Should you add bone infarct to your monostotic aggressive bone lesion?

JAVMA 2020

Sarah A. Jones, Lindsey J. Gilmour, Catherine M. Ruoff and Roy R. Pool

Background
Bone infarcts, areas of osteonecrosis due to ischemia, have varying etiologies in dogs, including surgical procedures and neoplasia. While radiographic features of neoplastic bone infarcts have been described, the characteristics of benign bone infarcts and their differentiation from malignancy-associated infarcts remain unclear. This study aimed to describe radiographic features of benign and malignancy-associated bone infarcts and evaluate the utility of radiography in distinguishing between the two.

Methods
A retrospective cohort study was conducted on 49 dogs with histologically confirmed bone infarcts, classified as benign (n=33) or malignancy-associated (n=16). Radiographs were reviewed by two blinded, board-certified veterinary radiologists to evaluate features such as cortical destruction, transition zone, medullary lysis pattern, and periosteal proliferation. Agreement between reviewers and statistical associations between radiographic features and histologic diagnoses were analyzed.

Results
Radiography poorly distinguished between benign and malignancy-associated infarcts, with only 48% and 38% of benign and malignancy-associated infarcts correctly identified, respectively. Aggressive medullary lysis was observed in all malignancy-associated cases but also in 70% of benign cases. Aggressive periosteal proliferation was more common in malignancy-associated infarcts (50%) compared to benign infarcts (21%). Sensitivity for identifying benign infarcts ranged from 52% to 70%, with moderate interrater agreement (κ=0.438).

Limitations
The study was limited by its reliance on a referral population, potentially introducing selection bias. Not all biopsy samples may have been representative of the lesion. Additionally, the radiologists' blinding to patient signalment was incomplete due to recognizable breed-specific skeletal features.

Conclusions
Radiography alone was inadequate for differentiating benign from malignancy-associated bone infarcts in dogs, owing to significant overlap in radiographic features. Additional diagnostic testing, including histologic analysis, is recommended for osseous lesions with aggressive radiographic appearances. Polyostotic disease was observed only in benign infarcts, suggesting this as a potential distinguishing feature.

Mediolateral (A) and craniocaudal (B) radiographic images of a 2-year-old Labrador Retriever with a benign infarct
involving the distal aspect of the femur, and photomicrographs (C and D) of a biopsy specimen from the lesion. On the radio- graphic images, there is a monostotic lesion with aggressive medullary lysis and periosteal proliferation, cortical destruction,
and an indistinct transition zone. Histologically, Haversian vessels and canals were avascular and degenerative and most of the
osteocyte lacunae were empty, indicative of chronic ischemia (C). H&E stain; bar = 400 µm. Intertrabecular marrow spaces
contained edematous fatty marrow and a few ischemic hematopoietic cells but no inflammatory cell exudate or neoplastic infil- trate (D). H&E stain; bar = 400 µm.

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