Acoustic Neuroma

Acoustic neuroma, also referred to as vestibular schwannoma Schwannoma Schwannomas (also known as neurilemmomas) are benign nerve sheath tumors in the peripheral nervous system (PNS), arising from Schwann cells that encase the peripheral nerves. Schwannomas are the most common tumors in the PNS. Schwannoma, is a benign tumor arising from Schwann cells of the vestibular component of the cranial nerve VIII. Acoustic neuroma forms within the internal auditory meatus and extends into the cerebellopontine angle. Vestibular schwannoma Schwannoma Schwannomas (also known as neurilemmomas) are benign nerve sheath tumors in the peripheral nervous system (PNS), arising from Schwann cells that encase the peripheral nerves. Schwannomas are the most common tumors in the PNS. Schwannoma is mostly unilateral. Bilateral vestibular schwannomas are associated with neurofibromatosis type II. Symptoms arise due to compression of the cranial nerves Cranial nerves There are 12 pairs of cranial nerves (CNs), which run from the brain to various parts of the head, neck, and trunk. The CNs can be sensory or motor or both. The CNs are named and numbered in Roman numerals according to their location, from the front to the back of the brain. Overview of the Cranial Nerves V, VII, and VIII, and the cerebellum Cerebellum The cerebellum, Latin for "little brain," is located in the posterior cranial fossa, dorsal to the pons and midbrain, and its principal role is in the coordination of movements. The cerebellum consists of 3 lobes on either side of its 2 hemispheres and is connected in the middle by the vermis. Cerebellum. The most common complaint is unilateral hearing loss Hearing loss Hearing loss, also known as hearing impairment, is any degree of impairment in the ability to apprehend sound as determined by audiometry to be below normal hearing thresholds. Clinical presentation may occur at birth or as a gradual loss of hearing with age, including a short-term or sudden loss at any point. Hearing Loss but acoustic neuroma can also present with vertigo Vertigo Vertigo is defined as the perceived sensation of rotational motion while remaining still. A very common complaint in primary care and the ER, vertigo is more frequently experienced by women and its prevalence increases with age. Vertigo is classified into peripheral or central based on its etiology. Vertigo, decreased facial sensation, Bell’s palsy, and ataxia. Diagnosis of vestibular schwannoma Schwannoma Schwannomas (also known as neurilemmomas) are benign nerve sheath tumors in the peripheral nervous system (PNS), arising from Schwann cells that encase the peripheral nerves. Schwannomas are the most common tumors in the PNS. Schwannoma is made with MRI of the brain with contrast. Treatment depends on the size of the tumor and symptom severity. Large tumors with severe hearing loss Hearing loss Hearing loss, also known as hearing impairment, is any degree of impairment in the ability to apprehend sound as determined by audiometry to be below normal hearing thresholds. Clinical presentation may occur at birth or as a gradual loss of hearing with age, including a short-term or sudden loss at any point. Hearing Loss are treated with surgical excision or radiation therapy, while small tumors with mild symptoms can be observed over time.

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Overview

Definition

Acustic neuroma is a benign tumor of Schwann cells that is most commonly found on cranial nerve VIII (vestibulocochlear nerve).

Classification of nervous system Nervous system The nervous system is a small and complex system that consists of an intricate network of neural cells (or neurons) and even more glial cells (for support and insulation). It is divided according to its anatomical components as well as its functional characteristics. The brain and spinal cord are referred to as the central nervous system, and the branches of nerves from these structures are referred to as the peripheral nervous system. General Structure of the Nervous System tumors

Table: Classification of nervous system Nervous system The nervous system is a small and complex system that consists of an intricate network of neural cells (or neurons) and even more glial cells (for support and insulation). It is divided according to its anatomical components as well as its functional characteristics. The brain and spinal cord are referred to as the central nervous system, and the branches of nerves from these structures are referred to as the peripheral nervous system. General Structure of the Nervous System tumors
Categories Specific tumors
Neuroepithelial tumors in the CNS
  • Astrocytomas, including glioblastoma multiforme Glioblastoma multiforme Glioblastoma multiforme is a high-grade astrocytoma, an aggressive brain tumor arising from astrocytes, with an unknown cause and a poorly understood link to risk factors. There are two main types: primary, a more aggressive form seen more commonly in older patients, and secondary, developing from lower-grade astrocytomas and seen more commonly in younger patients. Glioblastoma Multiforme
  • Oligodendroglioma Oligodendroglioma Oligodendrogliomas are malignant CNS tumors arising from neural glial cell precursors. Oligodendrogliomas often arise in the frontal lobes of the brain and have a generally favorable prognosis when compared to other gliomas. Oligodendrogliomas are the 3rd most common CNS tumor. The most frequent presenting symptom is a seizure. Oligodendroglioma
  • Ependymoma Ependymoma Ependymomas are glial cell tumors arising from CSF-producing ependymal cells lining the ventricular system. Ependymomas most commonly occur within the posterior fossa in contact with the 4th ventricle, or within the intramedullary spinal cord. Ependymoma and choroid-plexus tumors
  • Medulloblastomas (embryonal tumors)
Meningeal tumors
  • Meningiomas
  • Hemangioblastomas
Sellar region tumors
  • Craniopharyngioma Craniopharyngioma Craniopharyngiomas are rare squamous epithelial tumors with a solid and/or cystic structure that arise from the remnants of Rathke's pouch along the pituitary stalk, in the suprasellar region. Craniopharyngiomas are histologically benign but tend to invade surrounding structures; thus, they should be treated as low-grade malignancies. Craniopharyngioma
  • Pituitary adenoma Pituitary adenoma Pituitary adenomas are tumors that develop within the anterior lobe of the pituitary gland. Non-functioning or non-secretory adenomas do not secrete hormones but can compress surrounding pituitary tissue, leading to hypopituitarism. Secretory adenomas secrete various hormones depending on the cell type from which they evolved, leading to hyperpituitarism. Pituitary Adenomas
  • Pinealoma/pinealoblastoma
Primary CNS lymphoma Primary CNS lymphoma
Metastasis to the brain (5x more common than primary brain tumors) Most commonly arising from:
  • Lung, breast, and renal cell carcinomas
  • Melanoma Melanoma Melanoma is a malignant tumor arising from melanocytes, the melanin-producing cells of the epidermis. These tumors are most common in fair-skinned individuals with a history of excessive sun exposure and sunburns. Melanoma
Peripheral tumors
  • Schwannomas, including acoustic neuroma
  • Neuroblastoma Neuroblastoma Neuroblastoma is a malignancy that arises from the neural crest cell derivatives along the sympathetic chain (neuroblasts) and is most commonly located in the adrenal medulla. The tumor often presents in childhood with a flank mass that crosses the midline. Neuroblastoma

Epidemiology

  • Median age of diagnosis: 53 years
  • Most common tumor of cerebellopontine angle
  • Most commonly unilateral 
  • Incidence: 11 per 1 million people in the United States 
  • No difference in incidence by gender
  • Higher incidence in Asian Pacific Islanders

Etiology

  • Many cases have no known etiology.
  • Sometimes associated with mutation Mutation Genetic mutations are errors in DNA that can cause protein misfolding and dysfunction. There are various types of mutations, including chromosomal, point, frameshift, and expansion mutations. Types of Mutations in long arm Arm The arm, or "upper arm" in common usage, is the region of the upper limb that extends from the shoulder to the elbow joint and connects inferiorly to the forearm through the cubital fossa. It is divided into 2 fascial compartments (anterior and posterior). Arm of chromosome 22
  • Associated with loud noises, head and neck radiation therapy, and neurofibromatosis type 2 Neurofibromatosis type 2 Neurofibromatosis type 2 is a neurocutaneous disorder that can arise from mutations in the NF2 gene located in chromosome 22 and may be inherited in an autosomal dominant fashion or occur from de novo mutations. The main clinical features are bilateral vestibular schwannomas, intracranial/spinal meningioma, and intramedullary and extramedullary spinal tumors. Neurofibromatosis Type 2

Clinical Presentation

Symptoms of acoustic neuroma are divided into early and late phases.

Early phase

Tumor expansion in the internal auditory meatus exerting pressure on vestibulocochlear nerve (CN VIII):

  • Vestibular nerve compression:
    • Dizziness 
    • Postural imbalance
  • Cochelar nerve compression: unilateral sensorineural hearing loss Hearing loss Hearing loss, also known as hearing impairment, is any degree of impairment in the ability to apprehend sound as determined by audiometry to be below normal hearing thresholds. Clinical presentation may occur at birth or as a gradual loss of hearing with age, including a short-term or sudden loss at any point. Hearing Loss (most common symptom)

Late phase

Compression of adjacent structures in the cerebellopontine angle:

  • Facial nerve compression: ipsilateral facial weakness or complete facial paralysis (Bell’s palsy)
  • Trigeminal nerve compression:
    • Decreased ipsilateral facial sensation
    • Ipsilateral facial numbness
  • Ipsilateral cerebellar compression: 
    • Ataxia
    • Dysdiadochokinesia (impaired rapid alternating movements)
    • Dysmetria

Diagnosis

Cranial nerve testing

  • Vestibulocochlear nerve: audiometry
    • Sensorineural hearing loss Hearing loss Hearing loss, also known as hearing impairment, is any degree of impairment in the ability to apprehend sound as determined by audiometry to be below normal hearing thresholds. Clinical presentation may occur at birth or as a gradual loss of hearing with age, including a short-term or sudden loss at any point. Hearing Loss
    • Difficulty perceiving high-frequency sounds
  • Facial nerve:
    • Ipsilateral facial weakness
    • Ipsilateral facial twitching
  • Trigeminal nerve: 
    • Ipsilateral decreased facial sensation
    • Ipsilateral decreased corneal reflex

Imaging studies

  • MRI of the brain with contrast:
    • Initial imaging test of choice
    • Performed in patients with abnormal audiometry results and high suspicion for vestibular schwannoma Schwannoma Schwannomas (also known as neurilemmomas) are benign nerve sheath tumors in the peripheral nervous system (PNS), arising from Schwann cells that encase the peripheral nerves. Schwannomas are the most common tumors in the PNS. Schwannoma
    • Findings:
      • Enhanced circular lesion in internal auditory meatus
      • Expansion into the cerebellopontine angle
      • Cystic and fat degeneration are often seen.
  • CT of the brain with contrast:
    • Performed in patients not eligible for MRI (e.g., patients with a pacemaker or metal implant)
    • Findings similar to those of MRI scan

Histopathology

  • Strongly reactive for S100
  • Hypercellular areas with spindle cells alternating with hypocellular myxoid stroma
Schwannoma histology

Schwannoma histology:
Low-power view of schwannoma Schwannoma Schwannomas (also known as neurilemmomas) are benign nerve sheath tumors in the peripheral nervous system (PNS), arising from Schwann cells that encase the peripheral nerves. Schwannomas are the most common tumors in the PNS. Schwannoma illustrating the nuclear palisading (thin arrow) and the hyaline vessel walls (thick arrow). H&E stain ×300

Image: “Pathogenesis of vestibular schwannoma Schwannoma Schwannomas (also known as neurilemmomas) are benign nerve sheath tumors in the peripheral nervous system (PNS), arising from Schwann cells that encase the peripheral nerves. Schwannomas are the most common tumors in the PNS. Schwannoma in ring chromosome 22.” by Denayer E, Brems H, de Cock P, Evans GD, Van Calenbergh F, Bowers N, Sciot R, Debiec-Rychter M, Vermeesch JV, Fryns JP, Legius E. License: CC BY 2.0

Management

Large tumor with severe hearing loss Hearing loss Hearing loss, also known as hearing impairment, is any degree of impairment in the ability to apprehend sound as determined by audiometry to be below normal hearing thresholds. Clinical presentation may occur at birth or as a gradual loss of hearing with age, including a short-term or sudden loss at any point. Hearing Loss

  • Surgical excision:
    • Surgery cannot restore hearing loss Hearing loss Hearing loss, also known as hearing impairment, is any degree of impairment in the ability to apprehend sound as determined by audiometry to be below normal hearing thresholds. Clinical presentation may occur at birth or as a gradual loss of hearing with age, including a short-term or sudden loss at any point. Hearing Loss but can prevent further loss.
    • Intraoperative monitoring of cranial nerves Cranial nerves There are 12 pairs of cranial nerves (CNs), which run from the brain to various parts of the head, neck, and trunk. The CNs can be sensory or motor or both. The CNs are named and numbered in Roman numerals according to their location, from the front to the back of the brain. Overview of the Cranial Nerves to reduce risk of nerve injury
    • Complications:
      • Tinnitus
      • Hearing loss
      • Facial paralysis
      • Taste changes
      • Headaches
  • Radiation therapy:
    • Stereotactic radiosurgery or fractionated stereotactic radiotherapy
    • Goal of radiation is to control the tumor, prevent further growth, and sometimes cause a reduction in tumor size.
    • Complications:
      • Facial weakness
      • Malignancy

Small tumor with minor hearing loss Hearing loss Hearing loss, also known as hearing impairment, is any degree of impairment in the ability to apprehend sound as determined by audiometry to be below normal hearing thresholds. Clinical presentation may occur at birth or as a gradual loss of hearing with age, including a short-term or sudden loss at any point. Hearing Loss

Serial monitoring:

  • MRI scan every 6–12 months to track tumor progression
  • Hearing aids for hearing loss Hearing loss Hearing loss, also known as hearing impairment, is any degree of impairment in the ability to apprehend sound as determined by audiometry to be below normal hearing thresholds. Clinical presentation may occur at birth or as a gradual loss of hearing with age, including a short-term or sudden loss at any point. Hearing Loss (about 50% of patients who are observed for a decade lose functional hearing)

Differential Diagnosis

  • Meningioma: benign tumor arising from the meninges Meninges The brain and the spinal cord are enveloped by 3 overlapping layers of connective tissue called the meninges. The layers are, from the most external layer to the most internal layer, the dura mater, arachnoid mater, and pia mater. Between these layers are 3 potential spaces called the epidural, subdural, and subarachnoid spaces. Meninges of the brain or the spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord. Risk factors include radiation exposure. Meningioma presents with headache, vision disturbances, and possible seizures Seizures A seizure is abnormal electrical activity of the neurons in the cerebral cortex that can manifest in numerous ways depending on the region of the brain affected. Seizures consist of a sudden imbalance that occurs between the excitatory and inhibitory signals in cortical neurons, creating a net excitation. The 2 major classes of seizures are focal and generalized. Seizures. Brain imaging and biopsy are the main diagnostic tools. Meningioma is treated with surgical excision or radiation. 
  • Neurofibromatosis type II: autosomal dominant Autosomal dominant Autosomal inheritance, both dominant and recessive, refers to the transmission of genes from the 22 autosomal chromosomes. Autosomal dominant diseases are expressed when only 1 copy of the dominant allele is inherited. Autosomal Recessive and Autosomal Dominant Inheritance neurocutaneous syndrome caused by NF2 NF2 Neurofibromatosis type 2 is a neurocutaneous disorder that can arise from mutations in the NF2 gene located in chromosome 22 and may be inherited in an autosomal dominant fashion or occur from de novo mutations. The main clinical features are bilateral vestibular schwannomas, intracranial/spinal meningioma, and intramedullary and extramedullary spinal tumors. Neurofibromatosis Type 2 gene mutation Mutation Genetic mutations are errors in DNA that can cause protein misfolding and dysfunction. There are various types of mutations, including chromosomal, point, frameshift, and expansion mutations. Types of Mutations on chromosome 22. NF2 NF2 Neurofibromatosis type 2 is a neurocutaneous disorder that can arise from mutations in the NF2 gene located in chromosome 22 and may be inherited in an autosomal dominant fashion or occur from de novo mutations. The main clinical features are bilateral vestibular schwannomas, intracranial/spinal meningioma, and intramedullary and extramedullary spinal tumors. Neurofibromatosis Type 2 gene codes for the merlin protein. Symptoms depend on the tumors and their locations. These tumors include bilateral cataracts, bilateral acoustic neuromas, meningiomas, ependymomas, and neurofibromas. Diagnosis is made with genetic patient history, physical examination, imaging, and genetic testing. Management includes surgical excision or radiation for the tumors and hearing aids for any functional hearing loss Hearing loss Hearing loss, also known as hearing impairment, is any degree of impairment in the ability to apprehend sound as determined by audiometry to be below normal hearing thresholds. Clinical presentation may occur at birth or as a gradual loss of hearing with age, including a short-term or sudden loss at any point. Hearing Loss.
  • Meniere’s disease: typically, a unilateral inner ear disorder causing a periodic sensation of spinning, tinnitus, and fullness in the ear. Symptoms seem to be caused by fluid accumulation in the inner ear’s labyrinth. The disease is considered progressive and may cause hearing loss Hearing loss Hearing loss, also known as hearing impairment, is any degree of impairment in the ability to apprehend sound as determined by audiometry to be below normal hearing thresholds. Clinical presentation may occur at birth or as a gradual loss of hearing with age, including a short-term or sudden loss at any point. Hearing Loss. Diagnosis is based on clinical symptoms and hearing examination. Treatment is with antiemetics Antiemetics Antiemetics are medications used to treat and/or prevent nausea and vomiting. These drugs act on different target receptors. The main classes include benzodiazepines, corticosteroids, atypical antipsychotics, cannabinoids, and antagonists of the following receptors: serotonin, dopamine, and muscarinic and neurokinin receptors. Antiemetics and anxiolytics (acute episodes) and includes physical therapy, dietary changes (low-salt diet), and counselling (chronic management). Unlike acoustic neuroma, there is no mass seen on imaging in Meniere’s disease.

References

  1. Park, J.K., Vernick, D.M. (2020). Vestibular schwannoma Schwannoma Schwannomas (also known as neurilemmomas) are benign nerve sheath tumors in the peripheral nervous system (PNS), arising from Schwann cells that encase the peripheral nerves. Schwannomas are the most common tumors in the PNS. Schwannoma (acoustic neuroma). UpToDate. Retrieved May 23, 2021, from https://www.uptodate.com/contents/vestibular-schwannoma-acoustic-neuroma
  2. Martin, K.A. (n.d.). Patient education: Vestibular schwannoma Schwannoma Schwannomas (also known as neurilemmomas) are benign nerve sheath tumors in the peripheral nervous system (PNS), arising from Schwann cells that encase the peripheral nerves. Schwannomas are the most common tumors in the PNS. Schwannoma (acoustic neuroma). UpToDate. Retrieved May 23, 2021, from https://www.uptodate.com/contents/vestibular-schwannoma-acoustic-neuroma-the-basics
  3. Kutz, J.W. (2020). Acoustic neuroma. Medscape. Retrieved May 23, 2021, from https://emedicine.medscape.com/article/882876-overview

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