Retrocochlear and CANS Pathologies Flashcards
Lecture 10-11
Several conditions that affect the _____ and its connections to the ______?
Auditory nerve and Central auditory nervous system (CANS)
Retrocochlear disorders are?
several conditions that affect the auditory nerve and its connections to the central auditory nervous system
What are some common retrocochlear diseases and disorders?
- genetic/congenital conditions
- auditory processing disorders
- intracranial neoplasms
- trauma to auditory nerve and temporal lobe
- cerebrovascular accidents
- central auditory nervous system dysfunction
Neoplasia means?
new growth
neoplasm is?
Abnormal mass tissue
Neoplasm is a disorder of ?
the cell cycle
growth of neoplasm is?
uncoordinated, competes with normal cells/tissue for energy and nutrition
neoplasms are:
purposeless, prey on host, and autonomous
Intracranial neoplasms
-benign or malignant tumors
- mass lesions of brain parenchyma (functional tissue)
- meninge tumors
- tumors of structures near brain tissue (affect function of brain tissue)
intracranial tumors arise from?
neuroglia cells
Neuroglia cells are the _______ of central nervous system
non excitable; supporting cells
neuroglial cells are ____ than neurons; lack ___; and do NOT ____ with other cells
smaller, axons, synapse
what are the four type of neuroglial cells?
1) Astrocytes
2) Oligodendrocytes
3) Microglia
4) Ependymal cells
Astrocytes
- star shaped
- support nerve cells
- function as electrical insulators
Astrocytes provide a barrier
at synapses that contain neurotransmitters or hormones such as dopamine
- lack implicated in Parkinsons
Astrocytes play a role in formation of:
Blood brain barrier
Oligodendrocytes are active in ?
formation of myelin sheath for central nerve fibers
Microglia are:
small glial cells
Microglia are activated in presence of?
inflammation and degenerative processes within the CNS
what kind of function does Microglia have?
Phagocytic function
microglia ingest and removes?
neural residue
Ependymal cells are ?
epithelial cells that line the cerebrospinal fluid filled brain cavities and spinal cord
Some ependymal cells facilitate
CSF circulation and are involved in production of CSF
Benign tumors
- slow growing
- well defined borders, surgical removal effective
- DO NOT METASTASIZE
- not life threatening
Malignant tumors
- fast growing
- invasion and destruction of other structures
- life threatening
- Metastasize
Intra-axial tumors
tumor resides in the brain tissue
ex: astrocytoma, glioblastoma
extra-axial tumors
resides outside brain, originates from brain tissue
- neither neuronal/glial
EX: meningiomas/ pineal & pituitary
Where is the temporal bone positioned between?
middle and posterior cranial fossa
4 segments of the temporal bone
1) Petrous
2) Squamous
3) Mastoid
4) Tympanic
What segment of temporal bone houses inner ear?
Petrous (hardest part of temporal bone)
What segment of the temporal bone forms the EAC?
Tympanic (matures by 3 years of age)
Most vascular tumors of the temporal bone are ?
Benign
Two categories of vascular tumors for classification?
1) Hemangiomas
2) Vascular malformations
Hemangiomas result in malformation of ?
angioblastic fetal tissue
Hemangiomas are made of
extra blood vessels
Hemangiomas are characterized by
- rapid growth (proliferation phase)
- slow period of involution (decrease in size)
Vascular malformations are
abnormal development of blood vessels
what is more common Hemangiomas or vascular malformations
Vascular malformations
Vascular malformations are:
- present at birth
- grow in proportion with body w/o regression
- present any time during life
vascular malformations present either
in the IAC or geniculate ganglion of VII N located in the fallopian canal
why is there tumor preference for the region of CN VII
extensive blood supply surrounding the geniculate ganglion
For Vascular malformations and Hemangiomas when do patients typically present with symptoms
3rd decade of life
For vascular malformations/ hemangiomas: when the geniculate ganglion is site of origin, what is almost always present
VII N dysfunction (weakness or twitch)
Symptoms of vascular malformations and Hemangiomas
- hemifacial spasm
- tinnitus
- Conductive HL (geniculate ganglion eroding into ME)
- Progressive SNHL ( IAC site)
- Vertigo (lesion affecting CNVIII)
Diagnosis of vascular malformations and hemangiomas
- case history and symptoms
Diagnosis w/ Imaging for vascular malformations and hemangiomas ?
- high resolution CT Scan
-MRI with contrast
Imaging for vascular malformations and hemangiomas: T2 weighted images
lesions appear hyperintense on T2
fluid is bright on T2
Imaging for vascular malformation/ hemangiomas. Geniculate lesions
- difficult to visualize on MRI, but can be detected on high resolution CT
Differential diagnosis of vascular malformations/hemangiomas?
- meningiomas
- VII N schwannoma
- Cholesteatoma
Why is meningioma a DD of vascular malformations /hemangiomas
irregular margins and may contain specks of calcium
Why is CN VII schwannoma a DD of vascular malformations/ hemangiomas
hemangiomas prodcues facial nerve symptoms when smaller in size compared to CN VII schwannoma
Why are cholesteatoma DD of vascular malformations/ hemangiomas
vascular lesion seen in ME cavity or invades other nearby structures
treatment of vascular malformation and hemangiomas
surgical removal
myelin sheath covering myelinated axons in CNS is formed by
oligodendrocytes
in peripheral nervous system the myelin sheath is formed by ?
connective tissue cells, schwann cells
What are myelin sheath of schwann cells of all peripheral nerves referred to?
neurilemmal sheath of schwann
What is the most common benign tumor of the temporal bone and cerbellopontine angle?
Schwannoma
- 6% intracranial tumors
- 91% of all tumors in and around the temporal bone
Within the temporal bone, the anatomic location of schwannoma is typically in three sites
1) internal auditory canal from CN VIII N
2) Jugular foramen for CN IX and X
3) fallopian canal of the VII CN
vestibular schwannomas arise from ?
Schwann cells
Vestibular schwannomas are
- benign extra axial tumors
typically unilateral except for NF 2
Incidence in vestibular schwannoma
- rare before 30
- 40 to 60 , 6th decade diagnosis
higher incidence in females
Vestibular schwannoma has two phases related to pressure:
1) otologic phase
2) neurologic phase
The otologic phase of vestibular schwannoma
tumor compresses in the IAC
HL:
- compression of vascular supply of CnVIII
- direct compression of CN VIII in IAC
neurologic phase of vestibular schwannoma
tumor compresses on other intracranial structures
Signs and Symptoms of Vestibular schwannoma
- hearing loss
- headache
- tinnitus
- unsteady gait
- imbalance/diziness
- facial paralysis
Audiometric findings of vestibular schwannoma: PURE TONE
- unilateral high frequency SNHL
asymmetrical more profound at higher frequencies
Brainstem lesions show flat unilateral SNHL
Audiometric findings of vestibular schwannoma: TONE DECAY
positive tone decay
Audiometric findings of of vestibular schwannoma: OAES
Normal OAES
-decreased contralateral suppression
Audiometric findings of vestibular schwannoma: SPEECH
WRS worse than pure tone thresholds, WRS worse in noise
- positive rollover ratio
Audiometric findings of vestibular schwannoma: IMMITTANCE
- tympanogram normal
- ARTS = abnormal/absent (VIII lesion)
-abnormal ipsilateral/contralateral for affected side (right ipsi right contra)
brainstem lesion = cross over pathways affected normal ipsi, absent contra
positive retrocochlear sign
RD +++
reflex amplitude declines >50% in 5 sec at 500 and 1000 Hz
questionable retrocochlear sign
RD ++
reflex amplitude declines >50% in 5 sec at 1000 HZ but not 500 Hz
not a significant retrocochlear sign
RD +
reflex amplitude declines <50% in 5 sec at 500 and 1000 Hz
ABR findings with vestibular schwannoma
increased wave V latency
increased I-V inter wave latency
- absent/abnormal wave V on affected size
Treatment for Vestibular schwannoma
- observation
-stereotactic radiosurgery (radiation) - surgery
Meningioma
tumor that grows from membranes that surround the brain and spinal cord called the meninges
Meningioma Incidence
later decades of life
more common in females
- associated with progesterone and breast cancer
Meningioma etiology
- association with NF2
- radiation therapy to head
- genetics
- chromosomes 1,7,10, and 14 and telomerase activation
- Di George syndrome is AD caused by deletion parts 22q
Audiometric S/S of meningiomas
- progressive unilateral SNHL
-vertigo - tinnitus
- nausea/vomitting
Audiometric findings of meningiomas
- VIII CN involvement
- abnormal ARTS affected side
- normal tymp
- positive acoustic reflex decay
- positive roll over and poorer scores of speech in noise
- abnormal ABR
NORMAL OAES
Differential Diagnosis of Meningioma
- otitis media
- Paraganglioma (glomus tumor)
- Facial VII nerve involvement
- Vestibular schwannoma
Treatment of Meningioma
Surgical excision
complete resection
Benign Tumors of the temporal bone
- osteoma (tumor in the EAC)
- paraganglioma (glomus tumor)
- neurofibromatosis 2
- Facial nerve schwannoma
Cortical tumors affecting the auditory cortex may show normal results for
peripheral auditory tests
- Pure tone audiometry, ARTs, OAES
WRS poorer in noise
Cortical tumors with ABR
ABR will be normal if periphery is normal because ABR measures responses up to brainstem level
Cortical tumors what signs are common
headaches and diziness
Malignant tumors tumors of temporal bone examples:
adenocarcinoma and osteosarcoma
Malignant tumors are often diagnosed at late stages of disease and present with dismal prognosis
symptoms similar to chronic suppurative otitis media
Malignant tumors audiologic signs and symptoms are
- aural discharge with or without blood
- otalgia
- hearing loss
- tinnitus
Malignant tumors signs and symptoms of cranial neuropathies
- facial paralysis
- headache
- cochleovestibular deficits (SNHL and vestibular symptoms)
Metastatic tumors of the temporal bone is metastasis from other sites to temporal bones, include:
breast cancer
lung cancer
renal carcinoma
lymphoma and leukemia
thyroid cancer
osteoblastoma
melanoma
