Selective Neck Dissection
Robert L. Ferris
INTRODUCTION
Neck dissection has evolved to be more targeted and less invasive over the past 100 years since Crile described the classical radical neck dissection (RND). Another conceptual advance held that modified RND was technically feasible and oncologically sound, removing only lymphatic structures and retaining the sternocleidomastoid muscle (SCM), accessory nerve, and/or internal jugular vein (IJV). The potential then arose for removing less than all five levels of the ipsilateral neck for mucosal or cutaneous squamous cell carcinoma, with potential application of this “selective neck dissection (SND)” to thyroid or salivary carcinomas as well. Over the past 20 years, the SND has become more widely accepted, first as a staging procedure and more recently as a therapeutic approach to early (N1) lymph node metastasis.
The advent of this development toward SND was supported by the seminal contribution of JP Shah (1990) reporting on the specific levels in the neck where metastatic lymph nodes were observed, originating from certain subsites within the oral cavity, oral pharynx, larynx, or hypopharynx. Reporting on the patterns of metastasis in over 1,000 RNDs (all five levels dissected), it became clear that targeted SND could be adopted removing only three or four of the five cervical levels in selected patients based on the site of the primary cancer (Fig. 2.1A and B). As a staging procedure, the SND was found retrospectively to have removed microscopic N1 metastasis in more than 30% of cN0 patients. Thus, one or two metastatic lymph nodes, <3 cm in size and without extracapsular spread (ECS), can be adequately treated by SND, removing appropriate cervical levels according to the patterns of spread from the original primary site of the cancer.
Besides its oncologic value, SND has been demonstrated to reduce the morbidity and cosmetic deformity associated with more extensive modified radical neck dissection (MRND) or RND, due to avoidance of manipulation, mobilization, or transection of the spinal accessory nerve, which is the major morbidity of neck dissection. Thus, currently SND is the standard procedure for cN0 or cN1 disease in most patients with head and neck squamous cell carcinoma. For the N0-N1 neck, the SND provides crucial staging information, documenting the presence and extent of metastatic disease in the neck. Furthermore, it provides information regarding the presence of ECS a very poor prognostic factor warranting adjuvant therapy with chemoradiation. After SND, patients without high-risk features such as multiple lymph nodes positive (>3) or ECS can then undergo observation or (reduced) dose postoperative radiotherapy.
HISTORY
It is crucial to identify the site and extent of the primary cancer (mucosal, cutaneous, salivary, or thyroid) to guide appropriateness for SND. It is also important to inquire about associated features including dysphagia, mass in the neck, hoarseness, or other symptoms associated with the cancer in the upper aerodigestive tract. Any prior oncologic treatment or history of neck surgery should be elicited. For a squamous cell carcinoma with an unknown primary mucosal site, it is crucial to establish whether a prior tonsillectomy has
been performed. A history of cutaneous malignancy should not be overlooked, since aggressive squamous cell carcinoma of the skin, particularly in elderly or immunosuppressed individuals, may metastasize to the cervical lymph nodes.
been performed. A history of cutaneous malignancy should not be overlooked, since aggressive squamous cell carcinoma of the skin, particularly in elderly or immunosuppressed individuals, may metastasize to the cervical lymph nodes.
 FIGURE 2.1 A: Lymphatic drainage of the head and neck. B: Levels of the cervical lymph nodes. |
PHYSICAL EXAMINATION
A thorough examination of the head and neck should be performed in the office, palpating the neck for the presence of enlarged nodes, fixed lymphadenopathy, fixation of the overlying skin to the lymph nodes, or other signs of gross metastasis. Preoperative documentation is crucial and should be combined with radiographic imaging. I prefer a contrast-enhanced computed tomography (CT) scan of the neck from the skull base to the clavicles, since this will include retropharyngeal nodes. The rate of level IIB metastasis is very rare (1%) in the clinically and radiographically negative neck; however, the rate increases (10% to 15%) for metastasis to level IIB, when clinically positive lymph nodes are observed preoperatively. The SND would then include level IIB in the dissection. Indications for SND are preoperative clinical N0-N1 as a diagnostic and staging procedure. Postoperative identification of pathologic N1 status may be adequately treated with SND alone, in the absence of ECS. When a SND identifies N2b metastasis, multiple positives nodes >2, are a standard indication for adjuvant radiotherapy. More extensive lymph node metastasis should be discovered preoperatively since SND is not sufficient therapy in situations of clinical stage N2-N3.
INDICATIONS
An SND is indicated in the absence of palpable cervical metastases (i.e., in the elective surgical treatment of the N0 neck). Early metastatic cancer (cN1) is also an indication for SND.
CONTRAINDICATIONS
The SND is not indicated in the following situations:
Patients with multiple clinically obvious cervical lymph node metastases, particularly when they are found to involve or to be closely related to the spinal accessory nerve
Patients with a bulky metastatic tumor mass or with multiple matted nodes in the superior aspect of the neck
PREOPERATIVE PLANNING
Imaging
Various radiographic techniques may be used prior to SND. I believe that the CT scan using IV iodinated contrast is the most helpful preoperative test prior to SND. The size, number, and three-dimensional relationship of any suspicious lymph nodes can be identified and documented. It is fast, is relatively inexpensive, and emits a low dose of radiation. Ultrasonography (US) of the neck is appropriate particularly if the surgeon has access to this instrument in the clinic. US can identify suspicious lymph nodes, as well as size, number, and potential for ECS. It is also inexpensive and does not deliver radiation, therefore providing several advantages. A disadvantage is the lack of the transferable three-dimensional planar axial imaging for review by multiple individuals over time, since it is operator dependent. Magnetic resonance imaging has similar advantages to CT scans, but is used less often, due to greater expense and time to perform, reducing patient compliance and surgeon comfort with the images. Positron emission tomography-computed tomography (PET-CT) has become increasingly used for pretreatment staging of cancer of the head and neck and is often more accurate than contrast-enhanced CT alone. However, PET-CT is more useful for identifying occult distant metastasis, whereas false positives and false negatives reduce its utility in accurately staging the clinically negative (cN0) neck. In this situation, SND is the most accurate test for determining the pathologic status of the neck (pN status) and is superior to PET-CT in sensitivity and specificity.
Fine Needle Aspiration Biopsy
Fine needle aspiration biopsy (FNAB) is integral to the preoperative planning for SND and should be used (and repeated if necessary) to document cytologically the presence of cancer in a suspicious lymph node(s). Necrotic or cystic lymph nodes may emanate from the oropharynx (tonsil/base of tongue) or primary thyroid cancers, and repeat FNAB may be necessary with image guidance. Open biopsy should be strongly discouraged, unless frozen section is planned, with conversion to immediate SND if positive.
SURGICAL TECHNIQUE
The SND is performed similarly to the comprehensive, type III MRND, with the exception that all cervical levels (I-V) are not removed in the SND. In all cases of SND, no nonlymphatic structures are routinely removed, thus preserving the SCM, IJV, and spinal accessory nerve. An example is shown in Figure 2.2 for SND appropriate for cN0/cN1 oropharyngeal, laryngeal/hypopharyngeal primary cancers. The SCM should not be divided, but rather is retracted posteriorly to permit access to the cervical levels to be dissected. In some situations, early-stage metastasis to the neck (N1) with ECS may be attached to the SCM or jugular vein, and in these rare instances, these structures may need to be partially removed. However, this is quite rare, and in these situations, conversion to a comprehensive MRND would seem prudent.
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