Schwannoma of the vagus nerve, a rare middle mediastinal neurogenic tumor: case report

Schwannoma originating from the vagus nerve within the mediastinum is a rare, usually benign tumor. A 44-year old male was presented with chest pain. Chest radiography, CT scan and MRI showed a well circumscribed mass, 5 × 4 cm located in the aortopulmonary window. The mass was found at surgery to be in close proximity with the aortic arch and the left pulmonary hilum, alongside the left vagus nerve. The encapsulated tumor was completely resected through a left thoracotomy incision and it was found to be a benign schwannoma in pathology. The patient is free of recurrence 6 years after surgery.


Background
Neurogenic tumors represent approximately 20% of all adult and 25% of all pediatric primary mediastinal neoplasms. They are divided into nerve sheath, ganglion cell and paraganglionic cell neoplasms [1]. Neurogenic tumors are benign mediastinal tumors with rare exceptions [1][2][3]. Schwannomas or neurilemmomas originating from the vagus nerve are rare mediastinal tumors, accounting for 2% of all mediastinal neurogenic tumors, arising typically from the nerve sheath and extrinsically compressing the nerve fibers [1,4].
Scwannomas are lobulated, encapsulated spherical masses, different from neurofibromas in that matter. Men and women are equally affected in their third and fourth decades [1]. Usually, they are asymptomatic and benign, and very rarely malignant or multiple [2][3][4][5]. Shwannomas usually arise from a spinal nerve root, indeed they may arise from any other intrathoracic nerve [1,4]. Radiologically they are sharply demarcated with rare calcifications. CT contrast enhanced scan of the chest shows in accordance, a sharply demarcated mass with low densities and mild enrichment, rarely with calcifications and no fat. On MRI the schwannomas have low -to intermediate signal intensity on T1-weighted images and may have intermediate -to high -signal intensity on T 2 -weighted sequences [6,7].

Case Presentation
A 44-years old male presented with a sense of heaviness and pain in the left anterior chest wall. Preoperative chest radiography showed a sharply demarcated extrapulmonary mass withour calcifications in the middle mediastinal compartment, between aortic arch and left hilum.
Contrast-enhanced CT scan of the chest showed a 5.1 × 4 cm mass in the aortopulmonary window, with smooth and clear margins, low densities (HU: 9-15) and light enrichment after administration of contrast material (HU: 22-37), without calcifications and fat (Figure 1). On MRI, the tumor showed the characteristics as previously described (Figure 2).
He underwent a left anterolateral thoracotomy in the 4 th intercostal space preserving the latissimus dorsi instead of VATS procedure because of the proximity of the tumor to the aortic arch and the left main pulmonary artery. Complete resection, as is the case for benign schwannomas, was performed of this 5 × 4 cm tumor, located in close proximity to the vascular structures of the aortopulmonary window, alongside the left vagus nerve which was left intact. The tumor was removed with its entire capsule and was found to be benign at histology, because there were no atypia, mitoses, increased cellularity and necrosis. (Figure 3 and Figure 4) The patient had no postoperative complications and he is free of recurrence 73 months later.

Comment and Conclusion
Benign schwannomas of the vagus nerve are very rare middle mediastinal neurogenic tumors of nerve sheath origin [1,2]. Schwannomas of the vagus nerve occur usually on the left hemithorax while they may reach huge dimensions in rare instances [1,2]. Thoracotomy instead of VATS was preferred in the presented case because of the location of the tumor in the middle mediastinal compartment, close to the aortic arch and the hilum of the left lung. VATS resection is an alternative option for resection of mediastinal neurogenic tumors however the location of the tumor in the middle mediastinum and especially in the aortopulmonary window may necessitate thoracotomy for safe isolation of the tumor from the vital mediastinal structures and further, in order to avoid damage to CT contrast enhanced scan of the chestshowing the smooth and clear margins of the mass and its location inthe aortopul-monary window Spindle cells which are arranged in fasicles in a loosestroma (HEx200) Figure 3 Spindle cells which are arranged in fasicles in a loosestroma (HEx200).