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Non-contrast high resolution fast spin echo magnetic resonance imaging of acoustic schwannoma.

AIM OF STUDY
The current gold-standard of examination for the exclusion of acoustic schwannomas is contrast-enhanced magnetic resonance (MR) imaging. Many patients however, still cannot afford to pay for the cost of this examination. As a result, many clinicians still resort to contrast-enhanced computed tomography (CT) scan; an examination which could miss small intracanalicular acoustic schwannomas. The aim of this study was to report on our experience on the usage of the more affordable high-resolution fast spin-echo (FSE) MR imaging for the diagnosis of acoustic schwannoma.


METHODOLOGY
A study involving 123 patients with symptoms of sensorineural hearing loss, vertigo and tinnitus was carried out between August 1996 and March 1997. All cases were scanned with a 1.5 T MR unit using a quadrate head coil. The section thickness was 1.5 mm, with TR/TE of 4000/96. Any mass arising from the vestibulocochlear nerve was considered to be an acoustic schwannoma, and most of these positive cases underwent further contrast-enhanced MR imaging to confirm the diagnosis.


RESULTS
A total of 7 acoustic schwannomas were detected on high resolution FSE MR imaging and for 5 of these cases, the diagnosis was confirmed with contrast-enhanced MR imaging. Three of the 7 positive patients had contrast-enhanced CT scan done just prior to the MR study and the tumours were not detected on CT scan. The smallest acoustic schwannoma detected on high-resolution FSE MR imaging had a dimension of 0.5 x 0.4 x 0.5 cm.


CONCLUSION
High resolution FSE MR imaging is more sensitive than contrast-enhanced CT scan in the diagnosis of acoustic schwannoma. Although the sensitivity is less than that of contrast-enhanced MR imaging, high resolution FSE MR is more affordable and therefore can play a role in the screening for acoustic schwannomas in selected groups of patients.