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Neck Dissection Classification Update
Revisions Proposed by the American Head and Neck Society and the American Academy of Otolaryngology–Head and Neck Surgery
K. Thomas Robbins, MD;
Garry Clayman, MD;
Paul A. Levine, MD;
Jesus Medina, MD;
Roy Sessions, MD;
Ashok Shaha, MD;
Peter Som, MD;
Gregory T. Wolf, MD;
and the Committee for Head and Neck Surgery and Oncology, American Academy
of Otolaryngology–Head and Neck Surgery
Arch Otolaryngol Head Neck Surg. 2002;128:751-758.
INTRODUCTION
Since the first description of the radical neck dissection by George
Crile almost a century ago, many variations and modifications of the procedure
have been added. These include the functional neck dissection, the modified
radical neck dissection, and various selective neck dissections. In response
to the need for an organized approach in describing these operations, the
Committee for Head and Neck Surgery and Oncology of the American Academy of
Otolaryngology–Head and Neck Surgery (AAO-HNS) in 1988 initiated an
effort to develop a standardized classification system for neck dissection
(Table 1). During this process,
input was obtained from the Education Committee of the American Society for
Head and Neck Surgery (ASHNS) and its Council. The final product, endorsed
by the ASHNS and the AAO-HNS, was published in the ARCHIVES1
and as a monograph2 by the AAO-HNS in 1991.
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Table 1. Classification of Neck Dissection
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In 1998, 10 years following the initiation of the neck dissection classification
project, an ad hoc committee of the newly formed American Head and Neck Society
(AHNS) was convened to review the original classification scheme. This was
prompted by the AAO-HNS's desire to update its monograph on the subject and
include the recent revisions to the American Joint Commission on Cancer (AJCC)
staging system for head and neck cancer. However, there was also a need to
consider revisions to the neck dissection classification in light of new observations
regarding the biological function of lymph node metastases, further refinements
in selective neck dissection procedures, as well as a need to redefine the
anatomical boundaries of certain neck levels and be consistent with the anatomical
boundaries used in radiologic studies of the neck.
Chaired by the primary author (K.T.R.), the Committee for Neck Dissection
Classification of the AHNS met several times over a 2-year interval to complete
its work. Representation on the committee also included a radiologist, (P.S.), who had worked within his own specialty to define parameters by which
the orientation of lymph nodes in the neck could be accurately described in
relation to the level system.3-4
During this interval, the members serving at that time on the Academy's Committee
for Head and Neck Surgery and Oncology provided additional advice.
As the committee members reviewed the 1991 neck dissection classification
system (Table 1),1
there was a general consensus that the basic approach previously followed
had clearly achieved its original objective to standardize neck dissection
terminology using a system that was logical, straightforward, and easy to
remember. In fact, the committee members noted that the worldwide use of the
system was a testimony to its practicality and usefulness. Consequently, a
strong desire was expressed to maintain this structure because any radical
alterations carried a risk of losing the widespread support for a standardized
neck dissection classification. However, it was also believed there was an
opportunity to introduce certain modifications that would allow the original
classification to remain contemporary and in keeping with the current philosophy
for managing lymph node metastases.
DIVISION OF LYMPH NODES BY LEVELS
The committee supported the continued use of the level system to delineate
the location of lymph node disease in the neck (Figure 1).5 The level system is well
known and easy to remember and now serves as the basis for describing various
selective neck dissections. Contrary to the recommendations by others, it
did not recommend including additional levels such as level VII for the superior
mediastinum. It was believed that the 6 levels currently used encompassed
the complete topographic anatomy of the neck. Lymph nodes involving regions
not located within this region would be referred to by the name of their specific
nodal group. In addition to the superior mediastinum, other examples include
the retropharyngeal lymph nodes, the periparotid lymph nodes, the buccinator
nodes, and the postauricular and suboccipital nodes. Figure 1 depicts the topographical boundaries of the level system.
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Figure 1. The 6 levels of the neck.
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DIVISION OF NECK LEVELS BY SUBLEVELS
The committee decided to introduce the concept of sublevels into the
classification, since certain zones have been identified within the 6 levels,
some of which may have biological significance independent of the larger zone
in which they lie. These are outlined in Figure 2 as sublevels IA (submental nodes), IB (submandibular nodes),
IIA and IIB (together comprising the upper jugular nodes), and VA (spinal
accessory nodes) and VB (transverse cervical and supraclavicular nodes). The
boundaries for each of these sublevels are specified in Table 2.
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Figure 2. The 6 sublevels of the neck.
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Table 2. Lymph Node Groups Found Within the 6 Levels and the 6 Sublevels
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The risk of nodal disease in sublevel IIB is greater for tumors arising
in the oropharynx compared with the oral cavity and larynx. Thus, in the absence
of clinical nodal disease in sublevel IIA, it is likely not necessary to include
sublevel IIB for tumors arising in these latter sites. The dissection of the
node-bearing tissue of sublevel IIB (submuscular recess) is not without an
increased risk of morbidity. Adequate exposure necessitates significant manipulation
of the spinal accessory nerve (SAN) and may account for trapezius muscle dysfunction
observed in a significant minority of patients following a selective neck
dissection. Sublevel IA is another example in which many surgeons opt not
to remove this zone unless the primary cancer involves the floor of mouth,
lip, or structures of the anterior midface.
Level V is the third region in which the committee believed there was
merit in subdividing it into levels VA and VB. The superior component, level
VA, primarily contains the spinal accessory lymph nodes, whereas level VB
contains the transverse cervical nodes and the supraclavicular nodes, which
carry a far more ominous prognosis when positive for aerodigestive tract malignancies.
DEFINITION OF LYMPH NODE GROUPS
It was agreed that the names depicting the lymph node groups within
each of the 6 neck levels were well accepted and used in a uniform manner
(Table 2). Continued support of
this nomenclature would preclude the introduction of other terms that would
potentially be ambiguous (eg, deep cervical nodes). Table 2 also outlines the lymph node groups located within each
of the 6 neck levels.
ANATOMICAL BOUNDARIES OF THE NECK LEVELS
The anatomical boundaries of the 6 neck levels as identified in the
first article on neck dissection classification were well defined with the
exception of a few instances in which there were minor inaccuracies or ambiguities
(Table 3).1
For example, the stylohyoid muscle rather than the posterior belly of the
digastric muscle more accurately defines the posterior border of level IB.
Similarly, the plane defined by the sensory branches of the cervical plexus
has been added to delineate the boundary between the posterior borders of
levels II through IV and the anterior border of level V. This parameter is
in addition to the posterior border of the sternocleidomastoid muscle (SCM)
and provides a more practical intraoperative landmark for the surgeon (Table 3 and Figure 2).
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Table 3. Anatomical Structures Defining the Boundaries of the Neck
Levels and Sublevels
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CORRELATION OF NECK LEVEL BOUNDARIES WITH ANATOMICAL MARKERS DEPICTED
RADIOLOGICALLY
In the 1991 neck dissection classification,1
not all of the anatomical structures used to define the boundaries were readily
visible on radiologic studies such as computed tomography and magnetic resonance
imaging. Consequently, radiologists have now identified landmarks that more
accurately identify the location of lymph nodes according to the level system.3 Using radiologic landmarks, level I includes all of
the nodes above the level of the lower body of the hyoid bone, below the mylohyoid
muscles, and anterior to a transverse line drawn on each axial image through
the posterior edge of the submandibular gland. Level IA represents those nodes
that lie between the medial margins of the anterior bellies of the digastric
muscles, above the level of the lower body of the hyoid bone, and below the
mylohyoid muscle (previously classified as submental nodes). Level IB represents
the nodes that lie below the mylohyoid muscle, above the level of the lower
body of the hyoid bone, posterior and lateral to the medial edge of the anterior
belly of the digastric muscle, and anterior to a transverse line drawn on
each axial image tangent to the posterior surface of the submandibular gland
on each side of the neck (previously classified as submandibular nodes). Level
II extends from the skull base, at the lower level of the bony margin of the
jugular fossa, to the level of the lower body of the hyoid bone. Level II
nodes lie anterior to a transverse line drawn on each axial image through
the posterior edge of the SCM and lie posterior to a transverse line drawn
on each axial scan through the posterior edge of the submandibular gland.
However, any nodes that lie medial to the internal carotid artery are retropharyngeal
and not level II.
Level III nodes lie between the level of the lower body of the hyoid
bone and the level of the lower margin of the cricoid cartilage. These nodes
lie anterior to a transverse line drawn on each axial image through the posterior
edge of the SCM. Level III nodes also lie lateral to the medial margin of
either the common carotid artery or the internal carotid artery. On each side
of the neck, the medial margin of these arteries separates level III nodes
(which are lateral) from level VI nodes (which are medial).
Thus, the revised classification uses the horizontal plane defined by
the inferior border of the hyoid bone instead of the carotid bifurcation to
delineate the boundary between levels II and III. Similarly, the revised classification
uses the horizontal plane defined by the inferior border of the cricoid cartilage
instead of the junction between the superior belly of the omohyoid muscle
to delineate the boundary between level III and level IV. However, from a
surgical perspective it is important to note the significance of the anatomical
relationship between the omohyoid muscle and the internal jugular vein, since
lymph nodes usually are located in this region. These nodes would be included
in level III.
CONCEPTUAL GUIDELINES FOR NECK DISSECTION CLASSIFICATION
The definitions of types of neck dissection remain unchanged as previously
outlined in the 1991 classification article.1
These are (1) radical neck dissection is considered to be the standard basic
procedure for cervical lymphadenectomy, and all other procedures represent
1 or more alterations of this procedure; (2) when the alteration involves preservation of 1 or more nonlymphatic structures routinely
removed in the radical neck dissection, the procedure is termed modified radical neck dissection; (3) when the alteration involves preservation of 1 or more lymph node groups/levels routinely
removed in the radical neck dissection, the procedure is termed selective neck dissection; (4) when the alteration involves removal of additional lymph node groups or nonlymphatic structures
relative to the radical neck dissection, the procedure is termed extended neck dissection.
CLASSIFICATION OF NECK DISSECTION
Classification of neck dissection is outlined in Table 1. It is essentially the same as the 1991 version1 with the exception that specific names for certain
types of selective neck dissection have been deleted. As outlined in the section
on selective neck dissection, the rationale for this recommendation is based
on the increased number of variations, which have been introduced over the
past decade.
RADICAL NECK DISSECTION
Radical neck dissection (Figure 3)
refers to the removal of all ipsilateral cervical lymph node groups extending
from the inferior border of the mandible to the clavicle, from the lateral
border of the sternohyoid muscle, hyoid bone, and contralateral anterior belly
of the digastric muscle medially, to the anterior border of the trapezius
muscle. Included are all lymph nodes from levels I through V. The SAN, internal
jugular vein, and SCM are also removed. Radical neck dissection does not include
removal of the suboccipital nodes, periparotid nodes (except intraparotid
nodes located in the posterior aspect of the submandibular triangle), buccinator
nodes, retropharyngeal nodes, and midline visceral (anterior compartment)
nodes.
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Figure 3. The radical neck dissection.
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MODIFIED RADICAL NECK DISSECTION
Modified radical neck dissection (Figure
4, Figure 5, and Figure 6) refers to the excision of all lymph
nodes routinely removed by the radical neck dissection with preservation of
1 or more nonlymphatic structures (ie, the SAN, internal jugular vein, and
SCM). The structure(s) preserved should be specifically named (eg, modified
radical neck dissection with preservation of the SAN).
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Figure 4. Modified radical neck dissection
with preservation of the sternocleidomastoid muscle, spinal accessory nerve,
and internal jugular vein.
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Figure 5. Modified radical neck dissection
with preservation of the internal jugular vein and spinal accessory nerve.
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Figure 6. Modified radical neck dissection
with preservation of spinal accessory nerve.
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SELECTIVE NECK DISSECTION
Selective neck dissection refers to a cervical lymphadenectomy in which
there is preservation of 1 or more of the lymph node groups that are routinely
removed in the radical neck dissection. The lymph node groups removed are
based on the patterns of metastases, which are predictable relative to the
primary site of disease. For oral cavity cancers, the lymph nodes at greatest
risk are located in levels I, II, and III. The lymph nodes at greatest risk
for oropharyngeal, hypopharyngeal, and laryngeal cancers are located in levels
II, III, and IV, whereas for thyroid cancer, the lymph nodes in VI are at
the greatest risk.
Refinements in Selective Neck Dissection Nomenclature
Probably the most significant change in philosophy with regard to managing
lymph node disease over the past decade relates to the selectivity with which
lymph node groups at risk are being removed.6
Without question, the use of the selective neck dissection has become more
widespread despite some earlier concerns that it may not be as effective as
neck dissections in which all lymph node levels are removed, such as the modified
radical neck dissection. However, of equal significance have been the reports
indicating that certain neck levels may have less or greater importance than
previously thought with regard to risk of occult disease based on the specific
site of origin of the primary tumor. An excellent example of this is carcinoma
of the oral tongue. Although it is well appreciated that patients with oral
tongue cancer have a high risk of nodal involvement even for those with small
primary lesions without clinical evidence of positive nodes, the extent by
which the risk remains high for each neck level is controversial. Skip metastases
to level IV may be a potential problem, and many surgeons prefer to include
this region when performing an elective selective neck dissection. However,
the terminology to describe the neck dissection procedure for this situation
is vague. Some prefer to apply the term supraomohyoid neck
dissection because this is the standard elective procedure typically
used for oral tongue cancer. But this is inaccurate because supraomohyoid
neck dissection was intended to include only levels I through III. Others
prefer to use the term extended supraomohyoid neck dissection or anterolateral neck dissection, which more
accurately outlines the removal of levels I through IV. Unfortunately, acceptance
of these additional terms adds complexity to the nomenclature system and runs
the risk of adding confusion.
The 1991 neck dissection classification system did not provide an accurate
description of procedures in which the surgeon chooses to preserve certain
sublevels. For example, the buccinator nodes may represent the primary echelon
nodal basin for oral cavity cancers involving the buccal mucosal, hard palate,
and upper alveolar ridge. These nodes are not included in the standard supraomohyoid
neck dissection, and a better method is needed to define the inclusion of
such structures. To not further confuse this issue, it was determined by the
committee that exclusion of these "named" neck dissections would facilitate
the standardization and referencing of these procedures. Therefore, further
in this text, we will no longer refer to these "named" selective neck dissections
except in the description of specific levels.
Selective Neck Dissection (SND) for Oral Cavity Cancer
In the treatment of oral cavity cancer, the procedure of choice is SND
(I-III) (Figure 7). This refers
to the removal of lymph nodes contained in the submental and submandibular
triangles (level I), the upper jugular lymph nodes (level II), and the middle
jugular lymph nodes (level III). The cutaneous branches of the cervical plexus
and the posterior border of the SCM mark the posterior limit of the dissection.
The inferior limit is the junction between the superior belly of the omohyoid
muscle and the internal jugular vein. One of the justifications to eliminate
naming of dissections for oral cavity cancer comes from the observations regarding
invasive oral tongue carcinomas. In the case of oral tongue cancer, there
is evidence indicating level IV is also at risk.7
Thus, some authorities recommend the selective neck dissection procedure for
this subsite within the oral cavity to be SND (I-IV). For cancers involving
the midline structures including the floor of mouth and ventral tongue, the
lymph nodes on both sides of the neck are at risk and the procedure of choice
is a bilateral SND (I-III).
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Figure 7. Selective neck dissection (SND)
for oral cavity cancer: SND (I-III) or supraomohyoid neck dissection.
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