Synovial sarcoma: CT imaging of a rare primary malignant tumour of the thorax.

PURPOSE: This paper presents computed tomography (CT) features of three patients with primary synovial sarcoma of the lung (PSSL) who came to our attention and underwent surgery; reviews of the literature on this rare thoracic tumour are also presented.

MATERIALS AND METHODS: The patients, all men, with a mean age of 58 years, underwent clinical and radiological re-evaluation after receiving a histological diagnosis. None of the patients had multifocal disease or other concomitant neoplasms. All patients had undergone both chest X-rays and computed tomography, and two had also been studied with positron emission tomography (PET)-CT. Two patients underwent surgical removal of the tumour, whereas the third initially underwent surgery (following an incorrect diagnosis) and then thoracoscopic biopsy of the pleural lesions that subsequently arose.

RESULTS: In each case, chest X-rays showed changes, with the presence of pulmonary masses noted in all patients. In one patient, pleural effusion was also visible. CT scans showed parenchymal masses that were largely of a colliquative nature (in two out of three patients). Ipsilateral pleural effusion was present in two patients, associated in one with solid nodules within the pleura. Mediastinal lymphadenopathy, which was not radiologically significant, was present in only one patient. The two patients who also underwent PET-CT examination showed pathological tracer uptake confined to the lesion site without other thoracoabdominal or musculoskeletal localisations. CT-guided biopsy, performed in one patient only, was positive for mesenchymal tumour. In the two patients who underwent surgery, a definitive diagnosis of monophasic synovial sarcoma of the lung was made. The diagnosis of monophasic synovial sarcoma in the third patient was confirmed using thoracoscopic biopsy

DISCUSSION: Both in the cases described and in those identified in the literature review, standard chest X-rays mainly showed a parenchymal mass of pleural origin with either irregular or well-defined margins. CT characteristics are more definite, with evidence of a mass with regular and sharply defined margins, occasionally polycyclic, with inhomogeneous density due to the presence of colliquative areas within the tumour.

CONCLUSIONS: Although PSSL is a rare tumour, a pulmonary mass of inhomogeneous density, associated with pleural effusion but without lymphadenopathy, detected in an asymptomatic or poorly symptomatic patient, should lead to PSSL being considered in the differential diagnosis, provided that metastases from the more common synovial sarcomas of the musculoskeletal system have been excluded.