Which radiologic feature is characteristic of osteosarcoma?

Osteosarcoma is a type of bone cancer commonly seen in dogs and is characterized by specific radiologic features that help in its diagnosis. One of the most notable features is the presence of a "moth-eaten" or "permeative" pattern of bone destruction. This pattern indicates aggressive bone lysis where the integrity of the bone is compromised, and this radiographic finding is often due to the tumor infiltrating into normal bone structure.

The moth-eaten or permeative radiographic pattern typically signifies a high level of aggressiveness, which is consistent with osteosarcoma. It reflects the behavior of the tumor, which tends to invade surrounding tissues and can also lead to subsequent changes in the soft tissues surrounding the bone, such as swelling or soft tissue masses.

The other conditions mentioned may present with their own specific radiologic features; for instance, localized bone sclerosis can occur with certain types of bone diseases or injuries, areas of radiopacity may be associated with benign conditions or other types of tumors, and soft tissue swelling is a general sign of inflammation or tumor presence but is not specific for osteosarcoma. The unique and aggressive pattern of bone destruction is what distinctly identifies osteosarcoma in radiographic assessments.