MULTI MODALITY IMAGING APPROACHES TO INJECTION-SITE SARCOMA IN CATS

The aim of this study was to investigate different diagnostic imaging approaches for Injection-Site Sarcomas in cats (ISS) and their mutual relationships with the surrounding tissues between December 2014 and October 2016. In the literature there is a lack of anatomical references about the interscapular region of the cat, with very few publications displaying the musculoskeletal anatomy in transverse sections. Computed Tomography (CT) has been proven to be useful in the staging process of feline patients affected by ISS, not only for correct estimation of the volumetric balance of the tumour but also for thorough staging of distant and local metastatic spread. ISS are mesenchymal soft tissue tumours characterized by a typical interscapular location and highly infiltrative behaviour. CT can be considered the modality of choice for ISS staging and a double positioning (dynamic approach) was reported to successfully detect the exact amount of infiltration of the muscles. A correct estimation of the spatial relationship between neoplastic, inflammatory and normal tissue is crucial, since the indicated treatment is mainly characterized by wide surgical excisions of the neoplasm, including 3-5 cm of perilesional tissues. Our study consists of an anatomic atlas of the interscapular region of the cat in a clinically normal population, using magnetic resonance imaging (MRI), computed tomography (CT) and gross sectional anatomy. In addition we compared both clinical and CT findings for pre-surgical assessment of the tumour. We performed a final volumetric estimation utilising dynamic double positioning in a cohort of 84 patients. Results from our study provide a new and dynamic way to investigate the interscapular region of the cat, with anatomical references for in vivo CT and MRI, considering muscular changes according to forelimb positioning. Analysing the discrepancy between clinical and CT tumour measurements there was a tendency for CT measurements to be greater than clinical dimensions, and this difference increased with increasing tumour size. Based on our results, further studies focusing on ISS in cats, should specify the kind of assessment used to define tumour dimensions (CT versus clinical examination) in order to interpret surgical results and prognostic impact of this variable. Finally, results from the investigation of the use of the dynamic approach in patients referred for pre-surgical staging of interscapular ISS demonstrated good agreement between observers, with higher tumour volumes detected via the ellipsoid method. Lower tumour volumes showed slightly decreased muscular infiltration. In conclusion, the dynamic approach should be performed for a complete evaluation of the invasiveness of the ISS along with an appropriate selection of tumour volume methodology, which could potentially affect the pre-surgical assessment of ISS.