OBJECTIVE AND IMPORTANCEOf the primary intracranial mucoceles, those arising from the optic canal or anterior clinoid process are extremely rare. To our knowledge, only five cases have been reported. The pathogenesis of mucoceles at this unusual site is unclear, but the previously reported cases suggest that these mucoceles may originate from pneumatizing air cells in the anterior clinoid processes.CLINICAL PRESENTATIONA 43-year-old woman presented with diplopia. Magnetic resonance imaging showed a small mass, compressing the optic nerve, in the medial portion of the left anterior clinoid process. The medial portion of the anterior clinoid process surrounding the mass was eroded and the bony margins of the mass were well corticated in computed tomographic scans. There was no direct connection between any paranasal sinus and the mass cavity, as assessed in imaging studies and intraoperatively confirmed. The pathological diagnosis after the operation indicated a mucocele.CONCLUSIONConsidering the absence of air cells in the anterior clinoid processes, the mucocele in this case might have originated from ectopic mucinous tissue that appeared during the development of the optic canal, rather than from a pneumatizing air cell.