This 71-year-old female presented with a papule on her 3rd finger. The clinician submitted the biopsy as a possible wart. A digital mucus (myxoid) cyst, as the name implies, commonly involves the fingers and toes. It can be warty or more cyst-like, showing translucency and an attenuated epidermis. The etiology is controversial, as some authors claim they are herniations from synovial cavities (shown through injected dye studies) while other lesions are clearly separate and discrete. Myxoid cysts are not true cysts, as they often fail to demonstrate a lining. Histology in this case is typical, showing a pool of mucin merging into the surrounding dermis.
At higher power of the same lesion, no true cyst lining is identified. The mucinous material merges in with the adjacent dermal collagen. The lesion consists of delicate spindled-to-stellate fibroblasts, showing no cytologic atypia or mitoses.