Age / Sex : 39 / M

Chief complaint : Rt. knee pain

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Courtesy : 채희동, Hee-Dong Chae, 서울대학교병원, Seoul National University Hospital

Brown tumor (Primary hyperparathyroidism)

Discussion

Findings:

A skyline view of the right knee shows a well-defined osteolytic lesion in the patella. Axial T2-weighted SPIR image shows a multiloculated cystic lesion with a fluid-fluid level in the patella. The cystic lesion demonstrates peripheral and septal wall enhancement on a sagittal contrast-enhanced T1-weighted image, and there is no solidly enhancing component. There are also multiple cystic bone lesions in the pelvis and both femurs on the coronal reformatted CT image. Several subchondral bone erosions are visible in both sacroiliac joints. The patient's serum calcium level was 13.1 mg/dl (ref 8.8~10.5 mg/dl), and phosphorus level was 1.7 mg/dl (2.5~4.5 mg/dl).

Differential Diagnosis:

Giant cell tumor

Aneurysmal bone cyst

Discussion:

Brown tumor is a nonneoplastic lesion that occurs as a manifestation of hyperparathyroidism. It is also known as osteitis fibrosa cystica or osteoclastoma. The overproduction of parathyroid hormone leads to the increased osteoclastic resorption of bone. Localized areas of severe bone loss are filled with granulation tissue and vascularized fibrous tissue with hemosiderin deposition, resulting in “brown tumor”. Brown tumors usually resolve with the treatment of hyperparathyroidism, and local treatment of the tumor itself is usually not necessary.

Brown tumors tend to occur more frequently in patients with primary hyperparathyroidism (3 %) than those with secondary hyperparathyroidism (1.5-1.7 %). However, the overall incidence of secondary hyperparathyroidism is much more higher than primary hyperparathyroidism.

Brown tumors occur throughout the entire skeleton. Commonly involved sites include small tubular bones of hands, skull, pelvis, clavicle, rib, spine, and femur.

Brown tumors occur as well-defined, geographical osteolytic lesions that are centrally located, and may be slightly expansile. Brown tumors can exhibit either a solid or cystic nature or a mixture of the two. Solid portions have been reported to show isointensity to hypointensity on T1-weighted and T2-weighted images, and cystic portions may exhibit fluid-fluid levels.

References:

Kang HS, Ahn JM, Kang Y. Oncologic Imaging: Bone Tumors: Springer; 2017.