A lump appearing on the top of the shoulder, near the acromion, collarbone (clavicle), or upper trapezius muscle, can be concerning. The shoulder is a complex structure of bone, joints, muscle, and soft tissues, all of which can develop a noticeable mass. The origins of these lumps are diverse, ranging from simple fluid collections to structural changes or benign growths. Although many shoulder lumps are harmless, self-diagnosis is impossible. Any persistent or changing mass requires a medical consultation for proper evaluation.
Structural Issues and Traumatic Injury
A common cause for a prominent lump on the top of the shoulder relates directly to the underlying joint structure, often following a traumatic injury. The acromioclavicular (AC) joint, where the collarbone meets the shoulder blade, is frequently involved in this type of presentation. When a person falls directly onto the point of their shoulder, the stabilizing ligaments of the AC joint can become stretched or torn.
This injury is known as a shoulder separation. In severe cases, the complete tearing of the acromioclavicular and coracoclavicular ligaments allows the arm’s weight to pull the shoulder blade downward. The outer end of the clavicle then pushes upward, creating a visible, firm bump or “step-off” deformity on the top of the shoulder. The size of the lump corresponds directly to the degree of ligament damage and separation.
Lumps can also form due to degenerative changes within the joints, such as osteoarthritis affecting the AC joint. As protective cartilage wears down, the body may produce small, abnormal bony projections called osteophytes, or bone spurs. These hard, non-mobile growths create a firm lump that is often painless but may restrict movement. Fractures of the clavicle or upper humerus can also cause a sudden, painful lump accompanied by swelling and misalignment.
Benign Soft Tissue Growths
Many lumps on the top of the shoulder originate from the soft tissues just beneath the skin and are often benign. The most frequently encountered soft tissue mass is a lipoma, a collection of mature fat cells encased in a thin capsule. Lipomas typically feel soft, doughy, or rubbery, and they can be easily moved beneath the skin. They are usually painless unless they grow large enough to press on a nerve or develop near a joint.
Another common type of lump is an epidermoid cyst, which forms when surface skin cells become trapped beneath the skin. This sac fills with keratin, a thick, yellowish protein material. These cysts present as firm, rounded masses just under the skin and are generally painless unless they become inflamed or infected.
A ganglion cyst is a type of benign lump, consisting of a fluid-filled sac that develops from a joint capsule or tendon sheath. They contain a thick, jelly-like fluid similar to synovial fluid. When they occur near the shoulder, they are usually round or oval and feel firm yet somewhat compressible, sometimes causing pain if they impinge on a nearby nerve.
Inflammatory and Infectious Responses
Lumps on the shoulder can manifest the body’s reaction to irritation, overuse, or infection. Bursitis is a common inflammatory cause resulting from the swelling of a bursa, a small, fluid-filled sac that cushions bones and soft tissues. The subacromial bursa, located beneath the bony arch, is most often affected. When inflamed due to repetitive activity, trauma, or arthritis, the bursa produces excess fluid, creating a soft, spongy lump that is often tender and painful.
Infectious processes can lead to a noticeable mass, such as a skin abscess, a pus-filled lump usually caused by bacteria. An abscess is characterized by localized pain, redness, warmth, and a firm-yet-squishy texture. It may be accompanied by systemic symptoms like fever and chills.
Another inflammatory cause is lymphadenopathy, or swollen lymph nodes, which can be felt in the supraclavicular area or the armpit region. Lymph nodes swell in response to infection or inflammation elsewhere in the body. They present as small, rubbery, tender lumps that indicate an active immune response.
When to Seek Medical Attention
While many shoulder lumps are benign, a medical evaluation is necessary to accurately determine the cause, especially for a mass that is new or changing. Certain “red flag” symptoms suggest a more concerning underlying issue that requires prompt consultation. Any lump that begins to grow rapidly, is fixed or immobile to the underlying tissue, or feels unusually hard should be assessed by a healthcare professional.
Severe pain, particularly if persistent or worsening at night, warrants attention. This is also true for any lump accompanied by a visible deformity or sudden loss of shoulder function. Systemic symptoms, such as unexplained fever, night sweats, or unintentional weight loss, require immediate medical consultation.
The diagnostic process begins with a physical examination, where the doctor assesses the lump’s size, texture, mobility, and tenderness. Depending on the findings, the doctor may recommend further imaging studies. An ultrasound is often the first-line test for soft-tissue lumps, differentiating between a solid mass and a fluid-filled cyst. X-rays are useful for evaluating bone structure and joint alignment, especially if a fracture or bone spur is suspected. For deeper or more complex masses, an MRI or CT scan may be utilized. In some cases, a biopsy, which is the removal of a small tissue sample, may be performed to confirm the exact nature of the cells.