Recurrent and non-recurrent feline injection-site sarcoma: computed tomographic and ultrasonographic findings.

Objectives: This study describes the sonographic and computed tomographic (CT) characteristics of primary and recurrent feline injection-site sarcomas (FISSs).

Methods: Between 2005 and 2013, 32 cats were selected for prospective and retrospective studies. Tumor shape and margins, presence of thickening of the adipose tissue, muscular and bone involvement, pre- and postcontrast attenuation, blurring of fat planes, calcification and liquefactive necrosis, intratumoral areas and skip metastasis were analyzed in CT scans. Echogenicity, echotexture, tumor margins and peritumoral tissue characteristics were analyzed by ultrasound (US).

Results: Irregular shape (62.5%) with digitiform projections (100.0%), mixed (peripheral and intratumoral) contrast enhancement (67.7%), blurring of fat planes (68.8%) and signs of liquefactive intratumoral necrosis (68.8%) were the prevailing CT findings. Ultrasonography revealed irregular tumor margins, peripheral hyperechoic capsule-like rim, heterogeneous echotexture, and hyperechoic tissue contiguous with the formations and thickening of adjacent subcutaneous tissues in all cases. Mixed echogenicity with areas suggestive of tumor liquefactive necrosis was documented in 83.3% of cases. Skip metastases were highly correlated with tumor recurrence (P = 0.001). The incidence of muscular involvement tended to be higher (P = 0.003) in tumors presenting with thickening of adjacent adipose tissue.

Conclusions And Relevance: CT and US features common to FISS lesions were highlighted in this study. The imaging modalities employed allowed assessment of peritumoral inflammation, particularly adipose tissue inflammation. Imaging data may contribute to FISS diagnosis, therapeutic planning and patient follow-up.