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Address reprint requests and correspondence: Kathryn M. Van Abel, MD, Department of Otolaryngology-Head and Neck Surgery, Mayo Clinic, 200 First St SW, ochester, Rochester, MN 55905.
Deep lobe parotidectomy (DLP) is a critical procedure to master for any head and neck oncologic surgeon. This procedure is indicated for any deep lobe malignancy, a superficial lobe malignancy with extension into the deep lobe, refractory inflammatory conditions, and the presence of metastatic disease within a superficial or periparotid lymph node. This article describes the relevant anatomy and steps required to perform a deep lobe parotidectomy with and without facial nerve sacrifice. In addition, the history of the procedure, patient work up, indications, and possible complications are discussed.
The history of salivary gland pathologies and management dates back to 2,500 BC when the use of belladonna was recommended to stop the excessive flow of saliva.
Despite increased knowledge gained from the study of cadaveric specimens, it was not until 1765 that the first parotidectomy was described by Lorenz Heister, a German surgeon, who stated, “I cannot meet with any direction for extirpation of the saliva, maxillary and parotid glands, which are frequently indurated and enlarged to a monstrous size.”
As surgeons became more comfortable with parotidectomy, the next challenge became preservation of the facial nerve, which was tackled in the beginning of the 19th century. Dr John Beale Davidge performed the first total parotidectomy in 1823, without anesthesia, and reported that complete removal of the gland was “almost impossible.”
In 1825, the German surgeon and professor John Ferdinand Heyfelder reported successfully preserving the facial nerve and maintaining postoperative function.
The techniques advanced to include careful descriptions of nerve dissections, such as that reported in “the Science and Art of Surgery” by Dr John Eric Erichsen in 1869, in which he wrote, “injury to this nerve is best avoided by dissecting out the tumor by incisions parallel to its main trunk and chief branches, and especially by draping the mass well forward.”
In 1941, Dr Hamilton Bailey proposed releasing the gland capsule and initially localizing the facial nerve trunk and the “pes anserinus,” he also was a proponent of the concept set forward by LJ McCormack that the parotid should be divided into a deep and superficial lobe by the facial nerve.
In the early 1950s, Henry Samuel Shucksmith and Hayes Martin advocated that the safest approach to preserve the facial nerve was antegrade dissection of the nerve before resecting the parotid gland tumor
techniques, which are the mainstay for parotid surgeons 65 years later.
Relevant anatomy
To understand the surgical management of disease, the challenges faced by our surgical predecessors and contemporaries alike, one must have an excellent working knowledge of the anatomy in this region. As the gland begins to form in the sixth week of gestation from oropharyngeal ectoderm, the adjacent regional mesoderm begins to form lymphatic networks and lymph nodes that become entrapped by the unencapsulated parotid parenchyma.
The parotid gland can be found in the preauricular region, invested by the superficial layer of the deep cervical fascia, or the parotid or parotidomasseteric fascia, which extends into the parotid parenchyma, separating it into lobules.
This fascia is separate from the superficial musculoaponeurotic system (SMAS). The SMAS lies just superficial to the parotidomasseteric fascia and extends to join the platysma inferiorly and the superficial temporal fascia superiorly.
The deep portion of the gland is positioned between the mastoid tip, boney and cartilaginous external auditory canal, the ramus of the mandible, the posterior border of the medial pterygoid muscles, and the prestyloid region of the parapharyngeal space.
To enter the parapharyngeal space from the deep lobe of the parotid, a tumor must pass through the stylomandibular tunnel that is created by the skull base, styloid process, stylomandibular ligament, and the ramus of the mandible. The parotid gland is separated from the submandibular gland by the stylomandibular ligament, which is a thickening of fascia representing the fusion of the superficial and deep layers of the deep cervical fascia to the parotid gland before it splits to surround the submandibular gland.
This landmark is important when considering deep lobe parotidectomy (DLP) and will be discussed below.
Access to the deep lobe requires control of several vascular structures. Superior to the gland sitting just in front of the ear at the level of the zygomatic arch are the superficial temporal artery and vein, with the facial nerve usually lying just anterior to these vessels and crossing them superficially.
In this region, one can also encounter the auriculotemporal nerve, a branch of the trigeminal nerve (V3), which runs parallel to the superficial temporal vessels and anterior to the external auditory canal.
Inferior to the gland, the surgeon must identify the external carotid artery, which passes deep to, or through, the parenchyma of the gland. This is easily identified between the posterior belly of the digastric and the styloglossus muscle inferior to the mandible. Inferiorly, the superficial temporal veins and maxillary veins converge to form the retromandibular vein. If an operation requires dissection beyond the deep lobe, the surgeon must be aware that anteromedially lay both the internal carotid artery (ICA) and internal jugular vein.
The depth of the ICA can be roughly gauged based on the understanding that the styloid process sits lateral to the ICA as it enters the skull base. The final artery of interest is the internal maxillary artery, a terminal branch of the external carotid artery that passes medially to supply the infratemporal fossa and pterygopalatine fossa.
Finally, understanding of the parotid lymphatic basin is important in order to determine extent of surgery when dealing with metastatic disease to the parotid or primary parotid cancer with a propensity for lymphatic spread. During embryogenesis, lymph nodes become integrated into the parotid gland, both within the superficial and deep lobes. While initially considered 2 lymphatic levels, recent studies now support the interconnectivity of these lymph nodes and their lymphatic channels. The nodal distribution tends to mirror the amount of gland in the lobe, with 80%-90% of the nodes occurring in the superficial lobe or periglandular region and 10%-20% occurring in the deep lobe. This translates into a mean of 7 nodes (range: 3-19) found in superficial specimens versus a mean of 2 (range: 0-9) within deep specimens.
Patients presenting with deep lobe parotid tumors typically fall into 1 of 2 categories: (1) those presenting with a benign lesion that was found incidentally or has minimal associated symptoms (eg, recent onset of snoring) and (2) those presenting with a malignant mass and symptoms ranging from pain, numbness, facial nerve dysfunction, trismus, or overlying skin changes.
On exam, these lesions may be challenging to palpate, especially in those with elevated body mass indexes. In tumors that extend into the parapharyngeal space, it is possible to see palatal or lateral pharyngeal wall displacement. Mobility of the tumor is important; however, it can be challenging to assess.
While controversial, many authors recommend preoperative needle biopsy as a low-risk diagnostic tool that can improve preoperative counseling for patients. In the literature, the nondiagnostic rates for fine needle aspiration biopsy of parapharyngeal space lesions range from 21% to 31%.
In the future, there may be a role for genetic testing using markers, such as PLAG-1 for pleomorphic adenoma, to help clarify diagnoses and differentiate potential cytopathologic mimics such as adenoid cystic carcinoma or carcinoma ex-PA from pleomorphic adenoma.
However, core needle biopsy requires a larger bore needle, which is stiffer and harder to navigate, may increase the risk of hemorrhage or nerve injury and may increase the risk of tumor seeding and subsequent recurrence.
Finally, regardless of the bore of the needle, image guidance, be it ultrasound or computed tomography (CT), is often necessary in order to effectively target deep lobe parotid tumors that are hard to palpate and target.
Imaging of deep lobe parotid tumors is critical and provides important information about the size, extent, and borders of the tumor, the location of important adjacent structures, and the status of regional lymph nodes. Magnetic resonance imaging allows for excellent soft tissue resolution, tumor evaluation, and assessment of perineural invasion.
A CT scan with contrast through the neck and face (the exact protocol will depend on the location of the tumor and institutional preferences) can offer insight into the status of the mandible, temporal bone, styloid process, and skull base.
Finally, positron emission tomography/computed tomography (PET/CT) scans can assist in the workup for malignant disease but should be interpreted with caution as many benign inflammatory conditions and benign tumors (eg, Warthin tumor, oncocytoma) are fluorodeoxyglucose (FDG) avid.
When evaluating a deep lobe tumor, it is often acceptable to utilize more than 1 imaging modality to fully classify the tumor and complete workup. The primary question is often whether a tumor lies superficial or deep to the facial nerve, yet there is currently no study able to provide this information with any certainty. Landmarks that may help in orientation include the stylomastoid foramen, styloid process, mastoid process, posterior belly of the digastric, and the retromandibular vein (deep to the nerve).
Ultimately, the location of the nerve in relationship to the tumor can only be definitively ascertained at the time of surgery.
Differential diagnosis
The differential diagnosis for a deep lobe parotid mass closely mirrors that of superficial parotid masses. Considerations should include inflammatory (eg, chronic parotiditis, Sjögren syndrome, and sarcoidosis), congenital (eg, first branchial cleft cyst), and traumatic or neoplastic conditions. Neoplastic conditions can be broken down into primary benign (eg, pleomorphic adenoma, Warthin tumor, and oncocytoma), primary malignant (eg, mucoepidermoid carcinoma, adenoid cystic carcinoma, and adenocarcinoma), metastatic (eg, skin cancer and lung cancer), and systemic (eg, lymphoma).
Preoperative counseling
Surgeons should be prepared for all the options potentially necessary to treat a deep lobe tumor, with relevant risks and benefits thoroughly discussed with the patient. Patients should be counseled on planned incisions, temporary or permanent skin and ear lobe numbness, possible hematoma, seroma, sialocele or salivary fistula, infection, first bite syndrome, and Frey syndrome. Patients should be adequately counseled on temporary or permanent facial nerve injury, the possibility of facial nerve sacrifice and grafting, as well as the sequelae from facial nerve injury. For large or malignant tumors, patients should be prepared for the possibility of mandibulotomy or mandibulectomy if there is involvement of the mandible, and the aesthetic and functional impact this may have. Finally, patients should meet with radiation oncology and medical oncology prior to proceeding with surgery when possible if malignancy is suspected or confirmed. For those with likely benign tumors, a short discussion about the possible need for adjuvant therapy is often helpful when there is a surprise diagnosis of malignancy.
Indications for surgery
Surgical intervention is indicated for the majority of parotid neoplasms. Exceptions include benign tumors, such as a Warthin tumor, in a poor surgical candidate or for systemic disease such as metastatic lung cancer or lymphoma. However, surgery is the mainstay of treatment for most other indications. Specific indications for DLP include primary deep lobe tumors (benign and malignant), direct extension of tumors into the deep lobe, metastatic lymph nodes located within the deep lobe of the parotid gland, and for refractory inflammatory conditions.
Surgical decisions regarding management of the facial nerve, amount of gland to remove, and management of regional lymph nodes are largely dictated by the clinical findings and histopathology.
While previously controversial, there is rising evidence for total parotidectomy for management of the parotid nodal basin for malignant superficial parotid tumors with spread to superficial lymph nodes and for total parotidectomy when there is evidence of metastasis to the superficial parotid nodes from malignancies such as cutaneous squamous cell carcinoma and melanoma.
A partial DLP can also be selected for certain tumors, generally with facial nerve identification.
Management of the facial nerve
Unfortunately, there is currently no reconstructive option that perfectly replicates the normal function of the facial nerve. Therefore, if it is functioning preoperatively and there is no direct involvement of nerve by the tumor, every attempt should be made to preserve the nerve.
For patients that present with facial nerve paralysis on exam, tumor circumferentially obscuring the nerve, or obvious color or size changes from direct invasion, we recommend sacrifice of the nerve. In a review published in 2014, Lombardi et al discuss that when there is preoperative dysfunction, whether complete or partial, it is typically not possible to preserve the facial nerve.
Patients undergoing DLP should undergo endotracheal intubation under general anesthesia. For a deep or large tumor, access can be improved by using a nasotracheal intubation to allow for improved subluxation of the mandible. Long acting paralytics should be avoided. The patient should be positioned supine on the operating table with a shoulder roll in place. Their head should be turned, and endotracheal tube secured, away from the side of the tumor. We use a 4 lead facial nerve monitor throughout the operation to provide audible electrical feedback regarding the nerve, but counsel trainees and patients that the use of a monitor does not in and of itself protect the nerve. Safe surgical technique and a thorough understanding of anatomy are critical.
Incision planning depends on the extent of surgery for each individual patient. For anything but a deep lobe tumor located primarily in the parapharyngeal space or for a parapharyngeal space neoplasm, which is discussed elsewhere, the facial nerve should be identified and anterograde dissection of the facial nerve performed. Therefore, for the majority of cases a modified Blair incision should be used, marking a rhytid at the junction between the ear and the cheek from the root of the helix to just below the ear lobule. The incision is then continued down into the neck at a level 2 fingerbreadths below the mandible. Using right angles instead of curves for the incision can decrease postoperative pin cushioning. Standard flaps include skin, subcutaneous tissue, and the SMAS layer. In the standard approach, the flaps should be raised over the parotid fascia until the border of the parotid gland is appreciated at the masseter muscle.
After superficial parotidectomy is performed with preservation of the facial nerve, one can begin work on the en bloc DLP. The DLP can be considered in 5 relatively constant steps, which are reviewed here and highlighted in Table 1. The first step is to carefully free each branch of the facial nerve from the underlying parotid tissue. The assistant may use a nerve hook or closed blunt hemostat to help elevate the nerve and allow the surgeon to work “under the net.” There is typically 1 deep branch of the facial nerve that must be divided to fully free the nerve (Figure 1). Occasionally, there may be more than 1 deep branch or simply fascial bands that mimic deep branches that must be cut. Working anteriorly, the deep lobe of the parotid should be separated from the masseter muscle using bipolar cautery and blunt spreads (Figure 2). Throughout this operation, it is important to continuously recheck the location of the nerve and ensure that the surgeon and assistant are working together to decrease traction injury and inadvertent thermal or sharp injury to the nerve. Working inferiorly, the deep lobe is dissected off the posterior belly of the digastric, stylohyoid, and stylopharyngeus muscles. This an important step as it allows for easy identification of the external carotid artery and retromandibular vein, which must be divided. The external carotid artery (ECA) can typically be found running between the posterior belly of the digastric and the stylopharyngeus muscles. Each vessel should be independently suture ligated (Figure 3). The senior author (KDO) often leaves the retromandibular vein flowing until absolutely necessary in order to relieve venous pressure on the tissue and decrease bleeding during the case.
Table 1Summary of steps for a deep lobe parotidectomy following superficial parotidectomy with facial nerve preservation.
Summary of steps for a DLP (following superficial parotidectomy with facial nerve preservation)
1.
Elevate the nerve to work “under the net.”
2.
Divide the anterior gland from the masseter.
3.
Ligate the external carotid artery and retromandibular vein.
4.
Ligate the superficial temporal vessels.
5.
Dissect from superior to inferior (or vice versa depending on the pathology) to identify and ligate the internal maxillary artery and remove the gland.
Figure 1Step 1: Elevation of the nerve to work “under the net” and division of the deep branch(es) of the facial nerve. (D.F. @ Mayo 2004, E1147270-001-0).
Moving superiorly, the superficial temporal vessels should be identified and ligated, taking care to preserve the facial nerve branches that often run just anterior to these vessels (Figure 4). The gland should then be separated working superior to inferior, or vice versa depending on the pathology, separating the gland from the temporomandibular joint superiorly and from the posterior border of the mandible anteromedially. During this dissection, it is typical to encounter bleeding from the pterygoid plexus and requires slow progress with close attention to hemostasis using bipolar, surgical clips, and/or suture ligation. As the parotid gland is dissected free in this manner, the internal maxillary artery and veins will be encountered passing deep to the mandible and should be suture ligated (Figure 5). The surgeon can then finalize freeing the tissue and delivering the deep lobe beneath the facial nerve branches.
Figure 4Step 4: Ligation of the superficial temporal vessels. (D.F. @ Mayo 2004, E1147270-004-0).
Limited or selective DLP can occasionally be considered for benign disease. In 2013, Sesenna et al reported outcomes for selective DLP for pleomorphic adenomas in 11 patients treated from 1997 to 2010.
In this technique, the superficial gland is left attached to the skin flap, the facial nerve is dissected out, and the deep lobe of the parotid is resected, dissecting around only the nerve branches draping over the tumor. Sesenna at al argue that this approach may reduce complications such as facial nerve injury, poor aesthetic outcomes, and Frey syndrome. However, this technique should only be utilized in select cases by surgeons who have mastered the technique of a more traditional DLP.
Transoral resection of deep lobe parotid tumors may be considered when the tumor lies predominantly within the parapharyngeal space. This approach can be performed under direct visualization, via transoral microscopy, or via transoral robotic surgery. Typically, the patient is transorally intubated, and a mouth gag is used to expose the oropharynx. An incision is then made into the soft palate, extending inferiorly in front of the anterior tonsillar pillar. Using blunt dissection and thermal hemostasis, the tumor is identified and extracapsular removal is attempted. During dissection, the surgeon must maintain constant vigil for the ICA. An endoscopic Doppler can be used intraoperatively to help localize the artery if elusive. After removal, the incision can then be closed with horizontal mattress sutures. Patients can generally be extubated and return to oral diet immediately. While intriguing, this approach is fraught with difficulties. In 2013, Chan et al published a case series and systematic review of the literature published on transoral robotic surgery for parapharyngeal space tumors.
Of the 44 patients who were included in the study, 65.9% had pleomorphic adenomas. Unintended capsule violation or piecemeal removal occurred in 7 (24%) of this cohort. While there was a low rate of recurrence, mean follow-up time was only 18.5 months, far too short to adequately assess the true risks for this procedure.
There is no hard cut off for when to sublux, or anteriorly distract the mandible, during deep lobe parotid surgery. It is our practice to use nasotracheal intubation in all patients with a significant mass in the deep lobe or parapharynx to allow for easy subluxation if needed. A retractor is placed under the mandible, and an assistant pulls firmly forward in order to open the space between the temporal bone and mandible. This can also open the stylomandibular tunnel, which is the access to the parapharyngeal space.
Mandibulotomy is rarely needed for even large benign lesions; however, surgeons should be prepared to consider this technique if needed to ensure adequate oncologic resection. Mandibulotomy for access to the deep lobe parotid and parapharyngeal space has been described in the literature since the early 1950s, with osteotomies described in the ramus, angle, body, symphysis, parasymphysis, and at the condylar neck.
Bozzetti et al described their technique in which the periosteum of the mandible is identified after locating and preserving the marginal mandibular nerve.
The surgeon then splits the periosteum along the inferior border of the mandible. Dissection is carried out in a subperiosteal plane in the premolar region to allow an osteotomy to be made just anterior to the mental foramen. Bozzetti et al indicate the ideal location for the osteotomy is within the interproximal space between the canine and first premolar. These authors recommend plating the planned osteotomy site prior to making cuts in order to improve approximation and synthesis of the mandible postoperatively. The osteotomy is then made and the periosteum overlying the lingual surface of the mandible is elevated to the level of the lingula in order to identify and preserve the neurovascular pedicle including the inferior alveolar nerve. Moving the mandible laterally, the surgeon can assess access to the tumor. If additional access is needed, a second osteotomy at the base of the condyle can be planned, plated, and made to allow greater lateral and upward freedom of movement of the mandible. The tumor is then removed and the mandible re-plated.
If facial nerve sacrifice is required, the steps and technical skill required for a DLP are simplified considerably. The surgeon must assess the facial nerve and its branches for the possibility of grafting. Biopsies can be taken of perineurium if involvement of the nerve is unclear, or of the nerve itself. Once sacrificed, the surgeon can proceed with steps 2-5 (Table 1) much more efficiently than when constricted by the presence of the facial nerve.
Reconstruction
Following total parotidectomy with facial nerve preservation and skin preservation, the most common issues requiring the attention of the surgeon are a facial contour defect and the potential for Frey syndrome. When addressing facial contour restoration, it is important to understand the properties of each option and the long-term durability of the material used. Options include free grafts with dermal fat, acellular human dermis, SMAS flaps, sternocleidomastoid flaps, supraclavicular artery island flaps, submental flaps, and a de-epithelialized anterolateral thigh free flap.
In 1995, Davis et al stated that the ideal reconstruction of facial soft tissue voids should employ filler materials that are biologically inert, predictably durable, inexpensive, readily available, and suitable for single stage implantation, all of which is still true today.
While a detailed discussion of these reconstructive options is beyond the scope of this chapter, for total parotidectomy defects with facial nerve preservation and an intact skin flap, we favor using a free abdominal dermal fat graft for reconstruction. This is a relatively fast operation, which has minimal morbidity for patients. We aim to slightly overfill the defect to anticipate some degree of resorption, especially when there is a plan for postoperative radiation, and to fix the fat graft to stable surrounding tissue.
Postoperative care
All patients undergoing DLP have a suction drain placed and are kept in the hospital a minimum of 1 night. Most patients require 2 nights and 3 days before their drain output is appropriate to pull prior to discharge. We generally require the drain to put out <30 cc in 24 hours or average 10 cc or less per 8 hours. We encourage early ambulation, deep breathing, and start all patients on subcutaneous heparin prophylaxis. Patients receive scheduled acetaminophen and ibuprofen, with narcotics prescribed for break through pain. For any patient with postoperative facial nerve weakness resulting in inability to close the eye, we use artificial tears at least hourly throughout the day, a cellulose-based eye ointment prior to sleep as well as an “eye bubble” to protect the eye and keep it hydrated while sleeping. Incisions are routinely closed with subcutaneous 4.0 Vicryl suture and surgical glue.
Complications
Complications following parotidectomy were previously highlighted when discussing patient counseling prior to surgery. The most significant of which is facial nerve injury. In a study looking at 65 adults undergoing total parotidectomy for metastatic cutaneous squamous cell carcinoma or melanoma at our institution, the facial nerve was preserved in 53 (82%). Of these, the median early postoperative House-Brackmann score was 3 (range: 1-6), which improved to a median of 1 (range 1-3) 1 year following surgery.
Therefore, when facial nerve preservation is possible, one can anticipate return of good facial nerve function.
Conclusion
DLP is a critical procedure to master for any head and neck oncologic surgeon. Patients presenting with deep lobe parotid tumors may be asymptomatic and have difficult tumors to palpate. Magnetic resonance imaging, CT, and PET/CT can be considered, depending on the clinical scenario. A fine needle aspiration biopsy can offer helpful information for patient counseling and surgical planning, with relatively minimal risk. Patients should be counseled regarding risks, potential complications, the possibility of a more involved operation (including neck dissection and the available reconstructive options), and the potential need for adjuvant therapy. Prior to undertaking this procedure, an intimate knowledge of the relevant anatomy is critical. DLP is indicated for any deep lobe tumor—benign or malignant, a superficial lobe malignancy with extension into the deep lobe, refractory inflammatory disease, and the presence of metastatic disease within a superficial or periparotid lymph node.
DLP typically follows superficial parotidectomy with facial nerve preservation and can be thought of in terms of 5 basic steps: (1) elevate the nerve to work “under the net,” (2) divide the anterior gland from the masseter, (3) ligate the external carotid artery and retromandibular vein, (4) ligate the superficial temporal vessels, and (5) dissect from superior to inferior (or vice versa depending on the pathology) to identify and ligate the internal maxillary artery and remove the gland. Postoperative care is focused on drain care and preventive cares if there is any eye weakness. Most patients have excellent facial nerve function over time, and with good reconstruction, can have excellent facial contour outcomes long term.
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