Acoustic Neuroma / Vestibular Schwannoma / Neurilemmoma / 8th Nerve tumor

Magnetic resonance imaging (MRI) with gadolinium contrast is the gold standard for the diagnosis or exclusion of vestibular schwannoma (VS, acoustic neuroma).

An MRI scan also allows for surgical planning.

The MRI characteristics of a VS include a hypointense globular mass centered over the IAC on a T1-weighted image with enhancement when gadolinium is added. VS are iso- to hypointense on T2-weighted images. 

Vestibular schwannomas or acoustic neuromas originate in the internal auditory canal from the inferior or superior portion of the vestibular nerve.

Acoustic neuromas account for 8% to 10% of all intracranial tumours in adults.

The lack of a dural tail on MRI differentiates acoustic neuromas from cerebellopontine angle meningiomas.

Most tumours are unilateral. Genetic association is with a lack of tumour suppressor gene on Chromosome 22. 

• Vertigo precipitated by the movement of head in a specific direction: Benign positional vertigo.
• Intermittent brief vertigo with occasional drop attacks, ataxia, visual loss, double vision and confusion:  Vertebrobasilar insufficiency.
• Episodic recurrent vertigo, with auditory symptoms, headache, photophobia and aura: Migraine.
• Vertigo with facial weakness and loss  of taste sensation: Ramsay hunt syndrome.
• Triad of episodic vertigo, tinnitus and progressive deafness: Meniere’s disease.

The first symptom of an acoustic neuroma is hearing loss and the first sign diminished corneal sensitivity.

Vestibular symptoms seen in acoustic neuroma are imbalance or unsteadiness. True vertigo is seldom seen

Acute episode of vertigo is a rare presenting feature in acoustic neuroma since it is a slow growing tumor so there is adequate time for compensation.

B/L acoustic neuromas are a hallmark of Neurofibromatosis 2

• Neurofibromatosis Type 2 is an autosomal dominant highly penetrant condition
• Gene for NF-2 is located on chromosome 22q.
• Patients with NF2 present in second and third decade of life, rarely after the age of 60.
• M/C symptom/Presenting symptom = Hearing loss
• Skin tumors are present in nearly two thirds of patients of NF-2

-Current Otolaryngology 3/e

Auditory brainstem implant (ABI)

Brainstem implant is currently used only in patients with NF-2 and is always implanted simultaneously in the lateral recess of the fourth ventricle with tumor removal (usually during excision of the patient’s second tumor). It is useful in patients who have had both cochleovestibular nerves sacrificed, since this implant stimulates the cochlear nuclear complex in the brainstem Such an implant is 

In unilateral acoustic neuroma, auditory brainstem implant (ABI) is not necessary as hearing is possible from the contralateral side but in bilateral acoustic neuroma as in neurofibromatosis-2, rehabilitation is required by ABI

Dhingra 6th/ed 

Additionally more than 80% of patients have reported tinnitus.

The clinical features depend on the extent of tumor and involved structure :‑

1) When tumor is still confined to the internal auditory canal

• Cochleovestibular symptoms are the earliest symptoms of acoustic neuroma when tumour is still confined to internal auditory canal. The commonest presenting symptoms are unilateral deafness or tinnitus, or a combination of both. 
• Hearing loss is retrocochlear sensorineural type. There is marked difficulty in understanding speech, out of proportion to the pure tone hearing loss, a characteristic feature of acoustic neuroma. 
• Vestibular symptoms are imbalance or unsteadiness. True vertigo is very rare.

2) When tumor extends beyond IAC and involves other structures

V^thcranial nerve :- It is the earliest nerve to be involved. There is reduced corneal sensitivity and loss of corneal reflex which is the earliest sign of acoustic neuroma. Numbness or paresthesia of face may occur. Involvement of Vth nerve indicates that tumor is roughly 2.5 cm in diameter and occupies the CP angle.

VIP nerve :- Sensory fibres of facial nerve are involved. There is hypoesthesia of posterior meatal wall (Hitzelberg’s sign), loss of taste, and loss of lacrimation on Schirmer’s test. Motor fibres are more resistant.

IX^th and X^th nerves :- Dysphagia and hoarseness due to palatal, pharyngeal and laryngeal paralysis.

Brainstem :- Ataxia, weakness, numbness of arms & legs, exaggerated tendon reflexes.

Cerebellum :- Ataxia, Dysdiadochokinesia, Nystagmus.

Due to raised ICT :- Headache, neusea, vomiting, diplopia due to VI nerve involvement, and papilloedema.

Acoustic Neuroma

• Acoustic neuroma (vestibular schwannoma) is the most common lesion of the Cerebello Pontine Angle (C P Angle).
• These lesions may be entirely intracanalicular or both intracanalicular and cisternal.
• MRI is the imaging modality of choice to evaluate these tumors, clearly delineating the location and extent of disease.
• The typical acoustic neuroma is isointense on both T1W and T2W MRI sequences, and enhances densely following contrast administration.
• Far less common than acoustic neuroma, but the second most common CPA mass, is the meningioma