Differential Diagnosis for the Patient's Condition

The patient presents with a bump on the inside of his bottom lip, which has been present for about 1 year. He has noticed yellowish fluid coming out when he bites into it and has not responded to numerous rounds of antibiotics. Here is a differential diagnosis based on the provided information:

• Single Most Likely Diagnosis

  • Mucocele: This is a common condition where a mucus-filled cyst forms on the inner surface of the lip, often due to trauma (like biting) that damages a minor salivary gland. The presence of a bump and the discharge of yellowish fluid when bitten into are consistent with this diagnosis.

• Other Likely Diagnoses

  • Mucous cyst (ranula): Similar to a mucocele but typically found on the floor of the mouth. However, given the location on the lip, this is less likely but still a consideration.
  • Lip abscess or infected cyst: The history of antibiotic use without resolution could suggest a resistant infection or an abscess that hasn't been adequately drained.
  • Fordyce spots or granules: These are small, yellowish or white bumps on the lips that represent ectopic sebaceous glands. However, they typically do not discharge fluid.

• Do Not Miss Diagnoses

  • Squamous cell carcinoma: Although less likely given the duration and the patient's history of biting into the lesion without significant growth or other alarming symptoms, any oral lesion that persists should be evaluated for malignancy.
  • Tuberculosis or other systemic infections: Uncommon but possible causes of chronic lesions, especially if the patient has been exposed or has risk factors for these conditions.

• Rare Diagnoses

  • Dermoid cyst: A congenital cyst that can occur in various locations, including the oral cavity, but is less common on the lip.
  • Stafne bone cavity: An anatomic variant that can mimic a cystic lesion but is actually a depression in the mandible. However, this would not typically present with discharge.
  • Glandular odontogenic cyst: A rare type of jaw cyst that could potentially present in the lip area, though it's more commonly associated with the gingiva or mandible.