Clinical Pearls & Morning Reports
Published October 20, 2021
Central giant-cell lesions, giant-cell reparative granulomas, and brown tumors associated with hyperparathyroidism all have similar histopathological features. Read the NEJM Case Records of the Massachusetts General Hospital here.
Q: Are giant cells a histologic feature of fibrous dysplasia of bone, aneurysmal bone cysts, or ossifying fibroma?
A: Fibrous dysplasia of bone and multiple myeloma are not characteristically associated with giant cells. An aneurysmal bone cyst is often characterized by loculated regions and fluid levels, and is not associated with the presence of giant cells. Ossifying fibroma often occurs in the mandible; it is usually characterized by intact cortexes and the ground-glass appearance of fibrous replacement within the lesion. Giant cells are not typical of an ossifying fibroma. Giant cells can be present in brown tumors.
Q: What are brown tumors?
A: Brown tumors are non-neoplastic giant-cell focal lesions of bone that are associated with hyperparathyroidism and have histologic features similar to those of giant-cell tumors. Brown tumors typically regress after treatment of the underlying hyperparathyroidism with parathyroidectomy, but local surgery is sometimes needed, depending on the location and size of the tumor.
A: Non–PTH-mediated bone resorption may occur in patients with hypercalcemia that is associated with cancer or one of several inflammatory diseases (possibly due to cytokine-induced bone resorption), usually causing low circulating PTH levels. Hypervitaminosis D and defects in vitamin D metabolism (caused by mutations in CYP24A1, the gene encoding the vitamin D 24-hydroxylase) are typically manifested by hypercalcemia and suppressed PTH levels. Defects in renal phosphate transport can have secondary effects of increasing production of the active vitamin D metabolite 1,25-dihydroxyvitamin D, thereby resulting in hypercalcemia from both increased intestinal calcium absorption and increased bone resorption, with low circulating PTH levels.
A: Hyperparathyroidism–jaw tumor syndrome, which is caused by germline mutations in CDC73 (also known as HRPT2), is characterized by solitary or multiple, often asynchronous, parathyroid adenomas. These tumors may have aggressive pathological features such as fibrous bands or trabeculation, while still being classified as adenomas. Immunohistochemical staining of a biopsy specimen would indicate the absence of parafibromin, a protein encoded by CDC73. Accompanying jaw tumors, which are typically described as ossifying fibromas, may or may not be present; in the absence of jaw tumors, the condition can be described as familial isolated hyperparathyroidism. Because there is an increased incidence of parathyroid carcinoma among persons with CDC73 mutations, it is important for affected patients to undergo active lifelong surveillance.