Fascial compartmentalization of the neck provides the oncological safety for selective neck dissections by the inclusion of lymph nodes and ducts in a system of fascial spaces and barriers. It is possible to remove the lymphatic system without removing other neck structures as long as the tumor cells remain within the lymph node capsule.
The decision of whether to remove the whole lymphatic system of the neck or just a part of it will depend on several factors, including the location of the primary tumor, the N stage, and the experience and preferences of the surgeon.
The distribution of cervical lymph node metastases from head and neck tumors has been a matter of study and debate over the last decades. Nowadays we have a fairly consistent description of the most frequent metastatic areas for most primary sites in the head and neck. This situation allows the surgeon to preserve some nodal groups according to the location of the primary tumor without a significant risk of undertreatment. This is especially true in pathological N0 patients in whom the lymph flow should not have been disturbed by metastatic disease. However, in pN+ necks the situation may be different. Two problems must be considered in patients with metastatic disease in the lymphatic system of the neck.
1. The theoretical predictability of the lymph node metastatic pattern may have been modified by changes produced by the tumor cells contained within the lymphatic system. This may result in positive nodes outside the "normal" route. These nodes will be missed by a selective operation that otherwise could have been safe.
2. The presence of metastasis in the usual nodal areas significantly increases the chances for positive nodes in other less frequent regions for the primary site. In the preoperative clinically N+ neck with small palpable nodes this is the strongest argument against selective neck dissections. In these patients a complete functional neck dissection must be performed to include all the lymphatic system of the neck. The problem is different in the clinically N0 neck treated with selective neck dissection in which occult metastases are diagnosed after the operation. In these cases, selective neck dissection may be regarded as a staging rather than a therapeutic operation, and postoperative radiotherapy may be needed.
This is one of the strongest arguments against the extreme use of selective operations because the surgeon never knows before surgery which patients will show positive nodes at pathology after the operation. From the patient perspective, assuming the risk for a smaller operation is only justified on the basis of improved oncological results and decreased morbidity. The first criterion, oncological safety, has as yet only been demonstrated for a small number of selective operations. On the other hand, decreased morbidity is at least questionable when it comes to comparing the results of complete functional neck dissection with those of the most frequently recommended selective procedures. It is not preservation of lymphatic regions but of nonlymphatic structures that is related to surgical morbidity and sequelae in neck dissection.
The previous considerations support the important role that personal experience of the surgeon ultimately plays in selecting the type of dissection that should be used for different primary head and neck tumors. And personal experience is acquired only after years of practice with standard procedures and sound apprehension of fundamental concepts.
In conclusion, whereas the oncological safety of some selective neck dissections has already been proved, the feasibility of others still lacks scientific demonstration and should be documented by means of well-designed trials. While we wait for the confirmation of the oncological safety of these procedures, it is our policy to teach basic concepts rather than technical modifications in the hope that time and experience will allow well-trained surgeons to adequately adjust their operations to the best interest of their patients.
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