Laryngeal epithelial thickness: a comparison between optical coherence tomography and histology

Optical coherence tomography (OCT) is a new imaging modality analogous to ultrasound, with the exception that light from low-coherence sources rather than sound is used to create cross-sectional images of tissue,1 with an axial resolution approaching that of light microscopy (approximately 7 μm). This technology is already in clinical use by ophthalmologists for examination of both retina and cornea.2 Applications in the areas of cardiology, dermatology, urology, gastroenterology, and dentistry are in development.3–7 In otolaryngology, OCT has been used to image the mucosa of the upper aerodigestive tract, the middle ear, the cochlea, and the thyroid gland.8–11 OCT imaging is becoming increasingly important technology for the upper airway, especially in the larynx, where perhaps is the most promising application of this technology within the upper aerodigestive tract, because OCT can identify key structural features such as the basement membrane.8,12–14 This is particularly appealing for the management of early laryngeal cancers, as distinguishing between benign lesions and early carcinoma can be difficult without biopsy. Laryngeal microsurgery carries numerous risks including scarring and permanent vocal quality changes, and these concerns combined with the difficulty of diagnosing cancer on clinical examination alone have made the decision to pursue surgery often a considerable undertaking. Unlike advanced solid tumors of the head and neck whose boundaries and extension to other structures can be determined or estimated using CT or MR imaging, there are no imaging techniques in clinical use that can provide surgeons with the resolution needed to identify the axial spread of early cancer through the basement membrane and into the lamina propria. At present this information on tumor behavior at the tissue structural level requires a biopsy. OCT has potential to provide a means to image with high resolution (~7 μm) the vertical extension of early cancers and other neoplasms through the basement membrane of the delicate laryngeal mucosa. The potential clinical utility of OCT in the larynx has already been demonstrated in several publications. 8,12,14 However, while detailed OCT images of both benign and malignant laryngeal disease continue to be acquired and published, little is known about the normative microstructure of the laryngeal mucosa. This is important because the dimensions of the epithelium are generally thicker in early T1 cancers, dysplastic lesions, and benign disease, which may mimic cancer on clinical examination.8 If OCT is to evolve into a viable in vivo imaging modality to provide valuable information on the cross-sectional anatomy of the larynx, then it is absolutely necessary to know the dimensions of the tissue layers in the normal larynx. Just as in previous decades when CT and MRI images were compared with gross anatomy dissections and large whole body cross-sectional slices,15 with OCT the thickness of the different layers of the laryngeal mucosa measured in vivo using OCT must be compared with measurements made in ex-vivo histological specimens. The purpose of this study is to accomplish this basic task. It is important to emphasise that although the ideal study would be to correlate the in vivo OCT images with in vivo laryngeal histological specimens, but this is unethical, because it requires performing total laryngectomies on healthy patients after in vivo OCT images were taken.