Usefulness of Indocyanine Green Fluorescence Endoscopy for Intraoperative Differentiation of Intracranial Tumors and Adjacent Structures

Introduction: Indocyanine green (ICG) is a fluorescent dye used to evaluate vascularity and tissue perfusion. As each tumor type has characteristic contrast enhancement on imaging studies and variable disruption of/relationship to the blood brain barrier, intraoperative ICG fluorescence endoscopy has the potential to differentiate tumor from surrounding structures.

Methods: 40 patients undergoing endoscopic endonasal skull base surgery for tumor resection were prospectively enrolled in this study. ICG was administered intravenously during surgery under constant visualization with near-infrared endoscopy. Dosing of ICG was 25mg in 18 patients and 12.5mg in 22 and the degree of fluorescence of tumor and related anatomical structures was graded as low, moderate or high.

Results: There were 16 pituitary adenomas (PAs), 2 Rathke’s cleft cyst (RCC), 2 craniopharyngiomas, 6 chordomas, 12 meningiomas, 1 arachnoid cyst and 1 juvenile nasopharyngeal angiofibroma (JNA).

All hormone-secreting PAs had low fluorescence (n = 7) except for one case of prolactin-secreting PA, which had high degree of fluorescence.

Among nonfunctioning PAs, 62% (n = 5) had low enhancement and 37% (n = 3) had moderate enhancement.

81% (n = 13) of the PAs had a different enhancement compared with the pituitary gland.

All those PAs that could not be differentiated had low enhancement.

The two craniopharyngiomas were graded as low. 80% of chordomas had low enhancement and only one case was classified as moderate. The only case of JNA (post-embolization), arachnoid cyst, as well as the RCCs all had low degree of fluorescence. 44% of meningiomas were graded as low and 55% were moderate.

94.7% (n = 36) of the vascular structures had a high enhancement.

69.6% (n = 16) of anterior pituitary glands were moderate/high and 30.4% (n = 7) were low. The mucosa was always classified as moderate/high (n = 8).

Tumor fluorescence was different from normal surrounding structures in 32 cases (78%) and the median time of best visualization of this difference was 41 seconds after ICG injection (minimum of 5 seconds and maximum of 1 hour and 8 minutes.

Differentiation of tumor and surrounding tissues was related to higher ICG dosing (25mg)(p = 0.026).Neither tumor location (p = 1 for anterior, middle and posterior fossa) nor tumor size (p = 0.31) or tumor type (p = 0.715 for PAs and p = 1 for other tumor types) was correlated with visual differentiation.

Conclusion: Intraoperative use of ICG fluorescence endoscopy may help identify critical vascular structures and can be a useful auxiliary tool in differentiating tumor from adjacent structures, especially with 25mg of contrast.

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