Cerebral cavernous malformations (CMs) are vascular malformations of the central 
nervous system, which can be detected in the absence of any clinical symptoms. 
Nodules and cysts with mixed signal intensity and a peripheral hemosiderin rim 
are considered brain magnetic resonance imaging (MRI) findings typical of CMs. A 
48-year-old man was admitted to our hospital because of abnormal MRI findings 
without significant neurological symptoms. A cyst with an internal fluid-fluid 
level was found in the left basal ganglia on the initial brain MRI. We decided 
to observe the natural course of the asymptomatic lesion with serial MRI 
follow-up. On MRI at the 5-month follow-up, the cystic mass was enlarged and 
showed findings consistent with those of cystic CM. Surgical resection was 
performed and the pathological diagnosis was CM. Our experience suggests that 
the initial presentation of a CM can be a pure cyst and neurosurgeons should 
consider the likelihood of CMs in cases of cystic cerebral lesions with 
intracystic hemorrhage.