Age / Sex : 21 / M

Brown tumor

Discussion

Findings: There is a geographic osteolytic lesion in the distal metaphysis of left fibula on radiographs. There is no sclerotic margin. It is expansile with cortical remodeling. T1- and T2-weighted images demonstrate an eccentric mass with homogeneously low signal. It shows mild contrast enhancement anteriorly. It reveals no impeded water diffusivity on diffusion-weighted images. Time intensity curve shows rapid initial contrast enhancement followed by a washout phase. K trans and Kep are slightly high on quantitative dynamic contrast-enhanced MR images.

Differential Diagnosis:

1. Brown tumor  2. Giant cell tumor

Diagnosis:  

Brown tumor, left fibula

Discussion:

Brown tumors (osteoclastomas) is a bone lesion that arises in excess osteoclast activity, such as hyperparathyroidism. Brown tumors represent localized accumulations of fibrous tissue and giant cells, which can replace bone and may even produce osseous expansion. They may subsequently undergo necrosis and liquefaction, producing cysts. The characteristic brown coloration results from hemosiderin deposition. Brown tumors appear as single or multiple well-defined lesions of the axial or appendicular skeleton. Common sites of involvement are the facial bones, pelvis, ribs, and femora. On radiographs brown tumor shows lytic lesion, mildly expanded in long bones, generally without sclerotic margin.

MR appearance depends on the relative proportion of its components. The lesions, therefore, may be solid, cystic, or mixed. Solid components are intermediate to low intensity on T1- and T2-weighted images, while the cystic components are hyperintense on T2-weighted images and may have fluid levels. There can be enhancement of the solid component and septa.

With removal of the parathyroid adenoma, brown tumors may demonstrate healing with increased radiodensity. With treatment, brown tumor may hyperossify over time, differentiating it from deposition diseases.

References:

1. Resnick D, Kransdorf MJ. Bone and Joint Imaging. 3rd ed. Richmond,Va:Elsevier-Saunders, 2005


2. Diagnostic imaging, Musculoskeletal : non-traumatic disease. 2^nd ed.  Amirsys, 2010


3. Hong WS, Sung MS, Chun KA et-al. Emphasis on the MR imaging findings of brown tumor: a report of five cases. Skeletal Radiol 2011;40:205-13.