Amini B, Kearns C, Al Kabbani A, et al. Penumbra sign (intraosseous abscess). Reference article, Radiopaedia.org (Accessed on 06 Oct 2024) https://doi.org/10.53347/rID-1856
In musculoskeletal radiology, the penumbra sign represents a rim of vascularized granulation tissue surrounding an intraosseous abscess cavity, with a higher T1 signal intensity than the cavity itself 1. This finding is a specific (~98%) but relatively insensitive (~55%) sign to distinguish subacute, chronic, or acute-on-chronic osteomyelitis from malignant and benign bone lesions 5.
Radiographic features
The penumbra is the same as the inner ringdescribed by Marti-Bonmati et al. 2. They found that intraosseous abscesses had a characteristic four-layered appearance:
a center with low T1 and high T2 signal
an inner ring with muscle signal intensity on T1 and low intensity on T2
an outer ring of fibrotic reaction with low signal intensity on T1 and T2, and
a peripheral halo of bone marrow edema with low signal intensity on T1 and variable signal intensity on T2
1. Grey AC, Davies AM, Mangham DC et-al. The 'penumbra sign' on T1-weighted MR imaging in subacute osteomyelitis: frequency, cause and significance. Clin Radiol. 1998;53 (8): 587-92. - Pubmed citation
3. Mcguinness B, Wilson N, Doyle AJ. The "penumbra sign" on T1-weighted MRI for differentiating musculoskeletal infection from tumour. Skeletal Radiol. 2007;36 (5): 417-21. doi:10.1007/s00256-006-0267-1 - Pubmed citation
5. 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
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