JOCHEN A. WERNER
Department of Otolaryngology, Head and Neck Surgery, Philipps-University Marburg, Marbug, Germany
INTRODUCTION
The knowledge of the lymphatic system draining the upper aerodigestive tract is much less precise than the one of the blood vessel system of the mentioned region.
Discussions around the tendency of lymphogenic metastatsis are increasingly led on a molecular biologic level than on morphologic facts like the distribution and also the tightness of the regional lymph vessels.The latter aspect is of great significance because the tendency of lymphogenic metastatic spread is directly influenced by the density of the lymph vessels in the area of the primary tumor. The analysis of the lymphatic system, which is based on different examination methods, allows a nearly constant description of the architecture of the lymphatic network (1-4). In connection with the controversial discussion about optimized therapy for cases with no clinical evidence of lymphogenic metastasis, lymphatic distribution and density is of fundamental interest with regard to the value of sentinel node iden- tification in HNSCC.
Prognosis of patients suffering from squamous cell carcinoma of the upper aerodigestive tract is defined to a lesser extent through the size of the primary tumor. It is rather the extent of metastatic disease, which in squamous cell carci- noma predominantly occurs in a lymphogenous pattern that predicts the course of the disease. In the discussion that is increasingly led on a molecular biologic level concerning the tendency of lymphogenic metastatic spread, the morphologic facts
like the distribution and also the tightness of the regional lymph vessels become less important, an aspect that is of great significance because the tendency of lymphogenic metastatic spread is directly influenced by the density of the lymph vessels in the area of the primary tumor.
Adding the technique of the indirect lymphography, performed with dye or with a radioactive tracer, it is possible to integrate the lymphatic system of the upper aerodigestive tract in the cervical lymph node system. Proven regional dif- ferences concerning the density and also the orientation of the lymphatics of the upper aerodigestive tract are not only important regarding the direction and frequency of lymph node metastases, but are also significant considering the aspect of the type of neck dissection required to treat patients with squamous cell carcinomas of the head and neck (HNSCC). In connection with the controversial discussion about optimized therapy for cases with no clinical evidence of lymphogenic metastasis, lymphatic distribution and density is of fundamental interest with regard to the value of sentinel node identification in HNSCC.
MAIN DIRECTION OF LYMPHATIC DRAINAGE
The lymph fluid of the oral cavity is directed mainly in its anterior part to the lymph nodes of level I (5). From the edge of tongue and the posterior part of the floor of the mouth the lymph fluid is drained also in level II. An aspect that is possibly not well known refers to the metastatic spread in lingual lymph nodes (6, 7), which can be divided into a lateral and a median group (8). The lymph nodes of the lateral group are located either laterally to the genioglossal muscle or on the hypopha- ryngeal muscle alongside the lingual artery and vein. The lymph nodes of the median group are located alongside the central lymph vessels in direction of the floor of the mouth. Even though this might be rarely seen, these lymph nodes could be discussed as starting point of local recurrences (7). Ozeki et al. (6) were able to determine in carcinomas of the tongue three cases of metastases in the lingual lymph nodes (one metastasis in median and two in the lateral group).The possibility of metastatic spread in lingual lymph nodes induced the mentioned authors to indicate the necessity of an en bloc resection because the lingual lymph nodes located beyond the omohyoid muscle are normally not resected in the course of a classic neck dissection.
The physiologic lymphatic drainage of the nasopharynx flows from the nasal fornix first in dorsolateral then in dorsolaterocaudal direction (9). Furthermore, there is a lymphatic drainage parallel to the posterior midline that corresponds to the findings of Rouvière (8).According to his investigations, the lymph fluid drains from the fornix and from the posterior nasopharyngeal wall via 8–12 collectors parallel to the posterior midline.The collectors draw to the retropharyngeal lymph nodes as well as to the lymph nodes of level II and especially level V. Based on this nasopharyngeal carcinomas metastasize mainly into the mentioned groups of lymph nodes (10).
The lymphatic drainage of the palatine tonsil and of the base of the tongue is directed mainly to the lymph nodes of level II, sometimes also via collectors that drain to the retropharyngeal lymph nodes and to the lymph nodes in level III (11).
The lymphatic drainage of the posterior pharyngeal wall is directed into the retropharyngeal lymph nodes of which the lymph fluid is conducted via collectors to the lymph nodes in levels II and III.Thus, the high metastatic rate of oropharyn- geal carcinomas in retropharyngeal lymph nodes can be explained (12).
Furthermore, there is also a direct lymphatic drainage from the posterior pharyngeal wall into levels II and III.
At this point, the hint to another phenomenon should not be omitted. Occult oropharyngeal carcinomas may present via a large, necrotic lymph node metastasis predominantly located in level II.This lymph node metastasis is often misdiagnosed as so-called branchiogenic carcinoma (13).
From the hypopharynx the lymph fluid is drained via collectors mostly to the lymph nodes in levels III and IV. A direct connection to level I could not be detected.
Of course also lymphatic drainage to the lymph nodes of level II can be observed, even if they occur more rarely than to the levels III and IV. This concerns especially the cranial hypopharyngeal part (10).
The lymph fluid of the supraglottic and mainly also of the glottic region flows to the lymph nodes of levels II and III. From the subglottic space, the lymph fluid is conducted ventrally through the cricothyroid ligament and dorsally through the cricotracheal ligament. The subglottic lymph fluid flows to the lymph nodes of levels III and VI. The presence of a prelaryngeal lymph node located in level VI (so-called Delphi lymph node) depends on the age of the patient.Whereas this lymph node can be regularly observed in children up to the age of 10, only half of the examined adults between 40 and 75 are in its possession.
In summary, the direction of metastatic spread in laryngeal carcinomas corre- sponds in most of the cases to the above-described lymphatic drainage in the levels II and III (14).
According to the described mean lymphatic drainage of the upper aerodigestive tract, lymphatic metastatic spread into several lymph groups is depending on the location of the primary (Table 1), which directly influences surgical treatment concepts.
BYPASS OR CONTRALATERAL LYMPHATIC DRAINAGE
The direction and extent of lymphatic drainage and related lymphogenic metastatic spread are also influenced by tumor growth, accompanying inflammations, surgical measures, and radiotherapy.
The significance of these factors is also critically important in the metastatic process in contralateral cervical lymph nodes for which Ossof and Sission (15) con- sider three mechanisms as being responsible.The first pathway of metastatic spread occurs via afferent lymph vessels crossing to the contralateral side.This is especially true when ispilateral lymph vessels are interrupted (16). The second pathway of
Table 1. Mean metastatic spread according to the primary side Level according to
Lymph node Robbins et al. (18) Primary
Submental and submandibular group I Oral cavity
Buccal mucosa Mobile tongue
Craniojugular group II Tonsil
Soft and hard palate Base of the tongue Supraglottis Glottic
Mediojugular group III Larynx (glottic, supra-
and subglottis) Hypopharynx Caudal part of the base
of the tongue
Caudojugular group IV Hypopharynx
Subglottis
Group containing the posterior triangle V Epipharynx
Skin of the head
Group of the anterior compartment VI Thyroid gland
Subglottic
contralateral metastatic spread occurs in areas that are not divided by a midline.The third pathway of metastatic spread occurs via retrograde metastatic spread along crossing, efferent lymph vessels; this is observed in cases of extended regional lymph node involvement (17).
Another example of altered lymphatic drainage direction and related lymph node metastases in unusual locations is the development of metastases at the base of a myocutaneous pedicle of a flap placed after previous extirpation of a carcinoma of the oral cavity or the pharynx. In such cases, lymphogenic metastatic spread can occur through the myocutaneous flap in levels where usually no metastases develop (1).
CONCLUSION
The lymphatic drainage directions of the different primary tumor sites of the upper aerodigestive can be summarized as follows:
– The dominating metastatic region of pharyngeal and laryngeal carcinomas is mainly level II and less commonly level III.
– Carcinomas of the anterior oral cavity drain mostly into level I and less commonly into level II (18).
Accordingly, selective neck dissection of these lymph node levels can be expected to include the majority of clinically occult metastases.
With this background, it must still be clarified whether the intraoperative identification of the radiolabeled sentinel lymph node is appropriate to reduce the extent of selective neck dissection in the suspected N0 neck, or whether neck
dissection can be completely avoided in the case of histologically proven tumor-free sentinel lymph node. Opponents of such a procedure argue that selective neck dissection of one or two neck levels is much more precise and standardized than any identification of several lymph nodes encompassing the low morbidity for selective neck dissection that must not be considered. Supporters of sentinel lym- phadenectomy stress both protecting the intact, i.e., nonmetastastic, cervical lymph node systems, and reducing the extent of surgery. Scarring contractures, paresthesia, and persisting lymph edemas are supposed to be reduced by a selective sentinel lymph node dissection.
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