Correlation of high-frequency ultrasound backscatter with tumor microstructure in iris melanoma

This study aimed to correlate histologic characteristics with high-frequency ultrasound backscatter spectra in malignant melanomas of the iris. The study design was a cohort (case series) study of patients diagnosed with iris melanoma in the authors’ clinic. Sixteen patients with iris melanoma participated. The patients were scanned with a 50-MHz ultrasound unit equipped for digitization of raw echo data. Spectral parameter images representing the spatial distribution of size and concentration of tissue inhomogeneities were produced. The variation of spectral properties within and between tumors was determined. In the two tumors in this series for which histologic material was available, the authors compared scatterer concentration and size with histology and mathematically modeled the effect of melanocyte distribution on spectra. Ultrasound scattering characteristics differed considerably among tumors. Where histology was available, acoustic parameters correlated with the size and number of melanocytes present. Iris melanomas exhibited a wide range in acoustic backscatter properties. Whereas characteristics such as vascularity and necrosis might contribute to this, in the two cases examined here, backscatter characteristics could be largely accounted for by melanocyte distribution. A better understanding of the relationship of histology to noninvasive ultrasound data will enhance the diagnostic utility of this technique.