Findings: Image #1 is a plain film of the left hand demonstrating a well marginated lytic lesion within the diaphysis of the fourth proximal phalanx.

Image #2 is a plain film image of the right hand in a second patient with the same diagnosis. There are multiple well margined lytic lesions within the fourth middle phalanx, fourth metacarpal, and second metacarpal. In addition, there is diffuse periosteal bone resorption. Good radiologic examples of the subperiosteal bone resorption are demonstrated involving the radial aspect of the second and third middle phalanx.

Diagnosis: Brown tumors secondary to hyperparathyroidism.

Discussion: Primary and secondary hyperparathyroidism produce considerable osseous erosion involving the subperiosteal, subcortical and endosteal bone. Histologic examination of osseous tissue in hyperparathyroidism demonstrate replacement of marrow elements by highly vascular fibrous tissue as well as changes of osteoporosis and osteomalacia. The plain radiographs are characterized by osseous resorption. Subperiosteal resorption of cortical bone is virtually pathognomonic of hyperparathyroidism. This is most commonly identified along the radial aspect of the middle phalanges of the second and third digit. Additional regions where subperisoteal resorption may be identified include the phalangeal tufts as well as the tibia, humerus and femur. In addition to the characteristic subperiosteal bone resorption, there may be endosteal, subchondral, subphyseal, trabecular, and subligamentous osseous resorption.

Brown tumors (osteoclastomas) are highly characteristic of primary hyperparathyroidism although they may also occur in secondary hyperparathyroidism as well. Brown tumors appear as single or multiple well marginated lesions often located within the hands. The lesions are often eccentric and cortical in location. Other common sites of involvement include the facial bones, pelvis, ribs, and femora. Although the radiographic manifestation of a lytic lesion located within the phalanges is a somewhat nonspecific finding in which enchondroma would be in the differential, other manifestations of hyperparathyroidism are often apparent. Brown tumors are rarely associated with complications, but may on occasion result in spinal cord compression secondary to vertebral body collapse or pathologic fracture.

Reference:
Resnick D. Diagnosis of Bone and Joint Disorders, 2nd Edition.
W. B. Saunders, Philadelphia. 1998;20-40.

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