Shoulder giant schwannoma - a diagnosis to be considered in painless shoulder masses.

Tumours formed from peripheral nerve sheaths are rare in the shoulder. We present the case of a 80-year-old female referred to an orthopaedic surgery clinic because of a large painless mass of the right shoulder, with one year of evolution. There was no history of trauma, involvement of any other joint or systemic complaints. Given the clinical and imagiological suspicion of a giant synovial cyst, the patient underwent complete surgical resection of the mass, which took place without any complications or functional impairment. Histological diagnosis - schwannoma - was unexpected given the lesion characteristics and the low incidence of these benign tumours. They usually present as a slow growth mass, where pain and neurological deficits are uncommon. Among the complementary tests available, MRI is the gold standard. Still, the diagnosis is made preoperatively only in a minority of cases. We emphasize the need to consider this rare clinical entity in the differential diagnosis of slow evolution tumourations of the shoulder, in order to avoid unnecessary surgery and to minimize the risk of iatrogenic injury of the involved nerve.