ABSTRACT
Leptomeningeal metastasis is a very rare complication of infiltration of leptomeninges and subarachnoid space with malignant cells. It is an indicator of poor prognosis. Its incidence is 3.8% in non-small cell lung carcinoma (NSCLC). This rate is higher in patients with epidermal growth factor receptor (EGFR) mutation. Brain magnetic resonance imaging (MRI) is the first choice in the diagnosis. The diagnosis of leptomeningeal metastasis is difficult and often bypassed because it is rare and does not cause gross mass lesions such as brain metastasis. Systemic chemotherapy, intrathecal therapy, cranial radiotherapy and targeted treatment agents are an option in the treatment. It has been shown that targeted therapies can be promising because of the ability to switch to cerebrospinal fluid in appropriate patients. We present the case with EGFR positive lung adenocarcinoma whit leptomeningeal metastasis (LM) due to its rarity, difficulty in diagnosis and its association with EGFR mutation.