Intraoperative Sodium-Fluorescence Imaging in Peripheral Nerve Sheath Tumors (PNST)-A New Additional Promising Diagnostic Tool

Background: Through the development and implementation of specific fluorophore filters to microscopes in 2012, sodium fluorescein (SF) is currently experiencing a remarkable renaissance in neurosurgery. The present study examines its intraoperative application during surgical removal of peripheral nerve sheath tumors (PNST) and metastases.

Methods: This single-center study includes 10 cases of benign and malignant tumors as well as metastases of peripheral nerves (in total 11 PNST). Their surgical resections were all performed under microscope-based fluorescence with SF, which was administered intravenously (0.5–1.0 mg/kg body weight) during anesthesia induction. Microsurgical tumor removals were filmed and the collected data were retrospectively analyzed via ImageJ.

Results: Microsurgical tumor preparation was possible under the usage of fluorophore filter. In seven histological confirmed schwannoma (n = 6 patients) tissue differentiation between tumor mass and not involved fascicles was statistically significant for the colors green and red. Schwannoma maximum mean for green reached 254.7 pixel and 179.4 pixel for red, whereas passing healthy fascicles revealed a maximum mean for green 94.91 and for red 120.76 pixel. One case of neurofibroma achieved lower amount of pixel. Similar to schwannoma, the two MPNST cases showed a strong homogeneous fluorescence (max. mean green 215 pixel and red 124.51) involving the whole nerve segment. Subcutaneous tumor remnants were visualized and therefore resected. Via fascicular nerve biopsy a B-cell lymphoma of the tibial nerve could be detected. SF led to variable stain intensities in single fascicles. The resected fascicle revealed a max mean green of 100.54 pixel, whereas surrounding fascicles came up with max. mean green of 63.0 pixel.

Conclusions: Intraoperative SF visualization for PNST is feasible and of low risk. During resection of benign PNST, enhanced tissue differentiation between affected and not affected nerve segments is very useful. Tumor remnants can be detected safely and effectively. Its application during resection of malignant PNST is limited. Due to the infiltrative nature of those tumors, intraneural tissue differentiation is not possible. “Fluorescence-guided” biopsy can be regarded as an additional advantage in PNST surgery. Due to the encouraging experience in our institution SF was established as standard visualization tool in PNST surgery.

Sodium Fluorescein as Intraoperative Visualization Tool During Peripheral Nerve Biopsies

OBJECTIVE

Owing to technical development of specific fluorophore filters, the neurosurgical application of sodium fluorescein (SF) has regained value in brain tumor surgery. The aim of this study was to determine the usefulness of SF during nerve biopsies.

METHODS

This single-center study included 5 cases of nerve biopsies performed under microscope-based fluorescence with SF performed between March 2016 and February 2017. SF was applied intravenously (1 mg/kg body weight). After microsurgical dissection of the involved nerve segment, fluorescence-guided fascicular biopsy was performed. Selection of target fascicles was at the surgeon's discretion and took into account nerve stimulation for preservation of motor function and fluorescence intensity. Correlation to histopathologic examination was examined. Video analysis of intraoperative images comparing target fascicles with intense fluorescent response to adjacent fascicles of the same nerve segment was performed using ImageJ.

RESULTS

All patients had motor or sensory deficits. Magnetic resonance imaging findings were similar, depicting long segments of gadolinium enhancement (minimum 11.7 cm). Each biopsy sample was positive resulting in diverse histopathologic results. Digital image analysis revealed a statistically significant difference of the complementary color green (P = 0.0473).

CONCLUSIONS

Magnetic resonance imaging is the gold standard in diagnostic work-up of peripheral nerve disorders. Longitudinal nerve thickening with positive contrast enhancement is an unspecific magnetic resonance imaging finding. Various pathologies, such as tumors and inflammatory lesions, may cause this morphologic phenomenon. Nerve biopsies may be needed for diagnostic work-up. Intraoperative SF may help to depict the most affected fascicles and identify target fascicles for biopsy and increase diagnostic certainty of nerve biopsies.

Sodium Fluorescein–Guided Surgery in Peripheral Nerve Sheath Tumors: First Experience in 10 Cases of Schwannoma

BACKGROUND

The intravenous application of sodium fluorescein (SF) for brain tumor surgery goes back to the late 1940s. The development of specific fluorophore filters significantly reduced the required dosage of SF and therefore diminished possible side effects. This study investigates the application of SF in benign peripheral nerve sheath tumors (PNSTs), concentrating on its feasibility during microsurgical removal.

METHODS

The single-center study includes 10 consecutive schwannoma cases operated on between September 2016 and March 2017. Inclusion criteria were defined as age ≥18 years, preoperative magnetic resonance imaging with suspicion of schwannoma, and final histopathologic confirmation of schwannoma. Exclusion criteria were a history of intolerance to SF and renal insufficiency. The microsurgical part of each surgery was video recorded, and the collected material was retrospectively analyzed. Red, green, and blue values of various regions of interest set on tumor and normal nerve of each patient were evaluated using ImageJ, an open platform for scientific image analysis.

RESULTS

Digital video analysis confirmed the intraoperative impression of increased fluorescence of the tumor in contrast with normal nerve tissue. Because the color yellow is predominantly a mixture of red and green, values of these colors were significantly increased in schwannomas compared with normal nerve tissue (P = 0.0003 and P = 0.0023, respectively).

CONCLUSIONS

SF reveals increased fluorescence in schwannomas compared with normal nerve tissue. Intraoperative differentiation of tumor and normal nerve tissue becomes possible using a low dose of SF (0.5-1 mg/kg). No side effects occurred. Secure microsurgical preparation is feasible during application of the YELLOW 560 nm filter.