Does Indocyanine Green define margins in Wilms tumour? A novel macroscopic and microscopic ex-vivo study.
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INTRODUCTION: Wilms tumor (WT) is the commonest renal cancer in children. It has excellent overall survival rates of >85 %, but relapsed disease is difficult to treat. Surgeons usually undertake a total nephrectomy but can occasionally perform nephron sparing surgery (NSS) in selected cases to preserve renal tissue. However, if margins are positive, the child then needs chemotherapy intensification and radiotherapy. Intraoperative guidance is limited to knowledge of the anatomy and intra-operative ultrasound, neither of which is perfect. This study uses an ex-vivo platform to study whether Indocyanine Green (ICG) can define tumor margins at a macroscopic and microscopic level. MATERIAL AND METHODS: UK Research Ethics committee approved the study. Patients having nephrectomy were eligible and parents were approached for enrolment. Patient demographics, anatomy of tumor and remaining kidney, ex-vivo macroscopic and microscopic white light and near infrared (NIR) findings were assessed. Microscopic pixel brightness was recorded as grayscale with peak and range. Final histopathology was also recorded. Statistics were presented as median (range) and comparative data as Mann-Whitney U with a p of >0.01 taken as significant. RESULTS: Eleven consecutive patients having unilateral total nephroureterectomy for presumed WT. Two were excluded with nine kidneys (4F:5M) receiving ex-vivo intra-arterial injection of ICG. In all specimen's normal renal parenchyma exhibited macroscopic and microscopic fluorescence. Low (n = 1) and intermediate risk tumors (n = 6) had obvious margins under NIR at macroscopic or microscopic levels. High risk blastemal tumors (n = 2) showed fluorescence throughout the tumor as well as the parenchyma with no obvious margins. Grayscale readings showed blastemal was not significantly different to normal kidney (p = 0.477) but epithelial(E) (p = 0.01); stromal(S) (p = 0.003); combined E/S/necrotic(N) (p = 0.00018) and combined E/S/N/Tumor capsule (p = 0.00006) were. CONCLUSION: ICG and NIR can be used to assess tumor margins in low and intermediate risk disease but not in blastemal high-risk tumors. It can act as an additional measure of safety but should not be used alone.