The "Umbrella Sign": A Useful Clue in the Diagnosis of Melanocytic Lesions in Sun Damaged Skin.

As ultraviolet radiation is an important aetiological agent in melanoma development, the presence of solar elastosis is an important factor in the assessment of any melanocytic lesion. However, melanocytic naevi are also seen in chronically sun damaged skin, particularly in regions with high levels of ultraviolet exposure and fair skinned populations. It has previously been noted that the relationship of a melanocytic proliferation to elastic fibers in the dermis can be of discriminatory value in the separation of melanoma from melanocytic naevus, in particular, it has been proposed that naevi act as a "sunscreen," which may result in a histological clue that the authors colloquially refer to in practice as "the umbrella sign." The aim of this study was to evaluate the patterns of solar elastosis within and beneath melanocytic proliferations developing in sun damaged skin and to determine the utility of the "umbrella sign" in diagnostic practice. We assessed 81 melanocytic proliferations in sun damaged skin for the presence of an umbrella sign, that was present in 49/53 melanocytic naevi (92%) compared with only 2/28 melanomas (7%, P < 0.05). In addition, entrapped elastotic fibers displaying distinct purple discolouration were identified in 16 melanocytic naevi. This finding was not identified in any of the melanomas. The umbrella sign appears to be a useful clue in the distinction of melanoma from melanocytic naevus in sun damaged skin, although as with all histological features in melanocytic pathology, it requires interpretation within a multifactorial assessment cognizant of potential diagnostic pitfalls.