Acoustic+Neuroma

Figure 1. Reprinted from American hearing research foundation 1
 * **Epidemiolgy:** || Amanuel

Acoustic neuroma, also known as vestibular shwanoma, is a non malignant tumor of the 8th cranial nerve, vestibulochoclear nerve. 1 The nerve transmits sound and sends balanced information from the inner ear to the brain. Acoustic neuroma is usually a slow growing benign cancer, but it can also grow rapidly and press against the brain. Acoustic neuroma accounts for 6% of all intracranial tumors, 30% of brainstem tumors, and 85% of the tumors around the cerebellopontine angle. 1 About 2000 to 3000 new cases arise each year. 1 In addition, patients with hearing asymmetry, 1 in 1000 has acoustic neuroma. 1 || About 95% of acoustic neuromas are caused sporadically. 1  The only apparent environmental risk identified is an exposure of high dose radiation to the head and neck region. The association of acoustic neuroma to cell phone use and loud noises is a controversial subject, and is still being investigated. The rest 5% of acoustic neuromas are caused by inherited syndrome known as neurofibromatosis type II (NF2). 1  NF2 is an autosomal dominant disorder, where the mutation can be passed from one parent only. Each child of an affected parent has a 50:50 chance. About 1 in 40,000 people and 5% of patients with acoustic neuroma are affected by NF2. ||
 * **Etiology:** || Amanuel
 * **Signs & Symptoms:** || Lindsey

Signs and symptoms for CNS tumors depend on tumor location, associated expansion and surrounding edema. 2 Tumor growth along with edema may cause focal neurologic dysfunction, increased intracranial pressure and/or hydrocephalus. With significant cerebral edema or hydrocephalus, nausea and vomiting, headache, and papilledema (swelling of the optic nerve caused by increased intracranial pressure) are common. Headaches may be worse in the morning and focal neurologic deficits are also common. Long term increased intracranial pressure may lead to optic atrophy and even blindness. Seizures are also common, usually with low grade neoplasms. Lumbar back pain, bowel or bladder dysfunction may suggest lumbar metastasis. ||
 * **Diagnostic Procedures:** || Lindsey

Initial workup for CNS tumors includes a complete history and physical. 2 Following history and physical, a complete neurological exam should be performed including assessment of mental condition, cranial nerves, coordination/cerebellar function, sensation, power and reflexes. Ophthalmoscopy checks for papilledema as a sign of increased intracranial pressure should also be done. For MRI, T1 weighted images with and without gadolinium contrast, T2 weighted images, and fluid attenuated inversion recovery (FLAIR) images are all most useful. T1 weighted images show anatomy more clearly as well as areas of contrast enhancement. T2 and FLAIR images are more sensitive for detecting edema and tumor hyperintensity. CT with contrast is also useful. Staging of the neuraxis is essential for neoplasms at high risk of spread to cerebrospinal fluid (CSF). Neuraxis imaging is usually achieved with gadolinium enhanced MRI of the spine. Spinal imaging is usually combined with CSF cytology for complete neuraxis staging. Biopsy is also recommended for CNS tumors. However, selected patients with imaging and symptoms consistent with low grade glioma may be followed closely without biopsy. || Two histologic types of tissue have been identified in acoustic tumors. Antoni A tissue consists of elongated spindle cells with a palisading pattern. Antoni B tissue has a loose spongy texture and markedly reduced cellularity. A given acoustic neuroma may contain areas with both Antoni A and Antoni B tissue. Another histologic feature characteristic of schwannomas are rows of palisading nuclei called Verocay bodies. Although the histologic appearance of acoustic tumors is fairly straightforward, they can occasionally be difficult to distinguish from meningiomas. 3 At high magnification the schwannoma is seen to be an Antoni type B schwannoma. 4 The pattern is a loose texture of cells with a honeycomb appearance. The accumulation of lipids within the cells gives it its characteristic look. 4 || Absence of lymphatics in the brain; therefore no lymphatic drainage due to the blood brain barrier. || Acoustic neuromas are benign tumors, they do not metastasize. ||
 * **Histology:** |||||||| Kevin
 * **Lymph node drainage:** || Kevin
 * **Metastatic spread:** || Jenn
 * **Grading:** || Jenn

Grade I: Tumor is small, occurring only within the internal auditory canal.

Grade II: Tumor extends into the fluid spaces around the brainstem.

Grade III: Larger tumor (usually up to 2.5 cm in diameter). Extends up to the brainstem.

Grade IV: Very large tumor (up to 5cm in diameter) compresses the brainstem and often involves the nerves of swallowing and the 5th cranial nerve (face and eye sensation). 5 ||
 * **Staging:** || Rachel

An Acoustic neuroma is not cancerous. They are benign, and do not spread to other parts of the body. 6

Stage I: They slowly fill the Internal Auditory Canal (IAC), compressing the auditory and balance nerves. (usually 0 to 10 millimeters (mm))

Stage II: They protrude through the opening of the IAC on the brain side, into an area called the cerebellopontine angle, without touching the cerebellum nor the brain stem. (Usually 10 to 20 mm)

Stage III: The tumor has grown to come into contact with the cerebellum and/ or the brainstem, without compressing these brain structures. (Usually 20-35 mm)

Stage IV: If untreated, the tumor will deform the cerebellum, possibly resulting in writing and gait problems, and/ or the brainstem. (more than 35 mm) ||
 * **Radiation side effects:** || Rachel
 * Early Reactions: dizziness, nausea, vomiting, mucosa inflammation in the mouth and throat area, localized hair loss, headaches, numbness of the scalp. 7


 * Late Reactions: after several months can be vasoconstriction and fibrosis (scarring) of the connective tissue. These remain for life. ||
 * **Prognosis:** || Brandon

Treatment of most acoustic neuromas should offer a high local control. Along with local control, most patients should be able to preserve cranial nerve function as well as hearing function. In fact, up to one third of all acoustic neuroma patients should 'realistically' be able to preserve their hearing function as a result of treatment. Also, studies have shown that certain treatment techniques have offered 5 year local control rates of up to 97%. 8 ||
 * **Treatments:** || Brandon

The primary treatment choice for acoustic neuroma is microsurgery. There have been studies in the past that have shown external beam radiation to be useful retrospectively as well. Another treatment choice is stereotactic radiosurgery (SRS). This treatment option is very comparable to microscopic surgery and is less invasive for the patient. SRS is an option due to the fact that most acoustic neuromas have intense enhancement on magnetic resonance imaging (MRI) studies. Finally, adjuvant external bean radiation therapy (EBRT) has also shown to be an option for acoustic neuromas that are subtotally resected to decrease recurrence.

In 51 patients, fractionated stereotactic radiation therapy (FSRT), which is much like stereotactic body radiation therapy (SBRT), was used with a 5 year local control rate of 97%. However, more conventional daily fractionation is recommended. This entails treating the area to 50 to 66 Gray (Gy) in 1.8 to 2.0 Gy/fraction for a total of 5 to 6 weeks. 8 || The TD 5/5 is representative of the dose for 5% complication rate in 5 years 9 *Note: The information above is indicative of total organ limitations. ||
 * **TD 5/5:** |||| Ashley
 * Lens: 1000cGy (Cataract)
 * Retina: 4500cGy (Blindness)
 * Optic Nerve: 5000cGy (Blindness)
 * Optic Chiasm: 5000cGy (Blindness)
 * Cochlea: 5500cGy
 * Pituitary: 4500cGy (Hypopituitarism)
 * Brainstem: 5000cGy (Infarction, Necrosis)
 * Spinal Cord: 4700cGy (Infarction, Necrosis)
 * Brain: 4500cGy (Infarction, Necrosis)


 * **References:** || Ashley
 * 1) Hain TC. Acoustic Neuroma. American hearing research foundation. []. Accessed June 3, 2013.
 * 2) Chao KS, Perez CA, Brady LW. //Radiation Oncology Management Decisions//. 3rd ed. Philadelphia, PA: Lippincott, Williams, and Wilkins; 2011: 148-149.
 * 3) Kutz, JW. //Acoustic// //Neuroma//. eMedicine. 2011. Available at: []. Accessed: June 5, 2013.
 * 4) // Acoustic Neuroma // . University of Minnesota. Available at: [] . Accessed: June 5, 2013.
 * 5) Siegfried, J.Acoustic Neuromas. Brain-Surgery.com Neurosurgery Information. Available at: []. Accessed on June 6, 2013
 * 6) //Acoustic Neuroma Stages.// Acoustic Neuroma Association. Available at: []. Accessed on June 7, 2013.
 * 7) //Acoustic neuroma: Radiotherapy as a treatment option.// IGAN organization. Available at: []. Accessed on June 7, 2013.
 * 8) Chao K, Perez C, Brady L. //Radiation Oncology Management Decisions//. 2 nd ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2002.
 * 9) Hall, E. //Radiobiology for the Radiologist.// 7th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2012. ||

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