Acoustic Neuroma

Unheard
Didn't play the corresponding interactive case or want to try it again? Click here to do so.

Diagnosis and reasoning

Loss of hearing is a common outpatient complaint with a wide differential diagnosis encompassing conductive, sensorineural, and mixed causes of deafness. However, this patient demonstrates several clinical signs which help shorten the diagnostic pathway: right sided facial weakness suggestive of a lower motor neuron (LMN) lesion of the facial nerve, and right sided numbness of the entire face, potentially indicating a lesion of the trigeminal nerve. In addition, note that the Rinne test shows air conduction to be superior to bone conduction on both sides (i.e. there are no conduction defects), while the Weber test localizes to the left side. This indicates the presence of a right-sided sensorineural hearing loss; this is confirmed by audiometry. Thus, note that three nerves are involved: trigeminal (CN V), facial (CN VII) and vestibulocochlear (CN VIII); all of these originate from the pons. However, the facial nerve palsy is lower motor neuron in nature; this suggests that the lesion lies out of the brainstem. Could this be a cerebellopontine (CP) angle tumour? Magnetic resonance imaging (MRI) of the brain is the gold standard for diagnosing suspected CP angle tumours; this reveals a 1.7 x 2.2 cm mass at the right CP angle, entering the internal auditory meatus; this is consistent with a medium-sized acoustic neuroma. Note that a lumbar puncture is not indicated in his workup; outside of acute trauma, skull x-rays are only used for a few specific indications (such as a skeletal survey, or for evaluation of vault abnormalities). Considering the relatively young age of the patient, current neurological status, and tumor size, surgical excision is probably the best course of management. Note that in LMN palsies of the facial nerve, the cornea is exposed due to the inability to close the eye; thus protection via artificial tears and an eye-patch at night is important. Nerve grafting is only required if there is direct injury to a nerve, and is not indicated in this patient. Chemotherapy does not play a role in the management of acoustic neuromas.


Discussion

Acoustic neuromas are intracranial tumors arising from the Schwann cell sheath investing the vestibulo-cochlear nerve. As they enlarge in size, they tend to occupy the CP angle. They account for approximately 80% of tumors found within the CP angle; the remaining 20% include meningiomas, facial nerve neuromas, vascular tumors and lipomas. Acoustic neuromas are clinically diagnosed in 0.7 to 1.0 persons per 100,000 population. The incidence may rise in the future, due to increased detection owing to the widespread use of MRI. Unilateral hearing loss is the most common symptom present at the time of diagnosis, and is usually what makes patients seek medical attention; therefore any unilateral sensorineural hearing loss should raise suspicion of an acoustic neuroma. Headaches are present in 50% to 60% of patients at the time of diagnosis, although fewer than 10% of patients have headache as the presenting symptom; these appear to become more common as the tumor size increases, and are a prominent feature in patients who develop obstructive hydrocephalus associated with a very large tumor. Facial numbness occurs in about 25% of patients and is more common at the time of presentation than facial weakness. Vertigo is an uncommon presenting symptom. Gadolinium-enhanced MRI is the gold standard for diagnosis of patients with a suspected acoustic neuroma; this can demonstrate tumors as small as 1 to 2 mm in diameter. Audiometry and brain stem evoked potential testing (BAER) are helping in providing supportive evidence. Acoustic neuromas are benign tumors, although rare malignant cases have been reported in the literature. There is no widely accepted staging system. There are three key modalities of management: surgical resection, stereotactic radiosurgery, and conservative management. There are no studies that systematically compare these different treatment modalities; therefore, the decision of which technique to use is based on multiple factors including the age and medical status of the patient, tumor size and location, hearing status, and patient preference. Surgical excision is the treatment of choice in most patients; stereotactic radiosurgery has progressively gained acceptance as an alternative modality of excision. Note that the ability to preserve hearing and facial nerve function has increased substantially over the last decade or two; currently, hearing can be preserved in 30% to 80% of properly selected patients. Unfortunately, facial nerve outcomes continue to vary according to tumor size. With tumors smaller than 1.5 cm, good facial nerve function can be expected postoperatively in more than 90% of patients. Recurrence following tumor removal is uncommon, with an overall recurrence rate of less than 5%. Surveillance for postoperative tumor recurrence should persist for 8 to 10 years postoperatively. Note that careful observation via serial MRIs may be considered in older patients, patients with comorbidities which preclude surgery, and with small tumors (particularly if asymptomatic).


Take home messages

  1. Unilateral sensorineural hearing loss should raise suspicion of an acoustic neuroma.
  2. Gadolinium-enhanced MRI is the gold standard for detection of accoustic neuromas.
  3. Acoustic neuromas are benign tumors, although they may recur following excision.
  4. Excision via microsurgery or stereotactic radiosurgery is the treatment of choice in most patients.

Insightful, fun cases to improve your diagnostic skills

Use your detective skills, strengthen fundamentals faster, and access a wealth of knowledge.

  1. Bederson JB, von Ammon K, Wichmann WW, et al. Conservative treatment of patients with acoustic tumors. Neurosurgery. May 1991
  2. Clifton AG, Phelps PD, Lloyd GA.,The investigation of acoustic neuroma, Clin Radiol. 1991 Oct.
  3. Combs SE, Thilmann C, Debus J, et al. Long-term outcome of stereotactic radiosurgery (SRS) in patients with acoustic neuromas. Int J Radiat Oncol Biol Phys. Apr 1 2006
  4. Fucci MJ, Buchman CA, Brackmann DE, et al. Acoustic tumor growth: implications for treatment choices. Am J Otol. Jul 1999
  5. Isaacson B, Kileny PR, El-Kashlan HK. Prediction of long-term facial nerve outcomes with intraoperative nerve monitoring. Otol Neurotol. Mar 2005
  6. Jon E. ,Isaacson,Neil M. ,Vora, Milton S., Differential Diagnosis and Treatment of Hearing Loss, Am Fam Physician. 2003 Sep.
  7. Kirtane MV, Medikeri SB, Merchant SN, Desai MM, Bhanage BB. Electronystagmography findings in acoustic neuromas. J Postgrad Med 1985
  8. Kondziolka D, Lunsford LD, McLaughlin MR, et al. Long-term outcomes after radiosurgery for acoustic neuromas. N Engl J Med. Nov 12 1998
  9. Lunsford LD, Flickinger J, Coffey RJ. Stereotactic gamma knife radiosurgery. Initial North American experience in 207 patients. Arch Neurol. Feb 1990
  10. Moffat DA, da Cruz MJ, Baguley DM, et al. Hearing preservation in solitary vestibular schwannoma surgery using the retrosigmoid approach. Otolaryngol Head Neck Surg. Dec 1999
  11. Rosenberg SI. Natural history of acoustic neuromas. Laryngoscope. Apr 2000