The body’s lymphatic system circulates a colorless fluid called lymph, collecting waste, cellular debris, and foreign invaders before filtering them out. A significant cluster of these bean-shaped structures is located in the inner thigh, in the crease where the thigh meets the torso. These nodes play a role in immune defense for the lower half of the body by monitoring the fluid draining from the legs and the groin region.
Anatomy of the Inguinal Lymph Nodes
The lymph nodes located in the upper inner thigh and groin area are known as the inguinal lymph nodes. These nodes are divided into two distinct anatomical groups: the superficial and the deep inguinal nodes. The term “inguinal” refers to the groin region, which is the anatomical boundary between the abdomen and the thigh.
The superficial inguinal lymph nodes are the ones most easily felt, as they lie close to the skin’s surface, just below the crease separating the abdomen and the leg. There are typically around 10 of these nodes, forming a chain that extends slightly down the upper inner thigh. They are further subdivided into groups that are located superiorly and inferiorly within this region.
The deep inguinal lymph nodes are fewer in number, usually three to five, and are situated deeper within the connective tissue of the upper thigh. They are positioned closer to the major blood vessels, specifically medial to the femoral vein. The superficial nodes drain into these deeper nodes, which then send the filtered lymph fluid upward toward the nodes located in the pelvis.
What These Lymph Nodes Filter
The primary function of the inguinal lymph nodes is to filter lymph fluid from specific parts of the body. They serve as the main drainage pathway for the entire lower limb, including the feet and legs. Any infection, wound, or inflammation in the foot, ankle, or leg will cause the lymph fluid carrying the immune response to flow directly toward these nodes.
Beyond the lower limbs, these nodes filter the fluid draining from the external genitalia and the perineum, which is the region between the legs. They are also responsible for surveillance of the lower portion of the abdominal wall and the skin of the buttock area. This broad drainage area means the inguinal nodes are constantly exposed to information about the health status of a large section of the body’s lower half.
As lymph fluid passes through the nodes, specialized immune cells like lymphocytes and macrophages filter out harmful materials such as bacteria, viruses, and other foreign particles. If an invader is detected, the immune cells inside the node activate and begin to multiply rapidly to mount a defense. This filtering process is a normal, healthy function that occurs continually.
Why Swelling Occurs
Swelling of the lymph nodes, medically termed lymphadenopathy, happens when the nodes are actively engaged in fighting an infection or filtering inflammatory debris. The enlargement is caused by the rapid increase in the number of immune cells working within the node. When the inguinal nodes swell, it indicates a problem exists somewhere within their drainage area.
The most common reasons for swollen inguinal nodes are infections in the legs or feet, such as cellulitis or athlete’s foot. Infections in the groin area, including jock itch or minor skin infections, can also trigger a response. Because the nodes drain the genital region, sexually transmitted infections (STIs), such as syphilis or chlamydia, are also common causes of inguinal swelling.
While most cases of swelling are due to a localized, temporary infection, a persistent lump that does not resolve should prompt a medical evaluation. Swelling that is hard, fixed in place, or painless, or that occurs without any apparent local infection, can sometimes be a sign of a more serious, though much rarer, condition. These less common causes include systemic diseases or even the spread of cancer, such as from a melanoma or a carcinoma of the genital or anal region.