Background Despite the high prevalence of prostate cancer, its brain parenchymal metastasis is not common and intracranial hemorrhage due to such a metastasis is even less common. This report presents a challenging case of solitary brain metastasis secondary to prostate cancer that gave rise to intraventricular hemorrhage and acute hydrocephalus mimicking a giant aneurysm. Case presentation A 77-year-old man with a history of prostate cancer, hypertension, and morbid obesity presented to the emergency room with a severe headache. He was afebrile with a blood pressure of 144/79 mmHg, alert, without any sign of sensory or motor deficit. Shortly after admission, he became unresponsive and was immediately intubated. His blood tests revealed hypernatremia at 154 mmol/L; otherwise, the lab data including the COVID-19 screening proved normal. The cerebral CT and MR images, with and without contrast, were interpreted as a giant thrombotic aneurysm extending to the suprasellar region by the emergency radiologist. Also, moderate intraventricular hemorrhage, acute hydrocephalus, and sub-ependymal interstitial edema were observed. Upon further evaluation of the images, the lesion was determined to be an exophytic hemorrhagic hypothalamic mass, and the subsequent biopsy was consistent with prostate cancer metastasis. Conclusions The exophytic hemorrhagic hypothalamic metastasis can mimic a ruptured aneurysm on imaging. Given the improved survival of patients with prostate cancer, radiologists may encounter such unusual cerebral metastases from prostate cancers more frequently in the future.