Trigonal cavernous malformations (CMs) are very rare. This paper presents a case of trigonal CM mimicking intraventricular tumor symptomatically and radiologically. A 55-year-old female patient presented with headache. Magnetic resonance imaging revealed a trigonal mass in the right lateral ventricle, which was isointense on T1-weighted and hyperintense on T2-weighted imaging and showed heterogenous enhancement on contrast image. The lesion was completely excised using microsurgery with a transinferior parietal lobule approach. Histopathologic analysis confirmed the diagnosis of CM. The patient had excellent outcome. The review of the pertinent literature has revealed that trigonal CMs with atypical magnetic resonance imaging incongruent with any Zabramski type could be misdiagnosed as intraventricular tumors. Radical excision through transcortical approaches provide good outcome for patients with trigonal CMs.