Histopathological and Quantitative Correlates of Intraoperative Narrow Band Imaging in Brain Metastasis Surgery

Background/Objectives: Accurate intraoperative identification of the tumor–brain interface is important in brain metastasis surgery, but visual assessment under white light is subjective. Narrow-band imaging (NBI) enhances hemoglobin-dependent optical contrast without an exogenous agent; whether its intraoperative appearance corresponds to tumor tissue, and whether it measurably increases tumor-to-normal image contrast, has not been established in this setting. Methods: In this retrospective, single-center, exploratory study, we evaluated 25 consecutive patients with brain metastases resected using a 4K three-dimensional exoscope equipped with NBI. In three selected patients, spatially adjacent specimens were separately sampled from grayish-appearing and whitish-appearing regions and assessed histopathologically in a non-blinded, descriptive manner. In all 25 patients, paired white-light and NBI images were retrospectively analyzed in Fiji/ImageJ using regions of interest drawn over tissue visually judged to be tumor or normal brain. Results: In the three patients with paired histology, grayish-appearing specimens contained metastatic tumor cells and whitish-appearing specimens did not; this observation derives from a small, selectively sampled subset and should be regarded as preliminary. Across all 25 patients, absolute tumor-to-normal gray-value contrast was significantly greater under NBI than white light (69.628 ± 45.338 vs. 44.287 ± 29.640; mean paired increase, 25.342; 95% CI, 9.169–41.514; p = 0.0035; Cohen’s dz = 0.647), although this increase was not observed in all patients. Conclusions: In this exploratory, non-blinded, retrospective study, NBI increased objective image contrast between visually identified tumor and normal brain relative to white light, and its grayish appearance corresponded to tumor tissue in a small histologically sampled subset. These findings support NBI as a feasible, agent-free adjunct that warrants prospective, blinded validation before its diagnostic accuracy or clinical benefit can be assessed.