TITLE: Surgical Approaches to the Oropharynx
SOURCE: Dept. of Otolaryngology, UTMB, Grand Rounds Presentation
DATE: January 13, 1999
RESIDENT: Karen Stierman, M.D.
FACULTY: Christopher Rassekh, M.D.
SERIES EDITOR: Francis B. Quinn, Jr., M.D.

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"This material was prepared by resident physicians in partial fulfillment of educational requirements established for the Postgraduate Training Program of the UTMB Department of Otolaryngology/Head and Neck Surgery and was not intended for clinical use in its present form. It was prepared for the purpose of stimulating group discussion in a conference setting. No warranties, either express or implied, are made with respect to its accuracy, completeness, or timeliness. The material does not necessarily reflect the current or past opinions of members of the UTMB faculty and should not be used for purposes of diagnosis or treatment without consulting appropriate literature sources and informed professional opinion."


Anatomy

The oropharynx connects the nasopharynx and oral cavity to the hypopharynx. It extends from the level of the hard palate to the level of the hyoid bone. The oropharynx opens into the oral cavity anteriorly and is bounded by the circumvallate papillae, anterior tonsillar pillars, and the junction of the hard and soft palates. Anatomical regions of clinical significance include the lateral walls or tonsillar region, posterior wall, base of tongue, and the soft palate.

The pharyngeal walls are made of multiple layers of mucosa, submucosa, pharyngobasilar fascia, constrictor muscles, and buccopharyngeal fascia. The lateral walls of the oropharynx include the anterior and posterior tonsillar pillars, the tonsillar fossa, and a small portion of the lateral pharyngeal wall. The palatine tonsil lies within the tonsillar fossa. The soft palate projects posteriorly and downward into the oropharynx and is composed of the palatine aponeurosis and the following muscles: tensor veli palatini, levator veli palatini, the uvular muscle, palatoglossus, and the palatopharyngeus. The base of tongue in the anterior oropharynx extending from the circumvallate papillae to the pharyngoepiglottic and glossoepiglottic folds. The lingual tonsils lie superficial and on the lateral sides of the base of tongue. The irregular surfaces of the tongue base and tonsils make it difficult to identify small tumors. For this reason, panendoscopy with biopsy is often necessary to evaluate lesions in these areas.

The oropharynx is supplied with sensory and motor innervation mainly through the glossopharyngeal and vagus nerves. The hypoglossal nerve supplies motor innervation to the base of tongue and the trigeminal nerve (V2, V3) provided the motor and sensory innervation of the soft palate. The vagus and glossopharyngeal nerves have tympanic and auricular branches which make otalgia a frequent complaint in patients with tumors in this area.

The blood supply to the oropharynx is mainly from branches of the external carotid artery. Levels II and III of the neck provide most of the lymphatic drainage. Central structures such as the tongue base, soft palate, and the posterior pharyngeal wall drain to both necks. The posterior pharyngeal wall and the tonsillar region also drain to the retropharyngeal nodes. There is a high incidence of palpable and occult neck metastasis in cases of oropharyngeal cancer.

The oropharynx is surrounded by two potential fascial spaces. The retropharyngeal space is an area of loose connective tissue that lies between the buccopharyngeal fascia of the pharynx and the alar layer of the prevertebral fascia. It extends from the skull base to the superior mediastinum. It communicates with the parapharyngeal space laterally. The parapharyngeal space is defined by the space from the skull base to the hyoid bone lying lateral to the pharyngeal walls. The parapharyngeal space can be further be divided into prestyloid and poststyloid compartments by a layer of fascia that runs from the tensor veli palatini to the styloid. The prestyloid compartment contains fat, deep lobe of the parotid, and a small branch of the trigeminal nerve to the tensor veli palatini. The poststyloid compartment contains the carotid artery, jugular vein, cranial nerves IX to XII, sympathetic chain and lymph nodes.

Surgical Considerations

Most oropharyngeal tumors are operable. However, extension into the poststyloid compartment, prevertebral fascia or involvement of the carotid artery decreases the chances of curing the cancer to nearly zero. The tumors are normally resected with 1-2 cm border of grossly normal tissue. Frozen sections are taken from all margins until clear. Oropharyngeal cancers can be resected through three main surgical approaches. These include the transoral, transpharyngeal, and transmandibular approaches. The choice of approach depends on the size and location of the tumor and if a concomitant neck dissection is planned.

Preoperative assessment is crucial when deciding on which approach to use.

Visual inspection and palpation are the most accurate ways on determining the dimension of the tumor in the oral pharynx. Lesions in the soft palate, tonsil, and proximal tongue base may be best accessed through a mandible sparing procedure if the mandible is not involved. Adequate exposure is very important to ensure appropriate margins have been taken. When assessing the patient, note whether the entire lesion can be palpated in the office, whether or not it is fixed to the mandible, and if there is gross bony involvement.

Determination of bony involvement can be difficult preoperatively. Imaging studies, such as CT or MRI should be considered. Over 60% of the bone mineral must be lost before radiographic changes can become evident. Invasion of the mandibular cortex is best studied by CT scans. MRI, however, more accurately identifies spread through the medullary space. Technitium-99m bone scans may provide some benefit. The most accurate method of determining bony involvement seems to be direct intraoperative inspection. If the periosteum strips cleanly from the bone intraoperatively, then invasion of the bone is unlikely. Other imaging studies include plain films and Dentascan.

Neck dissection also needs to be considered preoperatively, especially in the case of squamous cell carcinoma(SCCA). In cases of neck disease or suspected neck disease, the neck should be treated with surgery or radiation therapy. In the case of surgery, which levels should be included in the dissection remains very controversial. Most commonly zones I, II and III are involved and should be considered for removal in the N0 neck in the case of a SCCA primary. In cases with palpable nodes or if the primary is large, a modified radical neck dissection or radical neck dissection may be necessary. If the tumor is in the tongue base, approaches the midline, or if large nodes are in the ipsilateral neck, a contralateral neck dissection should be considered. In most cases, a selective dissection of levels I - III should be sufficient.

Transoral Approaches

Transoral approaches include the oral approach and the lip splitting approach without mandibulotomy. The oral approach removes the tumor through the mouth with no external incisions. Due to its limited exposure, it is good for small(T1), superficial, or exophytic cancers of the upper or anterior oropharynx(e.g. soft palate, posterior pharynx, or anterior tonsillar pillar). A tumor that extends too far inferiorly(i.e. past the tip of the epiglottis) or too far laterally are not accessed well with this approach. In deciding whether to use this approach, the presence of trismus, obstructing dentition, excessive soft tissue, and the height of the mandible needs to be considered. Tumor involving the tonsillar fossa and soft palate can be exposed using an oral mouth gag such as a Crowe-Davis gag. The initial mucosal incision should be made as far posteriorly or inferiorly because this portion of the tumor will be the most difficult to visualize later on as the tumor is being elevated. The mucosal incision is then brought around both sides of the tumor to the most anterior or superior portion. The incision is then deepened. Before the specimen is freed, a suture should be placed to mark the specimen. This same suture can be used for traction. Once the tumor is removed, make sure that it is properly marked for the pathologist. Margins should then be taken from the specimen or the patient. Once margins have be read as clear, the issue of wound closure can be addressed. Posterior pharyngeal wall defects usually do not require skin grafting. The incised margins of the mucosa can be sutured to the prevertebral fascia in order to close the prevertebral space from oropharyngeal secretions. Tonsillar fossa and palatal defects can be left open to heal if small. If the defect is large and neck spaces are exposed, a split thickness skin graft can be used to help isolate the oral cavity from the neck. The graft if used will require a bolster and necessitate a tracheostomy if it interferes with an adequate airway. The lip splitting approach is discussed in the section on transmandibular approaches.

Transoral/Transcervical combined approach

Lingual-mandibular release is indicated mostly for base of tongue lesions. An incision is made through the floor of the mouth beginning at one tonsillar pillar and extending to the other pillar. This releases the tongue and floor of the mouth in order to pull these structure below the mandible into the neck. This technique does not require a mandibulotomy. However, if better access is desired into the parapharyngeal space, a transmandibular approach should be considered. Structures at risk for damage include the lingual arteries and nerve and the hypoglossal nerve.

Transpharyngeal approaches

Transpharyngeal approaches include the suprahyoid pharyngotomy and the lateral pharyngotomy. The suprahyoid pharyngotomy is used for small tumors of the base of the tongue and the pharyngeal walls(especially posterior). Entrance into the pharynx is through the vallecula. This procedure allows preservation of the lingual arteries and nerve and the hypoglossal nerve. Extension of the pharyngotomy laterally and inferiorly along the thyroid ala allows wider exposure. The main downfall of this approach is poor visualization of the superior margin of large tumors and in the worst case the possibility of cutting into tumor. This technique however provides excellent functional and cosmetic outcome.

The lateral pharyngotomy is also useful for small tumors of the base of tongue and pharyngeal walls. The pharynx is entered posterior to the thyroid ala on the least diseased side. Care must be taken to dissect and protect the hypoglossal and superior laryngeal nerves. Once in the pharynx, the larynx is retracted to the opposite side. This allows a good view of the posterior pharyngeal wall, opposite lateral wall, and base of tongue. If more superior exposure is needed, the pharyngotomy can be extended across the vallecula or this approach can be combined with a lateral mandibulotomy. The lateral mandibulotomy results in transection of the inferior alveolar nerve and risk of osteoradionecrosis if radiation is planned to this site.

Transmandibular approaches

Transmandibular approaches include mandibulotomy procedure and mandibulectomy procedures. If the patient has a full set of teeth, limited mouth opening, or a posterior location of the tumor, a mandible splitting approach should be considered. If neck dissection is planned, the tumor can be removed with the neck nodes en bloc if the neck dissection if left attached medial to the mandible.

Mandibulotomy should be avoided when the tumor has invaded the bone or the periostium of the mandible. In these cases, mandibulectomy should be considered. Mandibulotomy procedures include the lip splitting approach, the midline labiomandibular glossotomy, and the mandibular swing approach. The site of the mandibulotomy is based on the presence of dentition and the fact that it should be made between the two mental foramen. Lateral mandibulotomy, performed through the body of the mandible, is routinely not done due to the high complication rate in patients who required post operative radiation. This is due to division of the artery in the mental canal which results in ischemic necrosis when coupled with radiation injury. Therefore, most surgeons prefer to make the mandibulotomy anterior to the mental foramen. Making the mandibulotomy go through a tooth socket to help support the reconstruction plate. This may require a tooth extraction. However, incisor teeth are rarely extracted for this, therefore the bone cut is usually through a bicuspid tooth socket. If the mandibulotomy is performed between two teeth, both teeth may be lost.

The mandibulotomy may be a vertical, stair-step, or deep V(arrowhead) configuration. Prior to the osteotomy, a reconstruction plate should be selected and adapted to the mandible. Screw holes should be drilled. Do not place the osteotomy posterior to the mental foramen as this results in division of the inferior alveolar nerve, worse exposure, and as stated before, increased risk for osteoradionecrosis. After the mandibulotomy, the mandible is retracted laterally and the soft tissue is then incised. A cuff of 1 cm of the floor of mouth mucosa is left on the mandible for use in closure.

Most of the transmandibular approached require splitting of the lower lip. Some sources recommend using a scalpel to mark the vermilion border horizontally prior to lip splitting in order to facilitate reapproximation. There are many approaches to lip splitting. Most simply, a vertical incision can be carried through the full thickness of the lip, the mentum and into the upper neck. The lip is split in the midline if the marginal mandibular nerve is sacrificed to prevent eversion of the paralyzed lip with scarring. Another approach is the modified zigzag stepped technique which minimizes the risk of vermilion contracture. This technique also does not disturb the contour of the chin skin or damage the facial or mental nerves. The incision begins with an off-midline incision through the vermilion with a horizontal triangular flap at the border. This incision is extended vertically to the mental crease. Then the incision is carried around the chin pad in a broken geometric line which forms a half hexagon flap. Then the incision is connected with a high cervical incision with moderately sized triangular flap through the submentum. In those patients with a vertical cleft in the chin, the incision is made through this natural concavity.

The midline labiomandibular glossotomy is rarely used. It is useful for small and inferior midline posterior pharyngeal wall tumors ,small midline tongue base lesions, and inferior nasopharyngeal and clival tumors. When addressing nasopharyngeal or clival tumors, the palate must be split and retracted anteriorly. In this approach, the lip, gingiva, mandible, and anterior tongue are split in the midline. The incision can be carried through the base of tongue to the hyoid bone if exposure of the posterior pharyngeal wall is necessary. The hypoglossal and lingual structures are usually not injured.

The mandibular swing approach provides exposure of the entire oropharynx. It is the procedure of choice for an en bloc resection of the tumor and neck lymph nodes. It is useful for tumors that do not involve the mandible, for tumors that involve multiple sites, and for tumors that involve the parapharyngeal space. Neck dissection, if indicated, is performed first. The lip is then split as described in the lip splitting approach. The osteotomy is placed anterior to the mental nerve on the ipsilateral side at the site of a missing or extracted tooth. A full thickness cut is then made through the floor of the mouth until the anterior margin of resection is reached. This cut usually requires transection of the lingual nerve. The mandible and the tongue are then retracted exposing the tumor. Exposure for posterior oral cavity or oropharyngeal tumor sites is improved when the mylohyoid muscle is divided while the submandibular gland and its duct are retracted medially. The tumor is then removed with margins. Closing the soft tissue defect may require a flap. Reapproximating the mandible is performed using compression plates with two screws on either side of the mandibulotomy site.

Mandibulectomy with oropharyngeal composite resection is necessary if the mandible is grossly involved with tumor and in cases when mandibular invasion cannot be ruled out. Squamous cell cancer that is large enough to warrant mandibulectomy usually requires a neck dissection. In those patients where neck disease is suspected, radiation therapy or surgery should be considered. Tracheostomy should be considered as it is necessary in many cases to prevent airway obstruction and aspiration.

Mandibular resection may either be segmental or marginal. In a segmental resection, the condyle to condyle continuity is disrupted by removing all or a portion of the ramus, angle, body, and parasymphysis. This is typically used for tumors with gross involvement of the mandible itself. In a marginal mandibulectomy, a portion of the mandible, typically the alveolus and the medial plate, is resected leaving the continuity intact. If the tumor is fixed to and only involving the periostium, a marginal mandibulectomy should be considered. Once the cancer has accessed the marrow spaces, tumor cells can spread not only to the marrow, but also to the neurovascular bundle. In the case of marrow spread, care must be taken to get wide margins of at least 2 cm beyond the visible extent of bony involvement.

As stated before composite resection usually begins with a neck dissection. The specimen is usually left attached superiorly at the periostium of the mandible. The dissection is continued over the periostium of the lateral plate of the mandible anterior to the masseter muscle. The masseter is then elevated from the angle of the mandible and the periostium is incised. If the tumor invades the soft tissue lateral to the mandible it may be necessary to sacrifice the facial artery and marginal mandibular nerve in order to get to the prevascular and postvascular nodes and the tumor out. Next, a lip splitting incision is usually used for access into the oral cavity. The lip is split and a cheek flap is begun by incising the full thickness of the buccogingival sulcus anterior to the tumor. As the flap is elevated, the mental nerve will have to be divided. Note, the periostium of the outer mandible may be left on the cheek if uninvolved with tumor. Wide stripping of the periostium at the site of mandibulotomy should be avoided as it devascularized the bone.

The anterior mandible cut is made with adequate margins from the tumor. Maximum preservation of the mandibular body is important. Placing the bone cut anterior to the planned mucosal cut will simplify coverage of the end of the bone. The osteotomy is made using a Gigli saw or a reciprocation power saw. Frozen sections of the inferior alveolar nerve are analyzed for tumor involvement. If there is mandibular canal invasion and/or the nerve sections are positive, the entire canal must be resected. This is the case because there is not a reliable method to determine bony tumor extension intraoperatively. The cranial mandibular cuts are made through the ramus again with adequate margins of uninvolved tissue. If the ramus is involved, the coronoid and the condyle are resected. The mandible is retracted laterally once the two cuts are complete and the tumor is removed. If the coronoid process is left on the specimen, the surgeon must divide the temporalis muscle. The disadvantage of this method is the functional and cosmetic deficits.

An alternative to the lip splitting approach to the oral cavity is the visor flap. An intraoral incisions is made in the buccogingival sulcus without a lip-split to allow elevation of the cheek flap as a visor. A suture can be placed at the tip of the tongue or on its lateral margin to stretch the mucosa prior to making the incision. The incision may be extended into the contralateral gingivolabial sulcus but care must be taken to avoid the contralateral mental nerve. The neck incision is then connected with the intraoral incision. Visor flaps have the following drawbacks: they can result in division of both mental nerves and they sometimes provide inadequate posterior exposure in the case of large tumors.

Reconstruction is accomplished by first reapproximating the floor of mouth mucosa. If a mandibulotomy was performed, the mandible is then plated with a dynamic compression plate(DCP) in edentulous patients to help ensure a watertight seal of the mucosa. DCPs can be inappropriate in patients with good dentition as they can modify occlusion. The lip and other soft tissues are then reapproximated. The lip should be closed in three layers: the orbicularis muscle, mucosa and skin. In the case of a mandibulectomy or composite resection, various techniques are available for reconstruction. Most commonly, the missing mandible is reconstructed using free vascularized bone or a metal construction plate covered by free vascularized or pedicled soft tissue. The worst complication associated with transmandibular approaches is mandibular nonunion and osteomyelytis.

Summary

The four main approaches to oropharyngeal tumors are transoral, transoral/transcervical, transpharyngeal, and mandibular splitting approaches. It is very important to take the time to perform a detailed history and physical exam when selecting which approach to take. The surgeon must also consider the type, size and location of the tumor to be excised. Bony involvement must be assessed as well. Selecting the proper approach preoperatively will save the surgeon time and frustration and benefit the patient by assuring adequate tumor resection.


Bibliography

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