**8.3 Hyperparathyroidism**

Most cases of primary hyperparathyroidism are asymptomatic and are unlikely to be associated with changes on bone scintigraphy. The diagnosis is made biochemically and the use of bone scintigraphy does not make sense with this goal. But bone scan may be useful to differentiate the causes of hypercalcemia, in particular, hyperparathyroidism vs malignancy, so that typical features of metabolic bone disorders may be recognized. There is increased skeletal turnover in hyperparathyroidism, commonly seen as part of renal osteodystrophy, and in the more severe cases, this will be evident scintigraphically. A bone scan may show several features in hyperparathyroidism, but the most important is the generalized increased uptake throughout the skeleton that may be identified because of increased contrast between bone and soft tissues. This is commonly termed the metabolic superscan to differentiate from superscans caused by widespread bone metastases. Other typical features that have been described in this context include a prominent calvarium and mandible, beading of the costochondral junctions, and a "tie" sternum (Fogelman & Carr, 1980). Severe forms of hyperparathyroidism may be associated with uptake of bone radiopharmaceuticals

Nuclear Medicine in Musculoskeletal Disorders: Clinical Approach 113

scintigraphy offers information about the vascularity of the bone lesion: Malignant tumors tend to be more vascularized and be uptake in all three phases of the scan, while benign bone tumors often do not show changes in the first two phases of the scintigraphy. Normal uptake, even in the third stage, is a sign for the mildness of the bone lesion. Osteoid osteoma is a benign bone tumor that constitutes an exception to this statement: It is highly vascular and provides uptake images in all three phases of the scan. In fact, a normal bone scan excludes its diagnosis. Aneurysmal bone cyst may show similar features. In patients with a benign tumor and a bone scan showing intense uptake, a fracture should be suspected.

In benign bone tumors, the uptake of radiopharmaceuticals (e.g. 99mTc) varies by type of tumor and may be normal, mild or severe. Bone scintigraphy is useful for the diagnosis of osteoid osteoma, especially when it is located at the spine, pelvis or hip, where radiological studies are usually not diagnosed. The typical scintigraphic finding is a round focal uptake lesion. CT is always necessary to confirm the diagnosis and surgical treatment. Most enchondromas appear like hot spots at bone scan study. This technique can locate these tumors in multiple enchondromatosis, but it can not differentiate between enchondroma and chondrosarcoma. The scintigraphic feature of the giant cell tumor is increased tracer uptake in all phases of this study, and the image of donut of the lesion, with a rim of uptake surrounding a central area of low uptake. Nevertheless, this image may also appear in other bone tumors. In fibrous displasia, characterized by replacement of normal bone tissue by abnormal fibro-osseous tissue with a high bone turnover, bone scan also display areas of increased uptake. In other bone lesions such as Langerhans cell histiocytosis, hemangiomas and aneurysmal bone cysts, the sensitivity of this technique is variable (Schneider, 2006).

Musculoskeletal sarcomas represent a heterogeneous group of malignancies involving bone and soft tissue. Multiple myeloma is the most common primary malignancy of bone in adults, with an incidence of 3 per 100,000 in the USA. It may affect any bone with hematopoietic red marrow. Patients affected are usually over 50 years of age with the most common age group being between 60 and 65 years of age. Excluding myeloma and lymphoma, malignant primary bone tumors constitute only 0.2% of all malignancies in adults and approximately 5% of childhood malignancies, and, excluding mieloma in adults, the overwhelming majority of cases consist of osteosarcoma or Ewings' sarcoma (Green, 2009). Both are more common in the pediatric than the adult population. Osteosarcoma is the most frequent primary bone malignancy in children and second in adults following multiple myeloma. The Ewing's sarcoma family of tumors is the second most frequent primary bone malignancy in children and young adults and it is the most lethal bone tumor. The most common presenting symptom for primary bone tumors is a painful swelling arising in the bone. The presentation may be similar to acute or chronic osteomyelitis with systemic symptoms of fever, malaise, weight loss, and leukocytosis. Approximatly 15% of patients have clinically evident metastasic disease at diagnosis. Metastatic spread is mainly hematogenous, and the lungs are the most common site of metastases, followed by bone and bone marrow. Anatomic imaging techniques including radiography, US, CT and MRI, currently play a dominant role in the evaluation of suspected and known sarcomas of both soft tissue and bone. Nuclear medicine techniques such as scintigraphy, Thallium-201, and 67Ga imaging have all been used in the assessment of primary bone tumors. However, PET

**9.1 Benign bone tumors and tumor- like disorders** 

**9.2 Soft tissue tumors and primary malignant bone tumors** 

into soft tissue, related with ectopic calcification. Focal skeletal abnormalities may represent associated Brown tumors, although these are relatively uncommon.
