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).