Radiological Classification of the Facial Nerve

Cochlear implantation done by mastoidectomy, posterior tympanotomy and round window membrane insertion or cochleostomy, if we have to. In cases with very laterally placed vertical segment of the facial nerve a trans- mastoid trans- attic approach used with trans canal monitoring as an alternative approach. Position of the vertical segment of the facial nerve (VFN) determined by coronal view HRCT of temporal bone, bone window of 0.6 mm thickness by using the cut posterior to the internal auditory canal at the level of lateral semicircular canal (LSCC) and then drawing a line parallel to the bony canal of the VFN and another parallel line on the outer bony wall of lateral semicircular canal (LSCC), and comparing level of both. The location of the facial nerve classified into normal if the FN is medial, same level or lateral to LSCC . Investigators referred the laterally placed FN (LPFN) when the whole vertical segment of facial nerve is lateral to LSCC. In addition, distance between VFN and LSCC was measured in cases of laterally placed FN.

Investigators proposed a radiological classification system of the mastoid segment of facial nerve to predict round window niche accessibility through posterior tympanotomy pre-operatively by using coronal view computed tomography scan of temporal bone. Facial nerve position classified into 3 types in relation to LSCC:

• TYPE I Medial to LSCC
• TYPE II Same level of LSCC
• TYPE III Laterally placed to LSCC III a) Less than 2mm III b) More than 2mm

Inclusion criteria

• All patient who underwent cochlear implant surgery with preoperative computed tomography scan and high resolution CT scan of temporal bone

Exclusion criteria

• None