[A case of choroidal malignant melanoma in which 123I-IMP scintigraphy was useful for diagnosis]

A case of choroidal malignant melanoma in which N-isopropyl-p-[123I]-iodoamphetamine (123I-IMP) scintigraphy was useful for diagnosis is reported. A 62-year-old man first visited our hospital 3 years ago complaining of decreases in left eyesight. CT showed a tumor with an arcuate high attenuation area on the aural side of the optic disk in the left eye. A crescent high attenuation area, evidence of retinal detachment, was also observed on the nasal side of the optic disk. T1-weighted MR images showed low signal intensity in most of the tumor and a high signal intensity area was seen in the center, T2-weighted MR images showed homogeneous and marked low signal intensity area. Differentiation from a hematoma or a vascular tumor associated with bleeding was impossible based on CT and MRI. However, because late-phase images obtained on 123I-IMP scintigraphy showed marked high accumulation in an area corresponding to almost the entire left eye, left eye enucleation was undertaken under a diagnosis of malignant melanoma. Histopathologic examinations showed tumor growth mainly in the subretinal area. The melanin content of the tumor was high in the periphery and relatively low in the center. Infiltration was observed into the sclera and around the vortex vein outside the eyeball, but this change could not be detected by CT or MRI. 123I-IMP scintigraphy was useful not only for qualitative diagnosis of choroidal malignant melanoma, but for the determination of the extent of the lesion as well.