Magnetic resonance imaging features of primary appendicular bone sarcomas in 20 dogs

Objectives
To describe the magnetic resonance imaging (MRI) features of primary appendicular bone sarcomas in dogs and to compare the intramedullary lesion extension between the different MRI sequences and computed tomography (CT).


Materials and Methods
Dogs with confirmed primary appendicular bone sarcoma presented at a single small animal referral centre were prospectively recruited between June 2023 and October 2024. All dogs underwent an MRI scan following a routine contrast‐enhanced CT examination conducted for staging purposes.


Results

Of the 20 dogs with primary appendicular bone sarcoma, 15 had osteosarcoma, four had primary bone sarcoma of uncertain origin and one had haemangiosarcoma. The most common MRI features were heterogeneous and hyperintense signals on T2‐weighted short‐tau inversion recovery images (
n
 = 20), heterogeneous and hypointense signals on both T2‐weighted and T1‐weighted images (
n
 = 20), medullary and cortical osteolysis (
n
 = 20), peripheral mass (
n
 =19) and a long transitional zone (
n
 = 17). Distant metastases in the same bone (skip metastases) were suspected in one dog but were not identified in the corresponding CT. In all dogs, the maximal extension of the intramedullary lesions in the longitudinal plane was significantly greater on T2 short‐tau inversion recovery sequences than in other MRI sequences and CT (
P
 < .001).



Clinical Significance
The MRI features of primary bone sarcomas in dogs were similar to those found in humans and those previously reported in canine axial osteosarcoma. Magnetic resonance imaging and, more precisely, T2 short‐tau inversion recovery images can be included in the local staging of appendicular primary bone sarcomas in dogs.