Calcium oxalate crystals in human pathology. Molecular analysis with the laser Raman microprobe

Calcium oxalate crystals in pathologic specimens were examined by the laser Raman microprobe, a nondestructive spectroscopic technique. Although research focused on the identification of calcium oxalate deposits in tissue sections, kidney stones were also studied to determine the in situ structural specificity of the technique.

Paraffin-embedded tissue specimens were cut into sections of 2 to 6 microns. The unstained sections were placed on metal (aluminum)-plated slides and excited with the 514.5-nm line of an argon-ion laser, which was focused to a 1-micron spot size using a high-resolution optical microscope.

The laser Raman microprobe technique generates spectra that differentiate the monohydrate (CaC2O4.H2O, whewellite) and the dihydrate (CaC2O4.2H2O, weddellite) forms of calcium oxalate inclusions in tissue sections.

Characteristic spectra were generated and provided unequivocal evidence for the identification of the dihydrate oxalate form of calcium oxalate crystals in cases of oxalosis of the myocardium and for the monohydrate oxalate structure in a case of oxalosis of the pituitary. Finally, the combined occurrence of both oxalate structures was confirmed in kidney stone specimens.

The results obtained in this investigation demonstrate the efficacy of the laser Raman microprobe as a useful adjunct in diagnostic pathology.