4.1.5 Crystalluric ATN

Definition: Deposition of organic or anorganic crystals in any compartment of the kidney.

Crystal or amorphous salt deposits in the kidney are common. Severe forms, may cause acute renal failure, less severe forms chronic renal failure or may have no effect.

Crystals and amorphous salt deposits may be found inside cells and /or in any compartment of the kidney.

Classification of crystal deposits

• Oxalate (Calciumoxalate)
• Calciumapatite or Calciumcarbonate
• Urate (Sodium –or ammonium urate)
• Hydroxyadenine
• Cystine
• Cholesterol
• Light chain crystals
• Drugs

Calciumoxalate deposits (Oxalosis), calcium apatite or calcium carbonate deposits Nephrocalcinosis) and urate deposits (acute or chronic uric acid /urate nephropathy) will be discussed in separate chapters.

Hydroxyadenine or cystine crystals are found in variable amounts in inherited diseases:cystinosis or hydroxyadenine-nephrolithiasis. These diseases are not of interest in this context. It is only important to recognise the shape of the crystals and their staining properties to differentiate this type of crystal from others.

Hydroxyadenine crystals are insoluble in aqueous fixatives. They are birefringent and can on the first glance easily be misinterpreted as oxalate crystals. In HE stain they are brownish. Crystals are found mainly in the tubular epithelium, in the tubular lumens and interstitial macrophages. In advanced cases interstitial fibrosis, tubular atrophy and limited inflammation are present.

Cystine crystals are water soluble. In case of suspicion the tissue should be fixed in absolute alcohol. The crystals are birefringent after alcohol fixation. They are rectangular or rhomboid shaped needles . The crystals may be found in tubular cells, interstitial macrophages, podocytes and more rarely in mesangial cells and the tubular lumens.

Cholesterol crystals are quite common. They dissolve during tissue preparation, have a characteristic wedge shaped appearance and are found in case of lipid storage in the renal cells e.g. endothelium, podocytes, meangial cells, tubular epithelium, interstitial foam cells. Exceptionally, cholesterol granulomas may be present in the interstitial space.

Light chain crystals and other protein crystals are mainly found in patients with plasma cell dyscrasia. Large light chain protein crystals (round, needle shaped or rhomboid) may be present in the tubular lumens (rarely in the interstitial space) in case of cast nephropathy.

In very rare cases diffuse tubular vacuolization is present, often indistinguishable by light microscopy from hydropic tubular change (“osmotic nephrosis”). The tubular cells contain rhomboid crystals consisting  mostly of kappa light chains. More rarely the podocytes are also affected. 

Drug crystals from the late 1940`s and early 1950 onwards many drugs have beeen described which may precipitate in the kidney and cause variable lesions.