Primary Hyperparathyroidism–Related Brown Tumors Mimicking Other Giant Cell–Containing Skeletal Tumors: Role of Correlative Imaging in Diagnosis

DISCUSSION

Giant cells can be seen in many bone tumors, including giant cell tumors, aneurysmal bone cysts, giant cell granulomas, giant cell–rich osteosarcomas, chondrosarcomas, and brown tumors associated with hyperparathyroidism (1). Because these various tumors resemble one another on imaging and pathology, our patient was erroneously diagnosed initially with an aneurysmal bone cyst involving the right femoral neck and subsequently with a giant cell granuloma of the left mandible. A combination of her clinical presentation, imaging findings, and the biochemical findings of primary hyperthyroidism related to a parathyroid adenoma led to the accurate diagnosis of multiple skeletal brown tumors. Thus, the extensive work-up usually done for suspected bone metastases (2,3) could be avoided.

Bone disease and renal stone disease are the most common clinical manifestations of primary hyperparathyroidism (4). The bone disease seen in hyperparathyroidism, also referred to as osteitis fibrosa cystica, is rare today, occurring mostly in cases of severe disease and clinically presenting as bone pain. Imaging findings may include osteopenia, multiple osteolytic lesions from brown tumors, bone cysts, a salt-and-pepper appearance of the skull, and the characteristic radiographic findings of erosions and subperiosteal bone resorption most commonly involving the radial aspect of the middle phalanges of the index and middle fingers (5).

Brown “tumors” of hyperparathyroidism are not actual tumors but result from excessive osteoclast activity. They consist of multinucleated osteoclasts (giant cells) and spindle-shaped stromal cells in a background of fibrous matrix and poorly mineralized woven bone. Their brown color is due to hemosiderin deposition. These tumors are known to regress after correction of hyperparathyroidism. Pathologic differentiation of brown tumors from other giant cell–containing bone lesions can be challenging (6). In addition to multiple osteolytic brown tumors, our patient also had the characteristic radiographic findings of hyperparathyroidism, including erosions and subperiosteal bone resorption on the radial aspect of the mid phalanx of the left middle finger, the latter incidentally seen in her initial radiograph (Fig. 4).

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FIGURE 4.

Frontal radiograph of left femur that incidentally included left hand depicts erosions and subperiosteal bone resorption on radial aspect of mid phalanx of middle finger (arrowheads) and brown tumors in proximal phalanges (arrows).