| III. Drainage Pathways
The lymphatic drainage of squamous cell carcinoma varies with the
anatomic subsite. Within specific subsites, however, the lymphatic
drainage occurs in a relatively predictable manner. The following section
will review the drainage of each anatomic subsite that was described by
Rouvière. As a result, some subsites will not be described. The intent is
to help the radiologist focus on the lymph node groups that are at greatest
risk for cervical nodal metastases in patients with squamous cell
carcinoma of different regions. The percentages of nodal involvement for
the lymph node levels presented below are derived from the classic articles
by Lindberg and Byers, which reported the distribution of cervical lymph
nodes metastases from various sites in the head and neck(21, 24). The
specifics of the analysis are described in the appendix(25).
A. Nasopharynx (Figure 10)
The lymphatic vessels drain in two general directions, lateral and medial.
The lymphatic channels of the lateral drainage pathway pierce the superior
constrictor muscle and drain into the lateral retropharyngeal, high Level
II and high Level V lymph nodes. Tumors that invade the eustachian tube,
external auditory canal, or tympanic membrane may occasionally drain to
the intraparotid lymph nodes(1, 25)
The lymphatic channels of the roof and posterior wall of the
nasopharynx drain medially. These channels penetrate the visceral fascia
at the skull base and drain into the median retropharyngeal lymph nodes(1,
25).
Often the lymphatic drainage is bilateral. So it should be remembered
that both sides of the neck are at risk for cervical nodal metastases from
nasopharyngeal cancer.
B. Oral Cavity
-
Floor of Mouth (FOM) (Figure 11)
The lymphatic drainage is divided into an anterior and posterior
complex. The anterior complex drains the anterior half of the FOM
and anterior portion of the sublingual gland. These terminate in
the Level I nodes.
The posterior complex drains the posterior two-thirds of the
FOM. These lymphatics primarily drain to the ipsilateral Level II
lymph nodes. Occasionally, there is a direct lymphatic drainage to
Level III nodes that bypass Level II nodes.
Anatomic studies have shown significant crossover of the
lymphatic drainage in superficial lymphatic capillaries. As a
result, both sides of the neck are at often at risk for metastases
arising from FOM malignancies(1, 25).
-
Oral Tongue (Figure 12)
A superficial and deep lymphatic network drains the oral tongue.
The superficial network extends from the tip of the tongue to the
circumvalate papillae and drains into the deep muscular network(1,
25).
There are three main components of the deep lymphatic network
for the oral tongue: anterior, lateral, and central. The anterior
(apical) pathway drains the tip of the oral tongue and primarily
drains to Level III or less likely Level I. The lateral (marginal)
group drains the lateral one-third of the dorsum of the tongue
from the tip to the circumvallate papillae. These lymphatic
channels drain to Levels I, II, or III. The central pathway
drains the central two-thirds of the tongue. These vessels drain
to the Group I nodes or course through a sublingual node and
terminate in Group III nodes(1, 25).
Cross-drainage in the oral tongue is common. As a result, both
sides of the neck at risk for nodal metastases(1, 25)
C. Oropharynx
- Tongue Base (Figure 13)
Similar to the oral tongue, the lymphatic drainage of the
tongue base also consists of superficial and deep muscular
lymphatic networks. The superficial network is continuous with
the superficial lymphatic network that drains the oral tongue.
The deep lymphatic drainage may drain ipsilaterally or have
direct branches that drain to the contralateral neck. Thus
both sides of the neck are at risk for nodal metastases(1, 25).
-
Palatine Tonsil (Figure 14)
The lymphatic drainage of the tonsil is to the ipsilateral
Level II and retropharyngeal lymph nodes. A less common route
of drainage is to the Level III nodes. Rouvière did not
describe cross-lymphatic drainage for this area(1, 25).
- Soft Palate (Figure 15)
Rouvière defined three separate drainage pathways for the soft
palate: anterior, middle, and posterior. Of these three, the
middle is the most constant pathway(1, 25).
The lymphatic vessels of the middle pathway extend from the
soft palate to the inner margin of the posterior belly of the
digastric muscle and drain primarily to Level II. The middle
pathway normally has crossed lymphatic drainage thereby placing
both necks at risk for nodal metastases(1, 25).
The lymphatics that comprise the posterior pathways are
present in 60% of cases. These vessels penetrate the superior
constrictor muscle into the retropharyngeal space and normally
drain into the lateral retropharyngeal lymph nodes. Crossed
drainage of the posterior pathways has been shown to be present
in 50% of individuals(1, 25).
The anterior pathway is present in half of individuals, and
drains into the Group I lymph nodes. This region has crossed
lymphatics in 50% of cases placing both sides of the neck at
risk for nodal metastases. Although both the anterior and
posterior pathways are potential drainage pathways for the soft
palate, the posterior pathway is the more common pathway for
the soft palate lesions while the anterior pathway is more
common for hard palate tumors(1, 25).
The above information necessitates treatment of the
retropharyngeal lymph nodes and both necks in patients with
soft palate carcinomas(1, 25).
D. Larynx
- Supraglottic Larynx (Figure 16)
The lymphatic drainage is separated into two components, a
superficial mucosal component that drains into a deep system of
collecting ducts. The deep system unites with the lymphatic
drainage of the inferior pharynx(1, 25).
The draining vessels of the unified deep system exit the
larynx through the natural defect in the thyrohyoid membrane that
permits passage of the superior laryngeal neurovascular bundle.
At this point, one component of the lymphatic drainage extends
superiorly and terminates in the ipsilateral Level II nodes while
a second component extends lateral and drains into nodes located
at the junction of Levels II and III. There is occasionally a
third component that drains into the nodes located in Level III
nodes(1, 25).
Tumors involving the supraglottic larynx are at risk for
crossed lymphatic drainage. However, the drainage mechanism is
unclear. There appears to be cross-drainage of the superficial
mucosal lymphatics, however, no consistent direct cross-drainage
of the deep collecting duct has been described(1, 25).
- Glottic Larynx (Figure 17)
There is a paucity of lymphatics draining the true vocal
cords (TVC). The superficial mucosal lymphatics form a
continuous layer along the posterior shtmlect of the larynx.
However, the lymphatics draining the TVC are sparse are form
a natural barrier between the supraglottic and infraglottic
larynx. The predominant lymphatic drainage of the advanced
TVC carcinoma occurs by acquiring the lymphatic drainage that
occurs by extension into the supraglottic or subglottic
larynx(24, 25).
E. Pyriform Sinus (Figure 18)
The lymphatic drainage is divided into anterior and posterior groups.
The anterior collecting system exits along with the lymphatics of the
supraglottic larynx through the natural defect in the thyrohyoid
membrane described above. These vessels course through pre-laryngeal
lymph nodes and primarily drain into the Levels II, III and the Level
VII nodes. Advanced disease may involve Levels IV and V(1, 25).
The posterior group penetrates the superior constrictor muscle and
drains into the lateral retropharyngeal lymph nodes and the internal
jugular chain. Cross-lymphatic drainage occurs from the superficial
lymphatics along the midline of the posterior pharyngeal wall(1, 25).
As a result, pyriform sinus carcinomas have a rich drainage
system. Both ipsilateral and contralateral lymph nodes from the skull
base to the base of the neck are at risk for metastases in patients
with moderately advanced tumors(1, 25).
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