Pre-operative diffusion tensor (DT) tractography is currently employed in our Institutions. We use it to predict the course of the facial nerve (FN) in the vicinity of vestibular schwannomas (VS) of the cerebellopontine angle (CPA). In this study we were interested to assess the inter-observer reproducibility of this method. Two Neuroradiologists (PMGP and TT) determined independently the location of the FN by tractography and compared the results with in-vivo findings of microsurgery of VS.

14 patients with histologically proven VS were evaluated. DT images (1,5T) and tractography of the FN was performed accordingly to the method of Taoka T. et al1,2. Briefly, DT images were obtained with a single-shot echo-planar sequence (TR 4900 msec, TE 85 msec, b 1000 sec/mm2, six-axis encoding, FOV 230 mm, matrix 128 x 128, spacing 3 mm, 4 averages, 35 slices). For each patient, the most convex angle that the FN tract formed between its extremities in the axial plane was calculated as an...

The FN position was illustrated by DT tractography in all the patients of this series, with a good correspondence between the CPA course of the FN found at surgery and tractography (one grade 4 VS had the FN intra-tumoral). As expected (Table), the FN bundles with more acute angles were associated with larger tumors (PMGP: R2=0,620 ; TT: R2=0,684). Additionally, tracts determined by each observer were highly correlated (R2=0,977 ; ICC=0,98 p<0,001). Figure 3 (A) Correlation between the displacement angle of FN tracts and Koos...

DT tractography of the facial nerves shows a consistent correspondence with the surgical findings and the displacement relates with the space occupying effect of the tumor. Using a strict consensus guideline, independent observers can reach a high level of agreement for the pre-operative position of the FN bundles.

Reference 1 - Taoka T, Hirabayashi H, et al. Displacement of the facial nerve course by vestibular schwannoma: preoperative visualization using diffusion tensor tractography. J Magn Reson Imaging. 2006 Nov;24(5):1005-10. 2 - Gonçalves Pereira PM, Neto D´Almeida G, et al. Surgical proven location of the Facial Nerve in the vicinity of Cerebellopontine Angle Tumours depicted pre-operatively by Tractography. ESMRMB 2012 p.394-395.

Pedro M. Gonçalves Pereira Radiology dept, Hospital dos Lusiadas, Lisboa, Portugal [email protected] Toshiaki Taoka Radiology dept, Nara Medical University, Nara, Japan [email protected]