A 35-year-old man suffered secondary generalized tonic-clonic convulsions due to a large brain abscess. Neuroimaging incidentally revealed another tumor-like lesion. Cerebral angiography confirmed that the lesion was an unusual giant venous varix associated with a high-flow pial arteriovenous fistula (AVF) and showed one more small arteriovenous malformation (AVM). Pulmonary AVF, which can cause brain abscess, was also detected. Surgical ligation of the AVF and removal of the small AVM via individual craniotomies resulted in successful extirpation of the cerebrovascular malformations. Although the typical mucocutaneous symptoms were absent in this patient, the combination of arteriovenous anomalies was highly suggestive of hereditary hemorrhagic telangiectasia.