Radio-active di-iodofluorescein in the diagnosis of intra-ocular tumours.

THE use of radio-active dyes in the localization of brain tumours has been described in recent years by various authors. For example, Boyack and others (1948) found that di-iodofluorescein in which the iodine had been rendered radio-active was preferentially taken up by brain-tumour tissue, so that the position of the tumour could be determined by Geiger-counter measurements made from outside the skull. In a series of 104 cases, Ashkenazy and others (1947) claimed 95 per cent. success in the localization of tumours to one particular quadrant of the brain. Recently Belcher and Evans (1951) and de Winter (1951) in a very detailed investigation, using the far more sensitive scintillation counter, have failed to confirm these results, nor could the selective uptake of the dye in neoplastic tissue be observed in any one of the specimens removed surgically. They concluded that, owing to variations in the vascular character of the brain tissues and radiation from other body organs, even a 20 per cent. change in count-rate due to concentration of activity in a brain tumour, would prove difficult to detect. In ocular tumours the circumstances are rather different. In the first place, we are dealing with a tissue mass which, although much smaller in volume, is located so superficially that the counter can be applied within 3 cm. of the tumour itself; and in the second place, it is not the localization of the tumour which is sought, that being usually all too apparent ophthalmoscopically, but assistance in the all-important and often perplexing differential diagnosis of such a mass. Although the reason for this concentration in neoplastic tissues and its preference for those of the central nervous system is quite obscure, it seemed likely that both of the important malignant intra-ocular neoplasia, and especially the retinoblastoma, might share this predilection, both being as a rule richly supplied with vessels. At any rate the paramount importance of such a diagnostic test, if it proved successful in determining whether an eye should be removed, seemed to justify this investigation, in spite of discouraging reports by Belcher and Evans, and by de Winter. It should be added that Davis (1951) has already found positive counts in two cases with large malignant melanomata.