Primary diagnosis of ruptured biceps tendon "Baker's-type cyst" using fine needle aspiration biopsy: A case report

Biceps tendon rupture is generally a clinical and radiographic diagnosis, and only rarely presents to the cytopathologist for fine needle aspiration biopsy. We present a case of ruptured biceps tendon associated with a cystic mass of the upper arm that was diagnosed using fine needle aspiration biopsy, and confirmed with subsequent MRI scan. We describe the clinical presentation, cytomorphology, and immunohistochemical profile of the marked chronic inflammatory infiltrate within the synovial fluid. We also provide a discussion of the differential diagnosis for a cystic mass associated with the biceps tendon on cytology.