Parotidectomy for parotid cancer includes management of primary salivary cancer, metastatic cancer to lymph nodes, and direct extension from surrounding structures or cutaneous malignancies. Preoperative evaluation should provide surgeons with enough information to plan a sound operation and adequately counsel patients. Facial nerve sacrifice is sometimes required; but in preoperative functioning nerves, function should be preserved. Although nerve involvement predicts poor outcome, survival of around 50% has been reported for primary parotid malignancy. Metastatic cutaneous squamous cell carcinoma is a high-grade aggressive histology whereby local control for palliation with extended parotidectomy can be achieved; however, overall survival remains poor.
Key points
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Adequate excision of a parotid cancer should be based on the extent of the primary tumor.
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Every attempt should be made to remove all gross tumor. Radiation therapy does not compensate for inadequate surgery.
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The extent of parotidectomy depends more on the extent and location of the tumor than the histology of the tumor.
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The anatomic relationship of the tumor to the nerve dictates the extent of surgery, not the histologic classification of the neoplasm.
Introduction
Malignancy of the parotid gland requiring surgical management can be considered in 3 groups. First include primary parotid salivary malignancies. Although this group represents a small minority of head and neck tumors overall, parotid cancers represent a high percentage of salivary malignancies. Next, when working up a parotid malignancy, metastatic disease must be considered. This second group most commonly includes cutaneous malignancies (melanoma and nonmelanoma), however, may rarely involve metastatic disease from a distant site. A third less common but encountered situation that requires surgical management is direct extension of tumor into the parotid gland. This extension can be seen in cutaneous malignances, such as in neglected basal cell carcinoma or extension from an advanced oral cavity tumor. For all 3 categories, local control goals and the anatomy encountered may be similar. However, long-term outcomes may vary greatly; therefore, overall goals of surgery should be considered when deciding the extent of surgery, degree of radicality, and preservation/sacrifice of structure and function. The histology of primary salivary malignancies is vast and outcomes vary. For metastatic disease to the parotid gland, this often represents a biologically aggressive tumor, which may harbor features of perineural invasion and a propensity for distant spread. In the current article, the authors discuss parotidectomy for parotid cancer: preoperative evaluation, technique, adjunct tools, and the controversies.
Preoperative evaluation
The preoperative approach to malignant disease in parotid tumors focuses on having adequate knowledge to plan the surgery as well as counsel patients and manage expectations. As discussed, most parotid tumors are benign; other than a detailed history and physical examination, additional diagnostic testing rarely alters surgical planning in most cases with well-circumscribed, mobile, slowly growing masses. However, when the history is atypical, the mass is ill defined, facial nerve (FN) involvement is present, or there is skin involvement, additional testing may offer information that defines anatomic boundaries when planning the extent of surgery as well as be useful with patient consulting. Additionally, if preoperative evaluation suggests FN sacrifice is likely, acquiring a team that can address facial reanimation at the time of surgery is beneficial. The authors discuss the history and physical examination with emphasis on findings associated with malignancy, radiographic assessment, and tissue diagnosis.
History and Physical Examination
Stigmata of parotid malignancy
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Rapid growth-fixed mass
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Pain
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FN paralysis
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Skin involvement
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Nodal metastasis
Rapid growth, pain, and FN paralysis represent the stigmata of parotid malignancy; however, in three-quarters of cases, patients will present with an asymptomatic preauricular mass. While pain can sometimes point to infection or inflammatory disease is present in 44% of patients with carcinoma. Facial palsy should always raise suspicion for malignancy and is present in 12% to 19% of patients with a malignant parotid mass independent of tumor size. Importantly, in patients diagnosed with Bell palsy that does not improve or worsens, parotid carcinoma should remain high on the differential. In these patients the deep lobe parotid gland can harbor an occult cancer; therefore, attention should be given to the oral cavity as patients can present with swelling of the lateral oropharyngeal wall or soft palate in these cases. Other findings consistent with malignancy include skin involvement and cervical lymph node metastasis. Although skin involvement is a late and alarming sign of parotid malignancy, cervical metastasis is more dictated by the biology of the tumor. For example, in salivary ductal carcinoma and high-grade mucoepidermoid carcinoma, metastatic lymph nodes at presentation are quite high.
Tissue Diagnosis
Indications for preoperative biopsy of parotid lesions
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Is it something other than a salivary gland tumor?
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Will a histologic diagnosis change the management?
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Is the FN dissection likely to be tedious or is FN sacrifice likely?
Options for preoperative tissue diagnosis
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Fine-needle aspiration (FNA)
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Ultrasound-guided core biopsy
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Open biopsy
There is much debate surrounding the need for tissue diagnosis before proceeding to the operating room for parotidectomy. Those that disagree with tissue diagnosis before surgery suggest surgery remains the primary treatment independent of tissue diagnosis. Alternatively, others note tissue diagnosis offers the surgeon the ability to risk-stratify patients, to counsel them appropriately, and to avoid surgery in those cases whereby it is not appropriate or unnecessary. The authors consider FNA beneficial in evaluating poorly defined salivary gland masses and to confirm clinical suspicion of malignant disease. FNA can be particularly useful if FN paralysis/paresis is present in order to counsel patients before surgery. FNA is also useful in the scenario of metastatic disease in order to restage and direct adjuvant therapy. Finally, if patients are poor surgical patients, a benign FNA can justify an observation protocol. Alternatively, if the FNA shows lymphoma, surgery is generally not indicated and, therefore, can be avoided. In general, FNA has a relatively low sensitivity in malignant disease, however, is fairly specific. The reported numbers are broad. It could be hypothesized this is secondary to the technique used (image guided vs without imaging), the experience of the person taking the sample (surgeon vs pathologist), the broad range of pathologies associated with salivary malignancies, as well as the expertise of the cytopathologist. Mallon and colleagues reported, for malignant disease, FNA has a sensitivity and specificity of 52% and 92%, respectively. In the authors’ practice whereby FNA is used selectively, the authors have reported that FNA in the diagnosis of a malignant or suspicious lesion had positive and negative predictive values of 84% and 77%, respectively. Many of the authors’ false-negative FNAs (10 out of 20) were identified as low-grade lymphoma on final histology; therefore, cytologic findings of a lymphocyte-predominant lesion should prompt further work-up to rule out lymphoma. This work-up may involve a core biopsy. Ultrasound-guided core needle biopsy has been reported to be safe with a higher sensitivity and specificity than FNA in management of parotid lesions. If FNA is nondiagnostic and a more definitive diagnosis is required or findings are concentrated with lymphocytes, ultrasound core biopsy should be considered to further clarify before proceeding to parotidectomy. Importantly, the predictive value of a negative FNA finding is low and should not take the place of clinical suspicion of malignancy. Additionally, FNA diagnosis is not used to make a critical intraoperative decisions regarding FN management or if the nerve is to be sacrificed. The management of FN in the operating room depends on the intraoperative findings.
Open biopsy of a discrete parotid lesion as a preoperative assessment before definitive surgery is rarely indicated secondary to the risk of FN palsy when the nerve is not defined intraoperatively, such as in a formal parotidectomy. Additionally, biopsy of a discrete lesion may result in tumor spillage and may predispose to tumor dissemination into surrounding skin and soft tissues. Open biopsy may be warranted in a very select group, including patients with a high suspicion of malignancy with likely FN sacrifice or in patients with suspected lymphoma and diagnosis cannot be made on FNA or core needle biopsy.
Imaging in Parotid Gland Malignancy
Indications for imaging in parotid malignancy
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Uncertain extent of disease
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Fixation to surrounding structures
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Parapharyngeal location
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Recurrent tumor
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Facial paresis or paralysis
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Cervical nodal involvement
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Patient under observation to document change in growth
Although imaging of parotid lesions can accurately predict malignant histology (MRI alone sensitivity 88% and specificity 77%), the role of imaging in parotid gland malignancy is often to define the extent of disease. This definition includes local invasion into surrounding structures, perineural invasion, regional involvement such as in cervical metastasis, and evaluation of distant dissemination in the case of metastatic disease to the parotid or advanced primary salivary malignancies. A detailed discussion of parotid gland imaging is presented in another article of this publication. Briefly, for preoperative evaluation of parotid gland malignancies computed tomography (CT) is used for tumors extending into bony structures, for instance, into the mandible or temporal bone such as when an extended lateral temporal bone resection is planned to resect a locally invasive cutaneous malignancy or primary/metastatic lesion of the gland. MRI is useful in evaluating deep lobe versus parapharyngeal space tumors, base of skull extension, and cranial nerve involvement. Neurotrophic tumors, such as adenoid cystic carcinoma or cutaneous squamous cell carcinoma (cSSC), can often spread to via cranial nerves centrally. Identifying these characteristics may change the surgical approach and in some cases classifies patients as unresectable. Often both MRI and CT are complementary and contributory studies in advanced malignant tumors of the parotid gland.
Extent of surgery for parotid malignancy
Variations in the extent of parotidectomy for malignancy
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Partial parotidectomy: limited, wide excision
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Superficial parotidectomy
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Total parotidectomy
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Radical parotidectomy
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Extended radical parotidectomy
Certainly parotidectomy using the technique of FN identification and parotid tissue resected is reasonably well standardized; however, the extent of parotid tissue needed to be excised to adequately address a malignant parotid neoplasm is a point of debate. Historically, surgical enucleation of parotid tumors resulted in high rates of FN palsy and tumor recurrence. Evolution of a less than superficial parotidectomy has been reported. This discussion mostly pertains to benign lesions. For primary parotid cancers, if a partial parotidectomy is oncologically equivalent to a more extensive operation is difficult to assess given the rarity of the tumors, the vast number of histologies and the long time interval for recurrence. There is little evidence that more extensive operations result in better outcomes. Retrospectively, conservative parotidectomy, defined as any procedure that is less than a superficial parotidectomy whereby less than a full FN is dissected, has been reported in a small series with comparable results with superficial parotidectomy. Importantly, about one-quarter of the patients in this series received adjuvant radiation; there was a median follow-up of less than 5 years, and only 43 patients were reported. Partial FN paralysis or paresis was 12%, comparable with Bron and O’Brien’s reported rates of 34% facial weakness for malignant tumors treated with complete superficial parotidectomy compared with 13% of those treated with a conservative parotidectomy. It seems reasonable that, for small tumors whereby an adequate margin can be achieved while limiting FN dissection, a more conservative approach may result in improved postoperative FN function without compromising oncologic outcomes.
Total parotidectomy involves removal of all parotid tissue superficial to the FN as well as tissue deep to the FN. A discussion of indications for a deep lobe parotidectomy must first begin with an understanding of the concept that the division between the superficial and deep portions of the parotid is iatrogenic, not embryologic. Removal of the parotid tissue deep to the FN, representing 20% of the parotid glandular tissue, can be considered as 2 entities. The first group includes primary malignant parotid tumors originating from the deep lobe. In this case removal of the primary tumor with a cuff of margin will require a total parotidectomy, including a superficial parotidectomy for nerve identification and access and deep lobe of the parotid gland to excise the tumor. It should be noted that some deep lobe parotid tumors, located mostly in the parapharyngeal space, may be amenable to an isolated cervical approach; therefore, a superficial parotidectomy may not be required. These tumors represent a small minority of tumors and are often benign pleomorphic adenomas. These tumors can generally be easily removed through a stylohyoid window.
The second scenario is considered in metastatic disease and requires an understanding of the parotid gland as a lymphatic basin. The parotid gland is the first draining site for cutaneous malignancies on the cheek, pinna, forehead, and temple. Anatomic studies have reported 7 lymph nodes in the superficial lobe (range, 3–19) and 2 in the deep lobe (range, 0–9). Although there are fewer lymph nodes that reside within the tissue deep to the FN, this is consistent with less volume of glandular tissue in the deep lobe. Sites including the conjunctiva, oropharynx, and middle ear can also involve parotid lymph nodes. Deep lobe lymph node metastasis can also arise from primary salivary gland malignances arising from the superficial gland. Controversy exists if total parotidectomy (extending the operation to clear tissue deep to the FN) is required when managing metastatic lesions to the parotid gland. Certainly, there is prognostic value to the identification of involved lymph nodes in the deep lobe tissue. Work by Thom and colleagues showed that deep lobe metastasis from cSCC was a significant risk factor of distant metastatic disease, disease recurrence, death from disease, and overall survival. However, does extending radicality to involve the tissue deep to the FN alter outcomes? Although this question has not been answered in a randomized prospective fashion, analysis of retrospective studies indicates there may be a benefit to total parotidectomy in some select cases. When considering increasing radicality locally, local recurrence rates without this maneuver should be recognized. In a large series from Australia of 87 patients with clinical metastasis to the parotid gland, 82% had a superficial parotidectomy and 86% had adjuvant radiation. Of the series, there was a local recurrence rate of 20%, with two-thirds observed in the deep bed of the parotid lobe. It is unclear if the recurrences were isolated to the group that underwent radical parotidectomy that were more likely to have a positive margin or if leaving tissue deep to the FN was a source of recurrence. Others have reported parotid bed recurrences ranging from 11% to 44%. The Mayo Clinic has published on their experience with the use of total parotidectomy for primary salivary and metastatic disease involving the parotid gland. Local parotid control rates of 93% (median follow-up 36.4 months) with metastatic cSCC and melanoma of 100% (median follow-up 30.6 months) was reported with the routine use of total parotidectomy for metastatic cutaneous malignancies. Although local control in the parotid bed was superior to other series, overall survival remained poor. With the goal of improving local control, deep lobe parotidectomy can be considered when metastasis to the deep lymph nodes is likely. These cases include patients with metastasis to any intraparotid lymph nodes, high-grade primary parotid cancers, and primary parotid cancer with metastasis to lymph nodes of the parotid gland or neck nodes.
Radical parotidectomy involves removal of all parotid tissue as well as sacrifice of the FN. This procedure is done in cases whereby the FN has been invaded by tumor or if preoperative FN function was impaired in the presence of malignant disease. Further discussion of indications and outcomes are included in the management of FN section.
Extended radical parotidectomy is carried out when the parotid tumor (primary salivary, metastatic disease, or through direct extension from a cutaneous malignancy) invades adjacent structures, such as the temporal bone, the mandibular bone, or the skin. These cases may require the performance of an extended total parotidectomy, which can include adjunct procedures, such as mandibulectomy, skin resection, infratemporal fossa dissection, and skull base or temporal bone resection. Prognosis for these patients is poor. Mehra and colleagues reported on 12 patients that underwent lateral temporal bone resection (LTBR) as part of an extended parotidectomy as part of management of primary parotid malignancies. In addition to LTBR, 58% had partial mandibulectomy and 83% had FN sacrifice. Aggressive management of the primary site resulted in locoregional control of 75%. However, the 5-year survival was 22%. These data would support that the inclusion of LTBR as an adjunctive procedure in extended radical parotidectomy achieves reasonable rates of locoregional control and palliates local symptoms; however, overall survival remains poor secondary to distant failure. Of note, extending the parotidectomy may be needed in order to provide an FN segment with negative margins in order to graft. Overall, temporal bone surgery is an important adjunct to the management of advanced, recurrent, and metastatic parotid malignancies.
Extent of Surgery for Accessory Parotid Gland Carcinoma
Sometimes, primary salivary malignancies can arise in the accessory salivary tissue. This tissue follows the Stensen duct and, therefore, can present as a cheek mass. In general, surgery for accessory parotid tumor involves the identification of the FN by first completing a superficial parotidectomy and then tracing out the branches distally. However, in some cases, if the tumor is discrete and separate from the parotid gland, superficial parotidectomy can be avoided, as there is no oncologic justification for removal of the superficial parotid tissue in this scenario if total excision with negative margins can be achieved. This surgical technique involves identification of the buccal and zygomatic branches distally at the anterior edge after elevation of the anterior skin flap. The branches are then meticulously dissected and preserved.
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