Case Report: Cerebrospinal fluid cytology as a diagnostic clue in hemorrhagic glioblastoma mimicking hypertensive intracranial hemorrhage.

BACKGROUND: Glioblastoma (GBM) rarely presents with spontaneous intracerebral hemorrhage (ICH) as the initial symptom. A massive hematoma can completely obscure the underlying tumor on imaging, leading to misdiagnosis and treatment delay. Cerebrospinal fluid (CSF) cytology is simple and inexpensive, but is underutilized in the diagnostic workup of atypical ICH. CASE PRESENTATION: A 60-year-old man with poorly controlled hypertension presented with sudden left-sided weakness and vomiting. CT showed a large right basal ganglia hemorrhage (87.1 mL, 72.8 HU) with a midline shift of 17.8 mm. After endoscopic hematoma evacuation, hypertensive ICH was diagnosed. However, two months after discharge, the patient was readmitted with bone-flap bulging and elevated intracranial pressure. Follow-up MRI showed only a cystic lesion, interpreted as postoperative or inflammatory change. Lumbar puncture was performed for CSF cytology. Three consecutive punctures all revealed numerous atypical cells with high nuclear-to-cytoplasmic ratios, pseudopod-like protrusions, and atypical mitotic figures. CSF biochemistry showed markedly elevated protein (7.03 g/L) and decreased glucose (0.9 mmol/L). Pathology later confirmed IDH1-wildtype glioblastoma (WHO grade IV) with leptomeningeal spread. CONCLUSION: When a large hematoma masks an underlying tumor on imaging and atypical imaging features or abnormal clinical recovery are present, CSF cytology can provide a crucial diagnostic clue. This case highlights that CSF cytology should be actively pursued in patients with atypical ICH, especially when follow-up imaging shows only non-specific changes.