Brown tumor

Brown tumour (also known as osteitis fibrosa cystica or rarely osteoclastoma) is one of the manifestations of hyperparathyroidism. It represents a reparative cellular process, rather than a neoplastic process.

Epidemiology

Brown tumours have a slightly greater frequency in primary than in secondary hyperparathyroidism (3% versus 2%). However, secondary hyperparathyroidism is much more common than primary hyperparathyroidism, therefore most of brown tumours that are seen are associated with secondary hyperparathyroidism.

Pathogenesis

In chronic renal disease, continual, excessive urinary calcium excretion can lower  serum calcium level and lead to a rise in parathormone secretion where skeletal calcium is mobilizedmobilised to maintain normal serum calcium levels.

This mobilizationmobilisation occurs through rapid osteoclastic turnover of bone, a direct effect of parathormone.

In localizedlocalised regions where bone loss is particularly rapid, haemorrhage, reparative granulation tissue, and active, vascular, proliferating fibrous tissue may replace the normal marrow contents, resulting in a brown tumor.

Haemosiderin imparts the brown colour (hence the name of the lesions).

Radiographic features

Plain film

Well-defined, purely lytic lesions that provoke little reactive bone. The cortex may be thinned and expanded, but will not be penetrated.

CT

Attenuation values on CT will be in the range of blood and fibrous tissue.

MRI

The MRI 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-fluid levels.

• T1 C+ (Gad(Gd): there can be enhancement of the solid component and septaesepta.

Angiography

Lesions are usually hypervascular.

Bone scan

Often shows intense uptake.

See also

• mnemonic for the differential diagnosis of a benign, lytic bone lesion: FEGNOMASHIC