Axillary Lymphadenopathy
Axillary lymphadenopathy means enlargement of the lymph nodes in the armpit. These nodes drain the breast, the arm, the chest wall, and the upper back, so they enlarge in response to anything affecting those areas—most often infection or inflammation, and less often cancer. They are among the few lymph node groups that can be felt easily, so enlargement is frequently noticed by a woman herself or found on examination, and they are also routinely assessed on mammography and ultrasound. The great majority of enlarged axillary nodes are reactive and settle on their own, but because the breast drains here, their assessment is a standard part of breast evaluation.
What is it?
Lymph nodes are small filtering stations positioned along the lymphatic vessels. Fluid drains from tissues into these vessels and passes through nodes on its way back to the bloodstream, where immune cells sample it for bacteria, viruses, and abnormal cells. When something is detected, the immune cells within the node multiply and the node enlarges. Enlargement is therefore a normal immune response rather than a disease in itself.
The axilla contains a substantial cluster of these nodes—typically twenty to forty on each side—arranged in groups and described surgically by their position relative to a muscle in the chest wall, as levels one, two, and three.
What these nodes drain determines what causes them to enlarge. They receive lymph from the breast, the entire arm and hand, the chest wall, the upper back, and part of the upper abdominal wall. Anything affecting any of these territories can produce axillary lymphadenopathy, and this breadth explains why a cut finger and a breast cancer can produce the same physical finding.
The causes divide into several groups.
Reactive enlargement from infection or inflammation accounts for the majority. A cut, scratch, insect bite, or infected hair follicle anywhere on the arm or hand produces enlarged nodes on that side, sometimes persisting for weeks after the original injury has healed and been forgotten. Skin conditions including eczema and psoriasis affecting the arm produce chronic mild enlargement. Infections of the breast, including mastitis and abscess during breastfeeding, cause prominent and often tender nodes.
Cat scratch disease deserves mention as a classic cause—a bacterial infection transmitted by cats, producing a small skin lesion followed by notable, sometimes dramatic, enlargement of the draining nodes.
Systemic infections including Epstein-Barr virus, cytomegalovirus, HIV, tuberculosis, and toxoplasmosis produce generalised lymphadenopathy including the axilla.
Vaccination is an important and frequently overlooked cause. Immunisation in the upper arm commonly produces enlargement of nodes on that side, which can be prominent and palpable, and which may persist for weeks. This became widely recognised during large-scale immunisation programmes, when enlarged nodes detected on breast imaging led to substantial numbers of recalls and unnecessary investigations. The practical implication is that anyone attending for breast imaging should mention recent vaccination and which arm received it, since this single piece of information frequently explains the finding.
Inflammatory and autoimmune conditions including rheumatoid arthritis, lupus, and sarcoidosis cause lymphadenopathy. Silicone from breast implants can migrate to axillary nodes and produce enlargement, as can material from tattoos on the arm, which is deposited in the draining nodes and can look alarming on imaging.
Malignant causes are the concern that drives assessment. Breast cancer is the most important in this context, since the breast drains directly to these nodes and axillary involvement is the single most significant prognostic factor in early breast cancer. Lymphoma commonly involves axillary nodes and may present this way. Melanoma and skin cancers of the arm, shoulder, or upper back spread here. Metastases from other primaries occur less often.
A specific situation worth knowing is occult breast cancer presenting with axillary nodes—where enlarged, biopsy-proven malignant axillary nodes are found but no breast tumour can be identified on examination or mammography. This is uncommon, and MRI identifies the primary in a substantial proportion of such cases. It is treated as breast cancer.
Interpreting an enlarged node depends far more on its internal structure than on its size, and this is worth understanding because it explains why reports describe nodes in the way they do.
A normal lymph node has a distinctive architecture: an outer rim of lymphoid tissue, called the cortex, surrounding a fatty centre known as the hilum, where blood vessels enter. On ultrasound this produces a characteristic appearance—an oval or kidney-shaped structure with a thin dark rim and a bright fatty centre.
Reactive nodes enlarge while preserving this architecture. The cortex thickens uniformly, the fatty hilum remains visible, and the node generally stays oval. Blood flow enters through the hilum in the normal pattern.
Involved nodes lose this structure. The cortex thickens irregularly or focally, the fatty hilum is compressed or disappears entirely, the node becomes rounded rather than oval, and blood flow enters from the periphery rather than through the hilum. Nodes may also become matted together or show irregular outer margins.
Size alone is an unreliable guide in both directions. Large reactive nodes are common, and normal-sized nodes can contain microscopic cancer deposits—a well-recognised limitation that is the reason sentinel node biopsy exists rather than relying on imaging to determine whether nodes are involved.
Symptoms vary and are frequently absent.
Where a node is noticed, it is felt as a lump in the armpit. Reactive nodes are often tender, mobile, and may have appeared in the context of a recent infection or injury. Nodes involved by cancer are more typically painless, firmer, and progressively enlarging, and may become fixed to surrounding tissue. These distinctions are tendencies rather than reliable rules.
Arm swelling suggests significant nodal obstruction and is more typical of extensive disease.
Systemic symptoms deserve particular attention. Unexplained fever, drenching night sweats requiring a change of bedding, and unintentional weight loss are associated with lymphoma and warrant prompt evaluation.
Accompanying breast symptoms—a lump, skin dimpling, nipple change, or discharge—substantially change the assessment and should always be reported.
Assessment begins with context, which frequently resolves the question without any investigation. Recent vaccination and which arm. Any cut, bite, scratch, or infection on the arm or hand, however minor and however long ago. Skin conditions. Recent travel. Cat exposure. Breast symptoms. Known breast cancer or other malignancy. Systemic symptoms.
Examination assesses the node’s size, consistency, mobility, and tenderness, along with the breast, the skin of the arm and upper back, and other node groups.
Ultrasound is the primary imaging test and is highly informative. It measures the node, assesses cortical thickness, determines whether the fatty hilum is preserved, evaluates shape, and examines blood flow pattern. These features together allow a reasonable judgement about whether a node looks reactive or suspicious.
Mammography frequently includes part of the axilla and may show enlarged nodes incidentally. Silicone and tattoo pigment in nodes have recognisable appearances.
MRI assesses axillary nodes alongside the breast and contributes to staging.
Ultrasound-guided needle sampling, either fine needle aspiration or core biopsy, provides tissue diagnosis where a node is suspicious. This is routine in the assessment of breast cancer, since knowing whether nodes are involved before surgery influences the operation planned.
Where lymphoma is suspected, removal of a whole node is generally preferred over needle sampling, because accurate subtyping depends on examining the node’s overall architecture, which a needle core may not capture.
Blood tests including a full blood count, inflammatory markers, and infection serology contribute where a systemic cause is suspected.
Important to Know
Most enlarged axillary nodes are reactive and resolve on their own. The purpose of assessment is to identify the minority that are not, and in many cases a straightforward explanation emerges from the history alone. Care is typically managed by primary care clinicians and breast services, with haematology involvement where lymphoma is suspected.
Several practical points shape how this finding is approached.
Mentioning recent vaccination is genuinely useful. Immunisation in the arm is a common and entirely benign cause of enlarged nodes on that side, and this single piece of information prevents a substantial number of unnecessary investigations. Anyone attending for breast imaging should volunteer it, including which arm, since it will not otherwise be apparent. Where vaccination explains the finding, repeat imaging after a period—commonly six to twelve weeks—confirms resolution without further intervention.
Recalling minor injuries matters too. A scratch, insect bite, or infected hair follicle on the arm can produce nodes that persist well after the skin has healed, and the connection is easily missed because the original event seemed trivial.
Tattoos on the arm or shoulder deposit pigment in the draining nodes, which can appear abnormal on imaging and be palpable. This is benign and permanent, and mentioning tattoos avoids unnecessary concern.
Women with breast implants may have silicone in axillary nodes, which likewise produces recognisable imaging appearances and generally requires no action.
In a woman with a known or suspected breast cancer, the axilla is assessed as a routine and essential part of staging, since nodal status is the strongest single determinant of prognosis in early disease and directly influences treatment. Finding involved nodes does not mean the cancer is incurable—many women with node-positive breast cancer are cured—but it does affect the treatment recommended.
The management of involved nodes in breast cancer has changed substantially and for the better. Full axillary clearance, which removed all nodes and carried a significant risk of lymphoedema, has largely been replaced by sentinel node biopsy, which identifies and removes only the first draining nodes. Where limited involvement is found, evidence now supports treating the axilla with radiotherapy rather than surgery in many situations, or in some cases doing nothing further, with equivalent outcomes and far less morbidity. A woman told she needs her nodes assessed should understand that this no longer implies the extensive surgery it once did.
Lymphoedema remains the most significant long-term consequence of axillary treatment, whether by surgery or radiotherapy. It is persistent swelling of the arm resulting from disrupted lymphatic drainage, is not curable once established, and is managed with compression, specialist physiotherapy, and skin care. Prevention through less extensive axillary treatment is the main advance of recent decades. Women who have had axillary treatment should be alert to early swelling and seek assessment promptly, since early intervention is more effective.
Where no cause is apparent and nodes are not clearly suspicious, short-interval reassessment is a reasonable approach—reactive nodes regress while significant disease progresses, so stability or resolution over a few weeks is informative. Persistent or enlarging nodes warrant sampling.
Where nodes are confirmed malignant and no primary is found, MRI of the breast identifies a tumour in a substantial proportion. Where none is found, the condition is treated as breast cancer with outcomes comparable to node-positive disease of known primary.
A note on proportion is appropriate. A palpable node in the armpit is a frightening finding, and the instinct is to assume the worst. In the absence of a breast abnormality or systemic symptoms, and particularly where there is a recent infection, injury, or vaccination, the probability strongly favours a benign cause. Assessment is appropriate; alarm usually is not.
Care is managed by primary care with referral to breast services where breast pathology is suspected, and to haematology where lymphoma is considered. Imaging, clinical findings, and history are interpreted together, with the history frequently carrying more weight than the imaging in reaching an explanation.
Patient education plays an important role. Understanding that nodes enlarge as a normal immune response, that node structure matters more than size, that recent vaccination and minor arm injuries are common explanations worth mentioning, that nodal assessment in breast cancer no longer means extensive surgery, and that persistent or growing painless nodes warrant sampling all contribute to appropriate care.
Red flag symptoms include a painless, firm, progressively enlarging node; a node fixed to surrounding tissue; nodes in more than one area of the body; unexplained fever, drenching night sweats, or unintentional weight loss; swelling of the arm; an accompanying breast lump, skin dimpling, nipple change, or discharge; a new or changing pigmented skin lesion on the arm, shoulder, or upper back; persistent nodes that have not resolved after several weeks with no identifiable cause; and any new axillary node in a woman with a history of breast cancer. These warrant prompt medical evaluation.