Endoscopic stent placement plays an important role in the palliation of dysphagia secondary to esophageal cancer. Over the past decade, advances in expandable stent technology have led to smaller, more flexible delivery systems that are easier to manipulate than the original plastic stents. These attributes permit successful deployment without exposing patients to the risks of aggressive mechanical dilation.
Most plastic stents have an internal diameter of 10 mm and include a proximal funnel to collect food and liquids and a flange at the distal end to prevent migration. The two methods of insertion are traction and pulsion. Traction stenting requires a general anesthetic and a laparotomy incision. For traction stenting, a pilot bougie is inserted orally and retrieved through a gastrostomy. The stent is sutured to the bougie and pulled into place at the site of obstruction. Then the tube is trimmed to length and the gastroscopy closed. Pulsion stenting can be performed with sedation; however, general anesthesia is also often used. A guidewire is placed, followed by dilation at the obstruction site.
All plastic stents necessitate aggressive dilation to a diameter of 45F before placement. The need for aggressive dilation imposes a significant risk of perforation. Additional problems include tube displacement, food impaction, and intractable reflux for stents placed across the gastroesophageal junction. In a study of these older methods of stenting, significantly lower mortality was seen in the pulsion group (14%) than in the traction group (23%).1 Length of hospital stay was 8.4 days, compared with 18.6 days in the pulsion and traction groups, respectively. Clearly, these results are not acceptable by current standards of care, particularly when the intent is palliation rather than cure.
A new generation of stents has evolved. Chief among them is the expandable metal stent (EMS). The EMS eliminates the need for aggressive dilation before insertion and can be placed with sedation alone. Because the stent itself is embedded in the tumor, the chance for migration is low. Morbidity, mortality, and length of hospital stay have been equally reduced in comparison with the plastic predecessors.
The EMS is constructed of various metals, including cobalt alloys (Wallstent, Schneider, Minneapolis, MN), stainless steel (Gianturco, Cook, Bloomington, IN), and a nickel-titanium alloy referred to as nitinol (Esophacoil, Medtronic, Minneapolis, MN; Ultraflex, Microvasive, Natick, MA). These materials are resistant to corrosion and biologically inert. The wire stents can be woven (Wallstent), knitted (Ultraflex), or bent into a zigzag (Gianturco) or coil (Esophacoil) configuration. The stent design influences its retraction (i.e., shortening) properties. Retraction percentage is higher with the coil than with the zigzag configuration. The shape-memory characteristics of these metals and metal alloys permit the stent to reexpand to its original tubular shape even after it has been compressed into a delivery system. The available systems include stents that can be deployed from the proximal end, the center, or the distal end. Proximal delivery is better suited for proximal strictures, whereas distal delivery is more suitable for obstructions located close to the gastroesophageal junction.
The EMS also can be partially covered with polyurethane or silicone. Covered designs help to reduce tumor ingrowth but also increase the risk of migration. Of note, covered stents have properties especially suited for the management of tracheoesophageal fistulas.2 The wide range of available diameters and lengths permits use of the EMS for most esophageal lesions.
A recent innovation in stent technology is the self-expanding plastic stent (Polyflex Esophageal Stent, Boston Scientific, Natick, MA). As with the EMS, these stents can be placed without need for aggressive predilation. However, the self-expanding plastic stent also can be removed because there is no tissue ingrowth, and it is therefore preferred for benign strictures. The self-expanding plastic stent also may be considered for patients receiving chemotherapy and radiation, where it may be possible to remove the stent at the end of therapy. The self-expanding plastic stent does, however, suffer from an increased migration rate (up to 25%).3
PDT operates on the following basic principle: A photosensitive substance is injected that accumulates in target cells of the host tumor. This photosensitizing substance, when activated by light of a specific spectrum, causes selective tissue destruction (apoptosis). Photosensitizers used in surgical practice include purified hematoporphyrin derivatives [porfimer sodium (Photofrin), Axcan Scandipharm, Birmingham, AL], chlorines [Temoporfin, or m-tetrahydroxyphenyl chlorine (m-THPC)], and 5-aminolaevulinic acid (5-ALA). Optimal wavelengths of light absorption are 630 nm for porfimer sodium and 5-ALA and 652 nm for m-THPC. Currently, Photofrin is the only photosensitizer approved by the Food and Drug Administration for esophageal cancer and high-grade dysplasia of the esophagus.
Photosensitizers accumulate in all cells of the body. However, after 1–4 days, higher concentrations are found within tumor cells and in the interstitium of the tumor mass. Altered lymphatic drainage, neovascularization, and increased cellular proliferation are some of the mechanisms hypothesized to be responsible for this phenomenon. Laser light delivered directly to cancer cells that harbor the photosensitizer triggers a series of events culminating in cell destruction. When cells are bombarded with photons of a wavelength specific to the photosensitizer, the absorbed energy acts as a catalyst to the formation of highly reactive oxygen species (e.g., superoxide anions, peroxide anions, and singlet oxygen). The primary targets of photodamage are cellular membranes, amino acids, and nucleosides. Unlike the more commonly used thermal lasers, PDT uses a nonthermal laser consisting essentially of a wavelength of light that is specific to the photosensitizer (e.g., 630 nm for Photofrin). Since thermal energy is not used with this therapy, the risk of perforation is lower than with traditional thermal laser technique.