Localization of protoporphyrin IX during glioma-resection surgery via paired stimulated Raman histology and fluorescence microscopy.

The most widely used fluorophore in glioma-resection surgery, 5-aminolevulinic acid (5-ALA), is thought to cause the selective accumulation of fluorescent protoporphyrin IX (PpIX) in tumour cells. Here we show that the clinical detection of PpIX can be improved via a microscope that performs paired stimulated Raman histology and two-photon excitation fluorescence microscopy (TPEF). We validated the technique in fresh tumour specimens from 115 patients with high-grade gliomas across four medical institutions. We found a weak negative correlation between tissue cellularity and the fluorescence intensity of PpIX across all imaged specimens. Semi-supervised clustering of the TPEF images revealed five distinct patterns of PpIX fluorescence, and spatial transcriptomic analyses of the imaged tissue showed that myeloid cells predominate in areas where PpIX accumulates in the intracellular space. Further analysis of external spatially resolved metabolomics, transcriptomics and RNA-sequencing datasets from glioblastoma specimens confirmed that myeloid cells preferentially accumulate and metabolize PpIX. Our findings question 5-ALA-induced fluorescence in glioma cells and show how 5-ALA and TPEF imaging can provide a window into the immune microenvironment of gliomas.

The value of cryoablation in orbital surgery.

Aim of this article is to give an overview of the technical background and the advantages of modern devices for different applications of cryoablation in cranio-orbital neurosurgery.The treatment of orbital lesions is complicated by the complex and potentially inapparent anatomy due to retro-orbital fat. With the help of cryoprobes different well-defined lesions such as cavernous venous malformations can be safely and effectively removed thanks to the cryoadhesive effect. Their use has been described in several different approaches including traditional lateral or transcranial orbitotomy but also anterior transconjunctival as well as transnasal endoscopic approaches. Recently, single-use devices were introduced that allow the use of cryosurgery also without the need for large investment or service costs.