MRI findings associated with microscopic residual tumor following unplanned excision of soft tissue sarcomas in the extremities.

INTRODUCTION: MRI is often used to determine the presence of residual disease following unplanned excisions (UPE) of soft tissue sarcomas (STS). We sought to identify MRI features associated with histologic evidence of residual disease after TBE.
MATERIALS AND METHODS: This was an IRB-approved retrospective review of 27 patients with R1-type UPE of STS over a 32-month period, with subsequent MRI and TBE. MRI studies were retrospectively evaluated to determine depth of tissue involvement, presence of nodular enhancement, and maximum length of soft tissue edema normalized to extremity size. MRI findings were correlated with histology from unplanned excision and TBE.
RESULTS: Among the 21 subjects, there were 13 males and 8 females, mean age 58. Eighteen of 21 STS were grade 2 or 3. Deep compartments were involved in 5/21 cases. Original margins were positive in 17/21 UPE, with inadequate margin assessment in the remaining 4 cases. Residual tumor was present at TBE in 11/21 cases; it was found in 4/6 cases with nodular enhancement and 7/15 cases without nodular enhancement (sensitivity = 0.36; specificity = 0.80; PPV = 0.67; NPV = 0.53). Increased extent of soft tissue edema increased the likelihood of residual tumor at TBE (OR = 35.0; 95% CI = 1.6 to 752.7; p = 0.023).
CONCLUSION: Nodular enhancement is neither sensitive nor specific in predicting residual microscopic tumor in TBE following UPE. Extensive soft tissue edema on MRI after UPE increases the likelihood of finding a residual microscopic tumor, justifying ample margins at TBE and consideration of adjuvant therapy.