CTA and MRI identified a similar number of peritumoral lesions. The extensive overlap between imaging features of neoplastic and nonneoplastic lesions precludes definitive identification of neoplastic peritumoral FISS lesions using CTA or MRI.

Significant decreases in surgical margin length in FISS specimens occur immediately following excision (prior to formalin fixation). Subgross evaluation of tumor-free margins from on-slide GNSM to HTFM overestimates the actual (histologic) tumor-free margins.

OBJECTIVE To evaluate changes in the dimension and volume of feline injection-site sarcomas (FISSs) before (in vivo) and after surgical excision and formalin fixation (ex vivo) as determined by measurements obtained from 2-D and 3-D CT images. SAMPLE 10 excised FISSs. PROCEDURES The maximum length, width, and depth of each FISS were measured on contrast-enhanced 2-D CT images of the tumor obtained in vivo and ex vivo. Those measurements were used to estimate tumor volume with the standard ellipsoid formula. Tumor volume was also calculated from 3-D CT images with software that used a volume-rendering algorithm. Student paired t tests were used for comparisons between the in vivo and ex vivo assessments. RESULTS Small decreases were detected in maximum tumor length, width, and depth between the in vivo and ex vivo assessments; however, tumor length was the only dimension that decreased significantly between the 2 assessments. Median tumor volume decreased significantly between the in vivo and ex vivo assessments regardless of the method used to estimate it. Tumor volume estimated by the ellipsoid formula was significantly lower than that estimated by the 3-D CT software at both assessments. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that shrinkage of FISSs following excision and formalin fixation was small and may be less than that of grossly normal tissue. Tumor volume estimated by the ellipsoid formula was consistently less than that estimated by 3-D CT software and should not be used when accuracy of tumor volume is of particular concern and advanced CT imaging is available.

A marker containing a 10% solution of iodinated contrast medium mixed with water provided ideal contrast for both CT and MRI.

Computed tomographic angiography (CTA) and magnetic resonance imaging (MRI) have been described as methods for preoperative surgical planning in cats with feline injection site sarcomas (FISS), however, few published studies have compared these modalities. The objective of this retrospective, secondary analysis study was to determine if imaging features of FISS on CTA and MRI are predictive of neoplastic peritumoral projections. Archived data from a previous prospective study were retrieved for 10 cats with FISS. All cats had been evaluated in a single anesthetic episode with MRI and dual phase CT (CTA) imaging followed by surgical removal. Histopathological grading and targeted histopathology of imaging‐identified peritumoral projections were performed. Two observers evaluated the CTA and MRI studies for FISS shape, margination, size, enhancement pattern, postcontrast uniformity, pre‐ and postcontrast margination, the number of muscles involved, mass mineralization, and bone lysis. Metal was present in the imaging field of three of 10 cats, resulting in one nondiagnostic MRI. Peritumoral projections were detected in all cats with both imaging modalities, and most were benign. At least one neoplastic peritumoral projection was detected in six cats using MRI, five cats using CTA, and three cats with both modalities. Higher grade FISS were larger than low grade using MRI, and FISS were larger using MRI. Other FISS imaging features using MRI and CTA were similar. Findings supported use of either MRI or CTA for detecting neoplastic peritumoral projections in cats with FISS. Authors recommend CTA for cats with known metallic objects in the scan field.