The use of an endoscope in exoscopic transcranial neurosurgery for skull-base lesions has not yet been investigated. Thus, this study aimed to investigate the advantages, disadvantages, and safety of “simultaneous temporary use of an endoscope during exoscopic surgery” (exo-endoscopic surgery (EES)). Consecutive exo-endoscopic surgeries performed by experienced neurosurgeons and assistants were analyzed. Surgical complications and time were compared with previous consecutive microsurgeries performed by the same surgeon. A questionnaire survey was conducted on 16 neurosurgeons with experience in both “temporary simultaneous use of endoscope during microscopic surgery” (micro-endoscopic surgery (MES)) and EES. EES was performed in 18 of 76 exoscopic surgeries, including tumor removal (n = 10), aneurysm clipping (n = 5), and others (n = 3). There were no significant differences in operative time, anesthesia time, or complications from microsurgery by the same operator. According to the questionnaire survey results, compared with MES, EES had a wider field of view due to its lack of an eyepiece, was easier when loading and unloading instruments into and out of the surgical field, and was more suitable for the simultaneous observation of two fields of view. Overall, 79.2% of surgeons indicated that EES may be better suited than MES to simultaneously observe two fields of view.

当施設で外視鏡導入後の髄内腫瘍30例（神経膠腫10例，転移性脳腫瘍17例，脳悪性リンパ腫3例）で5ALA・NBI・ICGの有用性を術者の目視で定性評価した．5ALAは悪性神経膠腫で強い蛍光を示し顕微鏡と同等，ICGは血流評価に有用．NBIはあまり有用性が得られなかったが，低悪性度神経膠腫の脳表観察において，正常脳実質との境界を診断するのに有用となる可能性が示唆された．転移性脳腫瘍において，白色光に比べNBIは腫瘍本体と周囲白質との識別に有用である可能性が示唆された．なお易出血性腫瘍ではNBIは出血により黒色となってしまい，識別は非常に困難であった．しかしながら脳腫瘍摘出術における新たな蛍光診断の方法として，NBIは新規の蛍光診断の方法になりうる可能性を秘めている．

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.