[Staging and re-staging of soft tissue sarcoma using MRI. Usefulness of contrast media]

This study aims to evaluate the usefulness of paramagnetic contrast medium (Gadolinium) in the staging and re-staging of soft tissue tumors using Magnetic Resonance Imaging (MRI).

Sixty patients affected by soft tissue sarcoma of different histotype were retrospectively evaluated. Age ranged from 23 to 78 years. Data were obtained from the musculoskeletal tumor database of our Department of Radiology and cases from the last 7 years (1993-1999) entered this study. All the patients were submitted to ultrasound (US) and to routine and enhanced MR examinations (SE T1-weighted and Fast-SE T1 and T2-weighted before and after fat saturation pulse; GE T2-weighted sequences). At least two different scan planes were obtained depending on the major axis of the lesion. Once imaging information had been obtained all the patients underwent surgery and histology. After surgery, the mean follow-up period was 18 months. Paramagnetic contrast medium (0,2mmol/Kg) was administered in all the MR follow-up examinations.

Lesions included adipose histology in 15 cases; muscular histology in 12 cases; fibro-hystiocitic histology in 20 cases; synovial histology in 8 cases; mixed histology in 5 cases. Excluding lesions with mainly adipose content showing obvious high signal intensity on T1-weighted sequences, the other lesions rarely presented MR features specific to histological category also after contrast medium administration. In all the cases MRI allowed an accurate definition of the lesion boundaries to exclude or demonstrate neighbor region invasion. In 11 cases, MRI was able to demonstrate the presence of a recurrent tumor. In 2 out of 11 cases, recurrences were detected out only after intravenous administration of Gadolinium, plain MRI having failed to recognize them.

Despite the absence of specific MRI signs of the different soft tissue tumor histotypes also after Gadolinium administration, MRI remains the best imaging technique to establish the exact morphology of the lesions and to establish the invasion of the neighbor regions by the tumors. The presence of regional spreading of the tumor has to be considered a sign of malignancy. During the follow-up, the use of Gadolinium allows the MR examinations to reach high sensitivity levels and makes it also possible to recognize local recurrences of a very small size. Considering our experience we recommend, whenever a follow-up of resected soft tissue tumors is requested, to perform MRI examination before and after intravenous Gadolinium administration.