Endocrine Abstracts

Introduction: Brown tumors or osteitis fibrosa cystica are benign bone tumors complicating uncontrolled primary or secondary hyperparathyroidism. They may behave aggressively and can be destructive. Their osteolytic aspect may be misinterpreted as skeletal metastases.

Methods: A 37-year-old female patient with chronic renal failure on dialysis, presented with pain and swelling of her left knee for 10 days, with no associated trauma. She gave history of tubulo-papillary carcinoma on renal graft, four years after her renal transplantation, treated with transplantectomy since 2015.

Results: X-rays revealed no fracture, but multiple osteolytic lesions were found in the tibias and the right pubic bone. In view of the suspicion of bone metastases, a whole body computed tomography (CT) was performed, revealing renal osteodystrophy as well as multiple osteolytic and mixed lesions within the costal grid, the dorsal spine and the right pubic spine evoking bone metastases. MRI of the knee revealed a lesion of the 1/3 upper left tibia measuring 46×41×76 mm blowing the cortex, suggestive of brown tumor. Bone scan showed intense, symmetrical and diffuse uptake of the skull, facial bones and mandible. There was increased and diffuse radiotracer uptake in the dorsal spine and several foci of moderately increased uptake within the costal grid and the right pubis. These lesions were previously described on the CT scan however this appearance suggested a metabolic origin. The patient underwent biopsy from the left tibial lesion which showed histiocytic proliferation with large number of osteoclastic giant cells compatible with a brown tumor. The biological workup revealed hyperparathyroidism with elevated parathyroid hormone (PTH) at 1100 pg/ml (reference range; 15-65 pg/ml). ^99mTc- sestamibi scintigraphy was done which localized a left inferior parathyroid adenoma. Radiopharmaceutical uptake was also noted within several brown tumors.

Discussion and Conclusion: Brown tumors are rare skeletal manifestations of hyperparathyroidism. They can be monostotic or rarely polyostotic with preferentially affecting sites such as skull, jaw, phalanges, pelvis, clavicles, femur and ribs. These tumors give a pseudometastatic radiological appearance. Therefore, they should be considered in the differential diagnosis of osteolytic lesions to avoid unnecessary interventions.