LATERAL SKULL BASE

AMOLENDA, PATRICIA G.

LATERAL SKULL BASE

Anatomy

Internal auditory canal with the facial nerveJugular ForamenForamen lacerumForamen ovaleForamen 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 FracturessquLongitudinal temporal bone fractureTransverse temporal bone fractureIsolated 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 chinThe 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 fractureCaused by a diffuse, lateral traumatizing

force (ex. Falls, brain trauma)Fracture along the EAC and the anterior

border of the petrous pyramidSymptoms: otorrhea (blood or blood with

CSF), hearing loss, bloody rhinorrhea, facial paralysis

Longitudinal Temporal Bone Fracture

DiagnosisOtoscopy: tearing of the meatal skin and TM,

with bleeding into the ear canal Clinical auditory testing (Weber test):

lateralized to affected earNeurography: facial nerve functionThin slice CT scanPure tone audiometry

Longitudinal Temporal Bone Fracture

ComplicationsMeningitis, OM w/ TM perforation, facial

nerve paralysisTreatmentCover the ear with sterile dressingCorticosteroids: facial paralysisSurgical 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

DiagnosisClinical 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

ParagangliomaPrimary Cholesteatoma or EpidermoidCarcinoma of the MucosaSarcomaLymphoma

Paraganglioma

Also glomus tumor, chemodectomaMost common tumor of the middle ear and

adjacent lateral skull baseArises 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, AngiographyTreatment: Surgery-subtotal petrosectomy

Tumors of the Internal Auditory Canal and Cerebellopontine Angle

Vestibular SchwanommaMeningiomaHemangiomaLipoma

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: observe1-2.5cm: streotactic radiosurgery/ open

surgery>2.5cm: open surgery