INTRODUCTION

Dermatofibroma (DF), also known as histiocytic fibroma, is one of the most common benign skin tumors composed of fibroblastic and histiocytic cells [1]. Most commonly found in the dermis, dermatofibromas may also be found in subcutaneous soft tissue in rare cases [2].

Its classic form is small, reddish-brown skin nodules on the extremities. DF is easily diagnosed clinically yet is difficult to diagnose atypical cases and histologic variants [3,4]. Therefore, it is important to improve other non-invasive diagnostic tools, such as dermoscopy, to guide the diagnosis and limit the need for skin biopsy.

A pigment network and a central white patch have been described as the typical appearance of common fibrous dermatofibromas visualized by dermoscopy [5]. When present, the examiner can confirm the diagnosis and determine conservative therapy based on the pigment network and the central white patch [6]. However, variants and atypical DFs usually lack these features.

We aimed to study the different typical and atypical dermoscopic patterns of DF in our Moroccan population.

MATERIALS AND METHODS

This was a retro-prospective study, performed at the dermatology department at the Hassan II University Hospital in Fez, Morocco, over a thirteen-month period analyzing the dermoscopy of 102 lesions in 93 patients.

Clinical data was obtained for each patient, including age, sex, phototype, and location.

Dermoscopy images were documented with a DermLite 4^th generation dermoscope with and without polarization light as well as with and without immersion. In order to avoid the collapse of the vessels in the lesions, no pressure was applied.

Two independent dermoscopists experienced in dermoscopy at our department analyzed and evaluated the clinical and dermoscopic data. After excision, clinical, and dermoscopic images were retrospectively analyzed for atypical variants of DF confirmed by histology.

Microsoft Excel was used for data extraction. Data was analyzed using IBM SPSS Statistics, with descriptive statistics expressed as mean values and percentages.

RESULTS

The mean age of the patients was 35 ± 6.8 years (range: 18–61 years), and our sample was predominantly female (71%). All subjects had dark skin phototypes (98% of phototype IV, 2% of phototype V). The clinico-pathological forms included were the common (94%) and aneurysmal/hemosiderotic DF (6%).

The predominant location was in the lower limbs (55%), upper limbs (26%), and trunk (19%).

A total of thirteen dermoscopic structures were analyzed (Table 1): a pigmented network (60%), white pseudo-cicatricial area (59%), homogeneous pigmentation (59%), red areas (2%), an inverted network (2%), chrysalis (21%), fissures (7%), comedo-like openings (4%), pseudocysts (3%), ulceration (7%), scales (8%), papilliform structures (2%), and vascular structures (13%).

Table 1: Characteristics of the dermoscopic structures of the dermatofibromas found in our study.

Ten dermoscopic patterns were observed (Table 2), dominated by typical patterns (Fig. 1) (93%). In the lead, a central pseudo-cicatricial whitish area surrounded by a peripheral pigmented network (19%) was observed (Fig. 1a). Other patterns of also typical appearance were objectified, especially a total pigmented network (10%) (Fig. 1b), homogeneous pigmentation surrounded by a peripheral pigmented network (7%), homogeneous pigmentation (7%) (Fig. 1c), a total pseudo-cicatricial whitish area (6%), multiple pseudo-cicatricial whitish spots surrounded by a pigmented network (5%) (Fig. 1d), an inverted network surrounded by a peripheral pigmented network (4%) (Fig. 1e), a whitish area surrounded by peripheral pigmentation (2%).

Table 2: Typical and atypical dermoscopic patterns in our series.

Figure 1: (a-e) Examples of the typical dermatofibroma dermoscopic patterns observed in our series. (a) A central whitish pseudo-cicatricial area surrounded by a peripheral pigmented network. (b) Total pigmented network. (c) Total homogeneous pigmentation. (d) Multiple pseudo-cicatricial whitish spots surrounded by a pigmented network. (e) An inverted network surrounded by a peripheral pigmented network.

Regarding the vascular pattern, we observed vascular structures in 14% of the cases, dominated by dotted and linear vessels in 9%, followed by hairpin vessels in 08%, glomerular vessels in 6%, and comma vessels in 4%. Polymorphic vascularization was observed in 7% of the cases in our sample.

Atypical patterns were rare (Fig. 2) (7%), represented by a seborrheic keratosis-like (Fig. 2a) appearance consisting of a cerebriform pattern (3%), a keratoacanthoma-like pattern (1%) consisting of a central ulceration and white structures and radial vessels, and a multicomposite melanoma-like pattern (3%) (Fig. 2b).

Figure 2: (a-b) Examples of the atypical dermoscopic patterns of dermatofibroma observed in our series. (a) A seborrheic keratosis appearance with a cerebriform pattern. (b) A multicomposite melanoma-like pattern.

DISCUSSION

DF is a benign skin tumor usually found on the trunk and extremities of young and middle-aged adults. It presents as a firm, red-to-brown papule or nodule with a positive dimple sign [4].

DFs may have various morphology appearances with different histologic variants. Common DF, aneurysmal DF, and hemosideric DF were the variants in our study [5]. Even though this benign tumor can imitate melanocytic lesions, in particular, atypical melanoma. The determination of its meaningful dermoscopic features has been considerably slower than that of melanocytic lesions in comparison with the many studies conducted on melanocytic lesions [6,7].

A variety of dermoscopic structures have been described in the scientific literature [8]. The dermoscopic appearance of DF includes the presence of a fine, peripheral, light to medium brown pigment network with a well-demarcated central white cicatricial zone [4,7,9].

The incorrect diagnosis of DFs as melanocytic lesions is probably greater in our population because the patterns significantly associated with this benign tumor were characterized by pigmented features such as a pigmentary network, homogeneous pigmentation with a peripheral pigmentary network, a lentigo pattern type, or totally homogeneous pigmentation. This may be explained by the dark skin phototype of our patients, which further supports the necessity of better characterization of DF in the dark phototype [6].

The appearance of the pigment network may vary from a fine, irregular peripheral, and/or total appearance to a prominent and atypical, irregular peripheral, and/or total appearance [8].

Our study, as well as most previous publications, agrees that the light brown, fine peripheral subtype, varying from light to medium brown, predominates and is attributed to network ridge hyperpigmentation rather than melanocyte proliferation [4,7,8].

On the other hand, Aytekin et al. had a dermoscopic evaluation of 142 DFs from 72 patients and concluded that a pigment network was present in 57% of the cases, with the most common subtype being a fine irregular or asymmetric pigment network [9]. Similarly, the pigmentary network was darker in the center and became progressively lighter toward the periphery with fine brownish streaks in the study by Arpaia et al. [10].

Central white cicatricial-like area, well-demarcated, histopathologically characterized by varying degrees of dermal fibrosis, is frequently reported in dermatofibromas lesions, usually surrounded by a fine peripheral pigmented network [4,7–9]. These two structures, when associated, represent the typical dermoscopic appearance of dermatofibroma and allows the clinician to confirm the diagnosis and define a conservative therapeutic approach [11].

These central white patches may also be multiple, rounded, or sometimes linear, giving the appearance of white radial striations, giving a spitzoid appearance as described in the Zaballos et al. study [7].

In addition to this typical dermatofibroma pattern, about ten patterns have been frequently reported in the literature as variants of the latter, especially the total network and the total homogeneous pigmentation, which is consistent with our results [4,7,8].

Zaballos et al. and Ferrari et al. reported total homogeneous pigmentation in 5% and 11% of cases, respectively, and a total pigmented network in 15% and 3% of cases, respectively. They considered these as variants of the typical dermatofibroma pattern [4,7].

The white network, also known as the negative or inverted network, was less frequently reported in dermatofibroma lesions in our study and other previous publications [4,7,9]. Some authors have described atypical types of DF, although typical dermoscopic patterns are the most common in clinical practice [8].

The vascular pattern has been widely discussed; however, DFs may have peripheral, central, or total erythema; dotted, hairpin, glomerular, comma, or linear vessels; but also polymorphic and atypical vessels [8].

In fact, Ferrari et al. described two DFs with dotted vessel patterns, Aytekin et al. stated that the most common vascular structures in their study were erythema and dotted vessels, which is in line with our results; while Genc et al. found vascular structures to be the most common dermatoscopic feature and described a red-to-brown halo phenomenon in 4.9% of lesions [4,9,12].

On the other hand, there are clinico-histologic variants that present as atypical patterns on dermoscopy [3], most notably the rare aneurysmal DF (Fig. 3a), which presents clinically as a large, fast-growing, blueish-brown nodule [13] and dermoscopically as homogeneous red or bluish areas (Fig. 3b) that correlate with vascular clefts and hemosiderin deposits that characterize this variant histologically [14,15].

Figure 3: (a-b) Example of aneurysmal dermatofibroma. (a) Clinical picture showing an aneurysmal variant of dermatofibroma. (b) Dermoscopic image of an aneurysmal dermatofibroma showing bluish-red areas and whitish structures.

As for the hemosiderotic form, it has been considered by authors as an early stage in the development of the aneurysmal form, sharing the same clinical features. Histologically, this form is characterized by abundant vascularization and extravasation of red blood cells, which demoscopically translates into the frequent presence of vascular structures [14,15].

More rarely, DF may present with a multicomponent pattern on dermoscopy [7].

In fact, although dermatofibromas are usually easily recognized on clinical examination due to their morphology, location, and consistency, DFs sometimes show an irregular peripheral network, vessels, and bright white lines on dermoscopy, among others, which may lead to diagnostic uncertainty as these findings are also associated with melanoma. In such cases, unfortunately, a skin biopsy is essential [16].

Seborrheic keratosis-like DF has also been described less frequently in the literature, with the cerebriform pattern in this case reflecting the presence of marked hyperkeratosis and keratin-filled epidermal invaginations [17,18].

CONCLUSION

DF is a multifaceted tumor with a variety of benign patterns, a better knowledge of which will help to limit the recourse to skin biopsy.

Our study was in agreement with literature data showing the predominance of typical patterns.

Atypical dermoscopic findings are rare yet alarming and always require histologic confirmation to exclude differential diagnoses, especially malignant tumors.

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