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Background: Bone infiltration of the tumour is common in meningioma surgery. This may also affect patients without indicative signs of bone infiltration on preoperative imaging. Unrecognized bone invasion may lead to higher recurrence rates. 5-ALA fluorescence-guided resection (5-ALA-fg) could be a promising tool to help recognize possible bone invasion and/or tumour remnants. However, there is still little data about 5-ALA-fg resection in bone and soft tissue infiltrating meningiomas., Methods: We performed a retrospective study of 11 patients who were operated with the aid of 5-ALA due to bone and soft tissue infiltrating meningiomas at the University Hospital of St. Poelten between 2013 and 2019., Results: Strong and homogeneous fluorescence of the meningioma was observed in 9 cases (81.8%) and vague and heterogeneous fluorescence in 2 cases (18.2%). Hyperostosis on computerized tomography was evident in 3 of 6 cases (50%) and bone infiltration was visible in preoperative magnetic resonance imaging in 7 of 11 patients (63.6%). All eleven patients showed positive fluorescence of the bone infiltrating part. In all 7 cases where tissue could be collected, histopathological testing verified tumour infiltration (100%). There was also fluorescence of the periosteum in 3 cases and histopathological testing verified tumour infiltration in 100%., Conclusion: There is growing evidence that 5-ALA-fg resection can help to identify bone infiltration in meningioma surgery. Therefore, it may help to improve extent of resection. However, further studies are necessary to investigate the rate of false-negative fluorescence and its effect on progression free survival. If 5-ALA-fg resection of meningioma is performed, the attending surgeon should also consider investigating the adjacent periosteum under blue light for detection of possible fluorescence.

The exact role of 5-aminolevulinic acid (5-ALA) fluorescence-guided meningioma resection is as yet unclear. Although most of the meningiomas show positive fluorescence, the influence on outcome, fluorescence heterogeneity within the tumour, the correlation between fluorescence and the proliferation rate, as well as different quantitative measurements are a matter of debate. Positive fluorescence in bone infiltrative meningiomas is well described, whereas little data exist about 5-ALA fluorescence within soft tissue infiltration. We add a case of histologically confirmed fluorescent tumour infiltration into soft tissue. A 78-year-old woman underwent resection of an atypical meningioma at the University Hospital of St. Poelten. Preoperative imaging showed tumour infiltration throughout the calvaria. 5-ALA fluorescence of the tumour as well as bone, periost and temporal muscle helped to perform a gross total resection. Histological examination showed an atypical meningioma (WHO Grade II) and gave proof of tumour infiltration of the bone and temporal muscle. With the aid of 5-ALA fluorescence, a gross total resection could be performed.