Brain metastases from adenocarcinoma of the lung with truly cystic magnetic resonance imaging appearance.

Metastatic disease represents over half of all malignancies in brain parenchyma, and carcinoma when metastatic will often spread to the brain, with lung and breast tumors being the most common culprits. The suggestive features of metastatic disease on magnetic resonance imaging include peritumoral, vasogenic edema and avid postcontrast enhancement. We present the case of a 50-year-old male with an established diagnosis of metastatic adenocarcinoma of the lung treated with erlotinib who developed multiple cystic brain lesions on surveillance MRI. These cysts demonstrated T2 prolongation, suppressed completely on FLAIR, lacked surrounding edema, and featured a complete lack of enhancement. Due to the ambiguous imaging findings, brain biopsy was performed to establish the diagnosis. The pathology revealed a single layer of malignant cells lining brain parenchyma and focal areas of glandular growth. The intracranial lesions responded well to total brain radiation. This case is unique for the imaging findings most characteristic of simple cysts in biopsy-proven metastatic disease and may relate to the effects of erlotinib on metastatic brain tumors.