Anatomy of Facial Nerve MCQs

Processuscochleariformis Hook like projection on medial wall of middle ear. Surgical landmark for first genu of facial nerve. It demarcates the geniculate ganglion which lies just anterior to it. Tympanic segment of the facial nerve starts at this level. Reference: Diseases of Ear, Nose and Throat & Head and Neck Surgery by P L Dhingra, 8 th Edition, Pg. no. - 7, 108.

Facial recess is the surgical landmark for posterior tympanotomy. Boundaries: Medial boundary - Vertical segment of the facial nerve (mastoid segment) Lateral boundary - Chorda tympani Superior boundary - Fossa incudis (short process of incus) Reference: Diseases of Ear, Nose and Throat & Head and Neck Surgery by P L Dhingra, 8th Edition, Page Number-6.

SURGICAL LANDMARKS OF FACIAL NERVE For middle ear and mastoid surgery Processus It demarcates the geniculate ganglion which lies just anterior to it. Tympanic segment of the nerve starts at this level. Oval window and horizontal The facial nerve runs above the oval window (stapes) and below the horizontal canal. Short process of Facial nerve lies medial to the short process of incus at the level of aditus. Nerve runs behind the pyramid and the posterior tympanic sulcus. Tympanomastoid In vertical or mastoid segment, nerve runs behind this suture. Digastric ridge. The nerve leaves the mastoid at the anterior end of digastric ridge. Reference: Diseases of Ear, Nose, AND Throat by PL Dhingra, Pg.108,109

Explanation: Schwannomas are rare nerve sheath tumours that can occur throughout the body, and are symptomatic based on location, size, and impingement on adjacent structures. These tumours are often benign lesions that occur sporadically or as part of genetic conditions such as neurofibromatosis. Schwannomas may arise from peripheral nerves, gastrointestinal nerves, spinal nerve roots and cranial nerves. Facial nerve Schwannomas arise from cranial nerve VII and commonly involve the geniculate ganglion, labyrinthine segment, and internal auditory canal . While small lesions are asymptomatic, larger lesions can cause facial nerve paralysis and facial spasms. Lesions in the internal auditory canal can cause hearing loss, tinnitus, vertigo, and otalgia.

Labyrinthine segment is the narrowest part of the facial nerve. Hence it is the physiological bottleneck of facial nerve. Reference: Diseases of Ear, Nose and Throat & Head and Neck Surgery by P L Dhingra, 8 th Edition, Page - 107, 108.

Chewing is performed by muscles of mastication(Masseter, Temporalis, Pterygoids). These are supplied by the trigeminal nerve. Muscles of facial expression are supplied by the facial nerve. Reference: Diseases of Ear, Nose and Throat & Head and Neck Surgery by P L Dhingra, 8 th Edition, Page - 117.

B i.e. Medial pterygoid Temporalis, messeter and lateral pterygoid musclesQ are supplied by anterior division of mandibular nerve whereas medial pterygoid muscleQ is supplied by the main trunk of mandibular nerve.

Topodiagnostic Tests: Schirmer's Test - Reduced lacrimation - lesion proximal to geniculate ganglion(first genu) Stapedial Reflex - Lost in lesions above Nerve. to Stapedius(second genu) Taste test - Impairment of taste means lesion above chorda tympani origin In this question, Lacrimation - absentl Stapedial reflex - Abscent Taste sensation - Impaired So the level of lesion is above the first genu, in the labyrinthine segment. Reference: Diseases of Ear, Nose and Throat & Head and Neck Surgery by P L Dhingra, 8 th Edition, Page - 108.