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LATERAL SKULL BASE AMOLENDA, PATRICIA G. Anatomy Internal auditory canal with the facial nerve Jugular Foramen Foramen lacerum Foramen ovale Foramen spinosum Clinical Examination The symptoms of the diseases of the lateral skull base may cause deficits of CN 7, 8, 9, 10, 11 CN testing Oral cavity examination: CN 9 & 12 Indirect laryngoscopy: CN 10, recurrent laryngeal nerve Clinical Examination Cochleovestibular Syndrome Sensorineural HL Tinnitus Dysequilibrium and vertigo Clinical Examination Jugular Foramen Syndrome CN 9: palatal deviation CN 10: unilateral vocal cord paralysis and dysphagia CN 12: tongue deviation toward the affected side, lingual atrophy, lingual fasciculations Clinical Examination Petrous Apex Syndrome Triad Purulent otorrhea Stabbing ipsilateral facial pain (Trigeminal nerve irritation) Diplopia (CN 6 palsy in petrous apex abscess) Imaging Studies • CT Scan – Best for defining infiltration and destruction of bony structures • MRI – Better for defining and differentiating lesions especially tumor and inflammatory processes • Conventional Angiography – Assess disease processes in close proximity to major vessels – Embolization Surgery of the Lateral Skull Base • Intracranial-intradural – Most common: suboccipital and retrosigmoid approach • Intracranial-extradural (Transtemporal) – Exposes the petrous pyramid through a temporal craniotomy – The dura is separated from the surface of the petrous pyramid and elevated away from it with the temporal lobe – Used in surgical treatment of temporal bone fractures or tumors of the internal auditory canal Surgery of the Lateral Skull Base Extracranial-extradural (Transmastoid and infratemporal) Laterobasal Fractures Classification of Temporal Bone Fractures Squama-mastoid Fractures squLongitudinal temporal bone fracture Transverse temporal bone fracture Isolated meatal fracture Squama-mastoid Fractures Confined to the temporal squama and mastoid air cells Auditory and tympanic cavity may also be involved Isolated Meatal Fracture Most often caused by a posterior displacement of the mandibular condyle Usually due to a fall onto the chin The fracture penetrates the posterior wall of the glenoid fossa and the anterior wall of the ear canal and is often associated with a condylar neck fracture Longitudinal Temporal bone Fractures Most common burst fracture Caused by a diffuse, lateral traumatizing force (ex. Falls, brain trauma) Fracture along the EAC and the anterior border of the petrous pyramid Symptoms: otorrhea (blood or blood with CSF), hearing loss, bloody rhinorrhea, facial paralysis Longitudinal Temporal Bone Fracture Diagnosis Otoscopy: tearing of the meatal skin and TM, with bleeding into the ear canal Clinical auditory testing (Weber test): lateralized to affected ear Neurography: facial nerve function Thin slice CT scan Pure tone audiometry Longitudinal Temporal Bone Fracture Complications Meningitis, OM w/ TM perforation, facial nerve paralysis Treatment Cover the ear with sterile dressing Corticosteroids: facial paralysis Surgical exploration Transverse Temporal Bone Fractures Fracture that runs across the petrous pyramid along the internal auditory canal and//or through the labyrinth Caused by a traumatizing force in the frontal plane Symptoms: severe vertigo, nausea and vomiting, deafness Transverse Temporal Bone Fracture Diagnosis Clinical examination: Weber Test-Lateralized to the normal ear spontaneous nystagmus towards normal side Otoscopy: hemotympanum CT Scan Transverse Temporal Bone Fracture Complication Meningitis, Facial nerve paralysis Treatment Surgical closure Inflammations and Tumors of the Lateral Skull Base Otitis Media most common inflammation and infection that affect the lateral skull base region Cholesteatoma is one of its complications which arises from the middle ear and spreads to the lateral skull base Tumors of the Temporal Bone Paraganglioma Primary Cholesteatoma or Epidermoid Carcinoma of the Mucosa Sarcoma Lymphoma Paraganglioma Also glomus tumor, chemodectoma Most common tumor of the middle ear and adjacent lateral skull base Arises from the paraganglia of the temporal region, most commonly in the area of the jugular bulb and along the neural plexus of the tympanic cavity It may be located in the middle ear, jugular bulb, carotid bifurcation, and along the vagus nerve, and often extend to the temporal bone region Paraganglioma Manifestations: pulsatile tinnitus and conductive hearing loss, possible SNHL Diagnosis: MRI, CT Scan, Angiography Treatment: Surgery-subtotal petrosectomy Tumors of the Internal Auditory Canal and Cerebellopontine Angle Vestibular Schwanomma Meningioma Hemangioma Lipoma Vestibular Schwanomma Slow-growing, benign, tumor arising from the Schwann cells of CN 8, affecting more commonly the vestibular nerve Medial tumors arise from the intracranial part of CN8 while the lateral tumors are located in the internal auditory canal Clinical hallmark is a unilateral hearing disorder which may consist of tinnitus, hearing loss and dysacusis Vestibular Schwannoma Medial schwannomas can occasionally produce trigeminal nerve symptoms such as facial pain or numbness in the jaw Large tumors present with signs of brainstem compression and/or hydrocephalus with ataxia, nausea & vomiting Diagnosis: clinical examination: shows unilateral cochleovestibular d/o Audiometry: shows retrocochlear impairment with lengthening of auditory brainstem reposnses gadolinium enhanced MRI Vestibular Schwanomma <1cm: observe 1-2.5cm: streotactic radiosurgery/ open surgery >2.5cm: open surgery