Magnetic resonance imaging of soft tissue tumors.

ABSTRACT

The value of magnetic resonance imaging (MRI) in histological classification was studied in a series of 164 histologically proven soft tissue tumors (STT) and was rather limited. MRI was only valuable in characterization of lipomatous, vascular and fibrous tumors. There are two main reasons for this limitation i.e. STT belonging to the same histological group may have different composition or different proportions in tumor components resulting in different MRI signals. Secondly tumor components may change individually or proportionally during natural evolution or as a consequence of therapy. Because well known grading parameters such as cellularity, mitotic rate, matrix and presence of necrosis all influence MRI signal intensity, the value of MRI in predicting malignancy is potentially high. To assess this value we retrospectively studied the findings in the first 141 soft tissue tumors (84 benign, 57 malignant) and evaluated a wide variety of MRI features (size, margins, signal homogeneity, shape, signal intensity, neurovascular and bone involvement, degree and pattern of enhancement and evidence of necrosis after injection of Gd-DTPA). Statistical analysis was carried out to determine accuracy of parameters individually and in combination, for predicting malignancy. Highest sensitivity was obtained for "absence of low signal intensity on T2" (100%), "mean diameter > 33 mm" (90%) and "inhomogeneous signal on T1" (88%). Highest specificity was obtained for "evidence of necrosis" (98%), "bone or neurovascular involvement or metastases" (94%) and "mean diameter > 66 mm" (87%). Association of best sensitivity (81%) and specificity (81%) was seen for "absence of low signal intensity on T2", "signal inhomogeneity on T1" and "mean diameter of the lesion > 33 mm". In a prospective study of 23 consecutive patients we reevaluated sensitivity and specificity in predicting malignancy of all parameters. Excellent correlation with the results of the retrospective study was found. Although a quantitative approach to the staging potentials of MRI was not possible, well known staging parameters are evaluated to the best by this method (size, depth, compartmental versus extra-compartmental location, relationship to adjacent structures).