Measurements Of The Facial Nerve Canal On MSCT In Patients With Microtia

Objective To visualize and ascertain the location of the facial nerve canal on multi-slice spiral CT in patients with microtia and do some measurements.To study the relationship of facial nerve course and severity of deformity in auricle as well as severity of deformity in middle ear.Methods 25 patients with microtia who came to the first affiliated hospital during Jan 2007 to Dec 2008 were involved in this study. All the patients underwent multi-slice spiral CT (GE Light Speed 64) at the hospital. Multi-planar reformation (MPR) of axial, coronal, sagittal and oblique planes were used to best visualize different segments of the facial nerve canal. Establish an orthogonal coordinate system with the Bill bar as the basic point, and the line connecting the basic point and the midpoint of the porus acusticus as the basic line. Study the course of the facial nerve canal by using the orthogonal coordinate system and find its relationship with severity of deformity in auricle and severity of deformity in middle ear. Measure several distances( oval window to mastoid segment of facial nerve, vestibule to tympanic segment of facial nerve, tympanic segment of facial nerve to incus-malleus, mastoid segment of facial nerve to jugular bulb) to find the relationship of facial nerve and its neighboring structures.Results The incidence of anomaly of the facial nerve in patients with microtia was 62.1%. Anomaly varied, including facial nerve dehiscence, absence of tympanic segment of facial nerve, anterior mastoid segment of facial nerve, bifurcation of mastoid segment of facial nerve and so on. The facial nerve at the mastoid portion in patients with unilateral and bilateral microtia was respectively 3.1mm and 3.4mm anterior than that in control subjects. The difference between grade of auricle deformities was significant(P<0.05). Distance from cochlear window to mastoid segment of facial nerve was shorter in both unilateral and bilateral patients than that in control subjects, and the difference was 1.1mm and 1.2mm respectively. Distance from jugular bulb to mastoid segment of facial nerve was 1.5mm shorter in bilateral patients than that in control subjects, and the difference was significant(P<0.05).Conclusions MPR based on MSCT was able to visualize every segment of intratemporal facial nerve.62.1% patients with microtia had facial nerve anomalies .The facial nerve at the mastoid portion in patients with microtia was anterior than that in control subjects and the difference between grade of auricle deformities as well as the difference between middle ear deformites were significant(P<0.05). Distance from cochlear window to mastoid segment of facial nerve was shorter in patients with microtia. Mastoid segment of facial nerve was closer to jugular bulb in patients with bilateral microtia.