M Panconi

Virtual endoscopy of the middle ear

Abstract Virtual endoscopy is a computer-generated simulation of fiberoptic endoscopy, and its application to the study of the middle ear has been recently proposed. The need to represent the middle ear anatomy by means of virtual endoscopy arose from the increased interest of otolarygologists in transtympanic endoscopy. In fact, this imaging method allows the visualization of middle ear anatomy with high detail, but it is evasive and is essentially used for surgical guidance. Virtual endoscopy provides similar perspectives of the tympanic cavity but does not require the tympanic perforation. In the study of the middle ear, specific attention is given to the retroperitoneum. This region contains elevations of the medial wall (pyramidal eminence and ridge, styloid eminence and ridge, subiculum, ponticulus) and depressions (sinus tympani, posterior sinus tympani, facial sinus, fossula of Grivot, oval window fossula), which can be effectively displayed by virtual endoscopy. Virtual endoscopy is foreseen as a useful tool in preoperative management of patients who are candidates for middle ear surgery, since it can predict with high detail the patients specific anatomy by imaging perspectives familiar to otosurgeons.

LARGE VESTIBULAR AQUEDUCT IN DISTAL RENAL TUBULAR ACIDOSIS: High-resolution MR in three cases

High-resolution MR of the inner ear performed in 3 consecutive pediatric patients affected by distal renal tubular acidosis (dRTA) and progressive sensorineural hearing loss (SNHL) revealed enlarged vestibular aqueducts (LVA) (bilateral in 1 case and unilateral in 2). LVA is associated to sporadic, progressive SNHL, often secondary to minor head trauma and activities involving the Valsalva maneuver. We believe that the presence of LVA may have contributed to the onset of SNHL and its progression in our patients, and therefore want to stress the importance of morphological studies of the inner ear in patients affected by dRTA and SNHL.

Correlations Between Virtual Endoscopy and Otoendoscopy of the Retrotympanum

The aim of this study was to examine the anatomical landmarks of the retrotympanum using two different techniques, virtual endoscopy (VE) and fiberoptic endoscopy, and to correlate the results furnished by the two methods. Ten otosclerotic patients who were due to undergo stapedectomy were scanned using high-resolution spiral CT. Selected CT datasets were processed with Navigator 2.0 software to obtain virtual endoscopic views of the retrotympanum. Subsequently, during the surgical procedure, fiberoptic endoscopy was performed with 2.7-mm 0° and 30° rigid endoscopes. The ability of the two imaging methods to identify specific anatomical structures was then compared. In all cases the pyramidal eminence, pyramidal crest and sinus tympani were clearly identified in both VE images and otoendoscopy recordings, while fiberoptic endoscopy seemed to be less satisfactory than VE for studying the facial sinus, sinus of Proctor and fossula of Grivot. The two techniques proved to be equally sensitive for visualizing the ponticulus and subiculum, while the stapedius tendon could be visualized only by means of fiberoptic endoscopy. Overall, VE imaging appears promising for rendering important anatomical details of the retrotympanum, allowing identification of osseous landmarks and exploring recesses that are difficult to visualize via otoendoscopy.

Middle and Inner Ear

As in other anatomical regions, to generate three-dimensional (3D) reconstructions of the middle ear structures, a volumetric acquisition is required. In the case of the tympanic cavity, high-resolution computed tomography (HRCT) is the imaging modality of choice; although the term “high-resolution” is traditionally applied to acquisitions performed with millimetric or sub-millimetric collimation (even with conventional CT), volumetric study is more properly used when single-slice or multislice spiral CT is used. CT is generally introduced into the diagnostic investigation of middle ear pathologies when external otoendoscopy is unsuccessful at demonstrating the cause of the disease. Volumetric acquisitions allow the evaluation of most of the components of the tympanic cavity, such as the walls and ossicular chain, but fail to demonstrate the mucosal layer and ligaments.