Popcorn Effect

Abstract

To the Editor: In the late 1970s, neodymium yttrium-aluminium-garnet (Nd-YAG) laser photoradiation was used bronchoscopically by a group of French physicians to achieve recanalization of the bronchial lumen obstructed by exophytic tumors.1 Thirty years later, bronchoscopic YAG laser therapy still has an important role in the palliation of patients with inoperable lung cancer; particularly those requiring immediate relief of bronchial obstruction.2 Although fire in the airway is a well-recognized hazard of the use of the CO2 laser, only anecdotal reports have been described related to intratracheal combustion during Nd-YAG laser treatment of the endobronchial lesions.3 By adhering to safety principles for Nd-YAG laser applications in the endobronchial tree, airway fires or explosion can be effectively prevented or adequately controlled to achieve radical tumor resection without any significant risk.4 We report a case of isolated main carina metastasis from non–small cell lung cancer treated by rigid bronchoscopy (Fig. 1).FIGURE 1: Bronchoscopic view of the tumor before starting laser resection.Controlled Nd-YAG laser energy using long, low-power, single-pulse mode was delivered for coagulation. Suddenly the left half of the lesion exploded with a loud noise scattering the burnt tissue all over the tracheobronchial tree. Incidentally there was no damage to the surrounding structures (Fig. 2). At the end of the procedure the whole lesion was completely resected (Fig. 3). We continued with the procedure until the entire endobronchial portion of the lesion was ablated.FIGURE 2: Bronchoscopic view of tumor explosion caught in the act.FIGURE 3: Bronchoscopic view at the end of the procedure, disclosing complete tumor resection.The reported phenomenon is referred to as “popcorn effect.” Obviously it is difficult to document it in pictures. The degree of tissue effects caused by the laser is due to the combination of absorption, scatter, transmission, and reflection of the light (photon) within the tissue. At temperatures above 65°C, protein denaturation and surface blanching takes place. Tissue desiccates and shrinks at temperatures above 90 to 100°C; and over 100°C, carbonization of the tissue takes place. Blackening of the tissue leads to the focused absorption of the laser energy and eventual vaporization of the tissue. In addition, concomitant vaporization of the intracellular and interstitial water can cause rapid rise in its volume within the tissue, which eventually leads to noisy expulsion of the vapor (popcorn effect).5 This explosion is unrelated to the amount of FiO2 being delivered. The purpose of reporting this event is that popcorn effect is relatively benign and the bronchoscopist can continue to work through the event. This effect can be avoided by avoiding carbonization of the tissue and applying laser energy diffusely over the lesion. In conclusion, Nd-YAG laser tumor resection is a safe procedure. Side effects such as a “popcorn” explosion are intriguing, but in the experienced hands it can be effectively managed without any injury to the patient. Francesco Petrella, MD* Sergio Cavaliere, MD* Lorenzo Spaggiari, MD, PhD*,† *Division of Thoracic Surgery, European Institute of Oncology †University of Milan School of Medicine, Milan, Italy