Detection of Nonpalpable Tiny Axillary Lymph Nodes Surrounded by Adipose Tissue Using a Near-Infrared Camera

It is not always possible to detect nonpalpable small lymph nodes (LNs) surrounded by adipose tissue under the wavelength of visible light. A newly developed near-infrared camera with InGaAs element was able to capture photographs using light at >1000-nm wavelength, at which the difference in absorbance between water and lipids is large. This study investigated the ability to detect nonvisible small LNs using light at 1300-nm wavelength. Following retrieval of LNs through axillary LN dissection from 20 patients with breast cancer, residual specimens were simultaneously photographed using light at 970-, 1070-, 1200-, 1300-, 1450-, and 1600-nm wavelengths. A total of 45 specimens were observed pathologically at the selected portions in which the 1300-nm light was absorbed (high absorbance group [HA group], n = 25) and those in which the 970-nm light was absorbed instead (low absorbance group [LA group], n = 20). All specimens categorized in the HA group detected the LNs, whereas none of those categorized in the LA group detected an LN. The sensitivity and specificity in the identification of an LN were 1.0. The LNs detected using this camera were significantly smaller than those detected by surgeons (3.00 ± 2.93 mm vs. 5.90 ± 3.91 mm, p < 0.01). The light at 1300-nm wavelength was absorbed by axillary LNs. This camera detected LNs that were undetectable by surgeons. This novel technology may be applied to lymphatic microsurgery and contribute to the development of a minimally invasive LN dissection method.