Background. Soft tissue masses are frequently referred for imaging assessment. Magnetic resonance imaging (MRI) is the technique of choice for detection of these masses and local staging of the malignant one.

Purpose. The study is aimed to measure the apparent diffusion coefficient (ADC) values of different soft tissue masses and determine the cut-off value that can be helpful in differentiating between the benign and malignant histological types.

Materials and methods. A prospective study was conducted in the Radiology Department of the Oncology Teaching Hospital. A total of 37 cases enrolled during the period from 12th July 2019 to 20th February 2020. Diffusion weighted images (DWI) were performed for all cases. The mean ADC value for the enhancing component of each mass was measured on the generated ADC map done at high b-value of 800 sec/mm2.

Results. The benign soft tissue masses were recorded in 15 (40.5%), while malignant masses found in 22 (59.5%) of patients. The greatest ADC values (mean±SD) measured for the benign masses was (1.97 x10-3 mm2/s ±0.39) for hemangiomas. While the greatest ADC value results for the malignant masses was for myxoid liposarcoma (2.11 x10-3 mm2/s ±0.45). The lowest ADC values were observed in hematological tumors. In a selected group of masses which their enhancing componenet expressed low signal or intermediate hyperintense signal in T2-WI (n=26), the mean ADC value for the malignant masses (n=18) was lower than the mean ADC value of benign (n=8) (0.863±0.28 vs. 1.675±0.39), with statistically significant association (P-value=0.002) and the ADC cut-off value of 1.42 x10-3 mm2/s gives a high sensitivity of 94.44%, a high specificity of 87.5%, and accuracy of 92.31% for differentiating malignant from benign masses which was statistically significant (P-value <0.000).

Conclusions. In a selected group of soft tissue masses which their enhancing componenet express low or intermediate hyperintense signal in T2-WI, the mean ADC value was lower in malignant soft tissue masses than that in benign masses with a cut off value of 1.42 x10-3 mm2/s gives a high sensitivity and a high specificity.