Ultrastructure and mineral composition of urinary calculi from horses.

The research article explores the ultrastructure and mineral composition of urinary stones in horses. The findings reveal that these stones are largely composed of the mineral calcite, a form of calcium carbonate, though trace elements of other minerals are also present. The stones display both primary and secondary porosity, indicating their formation and dissolution are spontaneous, ongoing processes.

Research Study Design and Methods

• The study examined urinary calculi from 17 horses diagnosed with urolithiasis.
• To study the mineral content and ultrastructure of these calculi, the researchers used a variety of analytic methods. These included X-ray diffractometry, scanning electron microscopy, and electron microprobe analysis.

Microscopic Analysis of the Calculi

• Through stereoscopic dissecting microscope observation, the researchers identified that the calculi generally had nodular surfaces with a banded or granular-to-chalky interior.
• Further observation via scanning electron microscopy revealed a highly intricate pattern of irregularly concentric bands and spherules. These were characterized by finely banded, globular textures formed by ultrafine-grained radiating crystals.
• The original pore spaces among the spherules, bands, and between different generations of crystals were visible and classified as primary porosity.

Processes of Precipitation and Dissolution

• The study showed that these calculi’s formation (precipitation) and shrinkage (dissolution) are spontaneous, simultaneously occurring processes within individual stones.
• Another ultrastructural feature observed was secondary porosity, or spontaneous dissolution. It was found in the calculator’s early stages and was site-specific, making certain bands more vulnerable to pinpoint porosity.
• This dissolution, which increased secondary porosity, was noted not only on the calculi’s surfaces but also within their interiors.

Mineral Composition of Calculi

• The researchers found that all the examined stones were composed of calcium carbonate in the form of mineral calcite, with minor quantities of two other calcium carbonate polymorphs: minerals vaterite and aragonite.
• Calcite was found in all 17 samples, vaterite was observed in 5 samples, and aragonite was found in 1 sample.
• Trace elements of strontium and sulfur were also noted in 3 of the calculi, while magnesium was present in all examined stones.
• The study highlighted that magnesium was observed to replace calcium within the calcite crystal lattice in greater quantities than either strontium or sulfur.

Role of Magnesium in Calculi Formation

• X-ray dot maps, generated using an electron microprobe analyzer, indicated that magnesium distribution appears to follow the layer-by-layer growth of the calculi.
• Increased quantities of magnesium correlated to areas of higher porosity where preferential dissolution occurred.
• Observational data from the chemical analysis using the electron microprobe confirmed these observations.

Implications of the Findings

• These findings imply that the magnesium content within the calculi altered during their formation process.
• This suggests that changes in urine chemical elements might be reflected in the composition of the calculi formed.