Using coronary computerized tomographic images to predict the bulging second genu of the facial nerve in mastoidectomy.

The aim of the present study is to determine whether coronary CT images of the temporal bone are useful to predict a bulging second genu of the facial nerve (SGFN) in mastoidectomy by measuring and comparing the heights of the SGFN above the prominence of the lateral semicircular canal (PLSC) in medial-to-lateral dimension on coronary CT images and in mastoidectomy. The relationship between the SGFN and the PLSC in medial-to-lateral dimension, which may have big variability, can be evaluated on the coronary CT images of the temporal bone. The heights of the SGFN above the PLSC in medial-to-lateral dimension were measured on coronary CT images and in mastoidectomy in 184 patients. If the SGFN is above the PLSC in medial-to-lateral dimension, we called the SGFN a bulging SGFN. The data measured on CT images and in surgery were described in histograms and compared. The sensitivity and the specificity in the diagnosis of a bulging SGFN on CT images were calculated by comparison with surgical measurement. Cohen's kappa coefficient was calculated. The heights of the SGFN above the PLSC measured in medial-to-lateral dimension varied from -2.9 to 2.9 mm on coronary CT images and varied from -3.0 to 3.0 mm in surgery. The data measured in surgery showed that the SGFN was above the PLSC in medial-to-lateral dimension in 27.7% (51/184) patients, at least 1 mm above the PLSC in 15.8% (29/184) patients and at least 2 mm above the PLSC in 6.0% (13/184) patients. The sensitivity and the specificity for CT diagnosis of a bulging SGFN were 100% (51/51) and 91.0% (121/133), respectively. Bulging SGFN can be predicted by measuring the height of the SGFN above the PLSC on coronary CT images of the temporal bone.