Bruch's membrane abnormalities in dome-shaped and mushroom-shaped choroidal melanomas.

INTRODUCTION Mushroom-shaped choroidal melanoma is known to be associated with breaks in Bruch's membrane and is more likely to develop when Bruch's membrane is diseased. The study's goal is to determine if diseases causing breaks in Bruch's membrane predispose a choroidal melanoma to develop into a mushroom-shaped melanoma. MATERIALS AND METHODS A retrospective review of cases of choroidal melanoma seen at our institution was carried out to determine if mushroom-shaped melanomas are more common than dome-shaped tumours in patients with macular abnormalities involving a loss of Bruch's membrane integrity. Forty-nine eyes of 48 patients were included in this retrospective study. A dome-shaped or mushroom-shaped configuration was assigned to each tumour. Macular degeneration, macular drusen, retinal pigment epithelial (RPE) stippling, macular oedema, choroidal neovascularisation (CNV), angioid streaks, disciform scars, lacquer cracks, and myopia greater than -3.00 D, were considered to constitute evidence of potential Bruch's membrane breaks and were determined in both eyes. A chi-square evaluation was used to compare the proportion of eyes with macular abnormalities in the 2 tumour configuration groups. RESULTS The tumour was dome-shaped in 40 eyes (82%) and mushroom-shaped in 9 eyes (18%). Macular abnormalities, indicative of loss of Bruch's membrane integrity, were seen in 21 (53%) of 40 eyes with dome-shaped melanomas and 5 (56%) of 9 eyes with mushroom-shaped melanomas. The proportion of eyes with macular abnormalities was not statistically different between the dome-shaped and mushroom-shaped tumours, as assessed by chi-square analysis (P = 0.87). CONCLUSIONS Bruch's membrane disease does not influence the differentiation of choroidal melanoma into mushroom-shaped or dome-shaped tumour growth patterns.