PMC8421772_01
Craniocaudal (A) and mediolateral (B) radiographs of the right elbow. Note the smoothly marginated bony proliferation arising from the craniodistolateral humerus. Post-contrast transverse computed tomographic image of the right distal humerus. (C) Three-dimensional reformatted CT imaged displayed in a bone window and (D) lateromedial post-contrast transverse computed tomographic image of the right distal humerus. Note the lobular mineral proliferation arising from the craniodistolateral humeral metaphyseal cortex and lack of underlying humeral bone lysis. Left lateral thoracic radiograph (E): 5mm rounded nodule within the dorsal third intercostal space (white arrow). Transverse lung window (F) and dorsal reformatted bone window (G) CT showing the pulmonary nodule within the right cranial lung lobe (black and white arrows). The thin, mineralized rim with a soft tissue center is evident on the enlarged transverse CT image displayed in a bone window (H). Transverse (I) and dorsal (J) plane CT images in a bone window of the right elbow from repeat CT scan 217 days after completion of SBRT. Note that the soft tissue portions of the mass are more mineralized and the humeral cortex remains intact.
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F1
The owners reported that the dog had been mildly lame on his right forelimb for about two months, and then a firm lump on the lateral aspect of his elbow was detected. The primary care veterinarian radiographed the elbow and a lobular, smoothly margined, mineral structure was noted on or adjacent the right distal humerus (Figures 1A,B). Three-view thoracic radiographs were performed, and a 5 mm rounded soft tissue nodule was identified in the dorsal aspect of the right cranial lung lobe (Figure 1E). The pre- and post-contrast CT images demonstrated a 3 cm, soft tissue and mineral mass arising from the craniodistolateral right humeral metaphyseal cortex (Figures 1C,D). A round, smoothly marginated, well defined, 5 mm diameter nodule was present within the right cranial lung lobe (Figures 1F-H). The soft tissue portions of the mass were more mineralized and there were still no changes to the humeral cortex (Figures 1I,J).
Histopathology of the right elbow mass (A,B) and pulmonary mass (C,D). Both masses consisted of dense streaming bundles of mesenchymal cells interspersed with trabeculae of mineralized osteoid matrix (arrows) with scant woven bone and variable cartilaginous matrix (not shown). Hematoxylin and eosin. (A,C), bar = 200 mum. (B,C), bar = 50 mum.
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F2
On histopathology (Figures 2A,B), both lung and elbow masses were discrete masses that contained foci of mineralized osteoid and woven bone formation associated with a population of spindloid mesenchymal cells with mild anisocytosis, mild anisokaryosis, and low mitotic activity. The elbow mass also had foci of cartilage formation (Figures 2A,B). The similarities between the osteogenic mesenchymal cell populations in the elbow and pulmonary masses were supportive of an osteogenic malignancy (Figures 2C,D).