Signs Of An Abnormal Bone Scan

A bone scan, sometimes called bone scintigraphy, is a test performed to identify areas of increased, often abnormal, mineral activity of the skeleton. A radioactive chemical is injected into the bloodstream and x-rays are performed several hours later to see where those tracers accumulate. An injured or diseased area accrues more of the chemical tracer.

Hot Spots

L.N. McKinnis, in "Fundamentals of Musculoskeletal Imaging," 2nd Edition, explains that while normal bone is seen as a transparent grayish color on x-ray, the areas of abnormal bone activity with high levels of radioactive tracer appear black and dense. Physicians call these areas "hot-spots." A radiologist reads the bone scan to determine if there are any hot-spots present. Certain areas of bones, such as growth plates, normally have a high rate of mineral turnover and the radiologist must determine if the hot-spots are the result of an abnormal accumulation of the radioactive tracer related to disease or due to normal bone growth. Detailed medical history and physical examination performed by the physician help focus attention on the abnormal regions.

Causes

Some of the diseases and injuries that cause increased bone turnover and result in positive bone scan tests are stress fractures, bone infections such as osteomyelitis, arthritis, metastatic bone tumors, Paget's disease of the bone, and avascular necrosis, which is bone death due to an interruption of the blood supply. The scan is not, however, able to distinguish the exact reason for any increased bone activity. Other, more specific, diagnostic tools must be used for a differential diagnosis. In other words, the bone scan detects the presence of disease but is unable to identify the particular disease.

Next Steps

Once an abnormal area has been identified on the bone scan, other tests may be performed to isolate the disease process. For stress fractures and arthritis, a diagnosis is made based on the medical history and the positive bone scan. Paget's disease of the bone will often be diagnosed by a set of regular x-rays along with the positive bone scan results. Blood work is drawn to corroborate expected infection and sometimes a biopsy is warranted to identify the precise microbe. Magnetic resonance imaging or computed tomography scans may be performed to pinpoint avascular necrosis and cancerous tumors. Tumor biopsy may be necessary to identify the type of cancer and plan for appropriate treatment.