45% of intracranial tumors arise from ____________ cells. And what are these cells?
Neuroglia cells
- Neuroglia cells are supporting (non-excitable) cells that do not have axons nor do they synapse with other cells.
- Neuroglia outnumber neurons by 5-10 time and make up about one-half the volume of the nervous system.
Four types of Neuroglia cells:
Astrocytes: Function as electrical insulators
Oligodendrocytes: are active in the formation of myelin sheath (including Schwann cells)
Microglia: are active during inflammation and degeneration processes
Ependymal cells: line cavities of the brain and produce/circular CSF
3 Major types of 8th cranial nerve tumor types:
1) Schwannomas
2) Neurofibromas
3) Meningiomas
Schwannomas are most often found:
Found most often on the CN VIII and less often on the CN V, CN VII, and CN XI.
Neurofibromas (general) (from slide 3 p. 2 on Adult Applications)
Peripheral or Central in form.
Meningioma most often originate from:
90% originate in the supratentorial region, half of which are within the cerebellum or the CPA.
Vestibular Schwannoma signs & symptoms:
- Vestibular symptoms are not the earliest not the most pronounced due to compensation by the vestibular system.
- On the other hand, almost all patients complain of hearing problems, often accompanied by tinnitus (although tinnitus may be the sole symptom) and some unsteadiness.
Neurofibromatosis Type 1 (NF1)
- Peripheral
- Autosomal dominant (chromosome 17)
- Prevalence 60:100,000
- Onset in 1st decade
- Cafe-au-lait spots
- Neurofibromas
- Multiple freckles
- Optic gliomas
- Linch Nodules
- Osseous malformations
- Familial NF 1
Neurofibromatosis Type 2 (NF2)
- Central
- Autosomal dominant (Chromosome 22)
- Prevalence- 0.1:100,000
- Onset - 2nd to 3rd decade
- Bilateral acoustic neuroma
- Unilateral acoustic neuroma + 2 other specific tumors
- Familial NF 2
Signs & symptoms for ABR referral include:
1) Unilateral or asymmetrical tinnitus
2) Asymmetrical audiological findings
- Hearing thresholds
- WDS or rollover
- ART or AR decay
3) Vertigo or unilateral vestibular findings
4) Neurological findings esp. involving cranial nerves, e.g. facial nerve paresis
5) Sudden onset unilateral sensorineural loss
Criteria for ABR interpretation for neurodiagnosis:
1) Absolute wave V latency >2.5 SD re:norms, or > fixed value e.g., 6.2ms
2) Wave V ILD > 0.4 (typically correction factor for hearing loss is not advisable to use)
3) Interwave I-V latency abnormally prolonged re:norms; also include I-III & III-V comparison
4) Interwave ILD I-V, as well as I-III & III-V >0.3-0.4
