ACOUSTIC NEUROMA
Acoustic neuromas are intra-cranial tumors of the Schwann cell sheath covering the vestibular or cochlear nerve. The vestibular nerve is more commonly affected (95%). Symptoms of the acoustic neuromas depend on the the size of the tumor and its area of growth. For example. the tumor may compress the vestibular nerve, cochlear nerve, facial nerve of labyrinthe artery.
Incidence
Acoustic neuromas are diagnoses in 0.7-1.0 people per 100,000 population. However, this incidence may be rising partially because more widespread use of MRI has led to the diagnosis of more tumors. Even so, doctors take a personal approach to treating acoustic neuroma as symptoms can vary greatly between individuals.
Symptoms
The most common presenting symptom is unilateral hearing loss, usually caused by either direct injury to the cochlear nerve or damage to the cochlear blood supply (labyrinthe artery). Many patients also have difficulty in speech discrimination, especially as the volume of speech increases. Headaches are another common symptom,occurring in 50-60% of cases. Facial numbness occurs in 25% of patients. Facial hypoesthesia is common with larger tumors, as is is a decrease in the corneal reflex. Vertigo and disequilibrium are uncommon presenting symptoms but may more commonly ne see later.
In extreme cases, large acoustic neuromas can cause hydrocephalus due to disruption in the flow of cerebrospinal fluid through the ventricular system.
In extreme cases, large acoustic neuromas can cause hydrocephalus due to disruption in the flow of cerebrospinal fluid through the ventricular system.
Causes
No risk factors have been identified other than exposure to high-dose ionizing radiation. While once implicated, cell phone use is not associated with the risk of developing acoustic neuroma.
Defects in a tumor suppressor gene (22q12.2) have been identified in cases of acoustic neuromma. This defect leads to the production of a defective protein called merlin or schwannomin.
Defects in a tumor suppressor gene (22q12.2) have been identified in cases of acoustic neuromma. This defect leads to the production of a defective protein called merlin or schwannomin.
Diagnosis
Speech discrimination scores can aid in the diagnosis but are not a definitive diagnosis as patients may have normal or near-normal hearing and speech discrimination scores.
Most acoustic neuromas are diagnosed with gadolinium-enhanced MRIs. MRIs are usually conducted after a patient’s complaints of tinnitus or hearing loss
Most acoustic neuromas are diagnosed with gadolinium-enhanced MRIs. MRIs are usually conducted after a patient’s complaints of tinnitus or hearing loss
Treatment
Treatment will depend on many factors,including age, medical status, tumor size, tumor location, hearing status, and patients’ preferences.
The three main treatment approaches are:
Observation
Observation is the common first approach used for patients with small tumors, elderly patients, and patients with complicating medical conditions. Unfortunately, in some cases of observation the lack of action means that an initially operable tumor progress to an inoperable state.
Stereotactic radiotherapy
This is a relatively new treatment modality which has only emerged in the past 20 years as an alternative to surgery. Radiation is delivered precisely to the site of the tumor, avoiding damage to the surrounding tissue. As compared to surgical techniques for tumor removal, there is a decrease length of stay, decreased cost, rapid return to full employment, and lower immediate post-treatment morbidity and mortality. However, frequent re-scanning is needed to ensure tumor growth has been arrested. As the tumor is not removed and growth may continue, surgery can sometimes still be required. Additionally, secondary malignancies may result as following radiation exposure. This occurs in 1 of 1000 patients within 30 years.
The three main treatment approaches are:
- Surgical excision of the tumor
- Arresting tumor growth through stereotactic radiation therapy
- Careful serial observation
Observation
Observation is the common first approach used for patients with small tumors, elderly patients, and patients with complicating medical conditions. Unfortunately, in some cases of observation the lack of action means that an initially operable tumor progress to an inoperable state.
Stereotactic radiotherapy
This is a relatively new treatment modality which has only emerged in the past 20 years as an alternative to surgery. Radiation is delivered precisely to the site of the tumor, avoiding damage to the surrounding tissue. As compared to surgical techniques for tumor removal, there is a decrease length of stay, decreased cost, rapid return to full employment, and lower immediate post-treatment morbidity and mortality. However, frequent re-scanning is needed to ensure tumor growth has been arrested. As the tumor is not removed and growth may continue, surgery can sometimes still be required. Additionally, secondary malignancies may result as following radiation exposure. This occurs in 1 of 1000 patients within 30 years.
Surgical approaches
Three main surgical approaches are possible (retrosigmoid, translabyrinthine, middle cranial fossa) and each have their own advantages and disadvantages. Some techniques are associated with the possibility of damage to surrounding nerves.
Three main surgical approaches are possible (retrosigmoid, translabyrinthine, middle cranial fossa) and each have their own advantages and disadvantages. Some techniques are associated with the possibility of damage to surrounding nerves.
"About Vestibular Disorders." Vestibular Disorders. Johns Hopkins Medicine. Web. 25 Nov. 2013. <http://www.hopkinsmedicine.org/neurology_neurosurgery/specialty_areas/vestibular/>.
Kutz, Walter (2012). "Acoustic Neurmma." Retrieved November 24, 2013. emedicine.medscape.com.
Vestibular Disorders Association. Web. 25 Nov. 2013. <http://vestibular.org/>.
Kutz, Walter (2012). "Acoustic Neurmma." Retrieved November 24, 2013. emedicine.medscape.com.
Vestibular Disorders Association. Web. 25 Nov. 2013. <http://vestibular.org/>.