Case 4 cont'd
A. Osteoid osteoma typically involves teenagers/young adults. It is a benign bone-forming tumor associated with extreme pain, usually worsening at night. The most common affected area is the femur. On a bone scan, focal uptake of tracer will be seen in the area of osteoblastic activity, known as the nidus. The double density sign is a common finding in osteoid osteoma, whereby the nidus is characterized by intense radionuclide uptake and surrounded by less intense (but still high) uptake in the surrounding sclerotic region.
B. Rhabdomyolysis occurs due to skeletal muscle injuries. The calcium buildup causes higher tracer uptake, resulting in higher densities on bone scans. On a scan, typically uptake will be seen in soft tissues and localization corresponds to injured group of muscles.
C. Osteomyelitis presents with clinical symptoms, such as fever and/or swelling and redness at the infected area. It is most commonly caused by Staphylococcus aureus infections. On a bone scan, the typical finding is enhanced radiotracer uptake in the infected bone(s).
D. Stress fracture and shin splints. Shin splints typically present with mild to moderate posterior and medial tibial tracer uptake on a bone scintigraphy. Stress fractures on the other hand demonstrate intense focal uptake of tracer in the affected area. The stress fracture pattern is oval or fusiform with the long axis of increased uptake parallel to the axis of the bone.
Answer: D.
Discussion:
A shin splint in nuclear medicine is used to describe a constellation of findings, both clinical and scintigraphic. Presentation involves tibial pain induced by exercise along the medial/posteromedial area. This is accompanied by higher radiotracer uptake in that region on the patient’s bone scan. Typically, more than 1/3 of the bone is involved, from the middle to the distal aspect. Nuclear medicine plays a greater role in diagnosis of shin splints as opposed to stress fractures, as MRI scans have not been proven to adequately detect shin splints. By contrast, MRIs are a competitive contender for the diagnosis of stress fractures compared to nuclear medicine, as marrow edema may be identified early in the stress response. Unless a shin splint pattern demonstrates focal uptake of radiotracer, it is not a predictor of stress fracture in a given area. Arterial phase imaging helps distinguish stress fractures from shin splints, as stress fractures typically involve a high hyperemic state. Scintigraphic findings of stress fractures may be seen from 1 to 2 weeks before fractures are seen on x-ray images.