Histologic evaluation of interstitial lipolysis comparing 1064 nm, 1320 nm and 2100 nm lasers

Background and objectives: Laser lipolysis using a pulsed Nd:YAG laser has been shown to be a safe and effective modality for the treatment of small areas of fat in conjunction with microcannula liposuction. The purpose of this study is to compare the histologic effects on ex vivo human fatty tissue using three separate wavelengths of laser light (1064, 1320 and 2100 nm) at three predetermined energy levels. Study design/materials and methods: Nine samples of freshly harvested abdominal subcutaneous tissue were tumesced and then cannulated in a single tunnel in the superficial subcutaneous tissue. They were irradiated with a 320 pm polyimide fiber using a pulsed 1064 nm Nd:YAG, 1320 nm Nd:YAG and 2100 nm thulium holmium chromium:YAG (THC:YAG) laser at 4, 6 and 8 W (CoolTouch Corp., Roseville, CA). The fiber was withdrawn at a rate of 1 mm/second in a single pass. A tenth sample was cannulated without irradiation and served as a control. Irradiation with the 1320 nm Nd:YAG was performed in vivo on a lipoma in a similar fashion with repetitive tunneling. Fat was removed the following day by incisional punch biopsy for histologic evaluation. The tissue was studied in a blinded fashion with hematoxylin eosin staining. Results: Light microscopy after irradiation showed thermal damage in the subcutaneous tissue that preferentially affected the fibrous septae with some fat cell damage. The diameter of thermal damage around the fiber ranged from 1 to 4-5 mm depending on the laser wavelength and average power of the settings. No clear fat liquefaction was seen histologically in the ex vivo samples but was seen with the 1320 nm Nd:YAG irradiation of the in-vivo lipoma tissue. Conclusion: Laser lipolysis works through a combination of photoacoustic ablation and selective photothermolysis of fibrous septae. Acoustic damage occurs with thermal damage and is difficult to capture histologically. The greatest amount of thermal damage was seen in the specimens with the highest energy per pulse, however, the patchiness and variability of thermal damage within the cross-sections evaluated make it difficult to draw any strong conclusions. Further studies are warranted to more fully evaluate the histologic effects and mechanisms behind laser lipolysis.