73-year-old female with right axillary mass and concern for a right infraspinatus mass. Axillary masses seen on this MRI of the shoulder are comparable to those seen on the recent CT scan, when accounting for positional and technical differences. We have no prior MRI for direct comparison. There is extensive reticulation of the adjacent subcutaneous fat which may reflect prior surgery or radiation therapy. Although the masses and reticular signal abnormality abut the chest wall, we see no signal abnormality within the ribs. Signal abnormality also abuts the anterior margin of the subscapularis and deep margin of the pectoralis, but we see no muscular invasion. The axillary vessels are contained within this signal reticulation, again appearing comparable to that seen on the prior CT examination. This process extends superiorly to the level of the coracoid process and behind the clavicular diaphysis.There is fusiform increased signal intensity along the length of the infraspinatus muscle on the fat-suppressed T2-weighted imaging, with associated enhancement following contrast administration. The muscle fibers, however, remain visible, and we see no space occupying mass within the muscles. These findings most likely reflect isolated infraspinatus myositis. We see no signal abnormality in the adjacent scapula, or other bones or muscles. Increased signal intensity and enhancement in the dependent portions of the imaged right lung likely reflect dependent atelectasis.
Imaging findings of isolated myositis of the infraspinatus muscle without discrete mass within the muscle. Axillary masses and abnormality appearing similar to those seen on the prior CT scan.