Targeting Peritumoral Lesions Identified by Computed Tomography and Magnetic Resonance Imaging in Feline Injection-Site Sarcomas for Microscopic Examination.

Peritumoral lesions identified during in vivo imaging of feline injection-site sarcoma (FISS) are frequently interpreted as neoplastic. We recently showed that most peritumoral imaging-identified lesions (PTIILs) in FISS are non-neoplastic. In this article, we describe a protocol to target PTIIL for microscopic examination and report on the protocol's performance. Ten client-owned cats with FISS were prospectively enrolled. A fiducial marker sutured onto the skin, centered on the palpable mass, served as reference point throughout the study. Each FISS and surrounding tissue was imaged in vivo by dual phase computed tomography angiography and multiple magnetic resonance imaging pulse sequences and each PTIIL documented. Subgross measurements obtained during trimming aided localization and identification of PTIIL during microscopy. Histologic findings were categorized by descending clinical relevance: neoplastic, equivocal, non-neoplastic, within normal limits (WNL). Based on in vivo imaging resolution limits, histologic findings were ≥3 mm in at least one dimension and ≥3 mm apart. Surgical margins served as control tissue for PTIILs. Eighty-one of 87 PTIIL were examined histologically; 13 were neoplastic, 16 equivocal, and 28 non-neoplastic; 24 had no identified histologic correlate. Two neoplastic and 10 equivocal findings were located outside of PTIILs but none of them were located in sections of surgical margins. Computation of a simple confusion matrix yielded fair sensitivity (70.4%) and low specificity (59.7%) for prediction of PTIIL by histologic findings. After combining instances of normal microanatomy with non-neoplastic histologic findings, specificity increased (85.1%) and sensitivity decreased (35.8%). The protocol is a blueprint for targeting PTIIL for microscopic examination but may benefit from further refinement.

Quantification of surgical margin length changes after excision of feline injection site sarcomas-A pilot study.

OBJECTIVE: To evaluate degree length change of lateral surgical margins at various stages of processing for histological examination and quantify the length change between grossly normal surgical margins (GNSM) and pathologist-reported histologic tumor-free margin (HTFM) in widely resected feline injection site sarcoma (FISS) specimens. STUDY DESIGN: Prospective clinical study. ANIMALS: Five client-owned cats with injection site sarcomas. METHODS: All cats underwent wide surgical excision (35-55 mm gross lateral margins, 2 fascial planes deep). Gross normal lateral margin measurements from tumor edge were recorded in 4 directions (cranial, caudal, dorsal, ventral) at 5 time points: intra-op (in vivo GNSM); immediately following excision (ex vivo GNSM); following formalin fixation (post-fixation GNSM); after trimming and mounting on glass slides (on-slide GNSM); and HTFM at the narrowest point from the HTFM from the same slides used for on-slide GNSM. Percent change in lateral margin length from in vivo measurements was quantified at each time point and compared using 1-way repeated measures ANOVA. RESULTS: The largest mean decrease in percent GNSM length occurred immediately after excision (in vivo to ex vivo GNSM = 29%; P = .016). Formalin fixation, trimming, and mounting on slides did not result in additional significant changes in length. Mean HTFM length was significantly decreased compared to both in vivo GNSM (33%; P = .014) and on-slide GNSM (7%; P = .024). CONCLUSION: 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.

Changes in the dimension and volume of feline injection-site sarcomas following formalin fixation as determined by use of the ellipsoid volume formula and three-dimensional computed tomography software.

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.

Microscopic Evaluation of Peritumoral Lesions of Feline Injection Site Sarcomas Identified by Magnetic Resonance Imaging and Computed Tomography.

OBJECTIVE: Determine whether dual-phase computed tomography angiogram (CTA) or magnetic resonance imaging (MRI) detect more peritumoral lesions of feline injection site sarcoma (FISS) and determine whether CTA or MRI imaging characteristics of peritumoral lesions correspond with microscopic findings. STUDY DESIGN: Prospective clinical study. ANIMALS: Ten client-owned cats with FISS. METHODS: A fiducial marker detectable on CTA and MRI was sutured to the skin over the FISS as a standard reference point. All cats received MRI and CTA of the FISS, immediately followed by wide surgical excision. Targeted microscopic evaluation was performed on tissue with imaging-identified lesions and on the surgical margins. RESULTS: A total of 87 imaging-identified peritumoral lesions were examined microscopically (median 4 per cat, range 3-9) with 17/87 (20%) categorized as neoplastic, 51/87 (59%) as nonneoplastic, and 19/87 (22%) as equivocal. In 25 instances, peritumoral lesions were seen on both imaging modalities at the same location. Unique imaging characteristics were seen in 5/17 neoplastic peritumoral lesions (4 cats; all different lesions; 1 CTA, 4 MRI). The CTA and MRI appearances of the remaining 12/17 neoplastic lesions were nonspecific, being observed across more than 1 microscopic category. CONCLUSION: 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.

In vitro evaluation of a novel fiducial marker for computed tomography and magnetic resonance imaging of soft tissues in small animals.

OBJECTIVE: To construct and optimize a fiducial marker suitable for both CT and MRI. SAMPLE: Fiducial markers containing serial dilutions of iopamidol mixed with water. PROCEDURES: IV tubing sets were infused with serial dilutions (0% to 100%; increments of 10%) of iopamidol. Tubing ends were sealed; additional seals were added to create an equilateral triangle. A reference point was created by placing a crimp in 1 side. Markers were fixed to a gelatin soft tissue-attenuating phantom and evaluated by use of CT and MRI. For CT, simple linear regression analysis was used to assess the relationship between the percentage of marker contrast medium and quantitative variables, including marker attenuation, attenuation changes in the phantom, and beam-hardening artifact length. A subjective grading scheme for artifact creation on CT images and marker visibility on MRI images was used. Measurements were obtained by investigators who were unaware of the contents of each marker. RESULTS: Percentage of contrast medium in each marker was strongly correlated with marker attenuation (r(2) = 0.96), artifact length (r(2) = 0.765), and mean attenuation changes within the phantom (r(2) = 0.826) for CT. Subjective CT scores indicated that concentrations of contrast medium > 50% resulted in excessive artifacts. Markers with concentrations of iopamidol > 50% had poor subjective MRI visibility scores. No artifacts were seen on MRI. CONCLUSIONS AND CLINICAL RELEVANCE: A marker containing a 10% solution of iodinated contrast medium mixed with water provided ideal contrast for both CT and MRI.