Urogenital ImagingOxalosis
excessive accumulation of oxalate in the body. Oxalosis occurs when the kidneys fail and stop eliminating calcium oxalate crystals from the body through the urine. Because the kidneys stop functioning, oxalate crystals are deposited elsewhere in the body such as the eyes and other major organs. In the latter stages of oxalosis, crystals may be deposited in the bones and joints causing painful bone disease. Occasionally, bone disease occurs prior to diagnosis of kidney problems. This represents late diagnosis of previously present asymptomatic, but progressive
renal disease.
Hyperoxaluria, which leads to oxalosis, can be divided into primary, acquired and absorptive or enteric types. The factor common to all of these forms of hyperoxaluria is an excessive excretion of oxalate in the urine.
Primary hyperoxaluria is a rare inherited metabolic disease caused by excess hepatic production of oxalate. The excreted excess oxalic acid combines with calcium in the renal tubules and collecting systems, resulting in nephrocalcinosis and nephrolithiasis.
Acquired hyperoxaluria occurs when a person ingests an unusually large amount of oxalate such as rhubarb or another substance that is converted to oxalate by the liver. These substances include ethylene glycol (antifreeze) or vitamin C in doses in excess of 4 grams per day. Pyridoxine or thiamine deficiency can also cause acquired hyperoxaluria.
Absorptive hyperoxaluria occurs in about 10% of people who have undergone surgical removal of a portion of the bowel. Some patients who have chronic inflammatory bowel disease, chronic pancreatic disease, chronic biliary tract disease, primary small bowel disease with malabsorption, cirrhosis, bacterial overgrowth syndrome, blind loop syndrome, or jejunoileal bypass surgery may also develop absorptive hyperoxaluria. Absorptive hyperoxaluria causes unabsorbed fatty acids to combine with calcium. This results in excess oxalate absorption by the gut.
In any form of hyperoxaluria, calcium oxalate crystals or calcium oxalate kidney stones can produce severe kidney pain (renal colic), urinary tract obstruction, and blood in the urine (haematuria). The stones in the kidneys can cause progressive kidney damage and eventual kidney failure.
The first manifestation of hyperoxaluria may be kidney stones, haematuria, or kidney failure. This typically appears from infancy to mid-twenties. The severity of the disease varies widely from a complete absence of symptoms and late development of kidney stones to an extremely serious and progressive disease. It is generally believed that the earlier kidney failure occurs, the more severe the disease.
Hyperoxaluria is diagnosed by measuring the oxalic acid level in the urine of affected people.
Renal disease can present as two distinct patterns. The first is medullary calcinosis, which consists of calcifications involving the distal convoluted tubules. Calcifications present as radiographically grouped rounded/linear calcifications in the renal papilla. Calcifications can vary from small and poorly defined to large coarse granular calcifications (Fig.1). Calcifications are bilateral and renal size is normal but can decrease over time. This is the most common pattern and accounts for 95% of cases. The pattern of medullary nephrocalcinosis is associated with multiple other entities like primary hyperparathyroidism, multiple myeloma, Cushings syndrome, sarcoidosis, hypervitaminosis D, milk alkali syndrome and renal tubular acidosis and is therefore nonspecific. Ultrasound may be also useful and shows echogenic kidneys (Fig. 2).
Cortical nephrocalcinosis is only seen in 5% of the cases of primary hyperoxaluria. The appearance of these thin cortical calcifications is associated with decreasing renal size. Chronic membranous glomerulonephritis, acute cortical necrosis, Alport's syndrome and rejected renal transplants are other causes of cortical nephrocalcinosis.
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