Introduction
Mediastinal tumours are very rare and are growths arising in the mediastinum. Neurogenic tumours are more common in posterior mediastinum and commonly occur in children. Schwannomas being the most common neurogenic tumors with up to 9% cases in mediastinum.1 Thymomas, Germ cell tumors commonly arise in anterior mediastinum with schwannomas being very rare arising mostly from intrathoracic peripheral nerves.2 They are encapsulated develops from the peripheral nerve sheath.1, 2 Mediastinal tumours observed as well demarcated lesions with rare calcifications on radiological investigations including chest x-ray computed tomography (CT), magnetic resonance imaging (MRI).3 Histopathological testing through percutaneous puncture biopsy or post-surgery provides a confirmatory diagnosis.4, 5 Such tumours are treated by resection through thoracoscopy.
Case Report
A 51 years old male, complained of breathlessness, dyspnea and intermittent cough since 3 months. He had no history of hypertension, diabetes mellitus, asthma, tuberculosis, chronic heart disease, or allergies. His physical condition was stable, with blood pressure of 114/78 mmHg.
A cystic SOL measuring 7.8x6.1x8.4 cm was discovered during radiological examination (chest X-ray, and thoracic CT scan) (Figure 1) in the anterior superior mediastinum abutting the adjacent portion of arch of aorta. An abdominal ultrasound revealed that the structures of the liver, gallbladder, pancreas and kidneys were normal. Thus a mediastinal tumour was diagnosed. The CT guided fine needle aspiration biopsy (FNAB) results revealed no evidence of malignancy. The patient underwent thoracoscopic surgery, which revealed a cystic, encapsulated anterior superior mediastinal tumor. The tumor was excised (Figure 2). The gross pathology examination revealed that the tumor tissue was partially cystic and solid. On histopathology, the solid area consisted of hypocellular and hypercellular areas of monotonous appearing proliferating cells with oval-spindle wavy nuclei, fine chromatin. (hematoxylin and eosin staining) In denser areas, tumor cells were often arranged in palisades. On Immunohistochemical study it revealed strong staining of S-100 protein, thus clarifying our diagnosis of schwannoma No signs of malignancy were evident (Figure 3).
Written informed consent was obtained from the patient for the publication of the case report and accompanying images.
Discussions
Mediastinal masses based on the location are classified as anterior, middle and posterior mediastinal tumours. Primary tumours of Anterior mediastinum are mostly Thymomas, germ cell tumours where as neurogenic tumours are most commonly located in posterior mediastinum.6 12–39% of all mediastinal tumors are Neurogenic tumors of which schwannomas account for around 95%.7 Other neurogenic tumors include neurofibroma, neurinoma, sympathetic neuroma, neural sarcoma, paraganglioma, paraganglioma , pheochromocytoma and neuroblastoma.8 Schwannoma or neurilemmoma, is a benign peripheral nerve sheath tumor of Schwann cell origin.9, 10 Neurogenic tumors are slow growing, arising from mediastinal peripheral nerves, sympathetic and parasympathetic ganglia, and embryonic remnants of nerve sheaths.11 These tumors typically develop from spinal nerve roots, can also develop from intrathoracic nerves. Schwannomas can also be discovered in lungs in about 0.2% of cases.12
Clinical symptoms of mediastinal benign schwannoma include cough, chest discomfort and obstructive pneumonia. May sometime present as facial edema and pericardial effusion.13 Mediastinal tumors can be detected by radiological investigations like Chest X-ray, MRI, Enhanced chest CT where they appear as well-defined lesions with or without calcifications.12 On a CT scan, schwannoma appears as spherical, smooth, hypodense lesions with or without cystic patches. Histopathological examination of a schwannoma reveals macroscopic features of a grey-white tumor that is well-defined, encapsulated, solid may exhibit cystic degeneration.14 Microscopic histological examination revealed the proliferation of Schwan cells with spindle wavy nuclei and pointed ends, with 2 growth patterns identified: Antony A (hypercellular, with nuclei foci arranged like palisades called verocay bodies) and Antony B (hypocellular, loosely arranged).15 Subsequent immunohistochemical analysis with S-100 protein further aid in the definite diagnosis.16
The treatment for all benign neurogenic tumors is surgical resection, except for neuroblastoma.14, 15 The thoracotomy surgical technique is used for resection of large mediastinal tumors, whereas video-assisted thoracoscopy is ideal for smaller tumor masses free from surrounding vital structures.1
Conclusion
To conclude, schawannomas in anterior mediastinum is a rare finding. Multiple imaging techniques, such as CT, MRI along with histopathological and immunohistochemical studies aid to arise in a definitive diagnosis of mediastinal tumours. Schwannomas are treated surgically by thoracotomy or VATS (video assisted thoracoscopic surgery). Mediastinal schwannomas have good prognosis with no recurrence reported till date.
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