Fig. 13.1
Axial T1-weighted with gadolinium magnetic resonance images of a 78-year-old patient with prestyloid parapharyngeal pleomorphic adenoma; (a) preoperative, (b) 2 months postoperative
13.2 Surgical Anatomy
The parapharyngeal space (PPS) is a potential space lateral to the oropharynx. The PPS is shaped like an inverted teepee, extending from the skull base superiorly to the greater cornu of the hyoid bone inferiorly. The PPS is bound medially by the superior pharyngeal constrictors and laterally by the medial pterygoid muscle, mandibular ramus, and deep lobe of the parotid gland. The anterior border of the PPS is the pterygomandibular raphe and the pterygoid fascia. Posteriorly, the PPS extends to the cervical vertebrae and prevertebral muscles. An important landmark in the PPS is a fascial band extending from the styloid process to the tensor veli palatini. This structure further divides the PPS to an anteromedial compartment (i.e., prestyloid) and a posterolateral (i.e., poststyloid) compartment. The prestyloid compartment contains the retromandibular portion of the deep lobe of the parotid gland, adipose tissue, and lymph nodes associated with the parotid gland. The poststyloid compartment contains vital structures like the internal carotid artery, the internal jugular vein, CNs IX–XII, and the sympathetic chain.
13.3 Preoperative Evaluation
Patients should be assessed for cranial neuropathies, breathing disturbances, and trismus. Physical examination should include palpation of the neck and the parotid gland in search of lymph node metastases. Cranial nerves are evaluated. Mouth opening might be limited due to extension of the tumor into the pterygopalatine fossa. Mouth opening is particularly important since relative contraindications to TORS include inadequate oral exposure and limited cervical spine mobility. The extent of the oropharyngeal mass should be evaluated with flexible fiber optic evaluation of the oropharynx.
Imaging should include magnetic resonance imaging (MRI); however, contrast computerized tomographic (CT) scans are acceptable. Visualization of a vascular flow void on an MRI study is usually sufficient for the diagnosis of a vascular tumor such as a paraganglioma, but magnetic resonance angiography (MRA) may be added for a more precise diagnosis. If a malignant tumor is suspected, radiological staging is completed using a positron emission tomography-CT hybrid (PET-CT) for assessing the presence of regional and distant metastases. Surgeons must be acutely aware of a more medial position of the carotid artery as it passes through the PPS.
Preoperative tissue evaluation with fine needle aspiration (FNA) biopsy should be obtained, particularly in the setting of a suspected salivary gland malignancy or an enlarged lymph node. When radiographic studies are diagnostic of a vascular lesion, biopsy is not recommended. Awareness of the potential pathologies that might be encountered is important, and imaging should precede FNA, to avoid potential bleeding.
13.4 Operative Technique
13.4.1 Patient Positioning
The patient is placed in a supine position and is nasally intubated via the contralateral nostril. The operating table should be positioned with the patient’s head away from the ventilator to allow space for the robotic cart to fit under the bed. The patient should be positioned in the patient supine with a horizontally oriented shoulder roll. The patient’s arms do not need to be tucked for TORS; however, if a transcervical approach is expected, both arms should be tucked. Sterile draping is not required if TORS is done alone.
Suspension pharyngoscopy using the Feyh-Kastenbauer (FK) laryngeal retractor (Gyrus AMI, Southborough, MA) is performed, and the patient is placed in suspension. A 2-0 silk suture through the anterior tongue is placed for retraction to maximize exposure; gauze is positioned between the teeth and tongue to avoid tongue laceration. The patient’s eyes are protected with Opti-Guard® safety goggles.
13.4.2 Robot Setup
The da Vinci Surgical System (Intuitive Surgical, Inc., Sunnyvale, CA) is docked diagonally to the patient’s bed. The bed should be lowered to accommodate the robotic arms. A 0° 8°mm camera is installed and inserted to the mouth. The robotic arm ipsilateral to the lesion is installed with a 5 mm monopolar cautery with a spatula tip. Maryland dissector forceps is installed in the arm contralateral to the tumor. The robotic arms are positioned so that instrument tips are within the field of view of the endoscope with minimal angulation. As such, they are approximately parallel to the optical arm, minimizing collision with each other.
An assistant is positioned at the head of the bed. The assistant must be familiar with endoscopic techniques since he will be working off of the screen rather than by direct visualization. Moreover, the assistant must be familiar with the robot to troubleshoot device failures and interference of the arms. The assistant is equipped with a Yankauer suction, bipolar diathermy and LigaSure™ 5 mm blunt tip 23 cm for vessel sealing, atraumatic grasping, and blunt dissection. The latter enables cutting independent of sealing.
13.4.3 Dissection
The procedure is initiated with an incision over the prominent aspect of the mass, through the oropharyngeal mucosa, from superior to inferior. In case there is no prominence at the oropharynx, an inverted L-shaped incision is used along the lateral aspect of the anterior tonsillar pillar (Fig. 13.2). Next, dissection is undertaken through the submucosal muscle layer (Fig. 13.3). Traction and countertraction are important for dissecting through the superior constrictor musculature. Dissection through the superior constrictor muscles with the tip of the Bovie cautery eventually leads to an identification of the mass capsule (Fig. 13.4). At this stage, a well-defined plane is identified, and dissection proceeds along the mass (Fig. 13.5). As mucosal flaps are developed, lateral retraction of the anterior tonsillar pillar using pillar retractor or a suture increases exposure to the parapharyngeal space. The palate can be retracted anteriorly using a soft rubber catheter placed in the nose.
Fig. 13.2
Inverted L-shaped incision over anterior pillar mucosa
Fig. 13.3
Raising submucosal flaps at the palatoglossal fold
Fig. 13.4
Exposure of the superomedial aspect of the tumor
Fig. 13.5
Anterior tumor exposure
The Maryland dissector is used to gently grasp the superior constrictor musculature and pull it medially, and a combination of Bovie electrocautery and blunt dissection is used to further define the capsule. At this stage, the parapharyngeal fat may be visualized. The assistant can help with blunt dissection and retraction of soft tissues. When the anteromedial aspect of the mass is defined, a higher magnification can be used to appreciate its size and extent. If accessible, the inferior aspect of the mass is grasped and pulled medially to assist with the lateral dissection (Fig. 13.6). In case of a benign cystic mass, it can be decompressed at this stage, to facilitate its mobilization within the narrow confines of the oral cavity and to address the remaining superior-lateral attachments. The more cephalad medial pterygoid muscle may be visualized, and further lateral dissection should be avoided to minimize exposure of the carotid artery.
