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Background: Preoperative diagnosis of malignant collision tumors (MCT) is extremely difficult. The value of dermoscopy to improve the correct detection of these tumors has not been previously studied. This study aims to evaluate the diagnostic accuracy of MCT with and without dermoscopy and to describe the dermoscopic features of a large series of MCT., Methods: Dermoscopic images of 161 MCT were evaluated. Clinical and dermoscopic images of histopathologically proven MCT intermingled with other tumors were randomly presented to clinicians with different levels of experience, blinded to the diagnosis and objective of the study. The clinical and dermoscopic diagnostic accuracies were measured separately., Results: A total of 161 histopathologically proven cases of MCT were collected. The most frequent MCT was basal cell carcinoma-seborrheic keratosis collision tumor (CT; 37.9%), followed by basal cell carcinoma-melanocytic nevus CT (19.9%), and melanoma-seborrheic keratosis CT (6.8%). Diagnostic accuracy among experts on dermoscopy was 71.4%. The study included 119 participants. The percentage of correct diagnoses was 8% by naked eye examination and 36.4% by dermoscopy (p < 0.001). The presence of the malignant component in the cases of MCT was not recognizable in 19.1% of cases by naked eye examination and in 11.8% of cases by dermoscopy (p < 0.001)., Conclusions: The diagnosis of MCT can be assisted and clarified by dermoscopy. However, many of these lesions manifest complex morphologies and continue to be challenging, even for experts on dermoscopy. Atypical, uncertain, or non-classifiable lesions still need a complete excision for the final diagnosis., (© 2021 S. Karger AG, Basel.)

Background: Nodular hidradenoma is an uncommon, benign, adnexal neoplasm of apocrine origin which is a clinical simulator of other tumours., Objective: The aim of this study was to evaluate the morphological findings of a large series of nodular hidradenomas under dermoscopic observation., Methods: Dermoscopic examination of 28 cases of nodular hidradenomas was performed to evaluate specific dermoscopic criteria and patterns., Results: The most frequently occurring dermoscopic features were: (1) in 96.4% of cases, a homogeneous area that covered the lesion partially or totally, the colour of which was pinkish in 46.4% of cases, bluish in 28.6%, red-blue in 14.3%, and brownish in 10.7%; (2) white structures were found in 89.3% of cases; (3) in 82.1% of cases, vascular structures were also observed, especially arborising telangiectasias (39.3%) and polymorphous atypical vessels (28.6%)., Conclusion: Nodular hidradenomas represent a dermoscopic pitfall, being difficult to differentiate clinically and dermoscopically from basal cell carcinomas and melanomas., (© 2015 S. Karger AG, Basel.)

Background: Targetoid hemosiderotic hemangioma is an uncommon, vascular, benign solitary lesion of lymphatic origin that can be misdiagnosed as other tumors including melanomas., Objectives: To evaluate the dermoscopic features of a large series of targetoid hemosiderotic hemangiomas., Methods: Digital dermoscopic images of 35 histopathologically confirmed cases of targetoid hemosiderotic hemangiomas collected from 7 hospitals in Spain and Italy were evaluated for the presence of dermoscopic structures and patterns., Results: The results of our study reveal that the presence of central red and dark lacunae and a peripheral circular reddish-violaceous homogeneous area is the most common dermoscopic pattern in targetoid hemosiderotic hemangioma (71.4%). The targetoid hemosiderotic hemangiomas of our study were correctly diagnosed in 77% of cases., Conclusion: Dermoscopy is helpful in improving the diagnosis of targetoid hemosiderotic hemangioma. However, attention must be paid to those cases that dermoscopically may show nontargetoid patterns, which often mimic other lesions, including melanoma., (© 2015 S. Karger AG, Basel.)