When Brown Meets White and Blue: A Quiz in Three Hues

An 18-year-old Caucasian female with Fitzpatrick phototype II presented to our Dermatologic Clinic with a rapidly growing lesion on her right shoulder, first noted approximately 2 months earlier. The patient and her parents reported that the lesion appeared as a flat, brown macule that subsequently darkened and developed a palpable blue component (Figure 1). She denied any symptoms or history of trauma at the site. Dermoscopic examination revealed an asymmetric lesion measuring approximately 1.0 × 0.8 cm in diameter. The lesion exhibited a homogeneous light-brown network on an erythematous background, with an eccentrically located nodular bluish component, a structureless dark-brown blotch on the left and prominent bright white radial lines (Figure 2). The patient was otherwise healthy and not taking any medications. Her family history was unremarkable for melanoma or other skin malignancies. Due to the recent onset and the clinical and dermoscopic atypical features, an excisional biopsy of the lesion was performed for histopathological examination (Figures 3 and 4). Histopathological analysis with hematoxylin and eosin staining at 10x magnification revealed a storiform and whorled arrangement of spindle fibroblasts and histiocytes. The epidermis exhibited follicular induction and basilar hyperpigmentation, with sparing of the superficial papillary dermis (grenz zone). Extracellular hemosiderin deposition was also present. Non-endothelial-lined clefts and lakes containing erythrocytes were observed. Immunohistochemical staining for CD31 confirmed the presence of these clefts and blood-filled lakes (Figure 5). These findings were indicative of benign fibrous histiocytoma, specifically suggestive of the haemosiderotic/aneurismal variant. Dermatofibroma (DF), or fibrous histiocytoma (FH), is a benign dermal-based fibrohistiocytic proliferation and represents the most common soft tissue tumour encountered in routine dermatological practice. It typically presents in young adulthood as a solitary lesion on the lower extremities, although multiple lesions or involvement of other anatomical sites can also occur. Beyond the classic DF, several histopathological variants exist, including epithelioid, cellular, atypical, and lipidized subtypes. Among these, the haemosiderotic/aneurismal variant is one of the rarest and predominantly affects females, commonly presenting as a brown or blue papule rapidly growing on the lower legs [1]. Histologically, haemosiderotic/aneurysmal dermatofibroma (HADF) is a spindle-cell tumour with blood-filled spaces and hemosiderin deposition [2]. Specifically, haemosiderotic dermatofibroma (HDF) is primarily marked by extensive hemosiderin deposits resulting from blood cells extravasation within the lesion, while aneurysmal dermatofibroma (ADF) is characterised by blood-filled spaces lacking endothelial lining. It is has been proposed that HDF may represents an early stage of ADF. According to this theory, the hemosiderin in HDF forms as a result of the degradation of red blood cells that leak from vessels into the lesion, potentially due to trauma-induced vascular damage. Over time, chronic erythrocyte extravasation is thought to result in the formation of cleft-like spaces within the lesion. These spaces subsequently become filled with blood, giving rise to the characteristic features of ADF [3]. Conversely, other authors consider these two variants as different manifestation within the same pathological spectrum. Supporting this, a recent study of 197 cases of HDFs and ADFs found that approximately one-third of ADF cases did not exhibit hemosiderin deposition, challenging the traditional notion of HDF as a precursor to ADF. Moreover, the study suggested that HDF may originate from ADF, particularly in the context of venous stasis in the lower extremities [4]. The clinical diagnosis of HADHs is challenging, as these lesions often mimic melanomas and vascular tumours, among others [5]. Dermoscopy has proven to be a valuable tool in improving the diagnostic accuracy of HADFs. In 2006, Zaballos et al. [6] described the characteristic dermoscopic pattern in HADFs, which includes a central bluish or reddish homogeneous area, white structures, and a peripheral delicate pigment network. While these features are suggestive, they are not entirely specific, as similar patterns can be observed in melanomas, underscoring the need to always perform excision for histopathological confirmation [6]. More recently, a comprehensive study on 110 cases of HADFs revealed that these lesions are nearly always symmetric and exhibit a homogeneous area involving at least 50% of the lesion, typically bluish/purplish in colour, which was present in 100% of cases. Additionally, dotted vessels were frequently observed [7]. The authors continue to recommend excision as is not possible to definitively rule out malignancies such as melanomas, basal cell carcinomas or vascular tumours. In our case, the lesion appeared as a rapidly enlarging bluish-purple area with shiny white structures surrounded by delicate brown reticular pigmentation. However, it lacked symmetry, a prominent homogeneous bluish area, and vascular structures upon dermoscopic examination. As these findings contrast with the typical dermoscopic pattern described in the literature, an excisional biopsy was deemed necessary to confirm the diagnosis and primarily to exclude melanoma. In conclusion, AHDFs remain diagnostically challenging lesions due to their variable clinical and dermoscopic presentations, as demonstrated by our case, which lacked hallmark features described in the literature. Histopathological and immunohistochemical analyses remain essential to rule out malignancy and establish a definitive diagnosis. Conceptualization: Chiara Battilotti and Flavia Persechino. Writing – original draft preparation: Luigi Vittori and Chiara Battilotti. Writing – review and editing: Flavia Persechino and Giuseppe Soda. Visualization: Luigi Vittori. Supervision: Giovanni Pellacani. All authors have read and agreed to the published version of the manuscript. The authors have nothing to report. The authors have nothing to report. All patients in this manuscript have given written informed consent for participation in the study and the use of their deidentified, anonymized, aggregated data and their case details (including photographs) for publication. The authors declare no conflicts of interest. The authors have nothing to report.