Is MRI diffusion-weighted imaging a reliable tool for the diagnosis and post-therapeutic follow-up of extremity soft tissue neoplasms?

Purpose: The aim of this study was to evaluate the benefit of using quantitative diffusion-weighted imaging (DWI) with apparent diffusion coefficient (ADC) mapping in the initial diagnosis and post-therapeutic follow-up of extremity soft tissue masses. Patients and Methods: This study included 90 patients with extremity soft tissue masses. The DWI was obtained with 3 b values, including 0, 400, and 800 s/mm(2). Calculation of the ADC value of the lesion was done by placing the region of interest (ROI) to include the largest area of the lesion. ADC values were compared with the histopathology. Eighteen patients had posttherapeutic magnetic resonance imaging (MRI). Results: Benign masses, fibromatosis, and malignant soft tissue masses had mean ADC values of 1.18 +/- 1.0191 x 10(-3) mm(2)/s; 1.31 +/- 0.245 x 10(-3) mm(2)/sec; and 1.3 +/- 0.7 x 10(-3) mm(2)/s, respectively. Myxomatous malignant masses had an ADC value of 2.6 +/- 0.55 x 10(-3) mm(2)/s, while nonmyxomatous malignant masses had an ADC value of 1.1 +/- 0.8 x 10(-3) mm(2)/s. ADC cutoff value between benign and non-benign (including malignant and locally aggressive masses) was 0.6 x 10(-3) mm(2)/sec with 98.3% sensitivity and 50% specificity (P = 0.5123). The statistical difference between malignant soft tissue masses (mean ADC 1.309 +/- 0.723 x 10(-3) mm(2)/s) and fibromatosis masses (mean ADC value 1.31 +/- 0.245 x 10(-3) mm(2)/s) using a comparative T-test proved to be of poor significance level (P value similar to 0.9757). Nine patients with soft tissue sarcomas (STSs) had pre and post-therapeutic MRI examinations showing a mean increase of the recorded ADC values by about 0.28 x 10(-3) mm(2)/s in the post-therapy study as compared with the recorded initial pretreatment values. Analysis of the post-therapy follow-up studies of fibromatosis showed that lesions with favorable response to chemotherapy or radiotherapy (8/12) exhibited significantly lower ADC values than those showing progressive disease course. Conclusion: DWI with ADC mapping of extremity soft tissue tumors are so complicated that they alone may not be of much value in differentiating between benign and malignant tumors; however, it can be used as a tool for monitoring response to treatment.