It is estimated that 9% of all schwannomas occur in the mediastinum. Fifty percent of neurogenic tumors of the mediastinum are schwannomas. In our series, schwannomas represented 5% of all soft tissue tumors of the mediastinum. More than 90% of schwannomas are solitary, sporadic, and slow-growing neoplasms. These lesions affect both genders equally, all age groups reached a higher incidence between the fourth and sixth decades of life.[1-3] In our series, the average age was 51 years while women were found to be a decade younger than men.
The clinical history, physical examination and image evaluation must be considered. Mediastinal schwannomas can originate from spinal, paravertebral sympathetic branches, vagus, phrenic and intercostal nerves, respectively.[1-3,11] In our study, about half of cases originated in the paravertebral region. The classic presentation is an incidental asymptomatic mass found on routine investigations as simple as a chest X-ray. Interestingly, some patients experience paresthesia or chest pain from compression of adjacent structures or extensions of the tumor in the thoracic spine. Other clinical manifestations are dry cough, dyspnea, and dysphagia. In our study and in contrast to other international publications, 57% of the patients had symptoms attributable to a mediastinal schwannoma. The ideal treatment consists of video-assisted thoracic surgery with complete resection of the mass because of its subsequent growth and mass-effect.[1-3] In our study, all patients underwent open posterolateral thoracotomy as standard.
CT and MRI can help accurately to determine the exact location of the mediastinal tumor and also defines its relationship to adjacent structures. On CT scanning, schwannomas appears as well-defined rounded mass with smooth margins, they are isodense or hypodense in the paravertebral region or long the courses of intercostal nerves. They have a variable enhancement pattern after administration of the intravenous contrast material including multiple hypodense or cystic areas with central hypodensity and central enhancement, as well as peripheral hypodensity.[13,14] Calcifications are occasionally detected, and low attenuation correlates with areas of hypocellularity, cystic change, hemorrhage, and lipidisation.[3,15]
While there are few cases reports of giant mediastinal schwannomas, these are often identified incidentally by chest X-ray, followed by CT scans that show a clearly defined mass with low densities and mild enhancement.[4-6] Giant schwannomas are more heterogeneous with cystic degeneration. In our series, cystic degeneration was observed more frequently in tumors larger than 10 cm. Tumors smaller than 10 cm were more frequently homogeneous with solid areas in the absence of cystic degeneration. This supports the idea that degenerate changes directly related to the size of the tumor. Heterogeneous changes observed by CT have a histological translation. In our study, the schwannomas that were homogenous by CT more frequently identified in the histological analysis of classical areas Antoni A and Antoni B. While in tumors that were heterogeneous by CT scan, they presented microscopically extensive hypocellular areas with marked cystic degeneration, reticular pattern, edema, hemorrhage and sometimes calcifications. However, by IHC positivity for S100 protein confirms the diagnosis in all cases.
Mediastinal schwannomas can be misdiagnosed as lymph node metastasis from locally advanced breast cancer. The clinical distinction between mediastinal schwannoma and metastasis in cases that have a history of cancer, can be difficult and requires its surgical removal and histopathological analysis. The location and composition through imaging studies are critical to make a differential diagnosis. Even through sophisticated studies such a 18F-fluorodeoxyglucose positron emission tomography and computed tomography (18F-FDG PET/CT), mediastinal schwannoma can simulate metastases to breast cancer lymph nodes, as shown by Martinez-Esteve et al. Similarly, we found a patient with a clinical history of stage IIB breast cancer during follow-up showed a mediastinal mass on a chest X-ray that was initially thought to be a recurrence of the disease. However, when a CT scan was performed, the site of origin of the tumor was defined precisely and it proposed that it could correspond to schwannoma. Finally, it was resected and the histopathological analysis showed a schwannoma with diffuse expression of S100 protein and GFAP.
Cellular schwannoma are an infrequent variant with a predominantly cellular growth pattern, in the absence of Verocay bodies. Usually seen at paravertebral, pelvic, retroperitoneal, or mediastinal location. This variant can be confused with a malignant peripheral nerve sheath tumor or with a solitary fibrous tumor.[18,19] In our study, we found only one case of a cellular schwannoma (13%) with storiform pattern mimicking a solitary fibrous tumor. The diagnosis of schwannoma was supported by light microscopy and corroborated by S100 protein and GFAP expression and negative for CD34.