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Abbreviations
AFX

Atypical fibroxanthoma

AS

angiosarcoma of the head and scalp

BCC

basal cell carcinoma

DFSP

dermatofibrosarcoma protuberans

LAS

lymphoedema associated angiosarcoma

MCC

Merkel cell carcinoma

MFH

malignant fibrous histiocytoma

RIA

radiation induced angiosarcoma

SCC

squamous cell carcinoma

Introduction

  1. Top of page
  2. Introduction
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgement
  7. References

There is mounting evidence that dermoscopy significantly improves the clinical diagnosis of most skin tumours and in consequence, dermoscopy is nowadays an integral part of the clinical skin examination.[1-3] The dermoscopic patterns of most common skin tumours, including melanocytic naevi, seborrhoeic keratoses, dermatofibromas, vascular tumours, melanomas, basal cell carcinomas (BCC) and squamous cell carcinomas (SCC) are well defined and established in everyday practice.[4-6] However, a range of uncommon skin tumours exists and their dermoscopic patterns have been described only sporadically. Here we provide a review of the literature on the dermoscopic patterns of uncommon skin tumours along with representative examples from our database.

Methods

  1. Top of page
  2. Introduction
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgement
  7. References

In this retrospective study we searched our database for clinical and dermoscopic images of histopathologically diagnosed rare skin tumours using the following keywords: Merkel cell carcinoma (MCC), mesenchymal tumour, adnexal tumour and fibrous tissue tumour. Tumours diagnosed as any type of melanocytic naevus, melanoma, seborrhoeic keratosis, haemangioma, angiokeratoma, pyogenic granuloma, dermatofibroma, BCC and SCC were excluded. All dermoscopic images were evaluated by two dermatologists (AL and EM) in consensus for the presence of specific morphological patterns. The dermoscopic criteria included: (i) vascular pattern (morphology and distribution of vessels), (ii) background colour, (iii) pigmentation structures and (iv) additional structures. If a disagreement arose between both evaluators the criterion was judged as being absent. A review of the literature was performed on PubMed Central with the keywords ‘dermoscopy’, ‘dermatoscopy’ and the name of each tumour.

Results

  1. Top of page
  2. Introduction
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgement
  7. References

A total of 85 rare skin tumours with 26 different histopathological diagnoses meeting the search criteria were extracted from our database (Table 1). The outcome of the literature search included 48 studies describing dermoscopic criteria of 20 different entities (Table 1). Combining the results of our analysis and previously published data, in Tables 2 and 3 we summarise the dermoscopic criteria of 26 uncommon skin tumours.

Table 1. Histopathological diagnoses of tumours in our series and results of the literature search
TumourNo of cases in our seriesNo of cases published
Merkel cell carcinoma[7-10]623
Angiosarcoma[11, 12]  
Angiosarcoma of the head and scalp39
Radiation-induced angiosarcoma04
Primary cutaneous carcinosarcoma[13]11
Langerhans cell sarcoma10
Atypical fibroxanthoma[14]53
Malignant fibrous histiocytoma10
Dermatofibrosarcoma protuberans20
Sebaceous cyst260
Sebaceous hyperplasia[15-21]581
Sebaceous adenoma[19, 22]319
Sebaceoma[22, 23]33
Sebaceous carcinoma[24]22
Trichodiscoma10
Trichilemmoma10
Trichilemmal cyst[25]41
Trichoblastoma80
Trichoepithelioma[26-28]  
Classic12
Desmoplastic14
Pilomatricoma[29, 30]414
Trichilemmal carcinoma10
Cylindroma[31-33]13
Hidradenoma[34, 35]03
Spiradenoma10
Hidrocystoma[36, 37]33
Syringomas (eruptive)10
Syringocystadenoma papilliferum[38]21
Eccrine poroma[39-45]1035
Porocarcinoma[46, 47]22
Mucinous carcinoma[48]01
Table 2. Dermoscopic characteristics of uncommon skin tumours
TumourDermoscopic criteria
  1. AS, Angiosarcoma of the head and scalp; RIA, radiation-induced angiosarcoma.

Merkel cell carcinomaMilky red background
Polymorphous vascular pattern (dotted, glomerular, arborising, linear irregular)
Angiosarcoma 
ASCombinations of red, purple and blue colour
White lines
RIAHomogenous pinkish-white pattern
Primary cutaneous carcinosarcomaPolymorphous vascular pattern (dotted, linear vessels, red globules)
Ulceration
White (scar-like) lines
Langerhans cell sarcomaReddish background
Polymorphous vascular pattern (dotted, linear vessels, red globules)
White (scar-like) lines
Follicular plugs
Atypical fibroxanthomaReddish and whitish areas
Polymorphous vascular pattern (dotted, linear irregular, hairpin, tortuous)
Malignant fibrous histiocytomaPolymorphous vascular pattern (dotted, linear irregular)
Ulceration/haemorrhages
Dermatofibrosarcoma protuberansReddish background colour
Fine linear vessels regularly distributed
Table 3. Dermoscopic characteristics of adnexal tumours
TumourDermoscopic criteria
Sebaceous cystWhite/yellow central structure
Yellowish background
Peripheral telangiectasias (crown vessels)
Sebaceous hyperplasiaWhite polylobular central structures
White structureless centre
Central umbilication (bonbon toffee sign)
Peripheral telangiectasias (crown vessels)
Sebaceous adenomaCentral opaque whitish structure
Yellowish background
Peripheral telangiectasias (crown vessels)
SebaceomaHomogenous yellowish central structure
Peripheral telangiectasias (crown vessels)
Sebaceous carcinomaPolymorphous vascular pattern
Homogenous yellowish background
Ulceration
TrichodiscomaWhitish globular structures
Blue-grey nests
Blurred linear vessels
TrichilemmomaKeratin masses
Perivascular whitish halos
Trichilemmal cystWhite-yellowish central structure
Peripheral linear branched vessels
Diffuse homogenous blue pigmentation
TrichoblastomaArborising vessels and blue-grey dots or globules
Trichoepithelioma 
ClassicArborising vessels
Shiny-white areas
DesmoplasticIvory-white background colour
PilomatricomaIrregular white and/or yellow structures white streaks
Reddish homogenous areas
Linear vessels
Trichilemmal carcinomaPolymorphous vascular pattern
White-yellowish areas
Ulceration
CylindromaUnfocused arborising vessels
Blue-grey dots/globules
HidradenomaHomogenous blue pattern
Amorphous whitish areas
Linear/hairpin vessels
SpiradenomaFaint greyish-bluish hue
Whitish areas
HidrocystomaStructureless skin-coloured/yellowish to bluish areas
Linear vessels
Syringomas (eruptive)Yellowish-brownish structureless background
Scarce fine linear vessels
Syringocystadenoma papilliferumPolymorphous vascular pattern (linear irregular, glomerular vessels)
Perivascular whitish halo
Pinkish-white background
Eccrine poromaPolymorphous vascular pattern perivascular whitish halo
Arborising vessels
Blue-grey globules/nests
PorocarcinomaPolymorphous vascular pattern (dotted, linear irregular vessels)
Ulceration
Mucinous carcinomaWhitish network
Light-brown globules

Discussion

  1. Top of page
  2. Introduction
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgement
  7. References

Rare skin tumours may escape clinical diagnosis, since they are not at the frontline of a clinician's differential diagnosis spectrum. Moreover, their clinical presentation is often unspecific, impeding their discrimination from other common entities. Dermoscopy may aid the clinical diagnosis of rare skin tumours by displaying unusual criteria that do not match the well-defined patterns of most common skin tumours.

Merkel cell carcinoma

The incidence of MCC has tripled in recent years and is today estimated about 0.24 per 100 000 person-years.[49-51] MCC shows a predilection for elderly white men and immunosuppressed patients.

MCC is a very aggressive carcinoma, associated with a high risk of locoregional and distant spread and poor survival and, effectively, its early detection and wide local excision are mandatory. Clinically, MCC most commonly develops as a persistent, asymptomatic, red or pink nodule that rapidly increases in size over a period of weeks to months (Fig. 1). The most common sites of presentation are the head and neck region and extremities, followed by the trunk and oral and genital mucosa.[49] Because of its unspecific clinical presentation, the differential diagnostic spectrum of MCC is broad, including common malignant tumours (BCC, SCC, melanomas) and benign lesions such as dermatofibroma or haemangioma.[7-10] Diagnosis is often delayed, since more than half of MCC are thought to be benign at the time of biopsy.

figure

Figure 1. Clinical and dermoscopic image of a Merkel cell carcinoma arising on the right leg of a 60-year-old man. Dermoscopy revealed milky red areas and irregular linear vessels.

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Dermoscopy of MCC typically reveals a milky red background and a polymorphous vascular pattern, comprising dotted, arborising, linear irregular and glomerular vessels (Fig. 1). Less often, milky red areas are combined with only one morphological type of vessels, usually linear irregular. This dermoscopic pattern cannot be considered specific, since similar findings characterise amelanotic melanoma and other malignant tumours. However, dermoscopy may enhance the discrimination between MCC and benign tumours by revealing features predictive of malignancy. Specifically, milky red areas, which represent the commonest criterion of MCC, are very rarely present in benign lesions (with the exception of pyogenic granulomas), whereas they are frequently detected in amelanotic melanomas. Additionally, the synchronous presence of more than one morphological type of vessel (forming the so-called polymorphous vascular pattern) is also suggestive of a malignant tumour, such as melanoma or SCC. Effectively, detection of one or both of the above phenomena should warrant complete surgical excision. The latter is particularly relevant in clinical practice, helping clinicians to avoid diagnostic delay with undesirable consequences for the patient.[7, 9]

Cutaneous angiosarcoma

Cutaneous angiosarcoma is an aggressive neoplasm that is generally divided into three clinical variants: angiosarcoma of the head and scalp (AS), mainly affecting elderly men; lymphoedema-associated angiosarcoma (LAS) arising typically in the context of Stewart–Treves syndrome and radiation-induced angiosarcoma (RIA) arising in previously irradiated skin areas.[52] Recently, epithelioid angiosarcoma has been described, as a rare, aggressive variant.[53] The classic AS is characterised by a tendency to metastasize to regional lymph nodes and lungs, often after repeated surgical excisions of the primary growth. Prognosis is poor, with a 5-year survival rate of 12–33%.[52] Surgical resection represents the treatment of choice, but its application may be limited by the wide extension of the tumour. Alternatively, AS might respond to a combined treatment consisting of chemotherapy prior to irradiation of the tumour field.

From a clinical point of view, early AS lesions develop as ill-defined violaceous to bluish areas with an indurated border. At this stage, the disease has to be discriminated from bruising, rosacea, tumid lupus erythematosus or infections such as erysipelas and cellulitis. Diagnosis of AS is often suspected at advanced stages when lesions become elevated or nodular and occasionally ulcerated (Fig. 2). Extensive local growth is common, and margins are difficult to define surgically. In approximately half of the patients the disease manifests with multiple separate foci.

figure

Figure 2. Angiosarcoma of the scalp. Clinical image showing the multifocal presentation of an AS in a 70-year-old man. Dermoscopy of a nodular area revealed purple-blue colour and whitish lines.

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RIA and LAS tend to present as reddish to purple plaques with ill-defined borders.

On dermoscopy, the classic AS is characterised by combinations of the typical colours of vascular tumours, namely red, purple and blue (Fig. 2). At the nodular part, white lines corresponding histopathologically to fibrous septa between enlarged neoplastic vascular spaces can be detected. RIA, instead, has been reported to exhibit a more homogeneous pinkish-white pattern.[11, 12, 54]

Tumours of the fibrous tissue

Atypical fibroxanthoma (AFX) and malignant fibrous histiocytoma (MFH) are related tumours with similar histopathological characteristics, but they differ significantly in their prognosis. The former, despite its tendency to recur after incomplete excision, has excellent prognosis, whereas MFH possesses a considerable metastatic potential, being associated with an overall survival rate of 50%.[55-57]

AFX occurs mainly on the sun-exposed parts of elderly individuals. Clinically, it manifests as a rapidly enlarging, reddish, dome-shaped nodule, often with an eroded or crusted surface (Fig. 3a). Less often the tumour acquires a darker hue due to haemosiderin deposition. The clinical differential diagnosis includes melanoma, BCC, SCC and dermatofibrosarcoma protuberans (DFSP).[56] Dermoscopically, AFX displays reddish and whitish areas in combination with a polymorphous vascular pattern consisting of various combinations of linear, dotted, hairpin and highly tortuous vessel irregularly distributed over the surface of the lesion.[14] Ulceration, crusting and keratin masses may also be detected (Fig. 3b).

figure

Figure 3. (a) Atypical fibroxanthoma presenting as a rapidly growing reddish nodule on the scalp of a 68-year-old man. (b) Dermoscopy revealed reddish and whitish structureless areas, white/yellow crusts and a polymorphous vascular pattern consisting of dotted and thin irregular linear vessels in an asymmetric arrangement. (c) This bulky, ulcerated mass acquired this size in less than a year and was histopathologically diagnosed as malignant fibrous histiocytoma. (d) Dermoscopy revealed a highly polymorphous vascular pattern comprising dotted, short linear and thick linear irregular vessels, in combination with ulceration and haemorrhage.

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MFH develops as an enlarging subcutaneous nodule that may acquire significant size and ulcerate (Fig. 3c).[57] As shown in Fig. 3d, dermoscopy reveals a polymorphous vascular pattern comprising dotted, short, fine linear and thick irregular linear vessels, in combination with ulceration and haemorrhage. Like MCC, although findings of AFX and MFH cannot be regarded as specific, dermoscopy minimises the risk of evaluating the tumour as benign. Specifically, detection of a polymorphous vascular pattern should raise suspicion of a malignant tumour, warranting complete surgical excision.

DFSP is a relatively uncommon soft tissue neoplasm, characterised by a low-to-intermediate malignant potential. Analytically, although DFSP rarely metastasizes it is characterised by a locally aggressive biological behaviour and a high recurrence rate. Clinically, it initially presents as one or multiple firm erythematous nodules or plaques that may suppurate or ulcerate (Fig. 4a,c). At this stage, DFSP has to be differentiated from dermatofibroma. The primary lesions gradually enlarge and become confluent, forming characteristic bulky, protuberant neoplastic masses. Dermoscopy might facilitate the clinical recognition of early lesions by revealing a reddish background colour in conjunction with fine linear vessels (Fig. 4b,d).[58] Although the dermoscopic criteria of dermatofibroma have been extensively investigated, a similar pattern has not been reported up to date.[59] A delicate pigment network has also been described in DFSP but it lacks the characteristic peripheral arrangement observed in dermatofibroma.[58]

figure

Figure 4. (a,c) Two cases of early dermatofibrosarcoma protuberans, presenting as a solitary nodule. (b,d) Dermoscopy of the two tumours made similar findings, namely a reddish background colour in conjunction with fine linear vessels, distributed all over the surface of the lesion.

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Adnexal tumours

Adnexal tumours are classified according to their adnexal differentiation as follicular, sebaceous, eccrine and apocrine.[60, 61] Their natural course is generally favourable, although for several benign adnexal tumours a malignant counterpart has also been described. Adnexal carcinomas are associated with a poor prognosis, which is, at least partially, related to their delayed recognition. Our series of tumours included two sebaceous carcinomas, one trichilemmal carcinoma and one porocarcinoma (Fig. 5). As shown in Table 3, almost all malignant adnexal tumours described in the present and previous studies dermoscopically exhibit at least one feature suggestive of malignancy, most commonly a polymorphous vascular pattern.

figure

Figure 5. (a) A sebaceous carcinoma developing on the thigh of a 50-year-old man. (b) Dermoscopy revealed a polymorphous vascular pattern comprising linear irregular and tortuous vessels, associated with yellowish structures and ulceration. (c) A trichilemma carcinoma gradually enlarging on the scalp of a 65-year old man for almost 1 year. (d) Dermoscopy revealed a polymorphous vascular pattern, consisting of dotted, linear irregular and tortuous vessels, in conjunction with white-yellowish well-circumscribed areas and ulceration.

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Sebaceous tumours

Although consistent criteria for the diagnosis and nomenclature of sebaceous tumours are lacking, these tumours are traditionally classified as benign sebaceous hyperplasia, sebaceous adenoma, sebaceoma (sebaceous epithelioma) and sebaceous carcinoma. Apart from sebaceous cysts and sebaceous hyperplasia which are common entities, sebaceous tumours are generally rare and typically occur in the context of Muir–Torre syndrome.[62, 63]

Sebaceous hyperplasia is dermoscopically typified by a whitish umbilicated, polylobular or structureless centre, surrounded by elongated, scarcely branching vessels (crown vessels). A similar pattern consisting of central whitish/yellowish structures and crown vessels characterises sebaceous cysts.

Two main dermoscopic patterns of sebaceous adenoma and sebaceoma have been described. First, tumours with a central crater, dermoscopically characterised by elongated radial telangiectasias (crown vessels) surrounding an opaque, structureless ovoid white-yellow centre, which is at times covered by blood crusts. Second, tumours without a central crater, which reveal dermoscopically branching but unfocused arborising vessels over a white to yellow background and few loosely arranged yellow comedo-like globules.[22] The combination of yellowish structures with unfocused arborising vessels is suggestive of the diagnosis of a sebaceous tumour. Differentiating among sebaceous tumours is troublesome, not only clinically but often also histopathologically. Our own and previous results demonstrate that this similarity is reflected also in the dermoscopic patterns of these entities (Fig. 5a,b). Dermoscopy enables their differentiation from sebaceous hyperplasia, which is a common entity, in contrast to the remaining sebaceous tumours, which appear almost exclusively in the context of Muir–Torre syndrome.

Tumours of the hair follicle

In general, the dermoscopic pattern of follicular tumours displays features overlapping with BCC, namely linear branching vessels and blue-grey dots or globules.[64] The common presence of ‘white structures’ has been suggested as a dermoscopic clue, suggestive of the diagnosis of a follicular tumour (Fig. 6). Specific dermoscopic criteria have are associated with some tumours, such as the unique ivory-white background colour that typifies desmoplastic trichoepithelioma (Table 3). A whitish colour can be also detected in morpheaform BCC, but it has a rather scar-like, instead of ivory, hue. Furthermore, morpheaform BCC clinically presents as a flat or depressed firm lesion, unlike trichoblastoma and nodular BCC.

figure

Figure 6. (a) Clinically, a trichilemma carcinoma usually presents as a verrucous lesion, whereas dermoscopy reveals keratin masses and perivascular whitish haloes. (b) Dermoscopy of a trichoblastoma revealing findings similar to basal cell carcinoma, namely arborising vessels and a blue-grey nest. (c) Dermoscopy of desmoplastic trichoepithelioma reveals a unique ivory-white background colour. (d) Dermoscopy of pilomatricoma reveals irregular white or yellow structures, while linear irregular vessels and ulceration may be also present.

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Pilomatricoma or calcifying epithelioma of Malherbe represents the commonest follicular tumour, usually affecting children and adolescents.[60] Irregular white and/or yellow structures, white streaks, reddish homogenous areas and linear vessels represent the most frequent dermoscopic criteria of pilomatricoma, while ulceration and blue-grey areas are common additional findings.[29, 30] The white structures, histopathologically corresponding to calcification or keratin masses, represent the most useful single criterion for differentiating between pilomatricoma and malignant tumours, such as melanoma and BCC.

Sweat gland tumours

Eccrine poroma is the most extensively studied sweat gland tumour, concerning its dermoscopic pattern. It is characterised by a high degree of dermoscopic variability, which is possibly explained by the existence of distinct histopathological subtypes, depending on the location of the basaloid aggregations in relation to the epidermis. Analytically, eccrine poroma may display dermoscopically overlapping features with BCC, such as arborising vessels and blue-grey nests, but more often it exhibits a polymorphous vascular pattern or perivascular whitish haloes, mimicking amelanotic melanoma or keratinising tumours, respectively (Fig. 7).[39-45]

figure

Figure 7. Eccrine poroma presenting as an ulcerated papule on the palm. Dermoscopy revealed dotted vessels and reddish globules, irregularly distributed and surrounded by pinkish white structures.

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Mucinous carcinoma is characterised by eccrine sweat gland differentiation and represents a low-grade malignant tumour with the potential of local recurrence.[61] Dermoscopy of mucinous carcinoma has been reported to mirror its peculiar histopathology, revealing a whitish network and light-brown globules, which histopathologically correspond to fibrous septum and mucinous deposition, respectively.[48]

A limitation of our study, as well as of all previous studies reviewed here, is related to their design. Specifically, they were descriptive morphological studies without a control group and the accuracy of the proposed dermoscopic criteria cannot be assessed. Another limitation is the variability in definition of dermoscopic features among different studies. Although we attempted to use uniform terminology for the cases described in the current study, we cannot rule out the possibility that in previous studies different terms have been used to describe the same dermoscopic feature, or that some investigators ignored criteria that others included and vice versa.

In conclusion, our results, along with pre-existing evidence, show that dermoscopy, by providing additional morphological information, might enhance the clinical diagnosis of uncommon skin tumours. Although benign adnexal tumours are dermoscopic mimickers of BCC, specific clues such as the whitish structures of follicular tumours and the yellowish structures associated with the crown vessels of sebaceous tumours might aid their recognition. A dermoscopic examination is particularly useful in the context of clinically unspecific and biologically aggressive entities, such as MCC, MFH and adnexal carcinomas, which can often escape clinical detection, with severe consequences. The latter aggressive entities dermoscopically exhibit criteria such as milky red areas or a polymorphous vascular pattern which, although not pathognomonic for a specific diagnosis, are highly suggestive of a malignant tumour. Accordingly, the detection of one (or more) such feature should warrant surgical excision and histopathological confirmation of the diagnosis. Validation of the value of dermoscopy in the diagnosis of uncommon skin tumours requires appropriately designed studies for diagnostic accuracy.

Acknowledgement

  1. Top of page
  2. Introduction
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgement
  7. References

Study supported in part by the Italian Ministry of Health (RF-2010-2316524).

References

  1. Top of page
  2. Introduction
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgement
  7. References