Tumor shown in the photograph below first involves which of the following nerves?
The tumor shown in the picture above represents Acoustic neuroma.
- Synonym: Vestibular Schwannoma or Neurilemmoma or 8th Nerve tumor
- 80% of all Cerebello-pontine angle tumors
- Benign encapsulated, extremely slow growing tumors
- Tumors almost always arise from the Schwann cells of the vestibular division of VIII nerve.
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 : 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
- Vth cranial 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.
- VII 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.
- IXth and Xth 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.