Confocal laser endomicroscopy (CLE) offers high-resolution, real-time imaging enabeling visualization of tissue microarchitecture and clinical systems are able to address tissue autofluorescence (AF). Investigations on tissue sections of intracranial aneurysms proved that AF visualizes the hallmarks of vessel wall remodeling (Sehm et al, Sci Rep. 2020;10(1):12359). This study aims to investigate the feasibility of CLE as a real-time imaging tool for the visualization of microstructural features of intracranial aneurysms during surgical clipping.
CLE was performed during aneurysm clipping procedure in seven patients (MCA n=5, A. pericallosa n=1, PICA n=1). AF imaging was performed on the aneurysm wall, the transition zone and adjacent vasculature using a fiber-optic CLE probe and 488 nm excitation. Z-stacks spanning 70-200 µm were acquired. Reference histology and AF microscopy was performed on resected aneurysm domes (n=4).
In normal regions of the arteries, the tunica adventitia was identified by the characteristic diffuse AF signal of collagen while the external elastic lamina showed more intense and fiber-like AF of elastin. The tunica media was visualized ~80 µm beneath and presented with a patchy AF pattern. The penetration depth was limited to maximal 120 µm, and restricted imaging to superficial layers. Movement artifacts caused by pulsation and intraoperative handling, along with weak signal intensity, strongly impacted image quality and interpretability. As a consequence, detection of all three layers was possible in only one of the seven cases investigated. CLE imaging of aneurysms showed interspersed strong punctuate AF signal in the tunica adventitia which was confirmed by ex vivo AF microscopy. No AF signal of elastin of the external elastic lamina was detected. Clusters of strong AF were visualized in four cases, representing cells or calcifications in comparison to reference histology.
Label-free CLE allowed intraoperative, in situ visualization of histopathological aspects of the intact and pathological vessel wall. Current technical limitations, such as restricted penetration depth, motion artifacts, and weak signal intensity need to be addressed before it can be used as real-time intraoperative tool. Conceptually, in situ AF imaging holds great promise for comprehensive visualization of the entire vessel wall. This might enable surgeons to adapt to individual aneurysm morphology, therefore minimizing risk of intraoperative rupture.