Unusual magnetic resonance image of an insulinoma with extensive desmoplastic reaction.

CONTEXT Unlike other islet-cell tumors, insulinomas are usually benign. Most insulinomas have a high signal intensity on T2-weighted images and a low signal intensity on T1-weighted images, and are hyperintense on immediate post-gadolinium images. However, in rare cases, insulinomas may be hypointense on T2-weighted images and on immediate post-gadolinium images, mimicking a ductal adenocarcinoma. CASE REPORT We present a case of a surgically proven insulinoma which was hypointense on both T2-weighted and immediate post-gadolinium T1-weighted images, but hyperintense on late phase T1-weighted images. Histopathological examination of the surgical specimen revealed a prominent desmoplastic reaction which accounted for the low signal on T2-weighted images and the contrast enhancement pattern. Delayed contrast enhancement reflects the desmoplastic component of this tumor. CONCLUSIONS Insulinomas with an extensive desmoplastic reaction may appear hypointense on T2-weighted images with minimal enhancement on immediate post-gadolinium images. Late phase fat-suppressed T1-weighted post-gadolinium images may be useful in the detection of such tumors.