Differential Diagnosis for Subcutaneous Mobile Mass

• Single most likely diagnosis
  • Lipoma: This is the most common benign tumor of soft tissue and is often found in the subcutaneous tissue. It is typically mobile, soft, and painless, which aligns with the description of a subcutaneous mobile mass.
• Other Likely diagnoses
  • Cyst (e.g., epidermoid, sebaceous): These are common benign lesions that can present as mobile masses under the skin. They are usually filled with fluid or semi-solid material and can be found in various locations.
  • Fibroma: A benign tumor of fibrous tissue, which can be mobile and found in the subcutaneous layer. It is less common than lipoma but still a plausible diagnosis.
  • Hematoma: Although typically associated with trauma, a resolving hematoma can present as a mobile mass under the skin. However, it would usually have a history of injury.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed)
  • Metastatic tumor: Although rare, a metastasis to the subcutaneous tissue from a primary malignancy elsewhere in the body could present as a mobile mass. Missing this diagnosis could have severe consequences.
  • Sarcoma (e.g., liposarcoma): These are malignant tumors of soft tissue, which can present similarly to benign lesions but require urgent attention due to their potential for aggressive behavior and metastasis.
• Rare diagnoses
  • Neurofibroma: A benign tumor of nerve tissue, which can be mobile and found in the subcutaneous layer. It is less common and often associated with neurofibromatosis type 1.
  • Dermatofibroma: A benign growth that can appear after a minor injury, typically on the legs. It is firm and can be mobile but is less common than other diagnoses listed here.
  • Myxoma: A rare benign tumor of connective tissue, which can present as a subcutaneous mobile mass. It is less common than lipoma or cysts but should be considered in the differential diagnosis due to its potential for local growth.