Differential Diagnosis for Brain CT Scan Findings

Given the patient's history of treated melanoma and the presence of multiple hyperdense small lesions on the brain CT scan, the following differential diagnoses are considered:

• Single most likely diagnosis
  • A. Brain metastases by melanoma: This is the most likely diagnosis given the patient's history of treated melanoma. Melanoma is known to metastasize to the brain, and the appearance of multiple hyperdense lesions is consistent with this diagnosis.
• Other Likely diagnoses
  • Cerebral vasculitis or other inflammatory conditions: Although less likely than brain metastases, these conditions could potentially cause multiple small lesions on a brain CT scan.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Cerebral hemorrhages or microhemorrhages: These could be life-threatening and require immediate attention. Although the history of melanoma points towards metastases, it's crucial not to miss other potentially fatal diagnoses.
  • Infectious diseases (e.g., cerebral abscesses, toxoplasmosis in immunocompromised patients): These conditions can present with similar imaging findings and are critical to diagnose and treat promptly.
• Rare diagnoses
  • B. Hydatid cyst of the brain: This is a rare parasitic infection that can cause cystic lesions in the brain. It is less likely in this context, given the patient's history of melanoma, but should be considered in the appropriate geographical and exposure context.
  • Other rare conditions such as cerebral amyloid angiopathy or rare vascular malformations could also be considered, although they are less likely given the clinical context provided.