Cerebrospinal fluid cytology for the diagnosis of lung cancer brain metastasis: a case report.

Background: The examination of cerebrospinal fluid (CSF) cytology holds significant value in the field of neuropathology, serving as a key diagnostic tool for clinical physicians in completing differential diagnosis and clinical assessment. Particularly in the context of infectious diseases affecting the central nervous system (CNS), cerebrovascular diseases, brain tumors, meningeal carcinoma, and immune-related disorders, this examination is critical to facilitating accurate diagnoses and distinguishing between various clinical conditions.

Case description: A 57-year-old Han Chinese male was admitted to The First Hospital of Hebei Medical University for psychiatric symptoms. A series of diagnostic tests were sequentially conducted on the patient, including routine CSF examination, CSF biochemical analysis, test for autoimmune encephalitis antibodies and paraneoplastic syndrome autoantibodies, pathogen-targeted sequencing, cytokine analysis via flow cytometry, tumor marker tests, positron emission tomography-computed tomography, and cranial magnetic resonance imaging (MRI). The results showed an increase in CSF white blood cell count, CSF protein, and serum carcinoembryonic antigen. In conjunction with cranial MRI revealing multiple intracranial nodular abnormal signals, these can serve as effective evidence to aid in diagnosis. However, the definitive diagnosis of meningeal carcinomatosis (MC) ultimately depends on the cytological identification of atypical cells in the CSF. Given the patient's history of lung cancer, the final diagnosis was leptomeningeal metastasis from lung cancer, which belongs to the type of CNS metastatic carcinoma in MC.

Conclusions: In this case, the cytological identification of atypical cells in the CSF confirmed the diagnosis of MC.