|Year : 2021 | Volume
| Issue : 1 | Page : 28-34
Neurogenic tumors of parapharyngeal space – Clinical evaluation and management: Our experience
MB Bharathi, BS Rakesh, Babu Amabale Rudrappa, Nitish Aggarwal, Kumar Shankar de
Department of E.N.T, Head and Neck Surgery, JSS Academy of Higher Education and Research, Mysore, Karnataka, India
|Date of Submission||06-Jan-2021|
|Date of Acceptance||23-Jan-2021|
|Date of Web Publication||29-Jun-2021|
M B Bharathi
Department of E.N.T Head and Neck Surgery, JSS Hospital, Mahathma Gandhi Road, Mysore - 570 004, Karnataka
Source of Support: None, Conflict of Interest: None
Context: Neurogenic tumors are the second most common parapharyngeal space (PPS) lesions, with schwannoma being the most common neurogenic tumor seen. PPS tumors account for 0.5% of all head-and-neck masses, and most surgeons might not encounter it in their lifetime. Anatomical complexity and histological diversity of PPS pose various diagnostic and treatment challenges. Relevant literature about lesions of this space is growing but is still limited. Aims: The aim of our study was to evaluate neurogenic tumors of PPS and their management over a period of 5 years. Settings and Design: A retrospective study was conducted in our institution for a duration of 5 years from January 2014 to December 2018. Materials and Methods: Clinical features were analyzed. All patients were subjected to radio imaging-contrast-enhanced computerized tomography and contrast magnetic resonance imaging, and findings were noted. After imaging, patients were subject to fine-needle aspiration cytology. Transcervical approach was used for 11 cases and endoscopic-assisted transoral transpharyngeal approach (EATA) used for 4 cases. Results: A total of 27 patients with PPS tumors were evaluated and treated. The incidence of neurogenic tumors was 55.5% (15 cases). Out of the 15 patients with neurogenic tumors, 11 cases were schwannomas, 1 case was vagal neurofibroma, and 3 cases were paragangliomas from the carotid body. Conclusions: Neurogenic tumors of PPS are more common than traditionally thought. Neck swellings and oropharyngeal masses are the most common presenting features. FNAC is a very useful tool to establish a preoperative cytological diagnosis. Both external approach and EATA are effective approaches, provided that careful patient selection is done.
Keywords: Neurogenic tumors, parapharyngeal space, retrospective study
|How to cite this article:|
Bharathi M B, Rakesh B S, Rudrappa BA, Aggarwal N, de KS. Neurogenic tumors of parapharyngeal space – Clinical evaluation and management: Our experience. J Head Neck Physicians Surg 2021;9:28-34
|How to cite this URL:|
Bharathi M B, Rakesh B S, Rudrappa BA, Aggarwal N, de KS. Neurogenic tumors of parapharyngeal space – Clinical evaluation and management: Our experience. J Head Neck Physicians Surg [serial online] 2021 [cited 2021 Dec 5];9:28-34. Available from: https://www.jhnps.org/text.asp?2021/9/1/28/319739
| Introduction|| |
Parapharyngeal space is located lateral to the pharynx and can be viewed as an inverted pyramid with its base at skull base and apex towards greater cornu of hyoid bone. Parapharyngeal space tumours account for 0.5% of all head and neck masses. Since lesion in this region is locked by bony structures on three sides they tend to grow either medially into tonsillar fossa and soft palate or inferiorly into the retromandibular area.
Approximately 80% of primary neoplasms in this region are benign and about 20% are malignant. The most common primary tumors, accounting for 50% of parapharyngeal tumors, are salivary gland neoplasms, with pleomorphic adenoma being most common. Neurogenic tumors are the second most common tumors and include schwannomas, paragangliomas, neurofibromas, and malignant tumors. Considering the location of this space and the overall rarity of neurogenic tumors, clinical examination, diagnosis, and appropriate surgical approach is a considerable challenge. Recent advances have considered the use of endoscopes, microdebriders, neuronavigation, and robotic surgery to facilitate better tumor removal. We, in this study, share our experience of neurogenic tumors of this region, its incidence, clinical presentation, and management in a tertiary care setup.
| Materials and Methods|| |
A retrospective study was conducted in our institution for a duration of 5 years from January 2014 to December 2018. A total of 27 patients with PPS tumors were evaluated and treated. All patients were subjected to appropriate radiological investigations and Fine needle aspiration cytology preoperatively. Preoperative diagnosis was confirmed using Histopathological examination post surgery. Postoperatively, the patients were followed up for about 3 postoperative visits over 3 months to observe for postoperative complications.
| Results|| |
The incidence of neurogenic tumors out of the total parapharyngeal tumors recorded in our department was 55.5%. Out of the 27 cases of parapharyngeal tumors seen, 9 (33.3%) were of salivary gland origin, one each (3.7%) was of epidermoid cyst, lipoma, and venous malformation, and 15 (55.5%) cases were of neurogenic origin [Figure 1]. Out of the total 15 patients with neurogenic tumors, 11 cases were schwannomas (73.3% of neurogenic tumors), 1 case was vagal neurofibroma (6.6%), and 3 were paraganglioma from the carotid body (20%) [Figure 2]. All cases were confirmed by Histopathological examination (HPE).
|Figure 1: Incidence of various parapharyngeal space lesions seen in our study|
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|Figure 2: Incidence of various neurogenic tumors of parapharyngeal space as seen in our study|
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Eight cases of neurogenic tumors were seen in males and seven in females. All patients were diagnosed with schwannomas within 35–50 years of age. Patients of vagal neurofibroma were 48 years old, and all three patients of carotid paragangliomas were between 40 and 50 years of age.
Most patients of neurogenic tumors of PPS were asymptomatic, with the most common presenting symptom being a neck swelling. One hundred percent (15) of the patients in our study presented with a neck swelling which was insidious in onset and slow growing. Oropharyngeal mass with oropharyngeal wall, tonsil, and soft palate pushed anteromedially was seen in 60% of the patients (9 out of 15 cases). Four patients (26.6%) had dull aching pain. One out of 11 patients with schwannoma also presented with dysphagia. Patients with vagal neurofibroma along with pain also complained of change in voice and aural fullness [Figure 3].
|Figure 3: Presenting features of neurogenic tumors of parapharyngeal space|
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Examination of the neck swelling showed an almost ellipsoid mass in all cases of schwannoma which was soft to firm in consistency, nontender, and nonfluctuant. Carotid body paraganglioma was seen as an ovoid soft, pulsatile mass which was mobile in transverse but fixed in vertical direction. An audible bruit was also present. Case of vagal neurofibroma showed multiple subcutaneous nodules all over the body [Figure 4], café au lait spots, and axillary freckling. Ophthalmologic examination showed Lisch nodules on the left side.
|Figure 4: Case of vagal neurofibroma with neurofibromatosis type 1 showing multiple subcutaneous nodules|
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Contrast-enhanced computerized tomography (CECT) findings of schwannomas typically showed a hypodense lesion with moderate contrast enhancement. Out of 11 cases of schwannoma, 3 cases showed hemorrhagic and calcification signs and 2 had cystic changes and fatty degeneration. Magnetic resonance imaging (MRI) for these cases showed high signal intensity on T2 images which are characteristic of schwannomas. Anterior displacement of the internal carotid artery (ICA) was seen. Scan of vagal neurofibroma also showed anterior displacement of PPS fat with anteromedial displacement of ICA. Carotid paragangliomas showed a well-circumscribed heterogeneously intensely enhancing soft-tissue density mass causing splaying at the carotid bifurcation or the Lyre sign. Angiography/digital subtraction angiography was also done for all cases of carotid parangangliomas which along with Lyre sign showed an intense tumor blush with early emptying or the “early vein” sign.
A cytological diagnosis was established preoperatively using FNAC. It was done for all cases except those suspected to be carotid paragangliomas. All cases of schwannoma showed spindle cells of benign nature with wavy nuclei in the background of myxoid and hemorrhagic material pointing toward a diagnosis of benign spindle cell tumor possibly of peripheral nerve sheath origin. FNAC of vagal neurofibroma also showed clusters of benign-looking spindle cells against a background proteinaceous material and hemorrhage. Establishing a preoperative cell of origin by FNAC helps in the better management of the cases. In cases of benign pathologies like schwannomas, nerve of origin can be kept intact and the patient can be informed regarding the same. In cases of neurofibromas and malignant tumors, resection of the nerve is planned and the prognosis regarding loss of nerve function has to be explained to the patient.
All cases were managed surgically. Eleven cases underwent external transcervical approach and 4 cases of schwannomas were subjected to endoscopic-assisted transoral transpharyngeal approach (EATA). EATA was preferred in patients with FNAC suggesting schwannoma, and radio imaging localizing the tumor to the posteromedial aspect of the poststyloid compartment and in the prestyloid compartment tumor has to be medial to the stylomandibular ligament. Four patients fell into the abovesaid criteria in our study. Histopathological confirmation was done postsurgery. Case of vagal neurofibroma was excised using transcervical approach following which sural nerve grafting was done [Figure 5].
|Figure 5: Surgical field after excision of vagal neurofibroma and sural nerve grafting via a transcervical approach|
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Postoperatively, all patients were followed for a period of 3 months. Fourteen patients had no major complaints with no neurological deficits during the follow-up period whereas the patient of vagal neurofibroma complained of change in voice and regurgitation for which type 1 thyroplasty was done along with rehabilitation using swallowing exercises.
Final histopathology correlated with the cytological diagnosis established by FNAC in 100% of the cases. All schwannomas were well-circumscribed, capsulated masses consisting of benign spindle cells with wavy nuclei and hypercellular (Antoni A) and hypocellular (Antoni B) areas. Neurofibroma was a globular gray-white mass composed of spindle cells with bulky nuclei and moderate amount of eosinophilic cytoplasm consistent with the FNAC findings.
| Discussion|| |
The PPS is a virtual anatomic region classically compared to an inverted triangular pyramid extending from the skull base to the hyoid bone.
Lateral boundary is formed by the mandibular ramus, medial pterygoid muscle, and deep lobe of the parotid and is bounded medially by the buccopharyngeal fascia covering superior constrictor muscle. Posterior boundary is prevertebral fascia and muscles. PPS has been further divided into prestyloid and poststyloid compartments by the fascia of the tensor veli palatini muscle with prestyloid compartment consisting of the deep lobe of the parotid gland, parapharyngeal fat, lymph nodes, and small vessels and nerves. Most masses originating from prestyloid compartment are, therefore, salivary lesions and lipomas. Poststyloid compartment contains ICA, internal jugular vein (IJV), cranial nerves IX, X, XI, and XII, sympathetic chain, and lymph nodes. Therefore, neurogenic and vascular tumors are much more common in the poststyloid compartment also known as suprahyoid carotid space.
PPS tumors are difficult to diagnose early due to their location and plethora of presentation.
Shoss et al. presented the combined data from four studies representing 213 patients and showed that neurogenic tumors may account for more parapharyngeal lesions than traditionally thought. Similar findings were observed in our study where neurogenic tumors were found to be the most common PPS tumors accounting for 55.5% of the cases. Based on previous studies, schwannomas roughly account for 20% of all PPS tumors and 20%–40% of all schwannomas occur in the head-and-neck region.
Most tumors arising in this space follow a silent, asymptomatic course and are frequently diagnosed by chance, with neck swelling and pharyngeal mass being the common presentation. Similar observations were made in our study as 100% of the patients presented with a long-standing, slow-growing painless neck mass and 60% (9 out of 15) cases presented with an oropharyngeal mass. However, a fully formed tumor causes pressure on the surrounding tissues as seen in one of our patients of an advanced schwannoma presenting with dysphagia and the patient of vagal neurofibroma presenting with aural fullness and oropharyngeal pain.
Signs and symptoms of PPS tumors are subtle. Since it is impossible to directly examine PPS, an elaborate head-and-neck examination is essential. It is subsequently important to perform a systematic neurological examination to detect neural deficits that might help in the differential diagnosis of the mass. The presence of pain, trismus (caused by the infiltration of the tumor into the internal pterygoid muscle), and the paralysis of cranial pairs must alert us to the presence of a malignant tumor, neurinomas, or paragangliomas. No cranial nerve deficits were, however, seen in our study.
Some characteristic examination findings can also be demonstrated such as the Fontaine sign which is the reduced mobility seen in vertical plane in carotid paragangliomas and was seen in all cases of carotid paragangliomas in our study as well. Neurofibromatosis type 1 is associated with tumors along the nervous system and classically present with subcutaneous nodules, café au lait spots, and Lisch nodules on ophthalmoscopy. All these classical signs of neurofibromatosis type 1 were present in our case of vagal neurofibroma who was diagnosed with this genetic disease.
Presenting symptoms and the systematic physical examination of these tumors are very nonspecific, and hence, it is essential to perform complementary imaging studies, i.e., CECT and/or contrast MRI for a topographical diagnosis as well to subsequently plan a surgical treatment which remains the mainstay of management. Both the CECT scans and the contrast MRI images can be used, but MRI provides us with more information. However, in our study, both MRI and CECT scans were obtained. Radiological studies provide us with information on the mass's prestyloid or retrostyloid origin. Retrostyloid origin can be made out with anterior displacement of parapharyngeal fat and ICA as we saw in our study as well where all neurogenic tumors were seen to arise from retrostyloid compartment.
Neurogenic tumors show a density less than that of muscle with cystic areas and minimal postcontrast enhancement. The hypodensity of these neurogenic tumors has been related to regions of both low cellularity and high lipid content. They have also been attributed to the entrapment of perineural adipose tissue by plexiform neurofibroma or cystic degeneration secondary to infarction or necrosis. MRI has also become a very useful diagnostic tool. The most common enhancing tumor is schwannoma followed by paraganglioma.
Typical radiological diagnostic characteristics of schwannoma are usually an ovoid or fusiform mass with well-delineated margins which is higher in attenuation than adjacent muscle or isodense, less commonly of lower attenuation than the adjacent muscle. Cystic and fatty degeneration, hemorrhage, and calcification may also be found as seen in our study as well. There is high signal intensity on T2 images on MRI which is similar to a pleomorphic adenoma as well, but the anterior displacement of carotid seen in schwannomas confirms their retrostyloid origin and helps to differentiate them from pleomorphic adenomas.
Carotid paragangliomas show the typical splaying at the bifurcation of external and ICA called the Lyre sign. Angiography can also be performed to confirm a carotid paraganglioma which along with splaying shows an intense tumor blush and early emptying of the tumor knows as the “early vein sign” due to arteriovenous shunting.
Histologically, schwannomas (also referred to as neurilemmomas) are benign encapsulated nerve sheath tumors composed primarily of Schwann cells in a poorly collagenized stroma. Similar findings were seen in our study as all patients except those suspected to be carotid paragangliomas were subjected to FNAC preoperatively. Final histopathology correlated with the cytological diagnosis established by FNAC in 100% of the cases in our study. Various studies in the past have established the sensitivity and specificity of FNAC for parapharyngeal lesions to be around 96% and 99%, respectively. Final histopathology of schwannomas showed benign spindle cells with wavy nuclei and hypercellular (Antoni A) and hypocellular (Antoni B) areas. Immunohistochemistry is required in cases not diagnosed by histopathology.
Schwannomas are the most common neurogenic neoplasm of the PPS as seen in our study as well. In the majority of the cases, cervical schwannomas are found in young- and middle-aged people between the age group of 30 and 70 years as seen in our study as well. There is no sex predilection. The most common site of origin is the vagus nerve, while the sympathetic chain is second. These can also originate from cranial nerves IX, XI, and XII. Less than 1% undergo malignant change. Two types are distinguished, central or peripheral schwannoma, located in bone or in soft tissues, respectively. Because schwannomas arise outside the involved fascicle, they tend to compress the nerve fascicles to the periphery as they enlarge and can usually be dissected free of all structures except the parent fascicle.
Paragangliomas also known as chemodectomas are the second most common neoplasm of the PPS. They arise from the nodose ganglion of the vagus nerve, extend into the PPS from the carotid body, or extend inferiorly from the jugular bulb. These are also retrostyloid masses. The glomus vagale from the vagus nerve is the most common type. Malignancy has been reported as 10%. These tumors are of neural crest origin and can secrete catecholamines causing hypertension and flushing which was not seen in our series, where 24-h vanillylmandelic acid was found to be within normal range.
Neurofibromas are the third most common neurogenic tumor of the parapharyngeal space. They originate from the Schwann cells and perineural fibroblasts. These tumors are unencapsulated, and intimate involvement of the nerve of origin is common. Sites of origin include the vagus nerve, glossopharyngeal nerve, sympathetic chain, and spinal accessory nerve. These lesions are often multiple and can be associated with neurofibromatosis type I as seen in our case as the patient presented with multiple subcutaneous nodules all over the body, café au lait spots, and axillary freckling.
Common types of surgical approach of PPS are transcervical External approach (EA) with/without digastric muscle section with or without resection of the submandibular gland, transcervical approach with/without mandibulotomy, and transoral approach with/without mandibulotomy. Also used are transparotid approach and infratemporal approach of PPS tumors. Transcervical approach is the most common method for removal of most poststyloid PPS tumors. Transoral approach can only be used for benign tumors confined to the PPS which is localized to the posteromedial aspect of poststyloid compartment and in the prestyloid compartment not extending lateral to stylomandibular ligament. We also used transoral approach for tumors confined to PPS located medial to great vessels which were nonvascular, palpable transorally, and proven nonmalignant lesions on FNAC. All transoral surgeries were done under general anesthesia with nasotracheal intubation. A transoral pharyngotomy was performed by linear vertical incision through the overlying mucosa followed by division of mucosa, submucosa, and superior constrictor muscles with electrocautery. Dissection was carried out down to the level of the tumor with assistance of 0° and 30° rigid endoscopes. Meticulous sharp and blunt dissection was used to expose and completely free the tumor while making no sure no injury was inflicted to the capsule and surrounding neurovascular structures [Figure 6]. ICA, IJV, and lower cranial nerves were identified and protected. The tumor mass was removed en bloc in cases where it was possible and in piecemeal if it was big. In a large, FNAC-confirmed schwannoma, piecemeal excision was done where reaching the lateral aspect of the tumor was difficult in order to avoid injury to critical structures such as IJV and ICA. Postoperative management included perioperative steroid therapy and intravenous antibiotics along with airway observation in a monitored setting during the 1st postoperative day. Patients were started on a liquid diet on the 3rd–4th postoperative day.
|Figure 6: Intraoperative image showing schwannoma being operated using an endoscopic-assisted transoral approach|
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It was Work and Hybels in the year 1974 to advocate transoral approach for treatment of PPS neoplasms. However, a detailed step-by-step anatomical description of the transoral access was made by Dallan et al. in their study who stated that “it has an excellent surgical window that achieves greater exposure for the resection of PPS lesion.” Although there have been few recent reports claiming the transoral route operated cases with confirmed recurrences, patients should be carefully examined and only ideal candidate for the transoral approach should be chosen. However, All four patients operated via the transoral approach in our study had an uneventful postoperative period with no neurological deficits or recurrences.
A transcervical transparotid approach identifies and preserves various structures such as the facial nerve, external and ICAs, IJV, the cranial nerves IX, X, XI, and XII, and the sympathetic nervous system chain. We used transcervical approach for 11 out of 15 cases with satisfactory tumor clearance. Ten patients had no postoperative complications. Sural nerve grafting was done for the patient with vagal neurofibroma and complained of change in voice and regurgitation postoperatively for which type 1 thyroplasty was performed along with swallowing exercises and the patient showed significant improvement. If FNAC indicates schwannoma, a subcapsular dissection can be done to avoid injury to nerve of origin. Secondarily, mandibulotomy can be performed during a transcervical approach to improve access to the PPS, when the tumor is big and extending to the skull base. The mandibular ramus restricts superior and medial access to the PPS. A mandibulotomy should be considered for select patients including malignant neoplasms, recurrent neoplasms, large benign neoplasms, and highly vascular neoplasms with the need for improved vascular control and skull base extensions. It can be of various types including single or double mandibulotomy or a vertical and horizontal osteotomy. However, a single vertical paramedian osteotomy between the ipsilateral mandibular canine and first premolar teeth is the most commonly performed. In our study, however, adequate access was obtained in all cases without the need of a mandibulotomy.
| Conclusions|| |
Neurogenic tumors of PPS are more common than traditionally thought, with schwannoma being the most common neurogenic tumor seen. Neck swellings and oropharyngeal masses are the most common presenting features, and any patient presenting with these should undergo a complete head-and-neck examination along with radio imaging using CECT and contrast MRI. FNAC is a very useful tool to establish a preoperative cytological diagnosis. EATA is an effective approach, provided that the tumor is localized to the posteromedial aspect of poststyloid compartment and in tumor arising de novo in prestyloid compartment. Transcervical approach can be used in tumors localized lateral to carotid vessels, paragangliomas, and with the option of mandibulotomy in selected cases requiring increased access.
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Conflicts of interest
There are no conflicts of interest.
This material has never been published and is not currently under evaluation in any other peer-reviewed publication.
The permission was taken from Institutional Ethics Committee prior to starting the project. All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.
Informed consent was obtained from all individual participants included in the study.
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