BACKGROUND: Pure arterial malformations (PAMs) are rare intracranial vascular anomalies. As recently reported, PAMs have a benign natural history and can be treated conservatively. However, their etiology, natural history, and treatment have not yet been fully elucidated. METHODS: We present a rare case of the progression of a PAM involving the anterior cerebral artery. Magnetic resonance imaging showed a mass located in the suprasellar region associated with obstructive hydrocephalus. Digital subtraction angiography showed evolution of the arterial anomaly with progression compared with the studies 3 years earlier. Surgical trapping of the parent artery with electrophysiological monitoring was performed. Combined with previous data, the clinical features and therapeutic strategies for this unusual entity are discussed. RESULTS: The patient recovered uneventfully after surgery. Postoperative digital subtraction angiography confirmed complete obliteration of the lesion. Axial computed tomography also showed shrinkage of the aneurysm, with improvement of the hydrocephalus. Our review of the reported data showed only 4 patients with a definite or probable PAM who had undergone surgery. To the best of our knowledge, the present case represents the first report of changes in the vascular architecture of a PAM during the follow-up period. CONCLUSION: Whether the aneurysmal component of PAMs merits invasive treatment has remained controversial. The findings from our case raises the possibility of evolution for some patients with PAMs and stresses the importance of scheduled follow-up noninvasive imaging studies to rule out progression of these nosological entities, especially PAMs with an "aneurysm-like" component.