Shiny corner sign | Radiology Signs

Answer:

The shiny corner sign is focal sclerosis at the anterior corner of a vertebral body at the discovertebral junction, seen on the lateral radiograph as a bright triangular area. It represents the healing phase of a Romanus lesion, the erosive inflammatory lesion of early axial spondyloarthritis, and it is preceded by small anterior corner erosions that blur and square the vertebral body outline. On MRI the active lesion is seen far earlier as a focus of bone marrow oedema, high signal on STIR or T2 with fat suppression at the vertebral corner, and after treatment or with time it converts to a fatty corner lesion, high on T1, which is a marker of prior inflammation. This sequence, corner oedema to fat metaplasia to sclerosis to syndesmophyte, is the imaging expression of the disease process and is why MRI of the sacroiliac joints and spine, not radiography, is the modality for early diagnosis under the ASAS classification criteria. The differential for anterior corner sclerosis includes degenerative change, which is accompanied by disc space narrowing, vacuum phenomenon and osteophytes that project horizontally before curving, and DISH, in which flowing ossification bridges four contiguous vertebrae with preserved disc spaces and no sacroiliitis. Sacroiliac joint assessment remains the anchor for the diagnosis.

Why is it called so?

The sclerotic corner appears bright or shiny against the surrounding trabecular bone.

Pathophysiology

In axial spondyloarthritis, inflammation begins at the entheses, and the anterior corner of the vertebral body is the attachment of the outer fibres of the annulus fibrosus, the Sharpey fibres. Enthesitis there produces an osteitis with marrow oedema, followed by osteoclastic erosion of the corner, which squares the normally concave anterior surface of the vertebral body. Repair follows with reactive new bone formation, first as sclerosis at the corner and then as vertical ossification within the outer annulus, which forms the syndesmophyte that eventually bridges to the adjacent vertebra and creates the bamboo spine. This alternation of erosion and ossification, driven by IL-17 and IL-23 pathway inflammation at the enthesis, is the reason the same site shows different appearances at different stages.

Alternative names: Romanus lesion; anterior corner sclerosis

Other associated named signs: Squaring of the vertebral bodies, the bamboo spine, the dagger sign and the Andersson lesion

References

1. Barozzi L, Olivieri I, De Matteis M, Padula A, Pavlica P. Seronegative spondylarthropathies: imaging of spondylitis, enthesitis and dactylitis. Eur J Radiol. 1998;27 Suppl 1:S12-7. PMID: 9652496.