Extracranial non-vestibular head and neck schwannomas

Discussion

Schwannomas originate from perineural Schwann cells and grow extrinsic to their parent nerve fascicles; they can occur along both sympathetic and somatic nerves in the body, with the exception of the olfactory and optic nerves, as these lack Schwann cells.3 Due to the tertiary neurosurgical or otolaryngological treatment required for trigeminal and vestibular schwannoma patients, we only studied cases of extracranial non-trigeminal and non-vestibular schwannomas in this study. Accordingly, this study aimed to illustrate the clinical characteristics, diagnoses, treatments, and outcomes of extracranial non-vestibular schwannomas.

In the present study, schwannomas displayed a slight female predilection. In terms of patient age, schwannomas are most commonly reported in patients aged between 30 and 60 years. In the early stage, there are no specific symptoms or signs associated with schwannomas, and most patients present with an asymptomatic palpable solitary mass. Conversely, in the late stage, patients may endure physical discomfort, including neurologic deficits or obstructive symptoms.4 In our cases, the symptoms included hoarseness, radiating pain of the upper limb, and painless swelling of the neck, among others. In general, the symptoms of neurologic deficit are important for the diagnosis of Schwannoma, especially for diagnosing the nerve of origin. Our results instead agreed with those of Yafit et al,1 who reported that the most common nerve of origin is the brachial plexus. A preoperative diagnosis of schwannoma is difficult, and the differential diagnoses are diverse, including thyroid nodule, enlarged lymph node, paragangliomas, thyroglossal cyst, or tumor metastasis. To differentiate between schwannoma and these conditions, CT was performed in 30 patients in our study. On CT scans, small schwannomas are considered as homogenous, enhancing masses.5 When the size is large (>3 cm), the tumor is often heterogeneous, with randomly distributed areas of low attenuation observed, surrounded by a peripheral enhancing ring. In general, cystic elements may be observed.5 On MRI T1-weighted images, schwannomas show a low signal intensity ranging from the brain to the muscles, which can either be homogeneous or heterogeneous.3 On T2-weighted images, schwannomas have a higher signal intensity than the cerebrospinal fluid, and the signal may be either heterogeneous or homogeneous.3 After gadolinium injection, they are usually well enhanced.6 In terms of the CT and MRI findings in our cases, the nerve of origin could be visualized in some patients upon MRI, but in none upon CT. Further, while FNAC remains a useful diagnostic method for head and neck masses, in our series, the diagnosis was inconclusive in approximately 50% of the FNAC samples. In these schwannomas, samples obtained were not enough to make a specific diagnosis. Nonetheless, metastatic or primary tumors can be excluded, and the presence of benign tissue can be suggested using this technique.3 Moreover, in some cases, the FNAC procedure causes pain, and this was another reason for there being relatively few patients undergoing FNAC in our study.

Although CT, MRI, and FNAC may be somewhat helpful in distinguishing schwannomas from other tumors,5 postoperative histopathologic examination is still the gold standard, with the presence of a clear capsule, Antoni A and/or B areas, and a positive reaction for S-100 protein considered characteristic histopathological features of schwannomas.7 The Antoni A region can be described as a densely packed pattern of spindle cells, with frequent nuclear palisading arrangements, whereas the Antoni B region consists of loosely arranged spindle cells, with vacuoles and spindle-shaped nuclei prone to degeneration, hemorrhage, and cyst formation.5 In both patterns, the tumor cytoplasm is elongated and the nuclei are regular and oval.3 As schwannomas are both benign and radioresistant, complete surgical excision of the tumors by the appropriate approach is considered the standard curative treatment.1 However, owing to the potential neurological dysfunction associated with the surgery, conservative methods should be considered.1 In our study, most patients underwent complete surgical excision despite having symptomless isolated neck masses. Moreover, although there were no cases of recurrence in this study, it is also a controversial issue whether benign tumors can become malignant.4 Whatever the chosen treatment approach is, the nerves are likely to be influenced.1 Of note, previous reports have shown that significant recurrence did not occur during long-term follow-up in patients who received conservative treatment.6 Hence, due to the benign nature of this tumor, the above methods should be compared and assessed in the future in order to establish the optimal treatment for allowing preservation of nerve functions. However, it is still necessary to inform the patients of the possibility of neurological sequelae before the operation.3 Many studies have demonstrated the importance of preserving the nerve, while the preservation of structure does not always ensure functional preservation; thus, postoperative rehabilitation and neural reconstruction are highly important.6 Close observation and follow-up is another option, especially in selected cases of small incidental tumors at high risk of postoperative complications. Because of the multiple symptoms, wide range in location, size of the tumors, and rarity of the disease, establishing the optimal treatment is challenging. The limitation of this study is the small sample size, which weakens the stringency of results.

In conclusion, preoperative suspicion and awareness of the possibility of schwannoma are very important in making a proper diagnosis. Adequate imaging studies should be performed to increase the diagnostic rate preoperatively, and owing to the benign nature of this disease, the patients’ symptoms and willingness to undergo surgery should be taken into consideration when choosing the appropriate treatment modality.