2nd window ICG predicts gross-total resection/progression-fr
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Researchers conducted a prospective cohort study utilizing their technique of delayed near-infrared imaging with high-dose indocyanine green (called "second window ICG" or "SWIG") in the identification of brain metastases during surgery. All metastatic lesions enhanced under near-infrared light with the application of SWIG. SWIG can be used to predict the extent of gross-total resection and, more importantly, to predict progression-free survival.

Metastases are the most common intracranial malignancies and complete resection can provide relief of neurological symptoms and reduce recurrence. In this prospective cohort study, the authors evaluated intraoperative imaging and clinical outcomes of treatment using SWIG.

Patients were prospectively enrolled in an approved study of high-dose, delayed ICG (SWIG) and received 5 mg/kg or 2.5 mg/kg ICG 24 hours preoperatively. Intraoperatively, near-infrared (NIR) imaging was performed using a dedicated NIR exoscope. NIR images were analyzed and the signal-to-background ratio (SBR) was calculated to quantify fluorescence. Residual fluorescence on the postresection NIR view was compared and correlated to the residual gadolinium enhancement on postoperative MRI.

In total, 51 intracranial metastases were surgically treated in 47 patients in this cohort. All 51 metastatic tumors demonstrated strong NIR fluorescence.

The study showed;
-- In tumors ? 10 mm from the cortical surface, SWIG with 5 mg/kg ICG produced enhanced transdural tumor visibility compared to 2.5 mg/kg.

--Neoplastic margin detection using NIR fluorescence compared to white light improved sensitivity, albeit lowered specificity; however, increasing the SBR cutoff for positive fluorescence significantly improved specificity without sacrificing sensitivity, increasing the overall accuracy from 57.5% to 72.5%.

--A lack of residual NIR fluorescence after resection was closely correlated with a lack of residual enhancement on postoperative MRI.

--Among the 16 patients in whom tumor recurred at the site of surgery, postoperative MRI successfully predicted 8 cases, whereas the postresection NIR view predicted 12 cases.

--Progression-free survival rate at 12 months was greater for patients without residual NIR fluorescence than for those without residual enhancement on postoperative MRI.

The current study demonstrates the clinical benefits of the SWIG technique in surgery for patients with brain metastases. Specifically, this technique allows for dose-dependent, transdural localization of neoplasms and improved sensitivity in neoplastic margin detection.

Journal of Neurosurgery
Source: https://doi.org/10.3171/2020.8.JNS201810