Imaging and histopathological findings of a third metacarpal aneurysmal bone cyst and pathological proximal suspensory ligament avulsion fracture
Authors: Fletcher O., Mackinder J., Agass R., Bianco C., Ortiz A., Dixon J.
Journal: Equine Veterinary Education
Summary
# Editorial Summary A 10-year-old Quarter Horse mare presented with acute, severe lameness unresponsive to farriery, with pain localised to the proximal metacarpi on palpation. Radiography revealed a well-demarcated radiolucency in the proximal third of the left third metacarpal bone at the suspensory ligament enthesis, with ultrasonography confirming moderate ligament thickening and increased vascularity at this site. MRI characterisation, combined with subsequent histopathological examination, identified an aneurysmal bone cyst with an associated pathological avulsion fracture of the proximal suspensory ligament attachment and secondary bone remodelling. The lesion's intramedullary location, expansile nature and critical anatomical involvement rendered surgical correction unfeasible, ultimately necessitating euthanasia. This case underscores the clinical value of deploying advanced imaging—particularly MRI—alongside conventional radiography and ultrasonography when confronted with atypical or complex metacarpal lesions, as precise structural characterisation directly influences both prognostic assessment and treatment planning; whilst aneurysmal bone cysts remain rare in equine metacarpal bones, their potential to compromise load-bearing structures and vital soft tissue attachments warrants thorough multi-modal investigation to determine realistic therapeutic options versus palliative management.
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Practical Takeaways
- •When lameness persists despite farriery intervention and conventional radiography shows unusual radiolucencies near ligament attachments, advance imaging (MRI) is essential for accurate diagnosis and treatment planning
- •Aneurysmal bone cysts in the metacarpal region involving the suspensory ligament may have a guarded prognosis; imaging must characterize the lesion's extent and involvement of surrounding structures before committing to surgery
- •Multimodal imaging (radiography, ultrasound, MRI) is necessary for complex metacarpal lesions—no single modality captured the full pathology in this case
Key Findings
- •Aneurysmal bone cyst presented as a well-defined radiolucency in the proximal third metacarpal bone at the suspensory ligament enthesis
- •MRI provided definitive characterization of the expansile lesion and confirmed associated avulsion fracture that radiography alone could not fully delineate
- •Ultrasonography demonstrated moderate thickening and increased vascularity of the suspensory ligament at the lesion site
- •Intramedullary location, expansile nature, and involvement of critical anatomical structures precluded feasible surgical intervention