Ultrastructural and elemental characterization of gallstones in patients ≤40 years: a scanning electron microscopy study with histopathology correlation

Gallstone disease affects individuals of different ages, yet age-related variations in stone morphology, histology, and chemical composition remain insufficiently defined. Understanding these patterns may clarify pathogenic mechanisms and their potential links to clinical or metabolic profiles. This study investigated age-related differences in gallstone characteristics. Thirty-seven gallstones were analyzed and grouped into three age categories (<20, 21-30, and 31-40 years), with additional stratification by sex. Morphological classification was performed macroscopically and by scanning electron microscopy, while composition was assessed using energy-dispersive spectroscopy. Histological evaluation of the gallbladder wall focused on chronic inflammation, Rokitansky-Aschoff sinuses, fibrosis, and metaplasia. Female predominance was observed in all groups, reaching 100% in the 31-40-year category. Patients under 20 years presented heterogeneous stones, including pigmented and amorphous patterns, early structural changes, and chemically diverse profiles containing Calcium (Ca), Sodium (Na), Phosphorus (P), and Magnesium (Mg). Individuals aged 21-30 years showed mostly cholesterol stones, moderate histological alterations, and frequent Ca and Na incorporation with reduced elemental variability. In contrast, the 31-40-year group exhibited exclusively cholesterol stones with milder but consistent chronic changes and a homogeneous chemical composition mainly comprising Carbon (C) and Oxygen (O). These results demonstrate age-related transitions in gallstone morphology, chemistry, and associated gallbladder alterations.