2011 Radiology Exam - CT/MRI Case 1

History
• 1 year old, female Newfoundland with intermittent right pelvic lameness for 8 months
• Signs have got progressively worse; dog appears stiff after exercise or rest
• 3/10 lame right pelvic limb at trot and walk
• There is effusion, decreased range of flexion, and signs of pain on manipulation of the right tarsus

Images
• CT scans of both tarsi; series of images were clearly labeled right and left
• Transverse images in bone window plus selected sagittal and dorsal plane reformatted images

See Images below. Click to enlarge.

Signs

• Subchondral bone contour on the medial ridge of the right talus is flattened, resulting in widening of radiographic joint space
• Lucent defect in right medial malleolus
• Multiple calcified bodies associated with the right tarsus
• Soft tissue swelling of uniform attenuation centered on the right tibiotarsal joint compatible with effusion
• Small calcified bodies are associated with lucent defect in left medial malleolus
• Bilateral periarticular osteophytes, which are larger on the right

Interpretation
• Imaging findings are characteristic of tarsal osteochondritis dissecans and secondary arthritis
• Calcified bodies likely represent intra-articular fragments of articular cartilage that have subsequently calcified
• Signs of arthritis are more marked on the right, which correlates with the clinical findings

Comments: 36% candidates did not gain a passing score for this case. Common deficiencies in reports were lack of familiarity with the various anatomical structures, inability to identify periarticular osteophytes, and failure to detect the small lesions in contralateral limb.