Differential Diagnosis for a Lesion Resembling an Abscess but with Firm Fat Layers and No Pus on Incision

• Single Most Likely Diagnosis
  • Lipoma: A benign tumor composed of fat tissue. The presence of firm fat layers without pus upon incision strongly suggests a lipoma, as these tumors are made up of adipose tissue and do not contain pus.
• Other Likely Diagnoses
  • Epidermal Inclusion Cyst (EIC): Also known as sebaceous cysts, these can sometimes resemble abscesses but are filled with a cheesy material rather than pus. They can have a firm wall and may not drain pus upon incision.
  • Pilomatricoma: A benign skin tumor that originates from the hair follicle matrix. It can present as a firm, mobile nodule and might be mistaken for an abscess, especially if it becomes inflamed.
  • Dermatofibroma: A common, benign skin growth that can feel firm and may resemble an abscess, especially if it becomes inflamed.
• Do Not Miss Diagnoses
  • Necrotizing Fasciitis: Although less likely given the description of firm fat layers without pus, necrotizing fasciitis is a life-threatening condition that requires immediate attention. It involves infection of the fascia and can present with firm, woody skin that may not initially drain pus.
  • Cellulitis with Abscess Formation in Deep Tissue: It's possible for an abscess to form deep within the tissue, and only firm, inflamed tissue may be palpable on the surface. This condition requires thorough evaluation and possibly imaging to diagnose.
• Rare Diagnoses
  • Liposarcoma: A rare malignant tumor of fat tissue. While most lipomas are benign, the possibility of a liposarcoma, although rare, should be considered in the differential diagnosis of a firm, fatty mass.
  • Hibernoma: A rare, benign tumor of brown fat. It can present as a firm mass and might be considered in the differential diagnosis of a lesion resembling an abscess but composed of fat tissue.