3D Reconstruction Can Unlock Vertigo Mysteries
Three-dimensional reconstruction of high-resolution MR imaging sequences can be used to measure volume in the vestibular system in patients with vertigo, and help explain the symptoms, said the presenter of a Sunday session at RSNA 2013.
Vertigo is a common symptom in patients seeking medical help from ear, nose and throat physicians, said Nagy N. Naguib, M.Sc., of the Johann Wolfgang Goethe University Hospital in Frankfurt, Germany, and the Department of Radiology, Alexandria University in Alexandria, Egypt. In fact, according to Dr. Naguib, vertigo and headache account for two of the most common complaints of patients seeking medical help.
"While MRI is a useful tool in the evaluation of vertigo patients, there are still some cases that don't show any detectable structural changes on MRI," Dr. Naguib said. "We thought it would be helpful to assess the volume of the vestibular system as a part of patients' evaluation for cases presenting with vertigo and referred to radiologists for MR imaging assessment."
The research began as an attempt to make use of the available software and available resolution delivered by MR imaging in order to obtain a 3D reconstruction of the inner ear structures. The aim of these reconstructions was to provide the reading radiologist and referring clinician with an easy way to evaluate 3D images of the inner ear structures, which are located in the three planes and have a complex anatomy, Dr. Naguib said.
In performing the reconstructions, Dr. Naguib and colleagues noticed that in certain cases some of the semicircular canals seemed to be interrupted, were absent, or looked thinner than usual. While some of these structural differences—such as a missing semicircular canal—are easily evaluated, others require more experienced readers.
"Based on this we tried to assess all cases with an objective method of measurement—namely the volumetric assessment of the 3D figure obtained," Dr. Naguib said. "The sequence used for the reconstruction is already integrated in many of the examination protocols for the inner ear, and the new application of this routinely performed sequence represents the core of the current research."
Dr. Naguib and colleagues retrospectively studied 153 patients with a mean age of 48.9 years, 61 of whom presented with vertigo and 92 of whom presented with other diseases of the ear and normal vestibular function. In patients with vertigo the mean volume of the semicircular canals was 0.258 cm3 and the mean volume of the vestibule was 0.069 cm3. In patients without vertigo, the mean volume of the semicircular canals was 0.306 cm3 and the mean volume of the vestibule was 0.075 cm3.
Researchers concluded that the reduced volume of the vestibular system in patients presenting with vertigo could account for their symptoms.
Dr. Naguib pointed out that most studies addressing the subject in the past have relied on assessing the bony part of the inner ear using CT and that this method—while beneficial—does not accurately reflect the status of the contents of the bony cavities.
In addition, use of 3D reconstructions can be more than just a tool to impress other clinicians, Dr. Naguib said. "We think adding 3D reconstructions might open the horizon for other studies addressing the subject of inner ear pathology in general, and the subject of vertigo in particular. It's important to have the ability to assess the structural changes in an objective way that might be associated with vertigo rather than relying only on the subjective experience of the reader."