Fig. 5

A 60-year-old man with choroidal melanoma of the right eye treated with proton-beam radiotherapy. The patient underwent secondary enucleation about three years after radiotherapy because of local recurrence. Axial a T2-weighted turbo spin-echo STIR, b fat-suppressed T1-weighted, (c) DW (b = 1000 s/mm²) and (d) contrast-enhanced fat-suppressed T1-weighted images show an intraocular mass along the posterior aspect of globe, at the level of the optic disc. The central and lateral portions of the lesion (white arrows) exhibit intermediate signal intensity on T2-weighted image and high signal intensity on T1-weighted image and represent viable tumor. The medial portion of the mass demonstrates low signal intensity on T2-weighted image and moderately high signal intensity on T1-weighted image; it represents radiation-induced necrosis with dispersion of melanin pigment, responsible for the low T2 signal. Note the well-defined border between the two distinct portions of the lesion, particularly evident on T2-weighted image. On (d) axial contrast-enhanced fat-suppressed T1-weighted image, the viable tumor demonstrates mild enhancement (white arrow) compared to relatively lower signal intensity of the medial necrotic part (white arrowhead). On c DW image, the viable neoplastic tissue displays high signal intensity (white arrow), a finding consistent with restricted diffusion due to high cellularity, whereas the necrotic part (white arrowhead) is hypointense, lacking of restricted diffusion. Laterally to the lesion a retinal detachment is detectable (white asterisks), with intermediate signal intensity on T2- and T1-weighted images, without enhancement after contrast agent administration. Along the medial outer edge of the sclera, a small metal artefact due to tantalum clip is appreciable (white dotted arrows in b and d). e Histological examination: low magnification showing a poorly pigmented melanoma, protruding into the posterior ocular segment and containing a necrotic component (on the right) (H&E, original magnification 25×); f Higher magnification demonstrating the "abrupt transition" between vital tumor tissue (on the left) and necrosis with abundant dispersed melanin (on the right) (H&E, original magnification 50×)