A lump on the side of a finger, medically referred to as a mass, nodule, or swelling, is a common occurrence. These abnormal tissue growths can originate from the skin, soft tissues, joint, or bone. Most growths in this location are benign, meaning they are non-cancerous and pose no serious threat to overall health. Understanding the lump’s location and characteristics is the first step in identifying its likely cause. This review explores the most frequent origins of these growths specific to the finger’s side.
Cysts Arising Near the Finger Joint
The most frequent causes of a lump near the finger joint are fluid-filled sacs connected to the underlying joint or tendon structures. These growths are classified as either ganglion cysts or digital mucous cysts. Both types are filled with a thick, jelly-like fluid that resembles the synovial fluid found within joints and tendon sheaths.
Ganglion Cysts
Ganglion cysts are fluid-filled sacs arising from the irritation or mechanical stress of a tendon sheath or joint capsule. On the finger, they frequently manifest as a firm or sometimes soft, movable lump on the side or back of the digit. These cysts form when the synovial lining bulges out, creating a sac filled with viscous, clear fluid. A clinician may use transillumination, where a light shone through the mass reveals its fluid-filled nature. While generally painless, a ganglion cyst may cause discomfort or a dull ache if it presses against a nearby nerve or interferes with tendon movement.
Mucous Cysts (Digital Mucous Cysts)
A digital mucous cyst is a specific type of ganglion cyst that forms exclusively near the distal interphalangeal (DIP) joint, the joint closest to the fingertip. These cysts are closely associated with underlying osteoarthritis, where joint degeneration causes fluid to collect under the skin. They commonly appear on the side of the finger near the nail bed, often presenting as a translucent or slightly pinkish bump. Due to their proximity to the nail matrix, the pressure from a mucous cyst can sometimes cause a groove or deformity to form in the fingernail. The fluid inside is typically very thick and clear, and they can sometimes rupture, risking the introduction of bacteria into the joint space.
Other Common Skin and Soft Tissue Growths
Lumps not fluid-filled or directly connected to the joint space often originate from the skin or the soft tissues beneath it. These solid or semi-solid growths are distinct from cysts in their composition. They generally represent an overgrowth or accumulation of skin cells or fatty tissue.
Epidermal Inclusion Cysts
An epidermal inclusion cyst forms when surface skin cells, which produce keratin, are trapped beneath the skin’s outer layer, often following minor trauma. These cells shed and accumulate, creating a firm, round lump filled with a thick, cheesy keratin material. The lump is typically slow-growing and mobile, though it may feel tethered to the overlying skin. Unlike joint-related cysts, they do not transilluminate because they are filled with solid material. They can occur anywhere on the finger and may sometimes have a tiny, visible dark spot or central punctum where the cells were initially implanted. If the cyst becomes inflamed or infected, it can become tender, red, and rapidly increase in size.
Warts (Verrucae)
Warts (verrucae) are small, rough growths caused by infection with the human papillomavirus (HPV), leading to an overproduction of skin cells. They present as bumpy, grainy, or cauliflower-like lesions that can be flesh-colored or slightly darker than the surrounding skin. Warts are localized to the skin surface and do not involve deeper joint or tendon structures. A characteristic feature is the presence of tiny black dots visible within the center, which are minute clotted blood vessels. Warts on the side of the finger can be easily irritated by friction, but their distinct, rough surface texture makes differentiation from a smooth cyst straightforward.
Fibromas and Lipomas
Benign soft-tissue tumors, such as fibromas or lipomas, can also present as lumps on the finger, though they are less common. A fibroma is a firm mass composed of fibrous connective tissue, while a lipoma is a soft, often doughy mass made of mature fat cells. Both are typically slow-growing and painless. Lipomas are usually soft and easily movable beneath the skin, while fibromas tend to be firmer and more discrete. These masses originate from non-joint soft tissue elements.
Signs That Require Immediate Medical Attention
While most finger lumps are benign, certain accompanying signs indicate a need for prompt medical evaluation.
Signs of Concern
- Rapid growth over a short period (weeks to months) should be assessed immediately to rule out serious conditions.
- Signs of infection, including increasing pain, intense redness (erythema), localized warmth, and the presence of pus or drainage, require urgent care to prevent the spread of bacteria.
- A lump accompanied by a fever or general feeling of malaise suggests systemic involvement.
- New or increasing neurological symptoms, such as persistent numbness, tingling, or weakness, may signal that the mass is compressing a digital nerve.
- A lump that severely restricts the finger’s range of motion or causes mechanical locking should be evaluated promptly.
Diagnosis and Treatment Approaches
Managing a finger lump begins with a thorough physical examination to determine the mass’s characteristics. The clinician assesses the lump’s size, mobility, texture, and tenderness, often using transillumination to check for fluid content. The patient’s medical history, including any history of trauma, arthritis, or rapid changes in size, is also considered.
Diagnostic Imaging
Imaging studies are often used to confirm the diagnosis or rule out other causes, especially those involving the underlying bone or joint.
- An X-ray can detect bony growths related to osteoarthritis or show if the mass is eroding the bone.
- Ultrasound imaging is useful for differentiating between a fluid-filled cyst and a solid tumor, providing a clear visual of the internal structure.
Treatment Options
Treatment is guided by the specific diagnosis and the patient’s symptoms. For many asymptomatic, benign lumps like small ganglion cysts or lipomas, watchful waiting is often recommended, as some may disappear spontaneously. Symptomatic cysts can be treated with aspiration, which involves draining the fluid with a needle, sometimes followed by a corticosteroid injection. Surgical excision is the definitive option reserved for lumps that are painful, recurrent, interfere with hand function, or when the diagnosis is uncertain. For solid masses like epidermal inclusion cysts, complete surgical removal of the cyst wall is necessary to minimize recurrence risk. The goal of any intervention is to preserve the function and anatomy of the finger.