[Medullary osteoidosteoma of the os pisiforme]

A case of a medullary osteoidosteoma of the pisiforme bone is presented that appeared as a light bulb on MR-Angiography while causing diffuse hypointensity of the pisiforme bone and of the surrounding soft tissue on T1- and diffuse hyperintensity of these regions on T2-w and T1- w postcontrast images. Although not surprising according to the typical appearance of osteoidostomas on triple phase scintigraphy, the light bulb sign of osteoidosteomas on MRA has not yet been reported and familiarity with this findings may be of value in order to avoid their confusion with vascular lesions such as aneurysms or pseudoaneurysms during MR-angiography.