SURGICAL ANATOMY AND LANDMARKS OF TYMPANOMASTOID SEGMENT OF FACIAL NERVE USING MORPHOMETRY AS A MEASUREMENT TECHNIQUE: CADAVERIC TEMPORAL BONE DISSECTION STUDY

Introduction: Facial nerve is unique in terms of a long and tortuous course in a bony canal within the temporal bone.The intricate course of the nerve is of vital concern to all otologic surgeons as maximum otological surgeries involve tympanomastoid segment of the nerve.While removing the disease, surgeons need to pay attention to the adjacent reliable landmarks, to ensure complete removal of disease while avoiding injury to the facial nerve.Aim: To study the tympanomastoid course of facial nerve and to determine its effective surgical landmarks using morphometry Material and methods: The present study was conducted in the temporal bone dissection laboratory in the Department of Otorhinolaryngology, AFMC, Pune on 20 temporal bones (ten left and ten right) harvested from cadavers from the Department of Anatomy, AFMC Pune.The temporal bones were dissected under Karl Ziess Operating microscope with an inbuilt camera.Images were captured and morphometric analysis of the recorded images was performed with image analysis software.Observations and Results: Standard surgical approach was commenced with cortical mastoidectomy followed by facial recess approach.The distance between the facial and chorda tympani nerve was measured.Subsequently posterior canal wall was removed to study the relationship of Lateral semicircular canal and ossicles with the facial nerve.Normal surgical landmarks are often distorted in the diseased mastoid.Therefore, the surgeon should use as many of the available anatomical landmarks which act as a frame of reference for the facial nerve location. Conclusion:Cochleariform process, distance of tympanic segment of facial nerve from the dome of lateral semicircular canal, short process of incus and pyramid were found to be constant landmarks.It is extremely important that surgeons are well versed with the surgical anatomy of facial nerve and various landmarks for its identification.