What are speckled Short-Tau Inversion Recovery (STIR) hyperintensities on Magnetic Resonance Imaging (MRI) scans?

Speckled STIR Hyperintensities on MRI

Speckled STIR (Short-Tau Inversion Recovery) hyperintensities are focal areas of increased signal intensity on fat-suppressed MRI sequences that appear as small, scattered bright spots, typically representing regions of increased tissue water content from inflammation, edema, or other pathologic processes.

Technical Basis

• STIR sequences are designed to suppress signal from fat while simultaneously enhancing signal from tissues with long T1 and T2 relaxation times, making them highly sensitive for detecting increased water content in tissues 1, 2
• The technique uses inversion times of approximately 120-200 msec to reliably null fat signal, allowing clear detection of pathologic lesions as markedly hyperintense relative to suppressed fat 3, 2
• STIR sequences exploit both T2 and T1 changes, providing high sensitivity for detecting edema and inflammatory changes 1

Clinical Significance by Anatomic Location

Musculoskeletal Applications

• In bone and soft tissue, speckled STIR hyperintensities typically represent bone marrow edema, inflammatory changes, or stress reactions 1
• In sacroiliac joints, these findings indicate active inflammation in axial spondyloarthropathy, though bone marrow edema can be nonspecific and seen in up to 30% of healthy controls 1
• Deep bone marrow edema lesions extending at least 1 cm deep to the articular surface are more specific for pathologic inflammation 1
• In the spine, speckled STIR hyperintensities help identify stress reactions in pedicles (spondylolysis) and inflammatory or infectious processes 1

Cardiac Applications

• In myocardium, STIR hyperintensities represent myocardial edema from acute inflammation, as seen in myocarditis 1
• T2-weighted STIR sequences are necessary for evaluating marrow edema and detecting acute inflammatory lesions 1

Orbital/Neurologic Applications

• In the orbit, STIR hyperintensities can represent inflammatory changes in optic neuritis or other orbital inflammatory conditions 4, 3
• Fat-suppressed T2-weighted sequences (including STIR) are recommended for optimal optic nerve evaluation 4

Diagnostic Limitations and Pitfalls

• High sensitivity but limited specificity: STIR sequences detect 100% of lesions but cannot distinguish between tumor, peritumoral edema, and inflammatory changes 2
• Both neoplastic tissue and inflammatory edema produce increased signal intensity on STIR, limiting assessment of true pathologic extent 2
• The synergism of relaxation prolongation with STIR results in loss of information, as separation of T1 from T2 effects becomes impossible when STIR is the sole sequence used 3
• Speckled hyperintensities can be nonspecific and seen in normal aging, migraine, ischemic changes, vasculitis, and multiple other conditions 5

Recommended Imaging Approach

• STIR should never be used in isolation—always combine with conventional T1-weighted sequences to differentiate acute inflammatory changes from chronic structural changes 1, 3
• In sacroiliac joints, interrogation using both STIR and T1-weighted images is critical to identify both inflammatory and structural changes 1
• Contrast-enhanced imaging may improve detection of subtle inflammatory lesions but has not been shown to significantly increase diagnostic accuracy in most applications 1
• Clinical correlation is essential, as particular features (number, size, location, presence of edema, evolution over time) must be considered alongside clinical data 5