Musculoskeletal tumors and tumor-like lesions with "dark" signal intensity on T2-weighted MR images: A pictorial review.

Musculoskeletal tumors and tumor-like lesions have an indeterminate appearance on magnetic resonance (MR) images and often display varying degrees and extent of T2 hyperintensity. However, a subset of neoplasms and tumor-like lesions may exhibit prominent areas of T2 hypointensity relative to skeletal muscle. The hypointensity observed on T2-weighted MRI can be caused by various substances, including hemoglobin degradation products, lesions containing calcium and calcification substances, mature collagen fibers, melanin, turbulent and rapid blood flow, and highly cellular lesions. Careful evaluation of the presence and pattern of T2 hypointensity in lesions and consideration of potential causes in their associated clinical contexts can help to narrow the differential diagnosis between neoplastic and nonneoplastic lesions. Appropriate interpretation of signal intensity and analyses of lesion location and clinical symptoms enable the correct choice of a further diagnostic algorithm or, in many cases, a final diagnosis determined exclusively by MRI examination.