Fig. 12.1
Diffusion tensor imaging (DTI)-based fibre tracking of the facial nerve (FN) using commercially available software for navigational surgical planning. Fibre tracking findings are fused with anatomical images, acquired using MR constructive interference in steady-state (CISS) sequences. The FN fibres are reconstructed and the lesion is segmented to obtain 3D images. In this case the FN courses along the anterior middle third of the tumour. (a) Axial view showing the left FN fibres (red colour) on the anterior surface of the VS. (b) Sagittal and coronal view showing the FN fibres running on the anterior middle third of the tumour into the left internal auditory meatus
12.2.2 Clinical Study
To validate this technique we used this imaging protocol on 22 consecutive patients [18] with large VS classes T3a to T4b according to the Hannover VS classification system [19] and normal preoperative FN function (House-Brackmann [20] grade 1) (Table 12.1). The patients were all surgically treated in our institute. The surgical technique for tumour removal has been described in previous publications: all patients were operated in the semisitting position using the retrosigmoid approach [1, 19, 21, 22]. The FN is identified initially in the internal auditory canal and verified by electrical stimulation with a bipolar stimulus of 1 mA intensity. After debulking, the proximal segment of the FN at the brainstem is identified. The further dissection between the tumour capsule and the nerve revealed the exact location of the FN.
Table 12.1
Summary of patient population and results
Sex | Age | Tumour class | Tumour side | Facial nerve functiona | Facial nerve location – DTI-based fibre tracking | Facial nerve location – intraoperative findings | Facial nerve shape | |
|---|---|---|---|---|---|---|---|---|
1 | M | 20 | T4a | Right | 2 | Anterior middle third | Anterior middle third | Flat |
2 | M | 55 | T3a | Left | 1 | Anterior middle third | Anterior middle third | Compact |
3 | F | 50 | T3a | Right | 2 | Polar superior | Polar superior | Flat |
4 | F | 43 | T4b | Left | 4 | Anterior lower third | Anterior lower third | Compact |
5 | M | 47 | T4a | Right | 2 | Anterior middle third | Anterior middle third | Flat |
6 | M | 50 | T3b | Left | 1 | Anterior lower third | Anterior lower third | Compact |
7 | F | 31 | T4a | Left | 1 | Anterior upper third | Anterior upper third | Flat |
8 | F | 51 | T4b | Right | 4 | Anterior middle third | Anterior middle third | Flat |
9 | F | 40 | T3b | Left | 3 | Polar inferior | Polar inferior | Compact |
10 | M | 58 | T3b | Right | 1 | Anterior upper third | Anterior upper third | Compact |
11 | F | 52 | T3b | Left | 1 | Anterior lower third | Anterior lower third | Compact |
12 | F | 23 | T4b | Left | 4 | Anterior middle third | Anterior middle third | Compact |
13 | F | 37 | T4b | Right | 4 | Anterior lower third | Anterior lower third | Flat |
14 | M | 40 | T4b | Left | 3 | Anterior middle third | Anterior middle third | Flat |
15 | M | 52 | T4b | Right | 2 | Anterior middle third | Anterior middle third | Compact |
16 | M | 19 | T3a | Left | 1 | Anterior lower third | Anterior lower third | Flat |
17 | M | 41 | T4a | Left | 2 | Anterior middle third | Anterior middle third | Compact |
18 | M | 62 | T3b | Left | 1 | Anterior middle third | Anterior middle third | Compact |
19 | M | 39 | T4a | Right | 2 | Anterior middle third | Anterior middle third | Flat |
20
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