Differential Diagnosis for a Small Dent in the Skull

The patient presents with a small, painless dent in the skull, approximately 1 inch in diameter, accompanied by slight redness and occasional itchiness. The area around the dent is solid, and the patient reports no significant hair loss in the affected area. Given the patient's symptoms and presentation, the following differential diagnoses are considered:

• Single most likely diagnosis:
  • Lipoma or Epidermal Cyst: A small, benign growth under the skin that could cause a dent or depression, especially if it is located near the hairline. The presence of slight redness and occasional itchiness could be related to inflammation or irritation of the overlying skin.
• Other Likely diagnoses:
  • Fatty tissue loss or atrophy: As suggested by the patient's friend, a loss of fatty tissue under the skin could cause a depression or dent, especially if it occurs in a localized area.
  • Sebaceous cyst: A small, usually benign cyst that can form under the skin, potentially causing a dent or lump.
  • Keloid or hypertrophic scar: Although the patient does not report any history of trauma or surgery, a keloid or hypertrophic scar could potentially cause a raised or depressed area, accompanied by redness and itchiness.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed):
  • Osteomyelitis or bone infection: Although unlikely, an infection of the bone could cause a range of symptoms, including redness, swelling, and pain. If left untreated, osteomyelitis can lead to serious complications, including sepsis or bone destruction.
  • Skin cancer (e.g., basal cell carcinoma or squamous cell carcinoma): Although the patient's symptoms do not strongly suggest skin cancer, it is essential to consider this possibility, especially if the lesion is growing or changing over time.
• Rare diagnoses:
  • Dermoid cyst: A rare type of cyst that can form under the skin, potentially causing a dent or lump.
  • Langerhans cell histiocytosis: A rare disorder characterized by an overproduction of Langerhans cells, which can cause a range of symptoms, including skin lesions, bone lesions, and systemic symptoms.

Given the patient's symptoms and presentation, a referral to dermatology or a primary care examination to further evaluate the lesion and determine the best course of action is recommended.