Differential Diagnosis for Gynecomastia with Persistent and Tender Right Breast Tissue

• Single most likely diagnosis:
  • Physiologic gynecomastia with residual tissue: This is the most likely diagnosis given the patient's age of onset (14 years old) and the fact that the left side has resolved over time, which is consistent with the natural history of physiologic gynecomastia. The persistence of tissue on one side is not uncommon.
• Other Likely diagnoses:
  • Idiopathic gynecomastia: This diagnosis is considered because the cause of gynecomastia is not always identifiable, and some cases may persist without a clear reason.
  • Pubertal gynecomastia with uneven resolution: Similar to physiologic gynecomastia, this diagnosis accounts for the uneven resolution of breast tissue between the two breasts.
  • Lipoma or benign breast tumor: Although less common, a lipoma or another type of benign tumor could cause a palpable mass that is tender, mimicking gynecomastia.
• Do Not Miss diagnoses:
  • Testicular cancer: Although rare, testicular cancer can cause gynecomastia due to the production of human chorionic gonadotropin (hCG), which stimulates estrogen production. It's crucial to examine the testes and consider imaging or tumor markers if there's suspicion.
  • Pituitary or hypothalamic tumors: These can lead to an imbalance in hormone production, including an increase in prolactin, which can cause gynecomastia. Symptoms such as headaches, visual disturbances, or galactorrhea might accompany these conditions.
  • Thyroid disorders: Both hypothyroidism and hyperthyroidism can lead to gynecomastia, though this is less common. Other symptoms related to thyroid dysfunction would likely be present.
• Rare diagnoses:
  • Klinefelter syndrome: A genetic condition that affects males, characterized by an extra X chromosome, leading to hormonal imbalances that can cause gynecomastia, among other symptoms.
  • Androgen insensitivity syndrome: A condition where the body is partially or completely unable to respond to androgens, leading to the development of female secondary sexual characteristics in genetic males, including gynecomastia.
  • Estrogen-producing tumors: Rare tumors such as adrenal or ovarian tumors that produce estrogen can cause gynecomastia. These would be considered in the presence of other signs of estrogen excess or masses found on imaging.