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A bony sequestrum (pl. sequestra) is a piece of devascularised bone that becomes separated from the remainder of the bone in chronic osteomyelitis and acts as a nidus for ongoing infection 1.
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In the course of the inflammatory response in an infected bone, there is increased osteoclastic activity resulting in increased bone breakdown 2. As a result, a segment of bone may become separated and consequently loses its blood supply. Therefore bacteria within the sequestrum are isolated from antibiotics carried in the bloodstream, which means the infection cannot be properly treated. Sequestra are often surrounded by granulation tissue 3.
Within a bone showing other features of chronic osteomyelitis, a sequestrum may be seen as a fragment of bone with a lucent rim around it. When the sequestrum is small and surrounded by a lucent rim, it is known as a button sequestrum 4. These are usually seen in the calvarium.
CT is more sensitive than plain radiograph or MRI for the detection of sequestra 5. On CT a sequestrum appears as a fragment of bone separate from the remainder of the bone. Granulation tissue may be visible as a low attenuation rim, and an involucrum or cloaca may also be visualized.
A sequestrum may be difficult to identify on MRI. The sequestrum itself, like the cortex it is derived from, will appear as a low-intensity fragment on T1 weighted imaging. As it is devascularised, it will not enhance, although surrounding granulation tissue may enhance 1.
Treatment and prognosis
As a sequestrum is devascularised, antibiotics alone may not successfully treat it and therefore usually requires excision if cure is to be achieved.
History and etymology
From the Latin sequestrum meaning "something set apart".
In the presence of chronic infection, a sequestrum is essentially diagnostic of chronic osteomyelitis 1. However, sequestra may be seen in other entities such as eosinophilic granuloma (in which case they are often referred to as button sequestra) 4.
- 1. Alaia E, Chhabra A, Simpfendorfer C et al. MRI Nomenclature for Musculoskeletal Infection. Skeletal Radiol. 2021;50(12):2319-47. doi:10.1007/s00256-021-03807-7 - Pubmed
- 2. Maffulli N, Papalia R, Zampogna B, Torre G, Albo E, Denaro V. The Management of Osteomyelitis in the Adult. Surgeon. 2016;14(6):345-60. doi:10.1016/j.surge.2015.12.005 - Pubmed
- 3. Pineda C, Vargas A, Rodríguez A. Imaging of Osteomyelitis: Current Concepts. Infect Dis Clin North Am. 2006;20(4):789-825. doi:10.1016/j.idc.2006.09.009 - Pubmed
- 4. Krasnokutsky M. The Button Sequestrum Sign. Radiology. 2005;236(3):1026-7. doi:10.1148/radiol.2363031294 - Pubmed
- 5. Gold R, Hawkins R, Katz R. Bacterial Osteomyelitis: Findings on Plain Radiography, CT, MR, and Scintigraphy. AJR Am J Roentgenol. 1991;157(2):365-70. doi:10.2214/ajr.157.2.1853823 - Pubmed