Auditory Canal
What is the clinical term for infection of the external auditory canal?
Otitis Externa
What cranial nerves pass through the internal auditory meatus?
CN VII (Facial nerve) and CN VIII (Vestibulocochlear nerve)
What is the most common tumor of the CPA?
Vestibular schwannoma
What parts make up the external auditory canal structurally?
Cartilaginous portion (outer third), bony portion (inner two-thirds)
What is the most likely effect on hearing if the cochlear nerve is compressed in the IAM?
Sensorineural hearing loss
What is the clinical triad of a growing vestibular schwannoma in the CPA?
Hearing loss, tinnitus, imbalance
What is the name of the gland that secretes earwax?
Ceruminous gland
Which part of the temporal bone houses the internal auditory meatus?
Petrous part of the temporal bone
Why might a large CPA mass cause hydrocephalus?
A large tumor can compress the fourth ventricle, narrowing or blocking its outlets (foramina of Luschka and Magendie), which impedes CSF flow from the ventricular system into the subarachnoid space, causing an accumulation of CSF.
Which specific branch of which nerve is responsible for the Arnold reflex (cough when cleaning ear)?
Auricular branch of the vagus nerve (CN X)
What is the anatomical positioning of the nervous structures as they pass through the IAM?
Anterosuperior quadrant: Facial nerve (cranial nerve VII)
Anteroinferior quadrant: Cochlear nerve (branch of cranial nerve VIII)
Posterosuperior quadrant: Superior vestibular nerve (branch of cranial nerve VIII)
Posteroinferior quadrant: Inferior vestibular nerve (branch of cranial nerve VIII)
Why might facial twitching occur before weakness in a CPA tumor affecting CN VII?
Facial twitching can occur before weakness in a CPA tumor affecting CN VII because early compression irritates, causing hyperexcitement the facial nerve fibers, causing involuntary spasms. As compression or irritation continues, axon injury or degeneration occurs, impairing nerve conduction, causing weakness.
Which cranial nerves contribute to the sensory innervation of the external auditory canal? Which nerves innervate which parts?
V3 - Anterior and superior walls of the EAC, Anterior portion of the auricle
VII - Concha and parts of the posterior external canal wall
IX - Inner surface of the tympanic membrane (medial side), Tympanic cavity via Jacobson’s nerve (tympanic branch of CN IX)
X - Posterior and inferior walls of the EAC, Posterior part of the auricle, External surface of the tympanic membrane
During resection of a vestibular schwannoma confined to the IAM, inadvertent injury to which vascular structure could lead to sudden, irreversible hearing loss and vestibular dysfunction? Why is the damage often severe?
Labyrinthine artery - it is an end-artery with no significant collateral supply; injury results in ischemia of the cochlea and vestibular apparatus, causing permanent deafness and vertigo.
What structures mark the medial, lateral, posterior, superior and inferior borders of the cerebellopontine angle?
Medial: The pons
Lateral: The petrous part of the temporal bone, including the internal auditory canal.
Posterior: The cerebellum, specifically the anterior surface of the cerebellar hemisphere.
Superior: The tentorium cerebelli (membrane that separates the cerebrum from the cerebellum).
Inferior: The lower cranial nerves (IX, X, XI) and the cerebellomedullary cistern (large subarachnoid cistern between cerebellum and medulla containing CSF).