Differential Diagnosis for Left Frontal Scalp Soft Tissue Swelling and Generalized Soft Tissue Swelling Inferior to the Left External Auditory Canal

• Single Most Likely Diagnosis
  • Trauma-induced hematoma: This is the most straightforward explanation given the description of a small hematoma, which is often a result of trauma to the area.
• Other Likely Diagnoses
  • Infection (cellulitis or abscess): Soft tissue swelling can be a sign of an infectious process, especially if there's redness, warmth, and tenderness.
  • Allergic reaction: An allergic reaction could cause swelling in the affected area, though it might not typically be confined to the scalp and area around the external auditory canal.
  • Insect bite or sting: Similar to an allergic reaction, an insect bite or sting could cause localized swelling.
• Do Not Miss Diagnoses
  • Temporal arteritis: Although less common, temporal arteritis (giant cell arteritis) can cause scalp tenderness and swelling, and it's crucial to consider this diagnosis due to its potential for serious complications if not treated promptly.
  • Malignancy: Rarely, swelling in this area could be a sign of a malignancy, such as a scalp tumor or metastasis, which would have significant implications for treatment and prognosis.
  • Cavernous sinus thrombosis: This is a rare but potentially life-threatening condition that could present with facial or scalp swelling, among other symptoms.
• Rare Diagnoses
  • Angioedema: A rare condition that can cause significant soft tissue swelling, often involving the face, lips, tongue, or larynx, but it could potentially involve the scalp.
  • Relapsing polychondritis: An autoimmune disorder that can cause cartilage inflammation, potentially affecting the ears and leading to swelling around the external auditory canal.
  • Sarcoidosis: A condition that can cause inflammation in various parts of the body, including the skin, and might lead to swelling in unusual areas, including the scalp.