Baseline and follow-up MRI of the internal auditory canal after suboccipital resection of acoustic schwannoma: appearances and clinical correlations.

Prospective baseline MRI was obtained on 31 patients who had "total" removal of acoustic schwannoma 6 months to 9 years previously. Follow-up MRI was performed after 1-2 years on patients with questionable abnormalities. We found four patterns (1) internal auditory canals (IAC) with nonenhancing soft-tissue strands, possibly scars or distorted residual nerves (8); (2) IAC with marginal enhancement-reactive dura mater (16); (3) IAC with contrast-enhancing globular tissues suggesting residual or recurrent tumour (5); (4) high-signal intensity in the IAC before contrast medium administration, probably related to graft with fat/fascia/muscle (2). Prospective 1-to 2-year follow-up studies were available in 8, 5, and 1 patients in groups 2, 3, and 4 respectively. In group 2, dural enhancement remained unchanged in 5 patients and decreased in 3. In group 3 follow-up showed 1 tumour recurrence (surgically confirmed) and 4 stable abnormalities. In group 4, follow-up in 1 of the 2 patients was stable. In groups 1 and 2, the MRI features correlate well with complete tumor removal. Whether follow-up in these groups is indicated needs to be determined. In group 3 residual or recurrent tumor cannot be excluded. In group 4, grafts may prevent adequate visualization of the IAC.