A 70 yo F presents to the ED for 2 days of intermittent L UE weakness, paresthesias and tremors. She has a 40 pack year history of smoking and was recently diagnosed w/ lung cancer. A noncontrast head CT is done. What's the diagnosis? (scroll down for answer) 

Answer: R frontal mass (suspicious for metastatic disease) with surrounding vasogenic edema

• Vasogenic cerebral edema reprsents cerebral edema in which the blood brain barrier is disrupted 
• Most commonly seen due to brain tumors (primary and metastatic), cerebral abscesses or hemorrhage
• Only affects white matter and is caused by increased permeability of endothelial cells, resulting in leakage of fluid into the extracellular space
• On CT scan, vasogenic edema appears as hypoattenuation confined to white matter 
• Secondary effects include effacement of cerebral sulci and midline shift