42.1
Prestyloid and Poststyloid Tumors
The parapharyngeal space is a potential space in the deep neck, shaped like an inverted pyramid. The fascia, running posteriorly from the styloid process to the tensor veli palatini muscle, divides the parapharyngeal space into the prestyloid and poststyloid compartments.
It is difficult to evaluate tumor presence until they grow to at least 2.5–3 cm. The most frequent symptom and sign is an intraoral swelling (50%) or a cervical mass (47%). Other symptoms can be otalgia, dysphagia, and dysphonia.
Most parapharyngeal tumors are primary tumors. Approximately 70 different histologic subtypes of parapharyngeal space tumors are reported as 80% benign. Salivary gland tumors and neurogenic tumors comprise approximately 45% and 40%, respectively. Nasopharyngeal carcinoma can extend into the parapharyngeal space. Malignant tumors can metastasize to lymph nodes of the parapharyngeal space, most commonly thyroid cancer.
Imaging and Fine Needle Aspiration Cytology
Computed tomography (CT) and magnetic resonance imaging (MRI) are essential, providing important information including location, size, and lymph node metastasis. The prestyloid mass displaces the parapharyngeal fat and carotid sheath contents posteriorly. Neurogenic tumors of the poststyloid compartment can displace the internal carotid artery (ICA) and internal jugular vein (IJV) in different directions. Vagus schwannomas typically grow and separate the ICA and the IJV, whereas cervical sympathetic trunk schwannomas usually displace the ICA and the IJV together.
Fine needle aspiration cytology (FNAC) is considered useful; however, it can be inconsistent. It can be performed transorally or transcervically with CT or ultrasound-guided aspiration for small tumors. The overall diagnostic accuracy and nondiagnostic rate of FNAC are 94% and 25%, respectively. FNAC for schwannomas can be inconclusive in half of cases. Transoral biopsy can result in bleeding, tumor spillage, and injury to the ICA and the cranial nerves.
Surgical Approaches
Surgical candidates include patients with primary malignant tumors, salivary gland tumors, neurogenic tumors with pre-existing nerve deficits, tumors with mass effect symptoms, and selected metastatic cancers such as papillary thyroid carcinoma. Most prestyloid salivary gland tumors can be removed with little morbidity. The decision to resect neurogenic tumors is based on the patient’s age, comorbidity, mass effect on the adjacent nerves, and patient preference. In elderly patients, an asymptomatic schwannoma with no nerve deficit can be observed. Importantly, in young patients, schwannomas can be removed to prevent the future functional loss of the nerve of origin.
The choice of surgical approach is based on the size, location, and vascularity of the tumor, suspicion of malignancy, surgical morbidity, relation to the major vessels, and proximity and projection of the tumor to the oropharyngeal wall or neck.
Prestyloid Tumors
Tumors in the prestyloid compartment are most commonly of salivary gland tumor, and the most common salivary gland tumor is pleomorphic adenoma (64%). Prestyloid salivary gland tumors originate from the deep lobe of the parotid gland (dumbbell tumor passing through the stylomandibular tunnel), retromandibular portion of the deep lobe of the parotid gland (round tumor), minor salivary gland of the parapharyngeal space (round tumor), tail of the superficial lobe of the parotid gland, and minor salivary gland of the pharyngeal mucosa.
The transcervical approach is most commonly used ( Fig. 42.1.1 ). A single transverse skin incision is made at the level of the hyoid bone. The skin flap is elevated, and the marginal branch of the facial nerve is identified. The mobilization of the submandibular gland and retraction of the digastric muscle provides direct access. The parapharyngeal tumor is sharply dissected from the surrounding tissues under direct vision or bluntly using fingers at the superior and medial part of the tumor, avoiding tumor rupture and seeding.
The transparotid-transcervical approach is ideally used for the round or dumbbell tumors ( Fig. 42.1.2 ) arising from the deep lobe of the parotid gland. Removal of the prestyloid deep lobe parotid tumor requires identification and mobilization of the facial nerve. The superficial lobe of the parotid gland is dissected and pedicled anteriorly. The submandibular gland is mobilized, and the deep lobe of the parotid gland is dissected. The stylomandibular ligament is divided, and the mandible is retracted anteriorly. The dissected superficial lobe may be removed or repositioned to minimize contour deformity and Frey syndrome. Exposure of the parapharyngeal space can be facilitated by the use of nasotracheal intubation, submandibular gland mobilization, division of the stylomandibular ligament, dislocation or the anterior retraction of the mandible, division of the styloid process, digastric, stylohyoid, and styloglossus muscles, and the use of muscle relaxation.
Advantages of a transoral approach to small prestyloid tumors include direct access, decreased morbidity, early oral intake, and avoidance of a cervical scar. There is limited exposure and risks of damage to vessels, hemorrhage, tumor rupture and spillage, incomplete tumor resection, and increased risk of infection due to saliva contamination.
The combined transoral and transcervical approach is for tumors that require partial resection of the pharynx.
Poststyloid Tumors
Tumors arising in the poststyloid compartment are mostly of neurogenic origin. Most (95%) are benign. The most common benign lesions are schwannomas and vagal paragangliomas, followed by neurofibromas. The most common origins of schwannomas are the vagus nerve and cervical sympathetic trunk. A schwannoma is a slow-growing, well-encapsulated round or fusiform tumor. Neurofibromas are nonencapsulated tumors with nerve fibers passing through the tumor, while paragangliomas are highly vascular, slow-growing lesions. The functional deficit of the vagus nerve is present in 20–50% of patients with vagal paraganglioma at the time of initial examination. Familial paragangliomas occur in patients with certain genetic mutations such as the succinate dehydrogenase complex subunit B, C, and D mutations.
The poststyloid tumors are usually accessed by a transcervical approach ( Fig. 42.1.3 ) with no need for dissection of the submandibular triangle. Intracapsular enucleation of schwannomas minimizes neurologic sequelae. This technique consists of the longitudinal incision of the capsule and a careful enucleation of the tumor to preserve the surrounding nerve fibers. Functional preservation rate after intracapsular enucleation varies and ranges from 69% to 90%. In intracapsular enucleation, microscopic tumor can remain between the nerve fibers leading to recurrence. No definitive data concerning long-term follow-up are available. Intracapsular enucleation is not feasible in neurofibromas and vagal paragangliomas.
