3 The Conceptual Approach to Functional and Selective Neck Dissection
To sum up the essentials of the previous chapters, we may look at the issue of “less than radical” neck dissection under two different standpoints. The American evolution, which is based on the idea of preserving important neck structures that may not be involved by the tumor (e.g., internal jugular vein, spinal accessory nerve, and sternocleidomastoid muscle); and the Latin approach, which is based on the fascial concept developed by Osvaldo Suárez.
The end point may be similar but the journey is different.
3.2 Preserving Structures: The American Approach
This approach gave rise to the so-called modified radical neck dissections. After some years of debate, the oncological safety of these “less than radical” operations was finally accepted by all. A step forward in this evolution resulted in the appearance of “selective” neck dissections. In these, some nodal regions are preserved according to the location of the primary tumor. This new approach to neck dissection carried a need for a comprehensive classification inclusive of all types of modifications to the radical operation. Because the potential number of modifications is rather large, the resulting classification is complex and difficult to handle on a daily basis.
3.2.1 Selective Neck Dissections: Types and Indications
Martin objected to the selective approach because it lacked a statistical basis. However, subsequent evidence supports it. The anatomical studies of Rouviere demonstrated that the lymphatic drainage from normal head-and-neck mucosal sites is relatively predictable. Later, clinical studies concluded that oral cavity cancers mostly metastasized to the jugular digastric and midjugular nodes. Cancers of the anterior tongue, floor of the mouth, and buccal mucosa metastasize first to the nodes in the submandibular triangle. Some metastases may skip the submandibular and upper deep jugular nodes and go directly to the midjugular nodes on either side of the neck. The Lindberg study, and a subsequent study by Skolnik, observed that oral cavity and oropharynx tumors rarely metastasize to posterior or lower deep jugular nodes in the absence of metastases in the upper jugular and submaxillary nodal groups. Shah’s 1990 retrospective review of radical neck dissection specimens from patients with oral, laryngeal, and pharyngeal cancers concluded that oral cavity cancers metastasize most often to levels I, II, and III, whereas oropharynx cancers most often go to levels II, III, and IV. When cancerous nodes were found in other levels, they were usually positive in the areas of highest risk too. Bocca and others have observed that supraglottic cancers rarely metastasize to the submental and submandibular nodal groups. Nasopharyngeal and some oropharyngeal tumors can metastasize to the nodes in the posterior triangle of the neck. Finally, subglottic lesions and thyroid malignancies frequently involve the lymph nodes in the anterior central compartment of the neck.
Based on these findings, several selective neck dissections have been proposed. Its classification has varied through years and no terminology has been unanimously adopted. In an effort to standardize it, Ferlito and others in 2011 proposed a classification based on the symbol “ND” for “neck dissection” followed by the nodal groups and nonlymphatic structures removed. However, classic terms such as supraomohyoid, lateral, or posterolateral neck dissection are still common nowadays.
Selective Neck Dissection for Oral Cavity Cancer
The submental, submandibular, upper, and midjugular groups of nodes are the usual sites of metastases from the oral cancers. The term supraomohyoid neck dissection includes levels I, II, and III. In the case of invasive oral tongue cancer, including level IV is also recommended. In the absence of clinically evident neck metastases, there is no reason to include level V. Bilateral dissection is recommended for midline tumors (floor of the mouth, ventral surface of the tongue). In patients with significant (N2) nodal metastases in the ipsilateral neck, bilateral dissection or contralateral neck radiation is crucial.
These recommendations suggest that an operation close to a comprehensive functional neck dissection is appropriate for patients with oral cavity cancers with clinically evident metastases, and something less is acceptable for elective dissection. This approach to cancer codifies and structures what experienced surgeons have always done: make intraoperative decisions based on operative findings.
Selective Neck Dissection for Oropharyngeal, Hypopharyngeal, and Laryngeal Cancer
The lateral neck dissection is recommended for these sites. It removes nodal groups II, III, and IV, leaving levels I and V undissected. Level IIB is sometimes excluded in laryngeal and hypopharyngeal cancers. The procedure should be done bilaterally in all supraglottic and hypopharyngeal cancers, or if there are proven metastases to one side of the neck. In the case of subglottic or low hypopharyngeal invasion, including level VI is recommended.
Posterolateral Neck Dissection
This operation removes the nodes of levels II, III, IV, and V, the suboccipital, and the postauricular nodal groups. It is recommended for metastases from skin malignancies of the posterior scalp, posterior neck, and some parotid salivary gland cancers that have metastasized posteriorly. The dissection differs from the dissections favored for aerodigestive system metastases. It removes the lymph nodes and lymphatics containing fibrofatty tissue of the posterior neck, the subdermal fat, and fascia between the primary site and nodal compartments where there are no distinct fascial compartments.
Central Compartment Neck Dissection
The term central compartment has been widely accepted, and has superseded others like anterior compartment. This dissection removes only area VI, which includes the paratracheal, perithyroid, and precricoid (Delphian) nodes. The procedure is favored for thyroid cancer, cervical trachea, subglottic laryngeal cancer (subglottic or transglottic), cervical esophagus, and hypopharynx cancer. The procedure is usually bilateral for cervical esophageal and large hypopharyngeal cancer. It can be combined with a lateral dissection and occasionally needs to be extended to the upper mediastinum. This selective dissection clarifies the management of an area of potential metastases that has been largely neglected. Nevertheless, there is a dearth of statistical data to make rational decisions about when, how much, whether both sides, when to extend, and so forth. The central compartment dissection seems reasonable because of the definition of its scope.
3.3 Dissecting through Fascial Spaces: The Latin Approach
This approach is based on the anatomical compartmentalization of the neck. The fascial system creates spaces and barriers separating the lymphatic tissue from the remaining neck structures. The lymphatic system of the neck is contained within a fascial envelope, which, under normal conditions, may be removed without taking out other neck structures such as the internal jugular vein, sternocleidomastoid muscle, or spinal accessory nerve. The surgical technique that made this possible was initially referred to as “functional neck dissection” because it allowed a more functional approach to the neck in head-and-neck cancer patients. However, as previously emphasized, the most important but less well-known fact about functional neck dissection is that it represents a surgical concept with no implications regarding the extent of the surgery. Osvaldo Suárez never performed functional neck dissection as the comprehensive type of neck dissection that some have made of it. In fact, the operation he used for cancer of the larynx did not include the submandibular and submental lymph nodes (area I) in the resection, something that nowadays will be considered a selective neck dissection.
The question that arises at this point is if functional neck dissection was initially designed as a new approach to the neck regardless of the extent of the surgery, why did we make of it just another type of “modified” radical neck dissection? To understand the reasons for this misinterpretation we must take ourselves to the moment when both trends—American and Latin—merged.
The increasing number of reports from European surgeons in the English literature describing the good results obtained with functional neck dissection drew the attention of American surgeons to this procedure. However, the merging of ideas resembled more a collision than a mixture, and the final result was another modification to radical neck dissection. The operation was accepted as an oncologically safe procedure, but the idea was not understood. The battle of functional neck dissection had been won, but the war of the types of neck dissection, the war of the different ways to approach the neck, was lost. To sum up, the real concept of functional neck dissection was lost in translation.
3.4 Functional as a Concept
We are aware that the two approaches herein specified—American and Latin—may look similar to many observers. However, there is a great conceptual difference between them. In the first case the surgical technique is modified to preserve some neck structures, whereas in the second, a different approach is used to treat the neck that has a disease confined to the lymphatic system.
This difference may appear terminological and irrelevant when it comes to comparing “functional” versus “modified radical.” It may be said that, although the rationale is different, the end result is the same: the lymphatic system is removed from the neck, preserving the remaining neck structures. However, the situation becomes more complex when selective neck dissections appear in the surgical scenario.
Selective neck dissections are simple modifications of standard operations, whether they are functional or radical (we will see later that they are more closely related to functional than to radical neck dissection). They are just technical variations designed to fit the operation to the patient on a more individualized basis. Thus, their potential number is as high as the number of possible modifications to the original procedure. On the contrary, functional neck dissection as described here is a concept, allowing a different approach to the neck.
The key factor for the misunderstanding of functional neck dissection was the mixture between concepts and techniques that took place in the literature. This situation was favored by a linguistic factor that played an important role in all this confusion.
The functional concept reached the American surgeons through the experience of third parties because Osvaldo Suárez never published his ideas in English. Moreover, the few Spanish papers he published did not emphasize the importance of his approach—as often happens with important contributions, the author is the person least aware of the impact of the innovation. The result of this indirect transmission of information was the partial distortion of the implicit message: functional is a concept, not just another modification.
The functional concept implies dissecting along fascial planes, regardless of the nodal regions that may be preserved or included in the resection. Functional means using fascial compartmentalization to remove the lymphatic tissue of the neck.
The final conclusion for this reasoning is that functional neck dissection should not be identified with a comprehensive type of nonradical neck dissection, but with a conceptual approach to the neck. Whether the surgeon decides to stop above or below the omohyoid muscle in oral cavity tumors, remove or preserve the lymph nodes in the posterior triangle of the neck (lower part of area V) in hypopharyngeal cancer, or resect or spare the submental lymph nodes in laryngeal cancer patients constitutes only minor considerations in regard to the basic principle.
Now let us address the relations between the basic functional principle and selective neck operations.