Multicoloured rainbow pattern in a case of aneurysmal dermatofibroma

Dermoscopy of haemosiderotic/aneurysmal dermatofibroma: A morphological study of 110 cases

BACKGROUND

Haemosiderotic and aneurysmal dermatofibromas are uncommon and frequently misdiagnosed lesions, which can be considered as different histopathological stages of the same tumour. A dermoscopic diagnosis testing accuracy has not been performed for these tumours to date.

OBJECTIVES

To determine the diagnostic significance of dermoscopic structures and patterns associated with haemosiderotic/ aneurysmal dermatofibromas in a large series.

METHODS

Dermoscopic images of histopathologically proven cases of 110 haemosiderotic/ aneurysmal dermatofibromas and 501 other tumours were collected. The frequency, sensitivity, specificity, positive predictive value and negative predictive value of the dermoscopic structures and patterns associated with these lesions were calculated.

RESULTS

Haemosiderotic/ aneurysmal dermatofibromas are mostly symmetric lesions (86.5%), and a prominent homogeneous area was present in 100% of them. The presence of vascular structures was very common (86.4%), and dotted vessels were predominant (58.2%). Shiny white structures were seen in 85.5% of lesions, while a peripheral delicate pigment network was present in 69.1%. The most significant pattern was the one composed of a prominent homogeneous area and peripheral delicate pigment network, which showed a specificity of 100% with a relatively good sensitivity (69.1%). All the patterns containing a peripheral delicate pigment network showed very good specificities, positive predictive values and negative predictive values. Those patterns without a peripheral delicate pigment network showed the highest sensitivities, but they showed a significant overlap with other tumours, mainly with melanoma.

CONCLUSIONS

Dermoscopy is helpful in improving the diagnostic accuracy of haemosiderotic/ aneurysmal dermatofibromas. However, there is a considerable dermoscopic overlap between these tumours and melanoma, specifically when the peripheral delicate pigment network is absent.