This bone scan of a patient with metastatic breast carcinoma demonstrates the “superscan” phenomenon. Tracer uptake is so avid in bone that there is almost no renal excretion – the kidneys are barely visualised.
Causes of superscan are as follows: renal osteodystrophy; osteomalacia; hyperparathyroidism; hyperthyroidism; diffuse skeletal metastases; myelofibrosis; haematological malignancy; extensive Paget’s disease.
Of these, skeletal metastases is the most common cause.
Caution should be taken – absent renal tracer may also be due to renal failure – check for bladder tracer, which is present in a superscan.

Reference: Dahnert W. Radiology Review Manual, 5th edition. Lippincott, Williams and Wilkins 2003

Credit: Dr Laughlin Dawes