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Encyclopedia > Acoustic neuroma
Acoustic neuroma
Classification & external resources
ICD-10 C72.4
ICD-9 225.1
ICD-O: M9560/0
DiseasesDB 100
MedlinePlus 000778
eMedicine ent/239 

Acoustic neuroma (or Vestibular Schwannoma) is a benign primary intracranial tumor of the myelin forming cells called "Schwann cells" (Schwannoma) of the 8th cranial nerve --- also known as the acoustic nerve, (or more properly the vestibulocochlear nerve). The International Statistical Classification of Diseases and Related Health Problems (most commonly known by the abbreviation ICD) provides codes to classify diseases and a wide variety of signs, symptoms, abnormal findings, complaints, social circumstances and external causes of injury or disease. ... The following codes are used with International Statistical Classification of Diseases and Related Health Problems. ... // C00-D48 - Neoplasms (C00-C14) Malignant neoplasms, lip, oral cavity and pharynx (C00) Malignant neoplasm of lip (C01) Malignant neoplasm of base of tongue (C02) Malignant neoplasm of other and unspecified parts of tongue (C03) Malignant neoplasm of gum (C04) Malignant neoplasm of floor of mouth (C05) Malignant neoplasm of... The International Statistical Classification of Diseases and Related Health Problems (most commonly known by the abbreviation ICD) provides codes to classify diseases and a wide variety of signs, symptoms, abnormal findings, complaints, social circumstances and external causes of injury or disease. ... The following is a list of codes for International Statistical Classification of Diseases and Related Health Problems. ... The International Classification of Diseases for Oncology (ICD-O) is a domain specific extension of the International Statistical Classification of Diseases and Related Health Problems for tumor diseases. ... The International Classification of Diseases for Oncology (ICD-O) is a domain specific extension of the International Statistical Classification of Diseases and Related Health Problems for tumor diseases. ... The Disease Bold textDatabase is a free website that provides information about the relationships between medical conditions, symptoms, and medications. ... MedlinePlus (medlineplus. ... eMedicine is an online clinical medical knowledge base that was founded in 1996. ... Schwannomas, also referred to as Neurilomas, are slow-growing central nervous system tumours arising from the supporting cells of peripheral nerves, which include cranial and spinal nerve roots). ... Benign can refer to any medical condition which, untreated or with symptomatic therapy, will not become life-threatening. ... A brain tumor is any intracranial tumor created by abnormal and uncontrolled cell division, normally either found in the brain itself (neurons, glial cells (astrocytes, oligodendrocytes, ependymal cells), lymphatic tissue, blood vessels), in the cranial nerves (myelin-producing Schwann cells), in the brain envelopes (meninges), skull, pituitary and pineal gland... In neuroscience, myelin is an electrically insulating phospholipid layer that surrounds the axons of many neurons. ... Schwann cells are a variety of neuroglia that wrap around axons in the peripheral nervous system, forming the myelin sheath. ... Cranial nerves are nerves which start directly from the brainstem instead of the spinal cord. ... The vestibulocochlear nerve is the eighth of twelve cranial nerves, and also known as the auditory nerve. ... The vestibulocochlear nerve (also known as the auditory or acoustic nerve) is the eighth of twelve cranial nerves, and is responsible for transmitting sound and equilibrium (balance) information from the inner ear to the brain. ...


The term "acoustic neuroma" is actually a misnomer since the tumor never arises from the acoustic division of the vestibulocochlear nerve (cranial nerve VIII) and the tumor is not a neuroma but a schwannoma. The vestibulocochlear nerve (also known as the auditory or acoustic nerve) is the eighth of twelve cranial nerves, and is responsible for transmitting sound and equilibrium (balance) information from the inner ear to the brain. ...


Approximately 3000 cases are diagnosed each year in the United States with an incidence of about 1 in 100,000. Incidence peaks in the fifth and sixth decades and both sexes are affected equally.

Contents

Pathogenesis

Acoustic neuromas may occur sporadically, or in some cases occur as part of von Recklinhausen neurofibromatosis, in which case it may take on one of two forms. Neurofibromatosis type I (NF-1), also known as von Recklinghausen syndrome, comprises, along with neurofibromatosis type II (a. ...

  • In Neurofibromatosis type I, a schwannoma may sporadically involve the 8th nerve, usually in adult life, but may involve any other cranial nerve or the spinal root. Bilateral acoustic neuromas are rare in this type.
  • In Neurofibromatosis type II, bilateral acoustic neuromas are the hallmark and typically present before the age of 21. These tumors tend to involve the entire extend of the nerve and show a strong autosomal dominant inheritance. Incidence is about 5 to 10%.

The usual tumor in the adult presents as a solitary tumor, originating in the nerve. It usually arises from the vestibular portion of the 8th nerve, just within the internal auditory canal. As the tumor grows, it usually extends into the posterior fossa to occupy the angle between the cerebellum and the pons (cerebellopontine angle). Because of its position, it may also compress the 5th, 7th, and less often, the 9th and 10th cranial nerves. Later, it may compress the pons and lateral medulla, causing obstruction of the CSF and increased intracranial pressure. It has been suggested that this article or section be merged into Dominance relationship. ... Figure 1a: A human brain, with the cerebellum in purple. ... Intracranial pressure, (ICP), is the pressure exerted by the cranium on the brain tissue, cerebrospinal fluid (CSF), and the brains circulating blood volume. ...


Clinical manifestations

Earliest symptoms of acoustic neuromas include ipsilateral sensorineural hearing loss/deafness, disturbed sense of balance and altered gait, vertigo with associated nausea and vomiting, and pressure in the ear, all of which can be attributed to the disruption of normal vestibulocochlear nerve function. Additionally more than 80% of patients have reported tinnitus (most often a unilateral high-pitched ringing, sometimes a machinery-like roaring or hissing sound, like a steam kettle). Sensorineural hearing loss is a type of hearing loss in which the root cause lies in the vestibulocochlear nerve (Cranial nerve VIII), the inner ear, or central processing centers of the brain. ... This article discusses the way the word deaf is used and how deafness is perceived by hearing and Deaf communities. ... Vertigo, sometimes called a headrush, is a major symptom of a balance disorder. ... Tinnitus (IPA pronunciation: or ,[1] from the Latin word for ringing[2]) is the perception of sound in the human ear in the absence of corresponding external sound(s). ...


Large tumors that compress the adjacent brainstem may affect other local cranial nerves. Involvement of the 7th cranial nerve (facial nerve) may lead to ipsilateral facial weakness, sensory impairment, and impairment of glandular secretions; involvement of the 5th cranial nerve (trigeminal nerve) may lead to loss of taste and loss of sensation in the involved side's face and mouth. Involvement of the 9th and 10th cranial nerves are uncommon, but may lead to altered gag or swallowing reflexes. The brain stem is the stalk of the brain below the cerebral hemispheres. ... The facial nerve is seventh of twelve paired cranial nerves. ... The trigeminal nerve is the fifth (V) cranial nerve, and carries sensory information from most of the face, as well as motor supply to the muscles of mastication (the muscles enabling chewing), tensor tympani (in the middle ear), and other muscles in the floor of the mouth, such as the...


Even larger tumors may lead to increased intracranial pressure, with its associated symptoms such as headache, vomiting, and altered consciousness.

Main article: intracranial pressure

Intracranial pressure, (ICP), is the pressure exerted by the cranium on the brain tissue, cerebrospinal fluid (CSF), and the brains circulating blood volume. ...

Diagnosis

Contrast-enhanced CT will detect almost all acoustic neuromas > 2.0 cm in diameter and project further than 1.5 cm into the cerebellopontine angle. Those tumors that are smaller may be detected by MRI with gadolinium enhancement. Audiology and vestibular tests should be concurrently evaluated using the Weber's and Rinne's test to assess for sensorineural versus conduction hearing loss. This article does not adequately cite its references or sources. ... The mri are a fictional alien species in the Faded Sun Trilogy of C.J. Cherryh. ... General Name, Symbol, Number gadolinium, Gd, 64 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white Standard atomic weight 157. ...


Treatment

Indicated treatments for acoustic neuroma include surgical removal and radiotherapy. Radiation therapy (or radiotherapy) is the medical use of ionizing radiation as part of cancer treatment to control malignant cells (not to be confused with radiology, the use of radiation in medical imaging and diagnosis). ...


Conservative treatment

Because these neuromata grow so slowly, a physician may opt for conservative treatment beginning with an observation period. In such a case, the tumor is monitored by annual MRI to monitor growth. Records suggest that about 45% of acoustic neuromata do not grow detectably over the 3-5 years of observation. In rare cases, acoustical neuromata have been known to shrink spontaneously. Often people with acoustic neruromata die of other causes before the neuroma becomes life-threatening. (This is especially true of elderly people possessing a small neuroma.) The mri are a fictional alien species in the Faded Sun Trilogy of C.J. Cherryh. ... This article or section does not adequately cite its references or sources. ... 80 year old man (Paul Kruger in later life) For the song by Hole and Nirvana, see Old Age. ...


Since the growth rate of an acoustic neuroma rarely accelerates, annual observation is essential. Acoustic neuromata may cause either gradual or—less commonly—sudden hearing loss and tinnitus. A year is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... Hearing impairment is a full or partial decrease in the ability to detect or understand sounds. ... Tinnitus (IPA pronunciation: or ,[1] from the Latin word for ringing[2]) is the perception of sound in the human ear in the absence of corresponding external sound(s). ...


Surgery

Removal of acoustic neuromas may be performed using several approaches. Each approach has its advantages and disadvantages. Microsurgery for acoustic neuroma is the only technique that removes the tumor. Radiation treatment (discussed in another section) does not remove the tumor, but has the potential to slow or stop its growth. Surgery is the only treatment that will definitively treat balance symptoms associated with tumor growth, as the vestibular nerves are removed at surgery.


Choice of surgical approach is based on the patient's age, medical condition, size of tumor, and preoperative hearing thresholds and speech discrimination, as well as other tests such as electronystamography, imaging, and auditory brainstem response testing. The patient's and surgeon's preferences also play a significant role.


During removal of the tumor, the tumor along with the superior and inferior vestibular nerves are removed. This results in an acute loss of vestibular input to the brain from the operated side. However, vestibular function improves rapidly due to compensation by the other ear and other balance mechanisms.


Surgery carries risk to the facial nerve which is monitored with facial nerve monitoring during the procedure. Best results (normal or near normal facial function) are more likely with small acoustic neuromas.


Three surgical approaches are commonly used. The first is the translabyrinthine approach, which destroys hearing in the affected ear. Thus, it is often employed in patients who have poor speech discrimination in the affected ear. Any size tumor may be removed with this approach. There is no brain retraction with this approach, and so is often considered the safest route to remove the tumor. In patients with neurofibromatosis type 2 who undergo auditory brainstem implantation, this technique is used as it provides the most direct path of access to the lateral recess and cochlear nucleus, where the device is placed. There are very few or no other articles that link to this one. ... The lateral recess is a projection of the fourth ventricle which extends into the inferior cerebellar peduncle of the brainstem. ... The cochlear nuclei consist of: (a) the lateral cochlear nucleus, corresponding to the tuberculum acusticum on the dorso-lateral surface of the inferior peduncle; and (b) the ventral or accessory cochlear nucleus, placed between the two divisions of the nerve, on the ventral aspect of the inferior peduncle. ...


The two other approaches (suboccipital/(retrosigmoid) and middle fossa) are hearing preservation approaches, which have a chance of preserving some or all of the hearing in the affected ear. Neurosurgeons often prefer the retrosigmoid approach, as they are frequently more familiar with it from training.


The middle fossa approach is used for tumors typically less than 2cm in greatest dimension, where hearing conservation is to be attempted. This approach has the advantage over the retrosigmoid approach in its direct access to the lateral end of the internal auditory canal. Multiple reports have shown that the retrosigmoid approach cannot reach the lateral end of the internal auditory canal without violating the posterior semicircular canal, and hence destroying the hearing.


A less common approach is minimally invasive endoscopic surgery. This approach is available in specialized centres. This technique is not widely used due to concerns over bleeding and the inability to remove tumors from the internal auditory canal with this method.


Acoustic neuroma surgery is highly technically demanding, and patients are advised to seek out surgical teams with extensive experience.


Radiation Therapy

Radiation therapy is done in a variety of ways, but mainly by two methods: gamma knife radiosurgery or fractionated stereotactic radiotherapy. In the gamma knife approach, 201 beams of gamma radiation are focused on the tumor in a single session. The damage to the tumor at the convergence point may cause it to stop growing but usually does not cause it to shrink in the long term. It may cause short-term shrinkage due to necrosis in the tumor. The damage may be to the tumor cells and/or to the tumor vasculature. Clinac 2100 C100 accelerator Radiation therapy (or radiotherapy) is the medical use of ionizing radiation as part of cancer treatment to control malignant cells (not to be confused with radiology, the use of radiation in medical imaging and diagnosis). ... In medicine, Leksell Gamma Knife is a neurosurgical device used to treat brain tumors. ... Radiosurgery is a medical procedure which allows non-invasive brain surgery, i. ... This article is about electromagnetic radiation. ... Human circulatory system. ...


It is not clear what percentage of tumors are controlled by this method for long periods. In earlier times when higher radiation doses were used, the failure rate was about 12% (which then required surgery). Most surgeons feel that these tumors are much more difficult to remove after radiation treatment. Radiation does not remove the tumor, and when irradiated tumors are surgically removed, it is often found that they have growing tumor cells in them.


Two risks of radiation treatment are carcinogenic progression of the acoustic neuroma (conversion from benign to malignant) or induction of other tumors (such as glioblastoma) in the nearby irradiated brain tissue. The incidence of these events appears to be low, and it is often said to be one in one thousand or less. This calculation is done by dividing the number of obvious cases of tumorigenic progression or secondary tumor reported in the medical literature by the estimated number of gamma knife procedures done in the world to date. This is not a scientifically valid method of estimating the carcinogenic risk of medical radiation exposures, and involves a list of very questionable assumptions. In pathology, a carcinogen is any substance or agent that promotes cancer. ... Benign can refer to any medical condition which, untreated or with symptomatic therapy, will not become life-threatening. ... In medicine, malignant is a clinical term that means to be severe and become progressively worse, as in malignant hypertension. ... A glioma is a type of primary central nervous system (CNS) tumor that arises from glial cells. ... Tumorigenesis is the formation of tumors in the body, often caused by oncogenes. ...


The proper and scientifically valid way to estimate such risks can be found at the web site of the Health Physics Society (http://www.hps.org/), where estimates of the risks of CT scans and other procedures can be found. These calculations have never been made for gamma knife radiosurgery.


Due to the possibility of regrowth and the possibility of tumorigenic progression or secondary tumors, it is essential that radiation treatments for acoustic neuromas be followed by yearly MRI for the rest of the patient's life. MRI at this time (2005) cost about $3,000. Long-term secondary effects (for instance cognitive effects) on a scale of 10-20 years are not yet established for gamma knife surgery. 2005 (MMV) was a common year starting on Saturday of the Gregorian calendar. ... Cognitive The scientific study of how people obtain, retrieve, store and manipulate information. ...


Fractionated stereotactic therapy involves a beam of ionizing radiation focused on the tumor from a moving gantry. The beam is wider and less accurate than that of the gamma knife. The total dose is also much higher than that used in gamma knife radiosurgery, but the fractionation of the dose (done on many different days) spares normal tissue. This method has not been done on as many patients as gamma knife procedures and there have not been as many years of follow-up study. This means that the tumor control by this method is not yet established, and the incidence of secondary effects of the radiation are not yet known. ... Container ship Rita being loaded at Copenhagen by a portainer crane A portainer (also known as a gantry crane, container crane, container handling gantry crane, quay crane, ship-to-shore crane, STS crane or a dockside crane) is a very large crane used to load and unload container ships, and...


External links


  Results from FactBites:
 
Acoustic neuroma - WrongDiagnosis.com (855 words)
Acoustic neuroma: A benign tumor of the 8th cranial nerve which lies in the tube connecting the inner ear to the brain.
Acoustic neuroma is listed as a "rare disease" by the Office of Rare Diseases (ORD) of the National Institutes of Health (NIH).
This means that Acoustic neuroma, or a subtype of Acoustic neuroma, affects less than 200,000 people in the US population.
ACOUSTIC NEUROMA (4943 words)
Acoustic neuromas are a rare cause of unilateral hearing loss, dizziness, as well as rarely other symptoms related to the brain.
Acoustic neuromas, also known as vestibular schwannomas, are non-malignant tumors of the 8th cranial nerve.
Acoustic neuroma caused by type-II neurofibromatosis should be suspected in young patients and those with a family history of neural tumors.
  More results at FactBites »

 
 

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