Differential Diagnosis for a Largely Expanding Subcutaneous Cyst under the Collarbone
Single Most Likely Diagnosis
- Lipoma: A benign tumor composed of fat tissue, which can grow under the skin and cause a noticeable lump. Its location under the collarbone and description as a subcutaneous cyst make it a plausible diagnosis due to its common occurrence and ability to grow in various parts of the body, including under the collarbone.
Other Likely Diagnoses
- Sebaceous cyst: A benign, usually painless, lump under the skin that can appear anywhere, including under the collarbone. These cysts are common and can grow large enough to be noticeable.
- Epidermoid cyst: Similar to sebaceous cysts, epidermoid cysts are benign and can occur under the skin, sometimes growing large enough to be considered expanding.
- Abscess: An infected pocket of pus that can form under the skin, potentially causing swelling and expansion. While less common under the collarbone, an abscess could present similarly to a cyst if it becomes encapsulated.
Do Not Miss Diagnoses
- Metastatic cancer: Although rare, some cancers can metastasize to the skin or subcutaneous tissues, forming lumps or masses. Missing a diagnosis of metastatic cancer could have severe consequences, making it crucial to consider, especially if there's a known history of cancer.
- Lymphoma: Certain types of lymphoma can cause masses or swellings in various parts of the body, including under the collarbone, due to lymph node involvement.
Rare Diagnoses
- Dermatofibrosarcoma protuberans (DFSP): A rare type of skin cancer that can appear as a lump under the skin, which grows slowly over time. It's less common but should be considered in the differential diagnosis due to its potential for local invasion and rare metastasis.
- Hygroma: A rare, benign growth that usually appears as a soft, fluid-filled lump, often on the head or neck, but can theoretically occur under the collarbone in some cases.
- Neurofibroma: Part of neurofibromatosis type 1 (NF1), these are benign nerve sheath tumors that can grow under the skin and cause lumps. While more commonly associated with other symptoms, a solitary neurofibroma could present similarly to a subcutaneous cyst.