LATERAL SKULL BASE

1. LATERAL SKULL BASE AMOLENDA, Patricia G.

2. Anatomy • Internal auditory canal with the facial nerve • Jugular Foramen • Foramen lacerum • Foramen ovale • Foramen spinosum

3. 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

4. Clinical Examination • Cochleovestibular Syndrome • Sensorineural HL • Tinnitus • Dysequilibrium and vertigo

5. 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

6. Clinical Examination • Petrous Apex Syndrome • Triad • Purulent otorrhea • Stabbing ipsilateral facial pain (Trigeminal nerve irritation) • Diplopia (CN 6 palsy in petrous apex abscess)

7. 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

8. 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

9. Surgery of the Lateral Skull Base • Extracranial-extradural (Transmastoid and infratemporal)

10. Laterobasal Fractures

11. Classification of Temporal Bone Fractures • Squama-mastoid Fractures • squLongitudinal temporal bone fracture • Transverse temporal bone fracture • Isolated meatal fracture

12. Squama-mastoid Fractures • Confined to the temporal squama and mastoid air cells • Auditory and tympanic cavity may also be involved

13. 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

14. 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

15. 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

16. 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

17. 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

18. Transverse Temporal Bone Fracture Diagnosis • Clinicalexamination: • Weber Test-Lateralized to the normal ear • spontaneous nystagmus towards normal side • Otoscopy: hemotympanum • CT Scan

19. Transverse Temporal Bone Fracture Complication • Meningitis, Facial nerve paralysis Treatment • Surgical closure

20. Inflammations and Tumors of the Lateral Skull Base

21. 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

22. Tumors of the Temporal Bone • Paraganglioma • Primary Cholesteatoma or Epidermoid • Carcinoma of the Mucosa • Sarcoma • Lymphoma

23. Paraganglioma • Also glomustumor, 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

24. Paraganglioma • Manifestations: pulsatile tinnitus and conductive hearing loss, possible SNHL • Diagnosis: MRI, CT Scan, Angiography • Treatment: Surgery-subtotal petrosectomy

25. Tumors of the Internal Auditory Canal and Cerebellopontine Angle • Vestibular Schwanomma • Meningioma • Hemangioma • Lipoma

26. 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

27. 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

28. Vestibular Schwanomma • <1cm: observe • 1-2.5cm: streotactic radiosurgery/ open surgery • >2.5cm: open surgery