How does magnetic resonance imaging represent histologic findings in the equine digit?
Authors: Murray, Blunden, Schramme, Dyson
Journal: Veterinary radiology & ultrasound : the official journal of the American College of Veterinary Radiology and the International Veterinary Radiology Association
Summary
# MR Imaging in the Equine Foot: Validating Signal Changes Against Tissue Pathology Magnetic resonance imaging has become central to diagnosing equine foot lameness, yet clinicians lacked clear understanding of what MR signal alterations actually represent at the tissue level. Murray and colleagues directly compared MR findings from 51 cadaver feet (32 from lame horses, 19 controls) against histopathological examination, documenting signal intensity changes, tissue contour abnormalities, and structural damage across five key anatomical sites: the deep digital flexor tendon, navicular bone, distal and collateral sesamoidean ligaments, and navicular bursa. MR imaging demonstrated high sensitivity and specificity for detecting moderate-to-severe lesions in most structures, with particularly strong performance in the DDFT, collateral sesamoidean ligament, and navicular bursa, though the dorsal navicular bone proved less reliably visualised. The tissue-level pathologies corresponding to MR signal changes included structural fibre disruption, fibroplasia, fibrocartilaginous metaplasia, trabecular damage, osteonecrosis, and cortical defects—validating that signal alterations represent genuine pathology rather than imaging artefacts. For practitioners, this work establishes MR imaging as a reliable diagnostic tool for soft tissue and medullary bone lesions whilst highlighting caution when interpreting findings in specific anatomical regions, particularly the dorsal navicular cortex where MR performance is less robust and correlation with clinical significance requires careful clinical integration.
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Practical Takeaways
- •MR imaging reliably represents tissue damage in the equine foot and can be confidently used to diagnose moderate-to-severe lesions of the deep digital flexor tendon, collateral sesamoidean ligament, and navicular bursa
- •Interpret dorsal and proximal navicular bone findings on MR with caution, as agreement with actual tissue pathology is poor and may not reflect true disease severity
- •MR signal changes in foot structures correlate with specific histopathologic processes, validating its use as a diagnostic tool but emphasizing the importance of considering anatomic location and lesion severity when making clinical decisions
Key Findings
- •MR signal alterations directly correlated with histologic tissue-level changes including structural damage, fibroplasia, fibrocartilaginous metaplasia, hemosiderosis, osteonecrosis, and cortical defects
- •MR imaging demonstrated high sensitivity and specificity for detecting moderate-to-severe lesions in most structures, with particularly high specificity for DDFT, CSL, and navicular bursa pathology
- •Agreement between MR and histologic grading ranged from good (navicular bursa, DDFT, navicular bone medulla, CSL) to poor (dorsal and proximal navicular bone aspects)
- •MR imaging was sensitive for abnormalities in all structures except the dorsal aspect of the navicular bone, indicating variable clinical utility by anatomic location