4.1.8 Oxalosis

Definition: Calcium oxalate deposits in the kidney with variable sequelae.

Oxalate crystals (calcium oxalate) are insoluble in aqueous fixatives, biregringent, roundish and demonstrate radial bands in polarized light.

Two forms of oxalosis must be distinguished: Primary and secondary oxalosis

In primary oxalosis most kidneys at autopsy and in biopsy show, at low power magnification, advanced interstitial fibrosis accompanying tubular atrophy, glomerular obsolescence and intimal fibrosis in arteries. In the HE stain blueish deposits are found throughout the kidney. This can be even better seen with polarized light. All compartments of the kidney may be involved, even glomeruli and arteries. The tubulo-interstitial space is mostly flooded by crystals.  They may be found as small crystals also within tubular cells. Huge crystal aggregates may be surrounded by granulation tissue in the form of granulomas.

In secondary oxalosis, the situation is different. In nearly 100% of autosies individual oxalate crystals are found in the tubular lumens.These rare crystals have no functional consequences. In case of endogenous (overabsorption of oxalic acid from the gut, ingestion of large amounts of oxalate containing food) or exogenous poisoning (glycol intoxication), calcium oxalate crystals may be present in large amounts in the tubular lumens (mostly in the straight part of the proximal tubule) more rarely in the interstitial space also. Arteries and glomeruli are spared. The affected tubules are dilated and single cell necroses may be present. The interstitial space may be slightly edematous or fibrotic. Inflammatory cells are scanty. In case of severe glycol intoxication an endstage  contracted kidney may develop.