Clinical and Dermoscopic Features of Melanocytic Lesions on the Face Versus the External Ear

Introduction Melanoma of the external ear is a rare condition accounting for 7–20% of all melanomas of the head and neck region. They present classical features of extra-facial melanomas clinically and dermoscopically. In contrast, facial melanomas show peculiar patterns in dermoscopy. Objectives To evaluate whether there are clinical and/or dermoscopic differences in melanocytic lesions located either at the external ear or on the face. Methods In this retrospective study we reviewed an image database for clinical and dermoscopic images of melanomas and nevi located either on the face or at the level of the external ear. Results 65 patients (37 men; 63.8%) with 65 lesions were included. We found no significant differences in comparing face melanomas with melanomas at the level of the external ear, neither clinically nor dermoscopically. However, we provided evidence for differences in some clinical and dermoscopic features of melanomas and nevi of the external ear. Conclusions In this study, we reported no significant differences in comparing melanomas on the face with melanomas of the external ear, both clinically and dermoscopically. Furthermore, we provided data on clinical and dermoscopic differences comparing nevi and melanoma of the external ear.


Introduction
Melanoma of the external ear (MEE) is a rare condition, and its prognosis is still a matter of debate as long-term data are lacking. The external ear is considered as a special location as the skin is thin and lymphatic drainage is unpredictable.
About 25% of all cutaneous melanomas are located at the head and neck region and among those, 7-20% are located on the external ear [1][2][3][4]. Querying the Surveillance, Epidemiology, and End Results registry (SEER-registry) reveals 76,380 new diagnosed cases of MEE in 2016 in the United States.
2 population-based analyses suggest surgical removal as the treatment of choice; however, following recent data, wider surgical margins for melanomas of the external ear do not affect the overall survival [3,4]. Reviewing current literature shows, that melanomas of the external ear exhibit classical features of extra-facial melanomas, both clinically and dermoscopically (eg atypical pigment network, irregular dots and/ or globules, and peripheral streaks) ( Figure 1, A and B) [5].
In contrast, melanomas of the face are known to be associated with chronic sun-damaged skin and considered as slow-growing tumours. Their incidence increases mostly due to the higher cumulative exposure to ultraviolet radiation [5][6][7]. Stolz et al [6], first described a progression model from in-situ melanomas of the face (lentigo maligna) to dermoscopically invasive ones. At initial stages asymmetric pigmented follicles and grey dots around the follicles are observable. As the tumour progresses rhomboidal structures

Key messages
• Melanomas of the external ear and face melanomas differ in terms of their prevalence, clinical, dermoscopic appearance, and biological behaviour. Prognosis of ear melanomas is still a matter of debate. It is common knowledge that ear melanomas usually exhibit the classical features of extra-facial melanoma.
• To date, no study formally investigated possible clinical and/or dermoscopic differences in melanocytic lesions on the face versus the external ear. The results of this study show no significant differences when comparing melanocytic lesions on the face versus the external ear, thus indicating that face-specific criteria for melanomas are also valid for melanomas of the external ear and vice versa. Furthermore, data on clinical and dermoscopic differences comparing nevi and melanoma of the external ear are here reported for the first time. and finally homogenous pigmented areas and obliteration of the follicles are seen (Figure 2, A and B). Sensitivity and specificity of these features are reported to be 89% and 93% respectively [5][6][7].
The aim of this study was to evaluate whether there are clinical and/or dermoscopic differences in melanocytic lesions located either at the external ear or on the face.

Methods
This was a retrospective observational single-centre study conducted at the Department of Dermatology in Graz to evaluate whether there are clinical and/or dermoscopic differences in melanocytic lesions located either at the ear or in the face.
The study was conducted over a 1-year period. Ethics' committee approval was waived since we did not affect the stan- nosed a specific feature) to 5 (all 5 experts observed a single feature) in a specific patient. Comparison of means of these expert ratings across all patients was then done by analyses of variance.
Moreover, we also estimated the reliability of clinical and dermoscopic judgements, ie, the inter-rater repeatability using intraclass correlations (SPSS: Two-way mixed model testing absolute agreement of single raters). These correlation measures are reported in Table 1 and reflect the variation between the raters evaluating the same criterion in the same group of 65 patients examined in our study. The higher the coefficients, the higher was the consistency of ratings concerning a certain clinical or dermoscopic feature. Values lower than 0.5 are indicative of a poor reliability, ie, experts substantially differ in their ratings of that feature.

Comparison of Clinical Features of Melanomas on the Face vs. Melanomas of the Ear
No significant differences could be recognized concerning clinical features in these groups.

Comparison of Dermoscopic Features of Ear Melanomas Versus Nevi on the Ear
We found some dermoscopic patterns to be significantly different between melanomas and nevi at the ear: asymmetric pigmented follicles, scar-like depigmentation, annular-granular patterns, tan peripheral structureless areas and regular globules; detailed results are provided below ( Table 2).

Comparison of Dermoscopic Features of Face Melanomas Versus Ear Melanomas
No significant differences could be proven concerning dermoscopic features in comparing these groups.

Discussion
In this retrospective study including 65 patients we did not find any significant clinical or dermoscopic differences when comparing melanomas on the face and melanomas of the external ear. To the best of our knowledge, this is the first study providing data on this topic. These results somewhat contradict previous knowledge as skin' s structure and texture at the external ear and on the face seem to be very similar.
Consequently, face-specific criteria for melanomas should be valid and be used also for melanomas of the external ear. Of note, the limitation of this study relies on the fact that most of the included melanomas were invasive while just 8 tumors were in-situ melanomas. It is well known that -as melanomas progress -one can find similar clinical and dermoscopic features irrespectively of the tumor's localization [5,9,[11][12][13].
Moreover, we found significant differences in clinical and dermoscopic patterns when comparing melanomas and nevi on the external ear. Melanomas of the external ear exhibited the clinical feature "colour gray-blue" more than twice frequent when compared to nevi on the ear ( Figure 3, A-D). This is in line with data from the litera-ture, as gray-blue colour is considered as a strong clue for melanoma [5,9,11,12]. Moreover, we presented a number of dermoscopic features differing between melanomas and nevi of the ear respectively (Table 2). These results are again in line with current data as asymmetric pigmented follicles, scar-like depigmentation, annular-granular structures and tan peripheral structureless areas were significantly more frequent observed in melanomas, whereas regular globules typically indicate nevi [9,11,12]. The early differentiation of melanocytic lesions at the external ear is of clinical relevance.
A large study [14] comparing melanomas of the external ear and the head-/neck-region in over 130,000 patients proved that ear melanomas were an independent factor for tumor stage I and invasive behaviour. Furthermore, the authors found that men had a higher likelihood to develop MEE when compared to women.
Furthermore, significant co-occurrences among different dermoscopic patterns regardless of tumors' localization were observed. Notably, all positive correlations were found between face-specific and extra-facial criteria for melanoma.
In addition, we found a number of negative correlations in this group. Regular globules were negative correlated with asymmetric pigmented follicles and tan peripheral structures (p <0,021 and p <0,027, respectively); furthermore, a negative correlation between annular-granular patterns and regular globules could be proven (p <0,015). These results are well-established knowledge as regular globules in dermoscopy indicate a benign nevus whereas asymmetric pigmented follicles, tan peripheral structures, and the annular-granular pattern are strong indicators for melanomas [9,[11][12][13]. From this one can infer that the presence of dermoscopic patterns considered as "benign" excludes a melanoma and the other way round.
Our study has several limitations. First, due to the retrospective setting of our study, the interpretation of results is limited. Second, we did not include nevi of the face and can therefore not provide data about this entity in comparison to investigated entities. However, there is evidence that nevi of the face are mainly congenital and, especially in older individuals (>51 years), mostly present as raised, palpable, and hypopigmented lesions [13]. Third, the mean tumor thickness of melanomas on the face versus the external ear differed substantially (0,87 mm versus 1,47 mm). Therefore, comparison of these melanoma-types is limited. Fourth, we did not include information about the total number of nevi, personal or family history of melanoma or degree of photo damage.
To conclude, our study for the first time described that there are no significant differences when comparing melanomas of the face and melanomas of the external ear, clinically and dermoscopically. These results indicate that face-specific criteria for melanomas are also valid for melanomas of the external ear and vice versa. Furthermore, our study for the first time provided data on clinical and dermoscopic differences in comparing nevi and melanoma of the external ear.