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Lymphatic System and Lymph Nodes

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Last reviewed: October 4, 2026

Introduction

The lymphatic system is a network of thin vessels and small organs called lymph nodes that collects fluid from the tissues, filters it, and returns it to the bloodstream. The neck holds a large share of the body's lymph nodes, and they are often the first place a cancer of the head and neck spreads. For that reason, the lymph nodes of the neck matter in nearly every decision about head and neck cancer: how it is staged, whether the neck is treated, and how it is treated.

This page explains what lymph nodes are and how the neck is divided into lymph node levels, how lymph nodes are removed (neck dissection) and what is learned from them, sentinel lymph node biopsy, and lymphedema, the swelling that can follow treatment. A short summary and a numbered reference list are at the end. Where the evidence is limited or mixed, the page says so. Related pages include tumors of the neck, lymph nodes, and general tumor information.

Lymph nodes as filters

Lymph nodes are like filters throughout the body. They are connected by tunnels (channels) that allow fluid that has leaked out of the bloodstream to be filtered and collected and eventually shunt back into the bloodstream. This is part of the immune system, and germs or non-native molecules trigger an immune response in the lymph node, allowing the immune cells to fight back.

In more detail, a small amount of fluid constantly seeps out of the tiny blood vessels (capillaries) into the tissues. Thin-walled lymphatic vessels pick up this fluid, now called lymph, and carry it through a chain of lymph nodes before it drains into large veins at the base of the neck [2]. Each node is packed with immune cells. When lymph brings in bacteria, viruses, or abnormal cells, those immune cells can recognize them and mount a response. This is why nodes in the neck commonly swell and become tender with a sore throat or dental infection, then shrink again over a few weeks.

Lymph nodes of the neck

An estimated 150 to 300 lymph nodes sit in the neck [1]. Lymph from each part of the head and neck drains to fairly predictable groups of nodes. For example, the lip and front of the mouth tend to drain to nodes under the chin and jaw, while the throat and voice box tend to drain to nodes along the large vein on the side of the neck [1]. Because the drainage is predictable, surgeons and radiation oncologists can anticipate where a cancer is most likely to spread.

To describe these groups consistently, the neck is divided on each side into levels, numbered I to VI [3]:

Level I: nodes under the chin (IA) and under the jaw, around the submandibular gland (IB).
Level II: upper nodes along the jugular vein, near the angle of the jaw.
Level III: middle nodes along the jugular vein.
Level IV: lower nodes along the jugular vein, just above the collarbone.
Level V: nodes in the back of the neck (posterior triangle), behind the large muscle on the side of the neck.
Level VI: central nodes in front of the windpipe, around the thyroid and voice box.

Surgeons use these levels to describe which nodes are removed, pathologists to report where cancer was found, and radiation oncologists, who use a matching map on CT scans, to plan which areas to treat [3, 4].

When lymph nodes are a concern

Most enlarged neck nodes are reactive, meaning they are responding to an infection. A node that stays enlarged, grows, or is firm deserves an evaluation, which is described on the neck tumors page. Cancers that commonly spread to neck lymph nodes include squamous cell carcinoma of the mouth, throat and voice box; papillary thyroid cancer; and skin cancers such as cutaneous squamous cell carcinoma, melanoma and Merkel cell carcinoma. Lymphoma is a cancer that starts within the lymph nodes themselves.

Removal of neck lymph nodes (cervical lymphadenectomy or neck dissection)

When lymph nodes of the neck are either definitively involved with cancer or are at high risk of involvement with cancer, treatment typically includes the lymph nodes in that region. This can be done with radiation (± chemotherapy) or surgery. When the lymph nodes are surgically removed, the specimen is sent for pathology, allowing us to learn more about the cancer, such as how many lymph nodes were involved, and whether aggressive and high-risk features are present, such as when a tumor grows beyond the capsule of the lymph node. This additional information on the lymph nodes factors into any recommendation for possible additional treatment after surgery, such as radiation.

The technical goal of surgery to remove the lymph nodes is to thoroughly remove the lymph nodes in the area at risk, while preserving normal structures. Having said this, the surrounding structures are at some risk, and some numbness to the skin of the neck and ear, some weakness of the lower lip, and some weakness in raising the arm above the head in a jumping jack position may occur and typically improve with time.

• Link to a well-written article on the American Head and Neck Society website explaining the purpose and risks of removing lymph nodes in the neck,

Types of neck dissection

A neck dissection (cervical lymphadenectomy) removes the fat and lymph nodes from defined levels of the neck as one piece. The names describe how much is removed [3]:

Radical neck dissection: removes levels I to V together with the spinal accessory nerve, the internal jugular vein, and the sternocleidomastoid muscle. It is now used mainly when cancer directly involves these structures.
Modified radical neck dissection: removes levels I to V but keeps one or more of those three structures, most often the spinal accessory nerve.
Selective neck dissection: removes only the levels at highest risk for a particular cancer, for example levels I to III for many mouth cancers or levels II to IV for many throat and voice box cancers.
Extended neck dissection: also removes an additional node group or structure, such as a nerve or the skin.

More information on the operation is on the cervical lymphadenectomy (neck dissection) page, and the neck dissection recovery expectations page and surgical packet describe what to expect around surgery.

Treating the neck before cancer is visible

Cancer can be present in lymph nodes even when they look normal on examination and imaging. This is called occult (hidden) spread. An elective neck dissection removes the nodes at risk before any spread is apparent; a therapeutic neck dissection is done for nodes known to contain cancer.

The strongest evidence comes from early mouth cancer. In a randomized trial of 500 patients with early oral squamous cell carcinoma and a clinically normal neck, removing the nodes at the time of the primary surgery improved 3-year overall survival compared with watching the neck and operating only if a node appeared later (80% vs 67.5%). Disease-free survival was also higher (69.5% vs 45.9%) [6]. The American Society of Clinical Oncology (ASCO) guideline on the neck in mouth and throat cancer describes when neck dissection is indicated and what a high-quality neck dissection includes [5]. For some early mouth cancers, a sentinel node biopsy (below) is an alternative.

What the lymph nodes tell the care team

The pathology report on the removed nodes is one of the strongest predictors of outcome in head and neck cancer, and it guides decisions about further treatment:

Extranodal extension (ENE). This means the cancer has grown through the capsule of the lymph node into the surrounding tissue. Since the 8th edition of the AJCC/UICC staging system, ENE raises the nodal stage of head and neck cancers that are not caused by a virus [7].
Number of positive nodes. In a national database study of more than 14,000 patients with mouth cancer, the risk of death rose steadily with each additional node containing cancer [8].
Number of nodes removed. In a national study of about 64,000 patients, those with fewer than 18 nodes in the neck dissection specimen had an 18% higher risk of death than those with 18 or more, after adjusting for other factors [9]. These are observational studies, so they show association rather than proof of cause, but they are one reason a thorough dissection matters.

Treatment after neck dissection

When the pathology shows higher-risk features, radiation after surgery is often recommended. Two randomized trials published together in 2004 tested adding the chemotherapy drug cisplatin to radiation after surgery for higher-risk head and neck cancer. In the European trial, adding cisplatin improved 5-year overall survival from 40% to 53% [10]. In the North American trial, it improved control of the cancer in the head and neck region, but overall survival was not significantly different [11]. Both trials found more severe side effects with the combined treatment [10, 11]. A combined analysis of the two trials found that the benefit was clearest when there was extranodal extension or cancer at the edge of the removed tissue (a positive margin) [12]. More information is on the radiation therapy and chemotherapy and immunotherapy pages.

Neck dissection after chemoradiation

Some cancers, especially cancers of the tonsil and base of tongue, are treated first with radiation and chemotherapy. In the past, a planned neck dissection often followed. In a randomized trial of 564 patients with advanced neck disease, PET-CT scanning after treatment, with surgery only for patients whose scans showed an incomplete response, gave similar 2-year survival to planned neck dissection (84.9% vs 81.5%), with far fewer operations (54 vs 221) [13].

Recovery and risks

Shoulder problems are the most studied side effect. The spinal accessory nerve, which runs through the neck to the trapezius muscle, can be stretched or bruised even when it is preserved. A systematic review found shoulder pain in 9 to 25% of patients after selective neck dissection, with higher rates after more extensive operations; preserving the nerve lowers but does not eliminate the risk [14]. In a randomized trial of survivors with shoulder dysfunction after neck dissection, a 12-week progressive resistance exercise program reduced shoulder pain and disability and improved strength more than standard exercises [15]. Stiffness of the neck itself can also develop after treatment; see frozen neck.

A chyle leak is an uncommon but important complication. The thoracic duct, the largest lymphatic channel in the body, enters the veins in the lower left neck, and injury to it or its branches can cause lymph fluid to collect under the skin [16]. Many leaks settle with diet changes and drainage, and some need further procedures [16]; see chyle leak. Other possible effects include numbness of the skin, weakness of the lower lip, and, rarely, injury to the hypoglossal nerve (tongue movement) or the phrenic nerve (diaphragm).

sentinel node biopsy (sentinel lymph node biopsy)

The sentinel lymph node is the hypothetical first lymph node or group of nodes draining (filtering fluid from) a cancer. It is postulated that the sentinel lymph node is the most likely lymph node to be involved by a cancer if spread has occurred. Therefore, removing and testing a sentinel lymph node can indicate whether spread has occurred, even if too small to be felt on exam or seen on x-rays or other imaging. The sentinel node biopsy is the identification, removal and analysis of the sentinel lymph node (or sentinel lymph nodes if a few good candidates are apparent) of a particular tumor.

• Link to the National Cancer Institute webpage on sentinel node biopsy.

How it is done

A small amount of a radioactive tracer is injected around the tumor, usually on the day of surgery or the day before. A scan (lymphoscintigraphy) shows where the tracer travels. In the operating room, a handheld probe finds the nodes that took up the tracer, and these nodes are removed through a small incision. The pathologist then examines them in fine detail, often with extra thin sections and special stains to find very small deposits of cancer [17]. If the sentinel nodes contain cancer, treatment of the rest of the neck, usually a neck dissection, is recommended for head and neck squamous cell carcinoma.

Sentinel node biopsy for mouth cancer

For early (T1 and T2) oral cavity cancer with a normal-appearing neck, sentinel node biopsy is an alternative to elective neck dissection:

In a North American multicenter trial, a negative sentinel node correctly predicted a cancer-free neck in 96% of patients when detailed pathology was used [17].
In a European trial of 415 patients, a sentinel node was found in 99.5%. The negative predictive value was 95%, and about 14% of patients whose nodes were thought to be negative later had cancer appear in the neck, about half of whom were treated successfully [18].
In a French randomized trial of 279 patients with early mouth and throat cancer, control of the neck at 2 years was equivalent with sentinel node biopsy and with neck dissection (about 90% in each group). Patients in the sentinel node group had better shoulder and neck function in the first 6 months [19].
In a Japanese randomized trial of 271 patients with early mouth cancer, 3-year survival after sentinel node–guided surgery was not inferior to elective neck dissection (87.9% vs 86.6%), and neck function was better [20].

The trade-off is a small chance of missed spread, which makes close follow-up important, against less surgery for the roughly 3 out of 4 patients whose nodes turn out to be cancer-free. The accuracy depends on the experience of the surgical, nuclear medicine and pathology teams, and the technique is harder to apply for tumors in the floor of the mouth, where the tumor and the nodes sit close together [17].

Sentinel node biopsy for melanoma

Sentinel node biopsy is a standard part of staging for many melanomas. In a randomized trial of 2,001 patients, sentinel node biopsy gave important information about prognosis and, among patients with intermediate-thickness melanoma whose nodes contained cancer, sentinel node–based management improved melanoma-specific survival [21]. A second trial of 1,934 patients with a positive sentinel node found that removing the remaining nodes right away did not improve melanoma-specific survival compared with careful monitoring by ultrasound (86% at 3 years in both groups), although it did improve control of the cancer in the nodes, and it caused lymphedema more often (24% vs 6%) [22]. As a result, many patients with a positive sentinel node are now monitored rather than having a full dissection. See treatments for melanoma and the skin cancer page.

Lymphedema

Lymphedema is the condition of swelling (edema) of tissue relating to insufficient clearance by the lymphatic system. It can occur after treatment, either surgical, radiation, or both. New drainage pathways develop over time, but treatments such as manual lymphatic drainage performed by a physical therapist or a home-use device speed up and improve clearance of lymphedema. When severe and untreated, lymphedema can constrain movement, which can allow scar tissue to develop and limit movement permanently.

• Link to an article for patients explaining lymphedema and its treatment on the American Head and Neck website.

How common it is

Lymphedema is common after head and neck cancer treatment. In a study of 81 patients examined at least 3 months after treatment, 75% had some form of lymphedema [23]. It can be:

External: visible swelling of the face, under the chin, or in the neck.
Internal: swelling inside the throat and voice box, seen on a scope examination. In that study, internal lymphedema was more common than external, and half of the patients with lymphedema had both [23].

Internal lymphedema matters because it is linked to difficulty swallowing; in one study, the degree of swelling in the throat correlated with both patient-reported and measured swallowing problems [24]. See the swallowing page.

Treatment

The main treatment is complete decongestive therapy, given by a therapist trained in lymphedema. It combines manual lymphatic drainage (a gentle massage technique that moves fluid toward working lymph channels), compression garments, skin care, and exercise, followed by a home program. In a review of more than 700 treated patients at one cancer center, 60% improved, and patients who followed the home program closely were more likely to improve [25]. A systematic review found that manual lymphatic drainage is the best studied treatment, but that the evidence for all lymphedema treatments is limited by a lack of large randomized trials [26].

Advanced pneumatic compression devices are home-use garments for the face and neck that inflate in sequence to move fluid. A small randomized trial showed they were safe and reduced visible swelling [27]. A larger multicenter randomized trial of 236 patients compared the device with usual therapist-guided care. Both groups improved to a similar degree in symptoms; the device group had more improvement in visible external swelling at 2 months, and at 6 months both groups had maintained similar benefit [28, 29]. The trial authors noted that the device helps patients who face barriers to regular therapist visits [28].

Summary

The neck contains roughly 150 to 300 lymph nodes, grouped into levels I to VI, and they are a common first site of spread for head and neck cancers [1, 3].
For early mouth cancer with a normal-appearing neck, elective neck dissection improved survival compared with watching the neck in a randomized trial [6].
The number of positive nodes and extranodal extension are important predictors of outcome and guide whether radiation, with or without chemotherapy, is recommended after surgery [7, 8, 12].
After chemoradiation, PET-CT can safely spare most patients a planned neck dissection [13].
Sentinel node biopsy is an established alternative to elective neck dissection for selected early mouth cancers and a standard staging step for many melanomas [19, 20, 21].
Lymphedema affects most patients after head and neck cancer treatment to some degree and responds to therapy, although high-quality trial evidence is still limited [23, 26].

References

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