Leave it to the Brits to address such a common question with scientific rigor and analysis! Philip Michael, Niel Opie and Michael Smith, from Worcestershire Royal Hospital in the UK, published a short but information-packed article in the August edition of the journal Otolaryngology-Head and Neck Surgery (2010;143:219-22). They looked at seven different types of convertible cars (Audi A4, Porsche 911, Aston Martin V8 Vantage, Morgan Roadster, Bentley Continental GT, Toyota MR2, and a Mazda MX5) driving at 50, 60 and 70 mph with windows raised and down. They placed a noise sensor on the traffic side of the car (on the right in the UK- they drive on the wrong side of the road) and took 3 separate measurements in each condition (scientific method at work). All tests were done on similar roadways and in non-rush hour traffic to minimize data contamination.

What did they find?

Bilateral 8th cranial nerve tumors, also known as vestibular schwannomas or acoustic neuromas (see figure), are pathognomonic of a fascinating syndrome called central neurofibromatosis or neurofibromatosis type 2 (NF-2). NF-2 is a rare, autosomal-dominant disease with an incidence of 1 in 30,000 live births. The mechanism by which the genetic changes underlying NF-2 produce these tumors of a cranial nerve remains a mystery. Interestingly, two other associations are also sufficient to make a diagnosis of NF-2. These are unilateral VS at early age (< 30 years) plus two other specific lesions (meningioma, schwannoma other than VS, glioma or pre-senile cataract), and unilateral VS at early age with an affected first-degree parent, sibling or child. Patients with NF-2 usually present between the ages of 18 and 24 years with tinnitus, hearing loss and balance difficulties. Symptoms of unilateral tinnitus, asymmetric hearing loss or unresolving vertigo or imbalance warrant a gadolinium-enhanced MRI with a neurotological consultation to rule out brainstem pathology.

NF-2 is caused by inactivation of the NF-2 tumor suppressor gene on chromosome 22 (22q12.2) which encodes the "Merlin" protein. Like a double negative, inactivation of a tumor suppressor gene produces an autosomal-dominant inheritance pattern identical to classical activating mutations.

When a diagnosis of NF-2 is entertained, evaluation should include a complete family history; a detailed head and neck and neurological examination with attention to cranial nerve deficits, and an MRI of the brain with dedicated images to detect bilateral VS, meningiomas and optic gliomas. Spinal MRI with gadolinium should be performed to look for spinal meningiomas or schwannomas, and ophthalmologic evaluation should be obtained in cases with visual loss or with suspicion of juvenile cataracts.

Unilateral VS and NF-2