There is a large T1 and STIR hypointense mass that involves the entire common flexor compartment tendon sheath, 5th digital tendon sheath, and flexor pollicis longus tendon sheath. The mass violates the dorsal aspect of these compartments to extend between the first, second and third metacarpals proximally. The mass is well-defined and lobular without peritumoral edema. There are multiple, small, mildly enhancing foci throughout the lesion, most prominently within the mass between the first and second metacarpals, and anterior to the fourth metacarpal.