The Role of Calcium Salts in Pigment Gallstones and Their Spiculated Morphology

Pigment gallstones represent a heterogeneous group of concretions, classically divided into black and brown types, whose morphology and microstructure offer critical clues about their underlying pathogenesis. Gallstone formation (lithogenesis) is a complex process triggered when the physicochemical equilibrium of bile is disrupted. Background/Objectives: The spicules observed on the surface of certain black pigment gallstones have traditionally been attributed to the branching capacity of cross-linked bilirubin polymers. However, a growing body of experimental and spectroscopic evidence suggests that inorganic calcium salts, particularly calcium carbonate and calcium phosphate, play a central role in the formation of the distinctive spiculated or “coral-like” architecture. Materials and Methods: In our study, we examined a case series of 1350 consecutive patients with gallstone disease, identifying 81 patients who presented with solitary black pigment stones. We systematically explored the association between high calcium content, specifically calcium carbonate, and the occurrence of spiculated morphology. Our analyses demonstrated a robust correlation between an elevated concentration of calcium carbonate and the presence of well-defined spicules. Results: These results support the hypothesis that mineral elements, rather than organic bilirubin polymers, act as crucial determinants of the peculiar crystalline structure observed in a significant subset of pigment stones. Spiculated stones, due to their small size and sharp projections, have a higher likelihood of migrating, increasing the risk of potentially life-threatening complications, such as acute cholangitis and gallstone pancreatitis. Conclusions: Our findings, consistent with recent advanced crystallographic analyses, underscore the importance of considering mineral composition in the diagnosis and management of cholelithiasis. Understanding the factors that drive calcium carbonate precipitation is essential for developing new preventive and therapeutic strategies, aiming to modulate bile chemistry and reduce the risk of calcium-driven lithogenesis.