Understanding the Mechanical Properties of Pituitary Adenomas for Optimized Surgery

Pituitary adenoma (PA) is a common brain tumor located in a small cavity at the cranial base. It disrupts hormonal balance and compresses the optic nerves, leading to abnormal body growth, sexual dysfunction, vision loss, and mortality if untreated. Its surgical resection is highly challenging due to its small size, heterogeneous structure, deep location, and indistinct interface with surrounding nerves, arteries, and brain tissues. Mechanical properties of tumor tissues play a crucial role in their microstructure, growth, and progression. However, data on the mechanical properties of PA tissues is scarce. This study aims to provide detailed mechanical properties of various PA tissues and demonstrate the differences in stiffness between tumors and brain tissues. The viscoelastic properties and collagen content of postoperative PA tissues (n = 40) and normal human brain white matter (n = 7) were analyzed using in vitro nanoindentation and histological staining, respectively. Tumor consistency was also assessed preoperatively via magnetic resonance images (MRIs) and intraoperatively through surgeon feedback. PA tissues exhibited a considerable variation in viscoelastic properties; however, their average stiffness was significantly higher than normal brain white matter (p < 0.05). Tumors with firm consistency showed higher collagen content (29.8% $\pm$ 21.2%) than the soft (9.1% $\pm$ 8.1%) and medium (12.9% $\pm$ 9.7%) consistency tumors, however the correlation with mechanical properties was not strong (r = 0.40, p = 0.01). Strong correlations between preoperative predictions, intraoperative observations, and postoperative measurements emphasize the clinical relevance of these findings. These results underscore the potential of mechanical biomarkers to enhance surgical strategies, improve outcomes, and support applications in diagnosis, development of elastography and elastic image fusion algorithms, as well as in robot-assisted interventions.