FLEX October 2023

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

MATERIALS AND METHODS A selection of histologic specimens was taken from our database of 131 patients presenting with primary early glottic squamous cell carcinoma (T is –2), who had been treated with curative intent by TLM by the senior surgeon (C.E.P.) from February 2005 to December 2014. A retro spective chart review was carried out on this cohort of patients, having gained local hospital ethical approval. Patients were managed within the setting of a multidisci plinary head and neck clinic at a tertiary teaching hospital and underwent thorough clinical assessment and staging investigations. All patients underwent standard TLM. Details of the surgical procedure have previously been described. 29 Surgical resection was accomplished using a CO 2 laser (Sharplan 1040S; ESC Medical Systems, Yor knean, Israel) with a target spot of 0.25 mm. Power set tings of 1, 2, or 3 W were used, in continuous super pulse mode, and were kept constant for each patient. Lesions were excised with a type I, II, III, or IV cordectomy. 30 Routinely processed, representative sections, which had been stained with hematoxylin-eosin, were retrieved from the departmental archives and reviewed using an Olympus BX41 light microscope. A single section of each case was then selected and scanned using the Aperio Digital ScanScope at 20 3 magnification. Assessment of connec tive tissue and epithelial cytologic changes in each tissue sample was carried out independently by 3 investigators using the scanned images. The distance of the thermally induced coagulative effect at the connective tissue margin was measured at 3 different points with the aid of Scan Scope software. A mean measurement of denatured colla gen was then calculated for each specimen. The artifactual cytologic changes of the epithelial margins on either side of the specimen were quantified by assessing mean average distance of epithelial and collagen denatu ration. This data was correlated with the power setting (watts) that had been used during surgery. Statistical anal ysis for interobserver variability was undertaken using SPSS Statistics version 17.0 software. RESULTS Thirty laryngeal excision specimens were analyzed and measured. The wattage settings used during surgery were available for 14 cases (7 cases at 1 W; 4 cases at 2 W; and 3 cases at 3 W). Fifteen specimens showed evidence of unequivocal tumor at the surgical margin with no interference by laser-induced cytologic artifact in the histologic determi nation of the margins. These 15 patients were all subse quently successfully retreated with a wider laser excision. Histologically, the tissue damage caused by the laser consisted of collagen denaturation within the vocal cord lamina propria and deeper vocalis muscle, as well as structural alterations of the epithelium. The denatured connective tissue had a darker eosinophilic color, with loss of detail of the cellular component when compared with the unaffected, deeper connective tissue. In addition, thrombotic blood vessels were observed (Figure 1A). The artifactual epithelial changes observed included dehis cence, nuclear pyknosis, atypia, hyperchromasia, and

(multiple internal reflections within the tissue), and con duction, to varying degrees. Absorption is the most desir able outcome, and is influenced by the water content of the tissue. 16 The CO 2 laser beam is readily absorbed by water-rich tissues. Absorbed energy is converted into thermal energy, resulting in photothermal effects. Absorp tion length is the depth of tissue through which the beam is completely absorbed. As the beam travels through the tissue, the power density reduces exponentially. Power density determines the rate of removal of tissue, and is measured in Watts per cm 2 (cross-sectional area of the beam). Tissue beyond the absorption length may be affected because of heat conduction, as energy spreads in all directions. Diffusion of heat within the tissue is called thermal relaxation. 16 The CO 2 laser beam heats tissues. Above 55 8 C, protein is denatured irreversibly (coagulation), and inflammation ensues. With prolonged exposure, tissue undergoes ther mal necrosis and sloughs off. At 100 8 C, intracellular and extracellular water boils and vaporizes, cells desiccate and explode, and there is production of cellular debris. Desiccated debris wastes energy and reduces the speed of surgical progression. Charring of tissue occurs at 350 8 C, and incandescence may be observed as the beam strikes charred areas. As charred particles cross the path of the beam, further damage can occur as flares are created. The presence of blood in the surgical field increases charring. 16 Histopathologic assessment of the surgical margins is routine and gold standard for all carcinoma excision specimens. The connective tissue and epithelial margins are examined for involvement by tumor or dysplasia. Assessment of epithelial dysplasia is highly subjective between pathologists. 17 It has previously been reported that accurate interpretation of these margins may be com promised because of the thermal cytologic artifactual changes induced by the laser. 18,19 These changes include vacuolation of the superficial layer, separation of keratin, degeneration of basal cells, and their detachment from the underlying lamina propria, nuclear pyknosis, hyperchro masia, pleomorphism and elongation, and dehiscence of normal cellular architecture, all of which may mimic cytologic atypia, thereby making interpretation of dysplas tic epithelial lesions extremely difficult. 19–22 CO 2 lasers, in particular, traumatize the basal and suprabasal layers. 23 In addition, trauma, in the form of crush injury to or dis integration of the specimen, may occur intraoperatively as a result of handling with surgical instruments. 24–28 Finally, tissue contraction occurs during histopathologic preparation of the specimen, which may prevent reliable comment on completeness of excision by the patholo gist. 24 If the margin of the specimen cannot be assessed adequately with respect to involvement by tumor, more aggressive resection is required, and this can have adverse effects on upper aerodigestive tract function. The purposes of this study were 3-fold: (1) to evaluate the surgical margin after endoscopic CO 2 laser resection of early glottic carcinoma (T is [in situ], T1, and T2); (2) to assess the impact of CO 2 laser-induced artifact on interpretation of histologic margin; and (3) to assess the degree of epithelial and connective tissue denaturation according to CO 2 laser power (watts).

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HEAD & NECK—DOI 10.1002/HED APRIL 2016