Discussion
SS are rare malignant tumor .They are highly aggressive on soft tissue .Their pathogenesis is unknown (4). They account for 7-8% of malignancies of mesenchymal origin (2,5).
SS is found in 90% of cases in the para-articular regions and in 10% of cases in various anatomical sites unrelated to synovial tissue (2,3).
It has become increasingly evident that SS can occur in many other sites, including the head and neck, mediastinum, heart and esophagus. Only recently ,some cases of SS occurring in the lungs and pleura have been reported (6). Approximately ,about 30 cases of primary lung site tumors are described in the literature (3). The site is preferentially peripheral but a few cases are described in the bronchial tree (7).
Because of its rarity, SS of the chest wall is difficult to diagnose, its primitive nature is difficult to assert, the search for a primitive extra-thoracic tumour is fundamental before making the diagnosis (8,9).
Only the absence of extra-pulmonary tumor location in the past, at the time of diagnosis and after 2 years of follow-up will attest to the primitive nature of the lung tumor (3). In our case, no extra-thoracic signs were retained, allowing us to retain the diagnosis of a primary synovialosarcoma of the lung.
SS usually occurs between the ages of 20 and 40, but can be seen at any age (1). In our case the patient is 61 years old. In the literature a slight male predominance has been noted (2). The sex ratio is 1.5 (8.10).
Our clinical case is conformed with the literature results that indicate that the most common symptoms are chest pain, shortness of breath and cough, although up to 24% of patients remain asymptomatic with incidentally identified tumors (6).
The SS of the chest wall appears as a soft mass, gradually increasing in size over months or years (1,11), with a vaulted wall as it grows outside. It may be asymptomatic (12) or more often be responsible of a chest pain, gradually increasing, as has been observed in our case over several months (1). Its intra-thoracic development is most often responsible of dyspnea or cough (1,11).
A study by A. Duran-Mendicuti et al (1) described the difficulty that can be encountered to assign a specific site to a primary thoracic SS. This study included five patients with SS, the tumor was located in the lungs and/or pleura in one case, in the chest wall in two cases and masses involving both pleuro-pulmonary and chest wall tissue in two cases. In addition, the results highlight the large size (2-10 cm; mean, 6 cm) that can be achieved by a primary thoracic SS (1).
Chest x-rays are not very effective in determining the characteristics of the tumor, including its size, limits and location in the chest wall, pleura or lung parenchyma. It reveals calcifications in more than 25% of cases (8,9). In our case the chest X-ray showed the presence of an opacity that occupies almost the entire right lung without any image of calcification.
Thoracic CT scan allows a better appreciation of the site of the tumor, its endo- and exo-thoracic extension, and allows to show signs of malignancies like the heterogeneous appearance with central necrosis, presence of pleurisy and mediastino-pulmonary invasion (8).
On thoracic CT scan, the primary SS of the thorax most often presents as a very limited heterogeneous mass without calcifications, without notable mediastinal, hilar or axillary adenopathy and without bone invasion (1). Chest wall SS is rarely associated with pleural fluid effusion (11).
On MRI, about 90% of SS are very limited, sometimes with an encapsulated appearance. The presence of lobulations is frequent (8).
In their study Fujimoto et al (1,13) report report a chest wall SS showing, on MRI, ovoid and round areas of low signal intensity in T1-weighted images and high signal intensity in
T2-weighted images within the mass. These authors also described the fluid-fluid levels associated with sedimented blood products as reported in the SS of the extremities. MRI is the best radiological exam to better assess intra-tumoral heterogeneity and locoregional extensions (10,14).
The diagnosis of SS is based on the anatomopathological, immunohistochemical and cytogenetic analysis of the tumor tissue.
Macroscopically it is an oval or rounded tumor, sometimes multinodular, of very variable diameter (0.6 to 28 cm), often well defined and encapsulated. It is pale, with white or grey color, with a soft, firm or rubbery consistency and is dotted with necrotico-hemorrhagic and cystic foci, which reflect the heterogeneous radiological appearance (7,10,14).
Most tumors have a characteristic t(X; 18) translocation, which involves the SSX1 or SSX2 genes on the X chromosome (Xp11) and the SYT gene on chromosome 18 (18q11). Transcripts of the SYT-SSX fusion gene can be detected on anatomopathological specimens with a sensitivity of 96% and a specificity of 100% (8). The genetic study was not done in our case.
Surgery remains the main treatment option followed by radiotherapy on the tumor site (4).
The factors of a good prognosis are: Tumor diameter less than 5 cm, low mitotic index (less than ten mitoses for ten fields at high magnification), low proliferation index (Ki-67 < 10%), absence of tumor necrosis, absence of residual tumor after surgical resection (2).
Despite the use of new chemotherapy drugs, the prognosis remains poor. Five-year survival ranges from 76-35% and ten-year survival from 63-10% (10).