Kidney

an organ of the genitourinary system that filters blood and excretes end products of metabolism in the form of urine.

The kidneys are among the target organs affected by the action of vitamin D, which is thought to have a direct suppressive effect on the proximal renal tubules.

Parathyroid hormone regulates the excretion of calcium, phosphate, bicarbonate and other ions by the kidney. Also, see kidney.

2. Pathology

Carcinoma of the kidney may metastasize by direct extension, through lymphatic vessels, or by invasion of renal veins. The skeleton is a frequent site of metastasis. Among the sites involved are the thoracolumbar spine, pelvis, ribs, and femora. On radiographs the lesions are usually osteolytic and show soft tissue expansion; sometimes a pathologic fracture is present.

Chronic renal insufficiency and compensatory hyperplasia of the parathyroid gland chief cells secondary to phosphate retention and lowering of serum calcium level lead to renal osteodystrophy, a bone disease apparent in patients with chronic renal failure. The pathological and radiological findings consist of hyperparathyroidism, rickets and osteomalacia, osteoporosis, soft tissue and vascular calcification, and miscellaneous other alterations. Renal osteodystrophy is also a component of hereditary osteo-onychodysplasia (HOOD) or nail patella syndrome.

Osteosclerosis, a well-known feature of renal osteodystrophy, predominates in the pelvis, ribs, and superior and inferior portions of the vertebral bodies (rugger jersey spine). Periosteal neostosis is observed most commonly in the metatarsals, femur and pelvis.

The radiographic features of osteomalacia in renal osteodystrophy include osteopenia, deformities and Loosers zones. Looser's zones are most common in the pubic rami, ilii, ribs, femoral necks, scapulae and long bones.

Multicentric osteolysis with nephropathy may be associated with progressive renal failure, disappearance of the carpus and sometimes the tarsus, osteolysis of the elbow, and foot deformities.

Slipped epiphyses have also been observed in patients with chronic renal disease. Three radiographic signs may precede slipped capital femoral epiphysis in renal osteodystrophy: bilateral subperiosteal erosion on the medial aspect of the femoral neck, increase in width of the cartilaginous growth plate and bilateral coxa vara.

Pathologic fractures and insufficiency fractures are complications of renal osteodystrophy.

Soft tissue and vascular calcification may also be observed in patients with renal osteodystrophy. Secondary gouty arthritis and oxalosis of bone may develop as secondary manifestations of chronic renal failure.

Patients with chronic renal failure who are placed on maintenance haemodialysis may develop bone changes and other musculoskeletal abnormalities. Most patients with renal osteodystrophy show resolution of the bone changes when dialysis is adequate; however, spontaneous fractures of the ribs, femoral necks, vertebrae, pubic rami, tibiae and metatarsal bones may result from inc syndrome.html">carpal tunnel syndrome

Musculoskeletal abnormalities occurring after peritoneal dialysis include bone disease, soft tissue calcification and deposition of beta-2-microglobulin amyloid.

Similar changes also occur after renal transplantation; additional features are osteomyelitis, septic arthritis, crystal deposition, digital clubbing, dialysis cysts, tendinitis and spontaneous tendon ruptures, and olecranon bursitis.

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