Over the past several decades, flexible endoscopy has shifted the management of numerous gastrointestinal diseases from the surgeon to the endoscopist. What had started as a diagnostic discipline has now become one of advanced therapeutic potential. The concept of performing endoscopic surgery has become a reality with the advancement of endoluminal therapies for neoplasia, gastroesophageal reflux, and obesity. In addition, with the significant investigation into natural orifice translumenal endoscopic surgery (NOTES) and the development of advanced endoscopic tools, the ability to perform intraperitoneal therapies without abdominal scars continues to become more possible. This chapter will address the indications and techniques for upper and lower flexible endoscopy as well as the recent advances in imaging and interventional endoscopy.
The flexible endoscope was initially developed in 1957 as an imaging device dependent on the delivery of light and transmission of the image along multiple bundles of chemically treated glass fibers. The fiberoptic bundle is 2–3 mm wide and is composed of 20,000–40,000 individual fine glass fibers, each approximately 10 μm in diameter.1 The image undergoes a series of internal reflections within each fiber, which are coated with low optical density glass to prevent escape of light, as it is transmitted up the bundle. Due to formation of the fibers and surrounding material, a characteristic meshed image is seen in fiberoptic endoscopes, which inherently results in a lower resolution than that seen with rigid lens systems. In addition, if the fibers become cracked, the image is not generated at this site of the bundle and multiple black spots are seen.
When utilizing a fiberoptic endoscope, the endoscopist views the image through the eyepiece at the instrument head, or alternatively, a video camera can be affixed to the eyepiece to transmit the image to a video monitor. The progression from fiberoptic scopes to the videoendoscopes, we use today, has allowed for advancements in our ability to perform more involved therapies, educate physicians and endoscopic assistants, and obtain static and dynamic recorded data images for improved clinical management.
The majority of endoscopes in use today are videoscopic, although in many parts of the world, fiberoptic systems are still the standard. In these videoscopic systems, the visualized image is created from reflections onto a charge coupled device (CCD), which is a chip mounted at the end of the endoscope rather than via the fiberoptic bundles. The CCD chip has thousands of pixels (light-sensitive points), which directly increase image resolution.2
There have been many recent advances in endoscopic imaging techniques. The purpose of most of these techniques is early detection of dysplasia, which might elude standard endoscopic visualization. Clinical use of new imaging is limited principally to specialized centers, but future widespread application of an imaging method for early dysplasia detection is a certainty.
The aim of chromoendoscopy is to detect subtle mucosal abnormalities. Commonly used agents include Lugol's solution, methylene blue, indigo carmine, and Congo red. A 2–3% solution of potassium iodide (Lugol's solution) reacts with glycogen in keratinized squamous epithelium. Normal squamous epithelium stains a deep brown, but inflammation, dysplasia, and carcinoma do not stain because of a lack of glycogen. Lugol's solution has been shown to be effective in detecting Barrett's esophagus as well as screening for squamous cell carcinoma of the esophagus.3
In magnification endoscopy, a cap with a magnifying lens is fitted to the tip of an endoscope. The mucosa in contact with the lens is magnified without impairing the maneuverability of the scope. Degrees of magnification range from 1.5× to 115× and can be changed on the scope by turning a dial at the hand controls. The technique of magnification endoscopy is frequently used in conjunction with chromoendoscopy. Chromoendoscopy is used for broad surveillance of the mucosa followed by focused examination of suspicious lesions in magnification mode. This combined examination has been reported in case series to enhance detection of Barrett's esophagus, chronic gastritis, Helicobacter pylori infection, gastric dysplasia, and early gastric cancer.4–6
Confocal Fluorescence Microendoscopy
Standard endoscopy uses white light to visualize a large surface area with relatively low resolution. In contrast, confocal endoscopy aims to visualize the mucosa and submucosa with subcellular resolution, a technique deemed optical biopsy. The process of confocal magnification reduces out-of-focus light from above and below the focal plane at a magnification of 1000×. The system is designed to measure tissue fluorescence; therefore, an exogenous fluorophore (a molecule that causes another molecule to be fluorescent) is usually administered. Varying depths of tissue are examined by altering the focal plane, and images from different depths are stacked together to create an optical slice of tissue, thus the term optical biopsy.4
Most endoscopes now have the ability to switch from standard to narrow band imaging (NBI) with the push of a button. In narrow band endoscopy, filtered light is used to preferentially enhance the mucosal surface, especially the network of superficial capillaries. Narrow band imaging is often combined with magnification endoscopy. Both adenomas and carcinomas have a rich network of underlying capillaries and enhance on NBI, thereby appearing dark brown against a blue-green mucosal background.5 The use of white light as well as NBI has enabled endoscopists to provide an immediate assessment of small colonic lesions without histopathologic evaluation.7 Gastric mucosal abnormalities are also differentiated by NBI with and without magnification endoscopy.8 NBI can also differentiate squamous from nonsquamous epithelium to help identify Barrett's esophagus (Figs. 3-1 and 3-2).
Figures 3-1 and 3-2
Standard white light versus NBI imaging of the distal esophagus in patients with Barrett's esophagus (top). ...
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