FLEX October 2023

CO 2 LASER – INDUCED ARTIFACT AND GLOTTIC CANCER SURGICAL MARGINS AT VARIABLE POWER DOSES

difficult to control for tissue tension within and between cases, even if all procedures are performed by the same surgeon. Accurate wattage data could only be retrieved and corre lated with the tissue measurements in 14 of the cases, thereby reducing the sample size. Based on this small number of specimens, the power of laser (1–3 W) could not be used to predict whether a margin would be involved. Further studies with greater case numbers and a research methodology that takes into account duration of laser contact with the tissue and examination of the same sites are required to obtain a more statistically valid result. In the 15 patients with reportedly clear margins, the poten tial presence of laser-induced artifact means that it remains a challenge to be certain whether any artifact that was observed obscured evidence of epithelial dysplasia. The mean distance of thermal damage to the histologic margin by the CO 2 laser in this study was 380.83 6 178.79 l m. This is an important consideration for the surgeon, as a surgical margin of 1000 to 2000 l m must be created in the glottic specimen to achieve oncologic clearance, 44 compared with 2000 to 5000 l m in other sites of the upper aerodigestive tract. 45 If 30% to 40% of this glottic margin is uninterpretable by the pathologist because of laser ther mal artifact, this has significant implications for the techni cal aspects of oncologic treatment. It is imperative that the surgeon takes this knowledge into account at the time of TLM and ensures that the cancer is removed with a suffi ciently clear margin. Despite the small number of samples reviewed in this study, the amount of tissue damage seems to decrease as the power of the laser beam increases, although not statisti cally significant. The results are clinically significant as laser-induced cytologic atypia may confound the diagnosis, resulting in overtreatment. Assessment of surgical margins may therefore be compromised by the artifactual changes, which may obscure critical histopathologic features, result ing in undertreatment of patients. It is vital that the treating surgeon and pathologist know this, as this will have a prac tical impact on both TLM technique and histopathologic evaluation and reporting. Detailed knowledge of the laser effects on the surgical margin is paramount to ensure com plete oncologic resection, while preserving as much func tionally important tissue as possible. In conclusion, the depth of artifactual thermal burn decreases with the increasing power of the laser, presum ably because of increased efficiency of cutting at higher power, with less transfer of thermal damage to surround ing cells. The artifactual thermal damage is an important concept for both the surgeon and pathologist as it is hard to discern whether a margin is truly oncologically clear or if artifactual atypia is present. For this reason, it is essential for the surgeon to excise the glottic cancer with sufficient margins to ensure that there is enough noncan cerous tissue between the cancer and the superficial ther mal burn, thereby enabling the pathologist to report adequate oncologic clearance. REFERENCES 1. Strong MS, Jako GJ. Laser surgery of the larynx. Early clinical experience with continuous CO 2 laser. Ann Otol Rhinol Laryngol 1972;81:791–798. 2. Genden EM, Ferlito A, Silver CE, et al. Evolution of the management of laryngeal cancer. Oral Oncol 2007;43:431–439.

denuded the epithelium, the underlying lamina propria can be assessed for invasion, but not dysplasia. 31 A recent study comparing cold steel with laser excision of glottic cancers has demonstrated that, despite a greater extent of margin artifact with the laser ( p 5 .21), there was no significant difference in interpretability of the specimen by the pathologist ( p 5 .24). 31 However, the use of a laser did increase the risk of obtaining substantial margin artifacts or uninterpretability ( p 5 .024). Interest ingly, in the cold steel group, there was a greater preva lence of uninterpretability in margin status, but a lower degree of artifact. Despite the small sample size ( n 5 45), it was postulated that the mechanism of damage in the cold steel group was a crushing injury making the entire specimen uninterpretable, despite epithelial preservation. This contrasts with the laser, which denudes the epithe lium more readily as a result of vaporization. The finding in our study that the depth of tissue pene tration (ie, artifact damage) decreased, despite increasing laser power, was unexpected. We propose that this reflects a greater efficiency of laser cutting at higher power, while the tissue is maintained under tension. The greater speed of cutting at higher power provides less time for cellular damage, and the extent of artifact is reduced as the laser beam is in contact with the cells for less time. We use a CO 2 laser beam in superpulsed mode. Studies on benign vocal cord lesions have shown that pulsed CO 2 provides better wound incisions and healing than continuous wave CO 2 . 32–34 The pulsed cyclic wave form of heat followed by cooling enables tissue cutting followed by hemostasis. Although the energy is delivered at high peak power, the average power and resultant depth of coagulation are less, so thermal damage to sur rounding tissue is therefore limited, with resultant improved wound healing. Pulsed CO 2 laser results in comparable vocal outcomes and wound healing when used to excise or ablate benign vocal cord lesions. 35–37 Continuous wave CO 2 laser, however, results in thermal damage to surrounding tissue and delayed wound heal ing. 35,38–41 Although not routinely used for laser excision of glottic cancers, we anticipate that the more extensive artifactual damage induced by a continuous laser wave form would invoke an even greater diagnostic dilemma for the pathologist. It is worth considering the size of the laser spot used to excise glottic cancers. A small spot size of 0.25 mm ena bles precision cutting while enabling hemostasis and min imizing charring of tissues. 42,43 A larger beam spot size would scatter energy more widely, with imprecise cutting, risk of bleeding, potential for more widespread artifactual damage, and uninterpretability of the surgical margin. Also of note is the amount of tension applied to the tissue while the laser beam cuts. A greater traction undoubtedly results in more efficient cutting, as the pathologic tissue is prized apart from the vocal cord. Increased tension pro duces a thinner bridge of tissue, which is then excised more easily with an expected lesser degree of thermal damage. This may partly explain the wide range of meas urements determined at different sites along the excision margin by the investigators. However, excision of a glot tic lesion is a dynamic process, with continuous changes in tissue tension created by the surgeon. It is therefore

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HEAD & NECK—DOI 10.1002/HED APRIL 2016