Use of Ultrasound and Mri in Laryngeal Disease

Image Acquisition Ultrasonography of the larynx can be performed using standard ultrasound equipment suitable for musculoskeletal examinations. A 7-10 megahertz linear or microconvex transducer provides good resolution and adequate penetration. Sedation is often necessary, as it facilitates patient cooperation and relaxation to allow extension of the head permitting access to the laryngeal region. The hair can be clipped or soaked with isopropyl alcohol. The larynx is imaged from the lateral, dorsolateral, and ventral aspects. The lateral window allows evaluation of the arytenoid cartilages, thyroid cartilage, cricoid cartilage, cricoarytenoideus lateralis muscle, and vocalis muscle in longitudinal and transverse planes. By moving the ultrasound transducer to a dorsolateral window by moving slightly dorsally and angling slightly ventrally, the lateral portion of the cricoarytenoideus dorsalis muscle is imaged. From the ventral window, the basihyoid bone, vocal folds, thyroid cartilage, and cricoid cartilage are imaged. Magnetic resonance imaging usually requires general anesthesia as the design of standing magnets does not permit positioning of the laryngeal region within the magnet for most equine patients. Positioning of the horse in dorsal recumbency is often easier than lateral recumbency. A body coil may be used, but a surface coil is preferred and will result in superior image quality. Images are obtained in the transverse, dorsal, and median planes using a combination of T1 weighted, T2 weighted, proton density weighted and short tau inversion recovery (STIR) sequences. A more complete anatomic evaluation of the entire laryngeal region is possible with MRI as compared to ultrasound.