Characterization of mediastinal lymph node physiology in vivo by optical spectroscopy during endoscopic ultrasound-guided fine needle aspiration.

INTRODUCTION: Esophageal endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) is a minimally invasive staging procedure for mediastinal lymph nodes in patients diagnosed with lung cancer. But, a substantial false negative rate necessitates that patients returning a negative EUS-FNA result must undergo a subsequent surgical staging procedure. This study incorporates a fiberoptic reflectance spectroscopy device into the EUS-FNA procedure to asses the vascular physiology within the sampled lymph node. The aims of this pilot study were to determine the feasibility of incorporating a reflectance spectroscopy device into the EUS-FNA clinical procedure and to gather preliminary information about the vascular physiology within the center of normal and metastatic lymph nodes. METHODS: This study included 10 patients with proven or suspected lung cancer and an indication for EUS-FNA. The procedure was performed on seven normal (unenlarged, positron emission tomography negative) nodes and seven suspicious (enlarged, positron emission tomography positive), with the malignant status of all nodes cytologically confirmed. Reflectance spectra were acquired using a single optical fiber that fits through the end of the EUS-FNA biopsy needle, with an outer fiber diameter of 0.38 mm. RESULTS: The procedure was successfully performed and did not introduce complications. Model-based analysis of single fiber reflectance spectra provided quantitative information about the vascular physiology within the sampled lymph node. We observed that metastatic lymph nodes were characterized by lower microvascular oxygen saturation (50% versus 84%, p < 0.01) and lower blood volume fraction (5.6% versus 13.5%, p < 0.01) than normal nodes. CONCLUSIONS: Single fiber reflectance spectroscopy has the potential to detect abnormal lymph node physiology.