Acoustic Neuroma: Classification, Causes, Clinical Features, Symptoms

Acoustic neuroma is a benign tumor that arises from the no leading from the inner ear to the brain. This nerve is mainly the inferior vestibular nerve and rarely the popular or superior vestibular nerve. It is also called as vestibular schwannoma because it arises from the Schwann cells of the vestibular nerve. And it accounts for 10% of all brain tumors therefore it is very important to study it. It is usually slow growing but in a rare situation, it can grow quickly and become large enough to press against the parts of the Brain. 

Acoustic Neuroma Classification

• Small: size upto 1.5cm.
• Medium: 1.5cm to 4cm.
• Large: >4cm.

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Acoustic Neuroma Causes

• A gene on chromosome 22 is linked to the reason for acoustic neuroma.
• It has been studied that this gene produces a tumor suppressor protein that helps control the overgrowth of Schwann cells that cover these nerves.

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Acoustic Neuroma Clinical Features

• Acoustic neuroma comes from the inferior vestibular nerve and it can compress this superior vestibular nerve, cochlear nerve, and facial nerve.
• It is an encapsulated tumor and it originates from Schwann cells of the vestibular nerve but sometimes even arises from the cochlear nerve.
• After expansion it can cause widening of the canal and it appears in the cerebellopontine angle. 80% of the cerebellopontine angle tumors are of this type.
• Acoustic neuroma is more often seen in the age group of 40 to 60 years of age.
• It is mostly unilateral.
• It is very important to note that bilateral tumors are part of neurofibromatosis type 2 therefore other features of neurofibromatosis type 2 should also be noticed if present.
• The presentation of the tumor will be mainly unilateral and progressive sensory neural hearing loss with tinnitus.
• There will be difficulty in understanding speech.
• 5^th nerve is the earliest nerve affected due to the expansion of acoustic neuroma. If the 5^th nerve is affected that indicates the tumor is more than 2.5 cm and in the cerebellopontine angle. There will be reduced corneal sensation. 
• Anterior-superiorly it can involve the 5^th nerve and 6^th nerve. Inferiorly it can involve the 9^th, 10^th, and 11^th nerve.
• In later stages it can displace the brainstem and, and cerebellum. This can also lead to elevation of intracranial pressure.

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Acoustic Neuroma Symptoms 

• When a vestibular nerve is affected the imbalance can occur initially and soon it gets compensated by the opposite side. 
• In case of cochlear nerve involvement, sensorineural hearing loss will occur.
• Facial nerve can also be involved in some cases:
  • These sensory nerves are the first ones to get affected and that results in loss of sensation in the concha (Hitzelberger sign).
  • Later on, motor nerves are involved and cause motor paralysis of the face.
• Acoustic neuroma on expansion can cause some other disturbing symptoms:
  • It can compress the 5^th nerve which can lead to loss of corneal reflex.
  • It can also compress the 6^th nerve leading to abducent palsy.
  • There will be involvement of the 9^th, 10^th, and 11^th nerves causing swallowing and speech problems.
  • Brainstem and cerebellar compression can occur which leads to symptoms like ataxia.

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Acoustic Neuroma Diagnosis

• Audiology is done to diagnose the condition after the clinical evaluation.
• Rinne Test- Positive
• Weber Test- Lateralised to the normal side.
• Absolute Bone Conduction is Shortened.
• In Retrocochlear pathology, Speech discrimination is poor, and Acoustic reflex delay is positive.
• BERA-Delay in the appearance of wave 5. ( Investigation of choice)
• Vestibular tests:
  • The caloric test is reduced on the side of the lesion.
  • VEMP is also reduced.
• MRI with contrast is done to detect the tumor. It will be presented as an Ice cream cone appearance.

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Acoustic Neuroma Treatment

• Surgical excision is the treatment of choice if the size of the acoustic neuroma is more than 3 cm.
• Radiosurgery is done for small tumors in which size is <30 cc.
•  Biopsy shows typical ANTONI TYPEA and TYPE B cells.

Hope you found this blog helpful for your ENT Residency Otology Preparation. For more informative and interesting posts like these, keep reading PrepLadder’s blogs. 

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