Retropharyngeal Neck Dissection

Introduction

The retropharyngeal lymph nodes (RPLNs) are a small chain of lymph nodes located in the retropharyngeal space (RP) where they are divided into the medial and lateral groups. The boundaries of the RP are the carotid sheath laterally, skull base superiorly, prevertebral fascia posteriorly, and the pharynx anteriorly, and inferiorly, the RP is in continuity with the posterior mediastinum. The medial group of nodes are usually ill-defined and often absent in adults, thus not having a significant role in RPLN metastases. The lateral RPLN, which lies superior to the sympathetic ganglion at the level of C1, can harbor metastases from a variety of cancers; oropharyngeal cancer being the most common. There may be one to three nodes that are often difficult to identify in the absence of metastatic involvement. Typically, the lateral RPLNs are usually smaller than 4 to 4.5 mm in the greatest diameter of their shortest axis, where 6 to 10 mm has been described as the pathologic threshold for RPLNs.

Rouviere, in 1938, first mapped lymphatic drainage of the oropharynx and characterized the spread of oropharyngeal carcinomas to the RP. RPLN positivity in all oropharyngeal squamous cell carcinomas (OPSCC) has been found to be 10% to 27%, using a variety of imaging modalities. Additionally, RPLN involvement in OPSCC is an important prognostic factor and has been shown that there is an increased risk for regional recurrence (45% vs. 10%) and reduced rates of disease-specific survival (38% vs. 58%). RPLN metastases are more common from the soft palate and posterior pharynx, but they can occur from any subsite within the oropharynx. Due to the incidence of metastases, the RPLNs are routinely targeted during radiation therapy for OPSCC. Currently, when the lateral lymphatics of the neck are dissected in a conventional selective neck dissection, the RPLNs are not routinely dissected. With increasing use of transoral surgery (TOS) as a primary treatment modality for OPSCC, dissection of the RPLN during cervical lymphadenectomy becomes more important, especially in cases where no adjuvant treatment is recommended.

Key Operative Learning Points

• Approach can be transcervical or transoral

  • Transcervical approach preferred if a concurrent neck dissection is being performed

• Avoid injury to the sympathetic chain that is located lateral to the RPLN and can often be mistaken for lymphadenopathy

• A positive positron emission tomography (PET)/computed tomography (CT) of the RPLN has an excellent PPV and suggests that the RPLN needs to be addressed when primary or recurrent squamous cell carcinomas (SCC) are present.

Preoperative Period

The keys to deciding when to perform the surgery in the primary setting are: (1) to ascertain the risk of RPLN metastases based on the oropharyngeal cancer subsite and nodal cancer burden and (2) decide whether primary surgical treatment will be employed. If preoperative imaging suggests metastasis in the RPLN and a neck dissection is being performed, the RPLN can be safely dissected in this situation. If the RPLN is negative on PET/CT and another imaging modality (CT or magnetic resonance imaging [MRI]), then the RPLN can either be ignored or treated electively with radiation therapy, depending on the TNM staging and subsite ( Fig. 68.1 ). In the setting of lymph node metastasis persistence or recurrence after chemoradiation, PET/CT has demonstrated adequate accuracy at predicting RPLN disease and can be used to guide whether the RPLNs need to be addressed during a salvage-neck dissection. As with all head and neck cancers, I advocate for presenting the patient to a multidisciplinary tumor board and considering various factors, for example, the patient’s comorbidities, preferences, and social situation prior to proceeding with primary treatment.

The RPLN can be approached by using either a transcervical or transoral technique. I suggest a transcervical approach in the primary setting when performed in conjunction with an elective neck dissection. The technique for the transcervical approach, as outlined below, has been demonstrated to be a safe and reliable method of RPLN sampling during primary surgical management. For therapeutic removal of a metastatic RPLN, both the transcervical and transoral techniques can be used. If a concurrent neck dissection is being performed, I prefer using the transcervical approach to avoid violating the pharynx and creating a potential salivary fistula. If, however, the RPLN is the only node being removed (i.e., in the case of a previously dissected neck with only a RPLN positive node or a solitary papillary thyroid cancer metastasis), then a transoral approach can be considered to avoid an external incision based on the familiarity of the surgeon with the anatomy and techniques.

If primary surgical therapy is being considered for the oropharyngeal cancer, informed consent must include the usual potential morbidity associated with the primary resection of the cancer and the selective neck dissection. In addition to these risks, the RPLN dissection through a transcervical approach increases the risk of a salivary fistula due to the close proximity to the pharynx. Also, the dissection of the RPLN can include potential damage to cranial nerve (CN) IX and the sympathetic chain, which can increase the risk of aspiration and result in Horner’s syndrome, respectively. If the transoral approach is performed in isolation, there is minimal risk of a salivary fistula but the incidences of postoperative aspiration, Horner’s syndrome, and damage to major vessels are likely increased due to the limited exposure and technical difficulties associated with this approach.