Level of cervical nodal metastases
Oral cavity primary (elective ND)
Oral cavity primary (therapeutic ND)
Oropharyngeal primary (elective ND)
Oropharyngeal primary (therapeutic ND)
Hypopharyngeal primary (elective ND)
Hypopharyngeal primary (therapeutic ND)
Laryngeal primary (elective ND)
Laryngeal primary (therapeutic ND)
I
58
61
7
17
0
10
14
8
II
51
57
80
85
75
78
52
68
III
26
44
60
50
75
75
55
70
IV
9
20
27
33
0
47
24
35
V
2
4
7
11
0
11
7
5
Fig. 21.1
Percentages of total occult cervical nodal metastases from oropharyngeal primaries identified after elective neck dissection
21.3 Neck Dissection Classification
Neck dissection can be subclassified into comprehensive neck dissection and selective neck dissection based on the extent of surgical resection of key cervical structures.
21.3.1 Comprehensive Neck Dissection
The most extensive type of neck dissection is radical neck dissection which entails removal of the cervical nodes from levels I to V as well as the sternocleidomastoid muscle, spinal accessory nerve, and internal jugular vein. It is infrequently performed today; radical surgery is usually necessary for therapeutic neck dissection if key structures are involved with extensive nodal disease.
In contrast, modified radical neck dissection involves removal of cervical nodes located at levels I–V but with preservation of one or more of the following structures: the sternocleidomastoid muscle, spinal accessory nerve, and internal jugular vein. Modified radical neck dissection type I involves preservation of only the accessory nerve, while modified radical neck dissection type II involves preservation of the accessory nerve and the internal jugular vein. Type III modified radical neck dissection, also referred to as functional neck dissection, involves preservation of the internal jugular vein, accessory nerve, and sternocleidomastoid muscle. Sacrifice of these structures for TORS oropharyngeal primaries is appropriate only when these structures are clearly involved with disease. A clear surgical plane, not artificially created, should be present to ensure optimal oncologic outcome when preserving these structures but achieving gross total resection of all nodal disease.
21.3.2 Selective Neck Dissection
Selective neck dissection for elective management of the clinically negative neck entails removal of lymph nodes at nodal levels which are at the highest risk for metastatic spread with preservation of the internal jugular vein, sternocleidomastoid, and spinal accessory nerve. Nodal metastasis from oropharyngeal primaries occurs mainly to levels II–IV, and therefore selective neck dissection of the clinically negative neck in patients undergoing TORS for squamous cell carcinoma of the oropharynx should include these levels (also known as lateral neck dissection).
The need for dissection of level IIb, the nodal subdivision defined as the area posterior to the spinal accessory nerve in level II, for squamous cell carcinoma of the oral cavity and oropharynx is debated among surgeons. Recent analyses have shown that dissection of level IIb is beneficial particularly for squamous cell carcinoma of the tonsil and in all patients with oropharyngeal primaries who have clinically N+ disease (within and outside of level II) [5, 6]. In experienced hands, dissection of level IIb adds only minimally increased risk of accessory nerve dysfunction and can be safely performed for appropriate cases.
21.4 Clinicopathological Differences Between HPV Positive and HPV Negative Neck Disease
Recent work has genetically characterized HPV positive and HPV negative tumors as distinct entities in regard to the drivers of their oncogenesis [7]. Therefore, it is not surprising that nodal metastases from these two distinct cancer subtypes have different characteristics and behavior. The percentage of oropharyngeal tumors in the 1990s that were HPV positive is estimated to be approximately 50 %; however, recent analysis has shown that this percentage has dramatically increased to as high as 80 % currently in North America and Europe [8].
As the vast majority of oropharyngeal tumors are HPV positive, an understanding of their distinct characteristics is critical for TORS surgeons. These characteristics can aid surgeons in the preoperative workup of these patients as well as affect intraoperative and postoperative management. It is generally well accepted that HPV positive oropharyngeal squamous cell primaries are characterized by frequent and early nodal spread. This is in part due to the rich lymphatic drainage of the oropharynx. The prognostic impact of early and frequent nodal spread in HPV positive disease is believed to be not as important as nodal metastasis is for HPV negative squamous cell carcinoma. The physical characteristics of HPV positive and HPV negative nodal metastases are also distinct. Cystic cervical nodal metastases from squamous cell carcinoma have been associated with primary tumors which originate from Waldeyer’s ring (which includes the base of the tongue, palatine tonsils, and nasopharynx) in 72–90 % of cases in which the primary tumor is detected [9, 10]. Furthermore, the cystic nature of oropharyngeal nodal metastases has also been linked to HPV positivity [10, 11]. The precise reasons for the occurrence of cystic metastases in oropharyngeal carcinoma are unclear but have been attributed to malignant salivary gland-type cells that metastasize from the oropharynx to cervical nodes and which subsequently express their parental property in these lymph nodes [12]. Alternative explanations involve the transformation of keratinocytes which have an inherent propensity for cyst formation after malignant conversion to a transitional type of squamous cell carcinoma [10]. Regardless of the precise mechanism of formation of cystic nodal metastases in HPV oropharyngeal tumors, surgeons should be aware of their frequent occurrence in the preoperative evaluation of these patients. It should be noted, however, that the presence of cystic cervical node metastases also occurs in other diseases processes as well, such as papillary thyroid carcinoma and hypopharyngeal carcinoma.
21.5 Management of the Neck in HPV Negative and HPV Positive Oropharyngeal Disease
As HPV positive and HPV negative tumors represent biologically distinct tumor entities, we advocate that the elective and therapeutic management strategy of the neck should differ between these two cancer subtypes. Here, we outline our clinical practice in regard to the surgical management of the neck for oropharyngeal squamous cell primaries in the context of HPV status (Fig. 21.2).
Fig. 21.2
Proposed treatment paradigm for the surgical management of the neck in HPV positive and HPV negative squamous cell primaries of the oropharynx
21.5.1 The N0 Neck in HPV Positive and HPV Negative Disease
21.5.1.1 Selective Neck Dissection (Levels II–IV)
Occult cervical nodal metastases occur in approximately 30 % of early-stage tumors in both oral cavity and oropharyngeal primaries [13, 14]. As a result, elective neck dissection is usually offered to patients with a clinically and radiographically negative neck. As previously discussed, the nodal basins most commonly involved by both HPV positive and HPV negative oropharyngeal squamous primaries are located at levels II–IV of the ipsilateral neck. Occult metastases outside of these levels are extremely uncommon, and true isolated skip metastases to levels I and V are even rarer. As a result, we advocate elective ipsilateral levels II–IV selective neck dissection for management of the clinically N0 neck in well-lateralized HPV positive and HPV negative oropharyngeal tumors. Bilateral elective neck dissection of levels II–IV needs to be considered for base of tongue lesions that are centrally located or approaching the midline.
A recent publication reported an overall survival advantage for early-stage oral cavity cancer after elective neck dissection [15]. However, these results cannot be extrapolated meaningfully to the oropharynx because of the distinct biological behavior of HPV-related oropharynx cancer. On the other hand, the obvious utility of elective neck dissection in any head and neck cancer including oropharyngeal primaries is its ability to provide definitive histopathologic staging information that is otherwise not available from any other existing investigative modality including modern radiographic imaging. This information can then be used by the multidisciplinary team for designing an individualized therapeutic plan for the patient based on risk versus benefit rather than an empiric estimation of the possibility of nodal metastatic disease.
Elective radiation to the neck can be performed in select patients who have contraindications to or refuse elective neck dissection or whose primary tumor is amenable to treatment with radiation therapy alone. While generally outside of our treatment paradigm, close observation followed by surgical salvage if necessary may be an alternative option in these patients.
21.5.1.2 Role of Sentinel Node Biopsy
As the majority of patients with early-stage oropharyngeal cancer will not harbor occult nodal metastases when staged clinically and radiographically N0, some have advocated sentinel node biopsy in an effort to avoid the morbidity of elective neck dissection. Sentinel node biopsy entails lymphatic mapping in order to selectively identify nodes that are most likely to be involved via metastatic lymphatic spread. Current techniques employ the use of preoperative lymphoscintigraphy with a radiolabeled colloid solution which is injected around the primary tumor. Specialized gamma cameras and handheld gamma probes are used to identify the flow of radiolabeled colloid solution to the sentinel nodes. Once identified intraoperatively, these nodes are biopsied, and the need for subsequent treatment is determined based on the histological analysis of the biopsied sentinel node(s) as cancer metastases usually spread in a serial fashion and the first encountered nodes (sentinel nodes) will harbor cancer cells before progressive spread to subsequent nodal basins.
There is a paucity of data surrounding the accuracy of sentinel node biopsy for oropharyngeal cancer. Furthermore, logistic and technical difficulties exist with the injection radioactive tracer material preoperatively for hard to access areas within the oropharynx. A large multi-institutional trial specifically examining oral cavity squamous cancers demonstrated accurate prediction of the pathologically negative neck based on negative sentinel nodes as high as 96 % [16]. A recent trial evaluating the efficacy of sentinel node biopsy in oral cavity cancer (including oropharyngeal-bordering tumors) demonstrated a negative predictive value of 95 % [17]. It is unclear how well these results will translate to oropharyngeal primaries and sentinel node biopsy for oropharyngeal primaries is not currently recommended as standard-of-care outside of clinical trials.
21.5.2 Management of the N+ Neck in HPV Negative Disease
The management of the clinically N+ neck differs from that of the N0 neck. In a series of comprehensive therapeutic neck dissections done for oropharyngeal primaries, Shah demonstrated the presence of a significant number of level I and V nodal metastases as compared to those of patients who underwent comprehensive neck dissection for clinically N0 disease [2] (Table 21.1). We therefore advocate comprehensive dissection of levels I–V in patients with HPV negative oropharyngeal primaries with evidence of clinically N+ disease. Additionally, any grossly invaded cervical structures such as the sternocleidomastoid muscle, internal jugular vein, or spinal accessory nerve should be resected for optimal oncologic outcome.
21.5.3 Management of the N+ Neck in HPV Positive Disease
Previous studies examining the impact of nodal metastases on patient outcome did not take into account the effect of HPV status on tumor behavior and prognosis. As previously discussed, we now understand that HPV positive and HPV negative tumors are very different biological cancer subtypes that also have distinct clinical behavior. Given these inherent differences, questions have arisen regarding the ideal management of the clinically N+ neck in HPV positive oropharyngeal cancer and whether treatment paradigms should be the same as N+ disease in HPV negative cancers. A recent large retrospective analysis of 201 patients with surgically resected oropharyngeal cancer from our institution has provided significant insight regarding the differences in prognostic factors between HPV positive and HPV negative tumors [18]. Interestingly, pathologic nodal status had no impact on survival for HPV positive patients but showed a trend toward significance in HPV negative patients (Fig. 21.3). This suggests that nodal metastases in HPV positive patients are more indolent and generally do not portend worse clinical outcome as compared to HPV negative nodal metastases. As a result, our clinical practice for clinically N+ oropharyngeal HPV positive squamous cell primaries is to perform an ipsilateral selective neck dissection of levels II–IV (including any clinically involved neck levels). Some of these patients will go on to receive adjuvant postoperative radiation therapy based on their pathologic characteristics. Radiation therapy appears to be sufficient to address the rare occult nodal metastases in levels I and V that are not addressed surgically. The addition of postoperative radiation therapy in N1 disease remains at the discretion of the surgeon and multidisciplinary treatment team. N1 nodal disease that has been satisfactorily resected without adverse features such as extensive extracapsular nodal spread can be observed without the addition of postoperative radiation therapy. In contrast, N1 nodal disease that possesses adverse features such as extensive extracapsular spread may receive postoperative radiation at the discretion of the multidisciplinary treatment team. Further discussion of postoperative radiation therapy following neck dissection is detailed below.
Fig. 21.3
Kaplan-Meier plots demonstrating the impact of pathologic cervical nodal status in HPV positive and HPV negative tumors of the oropharynx on patient survival (Reproduced with permission from Iyer et al. Annals of Surgical Oncology, 2015 [18])
21.6 Pharyngeal Defects Following Primary Tumor TORS and Neck Dissection
When neck dissection is carried out concurrently with TORS resection of the primary tumor, there is always the possibility that a full thickness defect can be created through the pharyngeal musculature into the neck. Because of this risk, some surgeons prefer to delay the neck dissection until 2–4 weeks after TORS of the primary. However, the majority of surgeons now carry out neck dissection in conjunction with TORS in order to facilitate adjuvant radiation treatment in a timely fashion. Surgeons must therefore be aware of the potential for pharyngeal defects to result from such combined surgeries and be prepared to repair such defects. TORS of a large oropharyngeal primary can have significant implications for neck dissection. Through-and-through defects can create an open communication between the neck and pharynx that must be addressed intraoperatively. The presence of a pharyngocervical salivary fistula in close proximity to an exposed carotid artery increases the risk of carotid rupture postoperatively. Thus large primary pharyngeal resection beds may require primary closure or coverage with local flaps or free tissue transfer if a salivary communication exists or is likely to develop. Recently, the Classification of Oropharyngeal Robotic Defects (CORD) has been proposed to help guide reconstruction defects following TORS [19, 20]. This classification characterizes the surgical defect in terms of size, location, extent of oropharyngeal resection, presence of pharyngocervical fistula, and exposure of the carotid artery. Reconstruction can proceed, primarily, with local flaps or free tissue transfer through combined transoral and open approaches through the neck. Clearly, prophylactic transcervical arterial ligation (discussed below) should be avoided when reconstruction with microvascular free tissue transfer is anticipated. As discussed elsewhere in this book, a number of free flap reconstructive options have been used to repair pharyngeal/hypopharyngeal defects following TORS including radial forearm, anterolateral thigh, and jejunal flaps. Pedicled flaps have also been used including pectoralis major and supraclavicular artery flaps. Primary closure techniques with musculomucosal advancement flap pharyngoplasty have been described in order to decrease fistula rates and improve functional outcome following surgery [21]. In many of these techniques, including free flap reconstruction, the surgical robot has been utilized in performing parts of the reconstruction, including the microvascular anastomosis [22]. If the defect is small, most surgeons will allow the resection bed to heal by secondary intention, and neck dissection can thus proceed without any additional considerations for reconstruction of the primary site. Large resection beds are subject to salivary secretions and continuous movement of the oropharynx during deglutition, making the resection bed vulnerable to wound breakdown. This may increase the risk for postoperative pharyngocervical fistula, cervical infection, and/or vascular breakdown resulting in oropharyngeal hemorrhage. For these reasons, proper selection of cases for TORS is crucial, and we recommend avoidance of leaving large areas of the oropharynx to heal by secondary intention. Local, pedicled, or free flaps can aid in providing healthy tissue to cover the resection bed and can be inset during the time of neck dissection through combined open and transoral techniques.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
