bubble_chart Overview

Acoustic neurinoma accounts for 7.79% to 10.64% of intracranial tumors, 93.1% of intracranial schwannomas, and 72.2% of cerebellopontine angle tumors. The age of onset is mostly between 30 and 60 years, and it is rare in those under 20 years old. The incidence is slightly higher in women than in men. The vast majority are unilateral, while bilateral cases are mostly associated with neurofibromatosis.

bubble_chart Clinical Manifestations

The primary symptoms of acoustic neuroma are mostly stimulation or destruction symptoms of the auditory nerve, manifested as ipsilateral tinnitus, deafness, or vertigo, accounting for 74%. Tinnitus is high-pitched and continuous, and hearing loss often occurs simultaneously with tinnitus but is frequently unnoticed by patients. Many patients are only discovered during hearing tests due to other symptoms. Vertigo is usually not accompanied by nausea or vomiting, and a few patients may experience episodes similar to Ménière's disease. Other initial symptoms include increased intracranial pressure (14%), trigeminal nerve symptoms (8%), cerebellar dysfunction (5%), limb weakness (5%), and mental abnormalities (3%).

When the tumor extends into the cerebellopontine angle and compresses the trigeminal nerve root, it can cause ipsilateral facial numbness, reduced pain sensation, diminished corneal reflex, and, in rare cases, trigeminal neuralgia. Tumors smaller than 2 cm often do not present with symptoms of trigeminal nerve compression. Compression of the facial nerve may lead to facial muscle spasm, reduced ipsilateral tear production, and, in some patients, grade I peripheral deviation of the mouth. If the abducens nerve is compressed, diplopia may occur.

If the tumor grows medially and compresses the brainstem, contralateral limb weakness and pyramidal tract signs may appear, along with contralateral hemihypesthesia. Displacement of the brainstem and compression against the contralateral tentorial notch may result in ipsilateral pyramidal tract signs and sensory deficits. Compression of the cerebellar peduncles can cause ipsilateral cerebellar ataxia, unsteady gait, dysmetria, slurred speech, and dysarthria.

Downward growth of the tumor, compressing the 9th, 10th, and 11th cranial nerves, may lead to dysphagia, choking while eating, hoarseness, diminished or absent ipsilateral gag reflex, palatal paralysis, and weakness of the sternocleidomastoid and trapezius muscles. Involvement of the hypoglossal nerve is rare.

If cerebrospinal fluid circulation is obstructed, symptoms and signs of increased intracranial pressure may appear, such as headache, vomiting, papilledema, and secondary optic atrophy. If an occipital bone foramen magnum herniation occurs, neck stiffness may be present, but Kernig's sign is negative. Local irritation from the tumor may cause ipsilateral occipital pain.

The disease course is generally prolonged and progressively worsening, but sudden exacerbations or temporary relief of symptoms may also occur.

bubble_chart Diagnosis

Patients with typical cerebellopontine angle syndrome and an enlarged internal auditory canal can be definitively diagnosed. However, most cases have already progressed to a considerable extent. To reduce surgical mortality and morbidity rates, improve total resection rates, and enhance the preservation rates of facial and cochlear nerves, early diagnosis is crucial. Therefore, for patients with unexplained tinnitus and progressive hearing loss, in addition to general neurological examinations, the following tests should be performed.

1. Plain X-ray of the petrous bone: The main radiographic manifestation of acoustic neuroma on plain films is an enlarged internal auditory canal, which can be visualized through anteroposterior, Towne’s, and Stenver’s views. A difference of 1 mm in the width of the bilateral internal auditory canals is suspicious; if there is bone erosion at the roof or floor of the internal auditory canal, erosion of the posterior lip of the internal auditory porus, or asymmetry in the shape of the bilateral canals, it is diagnostically significant.

2. CT scan: Acoustic neuromas larger than 1.5–2 cm can be detected with contrast-enhanced scans, which also reveal deformation and displacement of the cisterns and the fourth ventricle, eliminating the need for further radiological examinations. However, tumors smaller than 1.5–2 cm are difficult to detect. In such cases, high-dose contrast-enhanced scans with overlapping techniques, using a 5 mm slice thickness and half-speed scanning, can identify tumors as small as 0.6 cm.

3. Cerebrospinal fluid examination: For tumors smaller than 2 cm, the protein levels are mostly normal, whereas those larger than 2 cm often show varying degrees of elevation.

bubble_chart Treatment Measures

Acoustic neuromas are benign tumors, so the principle of surgical treatment should be: to safely and completely remove the tumor while minimizing injury to the surrounding tissues.