Atypical Presentation of Bilateral Acromioclavicular Joint Cysts Extending Medially into the Trapezius Muscles: A Case Report and Literature Review.

Introduction: Acromioclavicular joint cysts represent a relatively rare clinical entity, often manifested as an enlarging mass adjacent to the acromioclavicular joint, which can raise concerns for a potential tumor. These cysts are identified for their association with shoulder pathology, particularly extensive rotator cuff tears, and present a diagnostic and therapeutic challenge for misdiagnosis as neoplastic masses. In this case, we are reporting on an unusual presentation of a patient presenting with a swollen mass in the left trapezius causing neck pain.