Penumbra sign (intraosseous abscess)

Last revised by Arlene Campos on 21 Jun 2024

Citation, DOI, disclosures and article data

Citation:

Amini B, Knipe H, O'Shea P, et al. Penumbra sign (intraosseous abscess). Reference article, Radiopaedia.org (Accessed on 27 Jun 2024) https://doi.org/10.53347/rID-1856

DOI:

https://doi.org/10.53347/rID-1856

Permalink:

https://radiopaedia.org/articles/1856

rID:

1856

Article created:

2 May 2008, Behrang Amini

Disclosures:

At the time the article was created Behrang Amini had no recorded disclosures.

View Behrang Amini's current disclosures

Last revised:

21 Jun 2024, Arlene Campos ◉

Disclosures:

At the time the article was last revised Arlene Campos had no financial relationships to ineligible companies to disclose.

View Arlene Campos's current disclosures

Revisions:

6 times, by 5 contributors - see full revision history and disclosures

Systems:

Musculoskeletal

Sections:

Signs

Tags:

cases, case1

Synonyms:

Inner ring (osteomyelitis)
Inner ring sign
Penumbra sign - bone

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 ring described 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