We report a case of symptomatic dorsal mass in a 72-year-old man, with onset of pain during daily life efforts. On the other side, the dominant hand, a similar mass without any impairment was present. Before surgery, the mass on the left nondominant wrist was diagnosed by ultrasound as synovial ganglion: during excision, a muscular belly was found and sent to isthological evaluation, confirming the existence of an alive aberrant muscular tissue, named Extensor Digitorum Brevis Manus. Being reported in literature as occasionally bilateral, we decided to perform, 3 months later, an MRI in the contralateral asymptomatic wrist: it was possible to reveal the presence of a similar but asymptomatic mass.