COLLAR-BUTTON CHOROIDAL MELANOMA - ANATOM IC-RADIOLOGIC CONFRONTATIONS

Malignant melanomas of the choroid are the most frequent symptomatic e ye tumours in adults. They often have a pathognomonic appearance, bein g collar-button or mushroom shaped due to rupture of Bruch's membrane by the tumoral mass. The ultrasonographic image of collar-button melan oma is well known: the head of the tumour is hyperechogenic and its ba se hypoechogenic. According to some authors, this is caused by differe nce in blood supply between the two parts. At MRI strongly pigmented m elanomas emit a high-intensity signal on T1-weighted sequences and a l ow-intensity signal on T2-weighted sequences, but these characteristic features are inconstant. We present a case of collar-button melanoma explored by ultrasonography, colour Doppler Flow Imaging (CDFI) ultras ound and MRI, then enucleated. Flows and signals were different in fro nt of, or behind the rupture of Bruch's membrane: ultrasounds showed a hyperechogenic image at the head and a hypoechogenic image at the bas e; on T2-weighted MRI sections intensity was greater in the head than in the base (head: 69 ms, base 180 ms) on CDFI, no flow was detectable in the head and very high flows were seen in the base of the tumour. Comparisons of these images with pathological findings, where there wa s no difference between head and base in melanin concentration and in cellular type (mixed or mainly epithelioid), led us to believe that th e differences observed in images were essentially due to differences i n blood supply between the two parts of the tumour constricted by the sides of the ruptured Bruch's membrane.