Lesion Characterization Based on MR Signal Intensities
Most soft tissue tumors exhibit nonspecific signal intensity on MR imaging: low signal intensity on T1-weighted images and high signal intensity on T2-weighted images. When a soft tissue tumor has a different combination of signal intensities, it can aid in specific diagnosis and differential diagnosis of soft tissue tumors. Tumors with high signal intensity on T1-weighted images may contain fat, subacute hemorrhage, high proteinaceous fluid, or melanin (Table 17.1). Fat-suppression techniques can be used to distinguish fat from the other T1-hyperintense components. Intratumoral low signal intensity on T2-weighted images can also be a clue to the diagnosis (Table 17.2). Soft tissue tumors with collagenous fibrous tissue, mineralization, hemosiderin, and vascular signal void structures can be included in the differential diagnosis of the T2 hypointense lesions. Occasionally, soft tissue masses have very high signal intensity similar to fluid on T2-weighted images (Table 17.3). These lesions include fluid cysts, bursitis, myxoid tumors, chondroid tumors, vascular tumors, and malformations. Contrast-enhanced MR images allow differentiation between truly cystic and solid masses.