Discovering a lump beneath the skin often causes concern about the underlying cause. These growths, known as subcutaneous nodules, arise from a wide variety of sources, ranging from simple, benign tissue changes to more complex medical conditions. While most nodules are harmless, understanding their characteristics and causes is important. A professional medical evaluation is the most appropriate first step to accurately determine the nature of any new or changing lump.
Defining Subcutaneous Nodules
A subcutaneous nodule is a firm, raised lesion that forms just beneath the skin’s surface, specifically in the hypodermis. The hypodermis is the layer of fat and connective tissue located below the dermis. The term “nodule” is typically reserved for lesions that are palpable and greater than 0.5 centimeters in diameter, distinguishing them from smaller skin bumps or papules. These growths can be felt or sometimes seen and range in size from a few millimeters to several centimeters.
Medical professionals describe these nodules based on physical characteristics to aid in diagnosis. These include consistency (soft, firm, or hard) and whether they are freely movable or fixed to the underlying tissue. The overlying skin may show changes like redness, warmth, or color change, and the nodule may or may not be painful. Understanding these descriptions helps narrow down the possible origins of the growth.
Common Localized Causes
Many subcutaneous nodules originate from an issue contained entirely within the local tissue structure and are generally considered benign. One of the most frequent causes is a lipoma, which is a non-cancerous growth of fatty tissue. Lipomas feel soft, rubbery, and are typically freely movable beneath the skin, often occurring on the back, neck, shoulders, or arms. They are usually not painful unless they press on surrounding nerves.
Another common localized cause is the epidermoid cyst, which results from the proliferation of epidermal cells within the dermis. These cysts are filled with keratin, a soft, cheese-like material, and often have a small, visible central pore. They feel smooth and firm and can become inflamed or rupture, leading to redness and tenderness.
Traumatic events can also lead to nodules, such as a hematoma, which is a collection of clotted blood following an injury. Over time, these hematomas may harden into a firm lump. They can also develop into scar tissue, which presents as a firm nodule.
Systemic and Serious Causes
Some subcutaneous nodules are manifestations of an underlying process affecting the entire body or a more aggressive local condition. These systemic causes frequently involve inflammation of the fat layer, known as panniculitis. Erythema nodosum is the most common form of panniculitis, characterized by crops of tender, red nodules, usually located symmetrically on the lower legs. This condition often signals a systemic trigger, such as a streptococcal infection, sarcoidosis, or inflammatory bowel disease.
Infectious agents, including bacteria and deep fungal organisms, can result in localized abscesses or deeper infections that present as warm, painful nodules. Autoimmune disorders frequently cause nodules, such as rheumatoid nodules seen in approximately one-fourth of individuals with rheumatoid arthritis. These are typically firm, non-tender masses found over pressure points, like the elbows or knuckles.
While rare, a nodule may represent malignancy. This can be a primary soft tissue sarcoma or a metastasis from cancer elsewhere in the body.
Medical Evaluation and Diagnostic Steps
The evaluation of a subcutaneous nodule begins with a detailed physical examination by a healthcare provider. The provider assesses the nodule’s characteristics, including size, consistency, and mobility, and determines if it is attached to the skin or deeper structures. They also take a comprehensive medical history, focusing on systemic symptoms, history of trauma, or pre-existing conditions. Clinical features like tenderness, rapid growth, or skin changes help guide the next steps.
Imaging is frequently the first diagnostic tool used, with ultrasonography being the preferred initial method. Ultrasound provides information on the nodule’s composition, revealing if it is solid, cystic (fluid-filled), or fatty, and its relationship to nearby tissues. If malignancy is suspected or the nodule is deeply situated, advanced imaging like a CT scan or MRI may be utilized.
A biopsy is the definitive procedure when the cause remains unclear after clinical and imaging assessment, or if a serious condition is suspected. This involves removing a small tissue sample for microscopic analysis to establish a conclusive diagnosis.