Diagnosis and Treatment of Paratracheal Nerve Schwannoma
Schwannomas are rare types of tumors accounting for only 5% of benign soft tumors, but nearly 45% occur within the head and neck region . Schwannomas that originate from the head neck typically involve the vagus nerve or the sympathetic nervous system . Physicians utilize perioperative imaging, endoscopy and morphological studies to determine tumor size, location, anatomical structure, and composition. Treatment includes observation, complete tumor excision, and intracapsular nerve enucleation . The objective of this study was to describe and discuss the diagnostic and therapeutic management of a paratracheal schwannoma.
A woman in her 60s presented with dysphagia, globus sensation and intermittent hoarseness, which had been worsening for 22 months. Her medical history was significant for non-Hodgkin lymphoma treated with chemotherapy and a cystic thyroid nodule treated with a left hemithyroidectomy. The patient reported having an incidental neck mass identified on previous computed tomography (CT) imaging (Figure 1). Biopsy specimens were previously obtained by fine needle aspiration. Cytopathology examination revealed spindle cells, which were strongly positive for S-100 on immunochemistry.
Figure 1. Computed Tomographic Image: Axial view of soft tissue window demonstrating a right paratracheal enhancing soft tissue mass which abuts the subglottic trachea leading to moderate luminal effacement.
Figure 2. Endoscopic photograph shows right submucosal tracheal mass causing approximately 40% obstruction of the trachea and is located 2.5 cm below the true vocal folds.
These findings were consistent with a possible schwannoma. She denied weight loss or dyspnea and had no lymphadenopathy, palpable neck mass or neck tenderness. Initial management consisted of observation and serial imaging over a period of 18 months the mass doubled in size. Magnetic resonance (MR) imaging demonstrated a well-circumscribed, enhancing, right paratracheal mass measuring 2.0 x 2.0 cm. There was a resultant narrowing of the subglottic trachea, but an apparent confluence of the mass with the esophagus was also noted. Esophagoscopy showed no masses or mucosal alterations. On tracheobronchoscopy, a submucosal mass was seen 2.5cm below the true vocal cords causing approximately 40% tracheal obstruction (Figure 2).
Figure 3. Spindled cells arranged in a palisading fashion is typical of schwannoma. Note also the hyaline thickening of a vessel wall, a common feature trachea leading to moderate luminal effacement
In preparation for the surgical excision the patient was intubated with a NIM EMG Endotracheal Tube (Xomed, Minneapolis, MN). During surgical excision, a firm yet rubbery necrotic mass abutting the right crico-tracheal region was encountered.
Figure 4. S-100 protein immunoreactivity is seen in schwannoma.
The recurrent laryngeal nerve was seen adherent to the mass, but the nerve was meticulously dissected and peeled away from the mass. Histopathologic examination confirmed the presence of spindle cells with strong, diffuse staining for S-100 (Figure 3, 4). Preservation of the recurrent laryngeal nerve was successful and the patient was without symptoms or voice alterations following the procedure. The final histopatholgic examination confirmed a benign schwannoma. Post-operative imaging (MRI scan neck) demonstrated no evidence of recurrence at 16 months.
Schwannomas are benign encapsulated nerve sheath tumors of Schwann cell origin. These tumors can arise on any peripheral nerve other than the olfactory or optic nerves, which are not ensheathed by Schwann Cells . They are categorized as Peripheral Nerve Sheath Tumors (PNST), and along with neuro- fibromas, make up the majority of benign tumors in this category. These two entities, as well as their malignant equivalent, malignant peripheral nerve sheath tumors (MPNST), must be differentiated by histology . Schwannomas of vestibulocochlear complex are well documented, while reports of paratracheal schwannomas are far less prevalent in the literature . Schwannomas are almost exclusively solitary lesions; therefore multiple occurrences should raise suspicion for syndromes such as Neurofibromatosis 2 (NF2) .
Clinical manifestations of schwannomas largely depend on the tumor size and location. The most common manifestation of non-vestibular head and neck schwannomas is a neck mass, while development of pain and nerve palsy is less common . This symptomatology is less concerning than that seen with schwannomas encroaching on airway structures. Para-laryngeal schwannomas have been shown to present with dysphagia, dysphonia and dyspnea. They most often arise on the internal branch of the superior laryngeal nerve and manifest as a supraglottic lesion . Paratracheal lesions, although only described in rare case reports, may present with cough, wheezing or stridor and have been misdiagnosed as asthma . The recurrent laryngeal nerve’s apposition with the trachea makes this nerve or a pharyngeal nerve branch the most likely candidate for the origin of the schwannoma. In our case the schwannoma did not appear to be directly arising from the RLN and may have represented a branch off the pharyngeal plexus.
Preoperative imaging is vital to providing information on tumor size, location and associated anatomic structures. Ogose et al.  demonstrated that central enhancement is typically seen in schwannomas on CT and MRI. This pattern may be correlated to the dense spindle cell core of these tumors. Additional characterization may be made on MRI as schwannomas tend to have low signal intensity on T1-weighted images but are markedly hyperintense on T2-weighted images .
While imaging suggests the diagnosis of schwannoma, microscopic evaluation confirms the diagnosis. Classic morphology shows areas of compact spindle cells (Antoni A areas) with elongated nuclei that form palisading sheets (Verocay bodies). These areas are intermixed with regions of loose myxoid stroma sparsely comprised of spindle cells (Antoni B areas) . Schwannomas arise within the nerve sheath and are thus completely encapsulated allowing for both Antoni A and B areas to be seen along a continuous capsule.7 Immunochemistry shows strong, diffuse staining for the S-100 protein, a characteristic which differentiates schwannomas from other PNSTs. In addition, schwannomas commonly stain positive for vimentin and myelin basic protein . Grossly, tumors are encapsulated and may undergo cystic degeneration and necrosis as they grow .
Management of schwannomas consists of complete tumor enucleation with ultimate consideration given to preservation of the nerve of origin . Valentino et al.  noted that neural fascicles might be displaced along the tumor capsule as it grows, making it extremely difficult to preserve the nerve of origin. In these instances, immediate reconstruction of the sacrificed nerve is indicated. Because of this potential morbidity and the benign nature of schwannomas, it is recommended that surgery be delayed until the tumor causes significant symptoms .
Identification of Schwannomas involves a myriad of diagnostic technique to accurately assess size, location, and morphology of the tumor. The symptoms experienced by our patient are consistent with para-tracheal schwannoma and was further validated by CT, MRI, immunohistochemistry and tracheobroncoscopy. Management of this type of schwannoma entails enucleation of the mass with preservation of the involved nerve.
11.Si Hong Kim, Na Hyun Kim, Kyung Rok Kim, Ja Hyun Lee, Hong-Shik Choi. Schwannoma in Head and Neck: Preoperative Imaging Study and Intracapsular Enucleation for Functional Nerve Preservation. Yonsei Med J. 2010, 51(6): 938-942.
12.Ryuji Yasumatsu, Torahiko Nakashima, Rina Miyazaki, Yuichi Segawa, Shizuo Komune. Diagnosis and Management of Extracranial Head and Neck Schwannomas: A Review of 27 Cases. International Journal of Otolaryngology. 2013, 2013 (2013): 1-5.