2008 Radiology Exam - Musculoskeletal Case 2

“Daisy Mae”

• 7 yr SF German shepherd
• 2 views of the right tibia

4 week right hind leg lameness
Painful, firm swelling of right distal tibia.

See images below. Click to enlarge.

Radiographic Findings:

• Predominately caudal-medial distal diaphyseal tibial lesion; lesion center is at the junction of the middle and distal 1/3rds of the diaphysis.
• New bone is solid with smooth surfaces proximal and distal and gradually blends into normal cortex. Centrally the new bone is irregular to palisade and disrupted.
• Cortical lysis is present from external to internal. Cortex is also remodeled, curving towards the medullary cavity at the central region of the lesion.
• The zone of transition is more gradual than discrete.

Radiographic Diagnosis (Synthesis):

• Chronic active moderately or semi-aggressive lesion whose appearance gives the impression of having started superficially or at the periosteal cortical surface.
• Ranked differential diagnoses –
  • Osteomyelitis – mycotic (blastomycosis, coccidiodomycosis as typical and aspergillus or other opportunistic fungi) more likely than bacterial
  • Primary or metastatic bone tumor

Recommendations/Management:

• Biopsy for histopathology and culture is necessary for diagnosis.
• Thoracic radiographs to screen for extent of disease, i.e. metastasis or thoracic evidence of systemic mycosis.

Candidate performance:
Candidates were expected to provide a good description of the lesion’s features using the standard roentgen signs. Based on the location of the lesion, osteomyelitis was expected to be the top ranked differential as opposed to the classic central osteosarcoma. Given the breed there was expectation that the opportunistic fungi such as aspergillus and other more unusual fungi be considered.