Osteoma is a common, slow growing bone tumor, and often affects the paranasal sinus. Typically, it shows a very hyperdense osseous lesion on computed tomography (CT) scan and low-intensity change on T2-weighted image on magnetic resonance imaging (MRI). No report has mentioned osteomas in blood supply on MRI. A 57-year-old male patient presented with a prolonged declined activity and a gigantic osseous tumor that originated from the frontal sinus, which markedly compressed the bilateral frontal lobe. MRI revealed a slightly enhanced front basal part of the tumor by gadolinium, with blood supply from ethmoidal arteries. The patient underwent surgery, and the diagnosis of osteoma was made based on histological findings. We reported a case of giant osteoma originating from the frontal sinus with unusual blood supply on 4-dimensional MR angiography.