Clinical Significance of Intramuscular Cysts in the Rotator Cuff and Their Relationship to Full- and Partial-Thickness Rotator Cuff Tears

Abstract

Secondary signs have been sought to help in the MR diagnosis of rotator cuff tears, especially partial-thickness tears. We sought to determine whether intramuscular cysts are always present with rotator cuff tears and the types of rotator cuff tears with which they present, and to establish the clinical significance of finding intramuscular cysts. Retrospective analysis of our institution's database of 5,101 MRI examinations of the shoulder during an 8-year period resulted in 187 examinations in 185 patients who were thought to have intramuscular cysts. Of the 187 examinations, 134 shoulders in 132 patients (62 women, 70 men) met our criteria for an intramuscular cyst. Of the 134 shoulders with intramuscular cysts, 102 (76.1%) showed imaging findings of both intramuscular cysts and rotator cuff tears. Thirty-two of the 134 (23.9%) shoulders were diagnosed with only an intramuscular cyst and were not associated with a rotator cuff tear. Fifty-five of 102 (53.9%) shoulders consisted of an intramuscular cyst associated with a full-thickness rotator cuff tear, and 47 of 102 (46.1%) shoulders presented with a partial-thickness rotator cuff tear. Forty-eight of 102 (47.1%) shoulders with both an intramuscular cyst and a rotator cuff tear also underwent the reference standard arthroscopy examination to confirm the MRI findings. In 46 of 48 (95.8%) shoulders that underwent arthroscopy, the findings confirmed the imaging evidence; the other two cases were shown to have an intact rotator cuff at arthroscopy. Our study echoes the findings of previous studies that suggest a relationship between intramuscular cysts and full- and partial-thickness rotator cuff tears but illustrates that the incidence of an isolated intramuscular cyst is higher than previously expected. When intramuscular cysts present with rotator cuff tears, they present with full- and partial-thickness rotator cuff tears in relatively equal proportions. The presence of an intramuscular cyst on MRI, although it may be an isolated finding, should prompt a thorough search of all the rotator cuff tendons for tears so that the patient may receive appropriate follow-up.