Computed tomographic features of pulmonary lesions in periarticular versus systemic histiocytic sarcomas in dogs.

INTRODUCTION: The aim of this retrospective study was to characterize and compare the computed tomographic (CT) appearance of lung lesions in periarticular histiocytic sarcomas (PAHS) and systemic histiocytic sarcomas (HS), identifying potential radiological differences. METHODS: The medical records of 45 dogs diagnosed with PAHS or systemic HS, undergoing thoracic CT imaging were reviewed. CT images were evaluated for various parameters. RESULTS: Results revealed that pulmonary lesions associated with systemic HS had larger lesion volumes, were mainly located ventrally 20/26 (77%) and were bronchocentric 23/26 (88%), often with irregular shapes 20/26 (77%) and air bronchograms 26/26 (100%). In contrast, PAHS pulmonary lesions were located predominantly interstitial 12/19 (63%), appearing round to ovoid 15/19 (79%) with less commonly observed air bronchograms 7/19 (37%). In systemic HS, lesion distribution showed no correlation with lung lobe volume (Spearman's ρ = 0.14; p = 0.78717), with lesions most frequently observed in the right middle lung lobe 16/26 (62%). Conversely, in patients with PAHS, the distribution of lesions within the lung parenchyma showed a strong correlation with the lung lobe volumes (Spearman's ρ = 0.94; p = 0.0048). Intrathoracic lymph node involvement was more frequent in systemic HS 21/26 (81%) than PAHS 12/19 (63%), typically with larger volumes in systemic HS. DISCUSSION: The nodular lung pattern in PAHS resembles the metastatic distribution seen in other high-grade sarcomas. Significant morphologic and distributional differences indicate distinct patterns of pulmonary involvement in PAHS and systemic HS, which may reflect differences in biological behavior or routes of metastatic spread and raise the possibility of distinct biological subtypes.