronystagmography, and brainstem auditory evoked response. Imaging studies were analyzed using a computer technique so that serial studies could be compared to determine growth rates.

RESULTS

Rigorous computer analysis of tumor size and growth rate was statistically the same as the radiologist's description of the tumor size and growth rate. Of 70 patients who were older than 65 years of age old at the time their tumor was discovered, 4 (5.7%) required intervention and 18 (26%) were dead of unrelated causes. These patients had a mean follow-up of 4.8 years (range, 0.01-17.2 y). Overall, growth rate for nonsurgical patients was 0.91 mm per year. Nonsurgical tumors did not grow or regressed in 42%. Overall postoperative growth rate for surgical subtotal resection patients was 0.35 mm per year. Surgical tumors did not grow or regressed after subtotal resection of acoustic neuroma in 68.5% of patients. Three patients (6.1%) required revision surgery because of tumor growth or the development of symptoms. Neither auditory nor vestibular testing was a reliable measure for determining tumor growth.

CONCLUSION

Measurement of the maximal tumor diameter on MRI scans is a reliable method for following acoustic neuroma growth. There is no need to perform a rigorous analysis of tumor size to determine whether the tumor is growing significantly. The vast majority of patients older than 65 years with acoustic neuromas do not require intervention. The indications for intervention should be based on a combination of rapid tumor growth with the development of symptoms.

Volume growth rate of acoustic neurinomas

Of 79 acoustic neurinomas seen between June 1980 and June 1984, at least two CT scans were available for each of 23 tumors (21 patients); the scans were performed at intervals of at least 6 months. The volume growth rate of the tumours was either moderate, with a volume doubling time ranging from 205 to 545 days, or slow, with a doubling time ranging from 1090 days to no observable growth. No single clinical, radiological or histological feature correlated with any type of growth rate. However, some conclusions were drawn. If a primary CT scan is negative, at least 1 year should elapse before it is worthwhile taking another scan, even though audiological findings suggest growth; after an apparently radical removal, at least 3 years should elapse before a check CT scan is worthwhile; and if a small acoustic neurinoma is diagnosed, but for some reason not operated upon, a second CT scan should be carried out 1 year later in order to reassess the case.

Postoperative CT findings in acoustic neurinomas operated upon by a translabyrinthine approach

The findings at CT examinations, performed on 46 patients with acoustic neurinomas about 6 months after translabyrinthine surgery, were analyzed and compared with preoperative findings. Direct as well as indirect signs of expansion had disappeared postoperatively. Bulging of cerebellar tissue towards the operative defect in the petrous bone, a finding not connected with local adhesions, was notable. Hypodensity in the vicinity of the removed tumor occurred either due to local widening of the subarachnoid space or due to changes within the cerebellar parenchyma. Local and general widening of the fourth ventricle as a sign of atrophy was a frequent finding.

Meningiomas of the cerebellopontine angle

The majority of cerebellopontine angle tumors are acoustic neurinomas; however, 10% to 15% are meningiomas. Meningiomas are benign lesions that must be removed but may require surgical approaches different from those used for acoustic neurinomas. To determine if meningiomas could be distinguished from acoustic neurinomas clinically, findings in 20 patients who underwent removal of a meningioma were compared to those in 131 patients who had an acoustic neurinoma removed during the same period. We found that in patients with meningiomas the tumors frequently are large at presentation, the otologic symptoms and audiometric findings are less dramatic, and roentgenograms of the skull and tomograms of the petrous apex rarely show erosion of the internal auditory canal. Computerized tomography is the most useful method for differentiating a meningioma from a neurinoma: when a meningioma is present the characteristic finding is a broad-based mass aligned with the petrous ridge, not centered over the internal auditory canal.

High resolution O2 computed meatocisternography in the differential diagnosis of internal auditory canal pathology

Recent introduction of O2 computed tomography cisternography and imaging with high resolution program have greatly improved the detection and preoperative evaluation of acoustic neuromas and other possible pathologies of the internal auditory canal. Sixty patients have been evaluated following the diagnostic protocol given in the text. Based on our results and on the experience as reported in literature HRO2CTC proved to be the most reliable method for detection and exclusion of intracanalicular and small extracanalicular acoustic neuromas and other pathologies at the internal auditory canal level.

CT of meningiomas on the Posterior surface of the petrous bone

A detailed analysis of the CT findings in 16 surgically verified cases of meningioma of the posterior surface of the petrous bone is presented. The results indicate that a correct preoperative diagnosis is possible in almost every case. Frequently occurring specific CT criteria for meningioma of the posterior surface of the petrous bone include: hyperdense, homogeneously enhancing, extra-axial, CPA mass; inverse relationship between precontrast attenuation value and degree of contrast enhancement of the tumor; oval shape; obtuse angle between lateral tumor border and posterior surface of petrous bone, and evidence of transcisternal supratentorial tumor extension. Infrequently occurring specific CT criteria include: tumor calcification; hyperostosis or exostosis of the posterior surface of the petrous bone; a comma-shaped tumor configuration in cases with transcisternal tumor extension and evidence of transtentorial tumor extension. Oxygen CT cisternography is the most sensitive and reliable technique for detecting small tumors. The CT differential diagnosis of meningioma of the posterior surface of the petrous bone is discussed.

Metrizamide cisternography in the diagnosis of acoustic neurinomas

Seventy-three cisternographies with metrizamide were performed on 69 patients, mainly for diagnosis of an acoustic neurinoma. Of the 31 patients with pathological findings on cisternography 26 underwent surgery for 23 acoustic neurinomas, one neurinoma of the facial nerve, and two meningiomas. For diagnosing small tumours of the cerebellopontine cistern, cisternography is superior to all other neuroradiological methods. Tomography of the porus acusticus internus and CT scanning are the initial radiological methods in patients with signs of cerebellopontine angle lesions; if no lesion is disclosed by these two methods cisternography with metrizamide should be performed to exclude a small tumour, particularly a small acoustic neurinoma.

Attenuation profiles of the petrous bone with acoustic neuroma

Attenuation profiles across the petrous bone covering the whole internal auditory meatus (IAM) were constructed from the printouts obtained by computed tomography (CT) with narrow collimation performed on 12 patients with 13 acoustic neuromas. In healthy patients the attenuation profiles of right and left petrous bone were very similar in shape. The attenuation values of the individual pixels in the pixel columns of the printout located at the site of the porus and the IAM reflected the demineralization of the petrous bone and the widening of the porus and the IAM caused by the acoustic neuroma. A widening deep in the meatus was demonstrated in a patient with an intracanalicular tumor, and therefore it seems possible to make this diagnosis by CT scanning combined with the construction of attenuation profiles across the petrous bone. In the presence of unilateral acoustic neuroma there was a significant and characteristic difference in shape between the attenuation profiles of the two sides with generally lower attenuation values on the tumor side together with signs of widening of the porus and the IAM. In cases of bilateral acoustic neuroma comparison of the attenuation profiles can be made with mean attenuation curves obtained from scanning normal petrous bones. The prevailing physical limitations for demonstrating a narrow bony canal like the IAM with CT was experimentally analyzed using bone-simulating plastic material.

Angiographic diagnosis of acoustic neurinomas and meningiomas in the cerebellopontine angle--a reappraisal

Forty-two acoustic neurinomas and seven meningiomas in the cerebellopontine angle were reviewed, and the radiological differential diagnosis of these tumors is discussed. Though enlarged internal auditory meati and characteristic CT findings were reasonably reliable indicators for the diagnosis of acoustic neurinomas, it was angiography which substantiated their correct diagnosis. An arcuate vein was frequently demonstrated with acoustic neurinomas, but never with meningiomas. Visualization of tangled veins seems to favor a diagnosis of acoustic neurinomas. Contrary to earlier reports, tumor stains were most frequently visualized using selective external carotid arteriography. The degree of tumor stains did not aid in differentiating acoustic neurinomas from meningiomas. The importance of using angiotomography, especially in the anteroposterior projection, and external carotid angiography during prolonged injections of large amounts of contrast media, is emphasized.

Evaluation of the internal auditory meatus with acoustic neuromas using computed tomography

Forty-seven patients with 48 unoperated acoustic neuromas have been studied by computed tomography (CT) with respect to bone changes. CT and conventional X-ray examination of the skull were compared. The importance of using a small collimator, proper selection of the plane of the CT section and changing of the window level is stressed. CT detects porus changes as accurately as conventional X-ray methods.

The differential diagnosis of pontine angle meningioma and acoustic neuroma with computed tomography

Seven pontine angle meningiomas were examined with computed tomography (CT). The result was compared with that of a study of 61 acoustic neuromas. These two tumor types differ in manner of growth, volume, shape, attenuation, attachment to bone, cisternal deformation, frequency of calcification, peripheral edema, and bone changes.