Module 12.1 Dermatoscopic Pitfalls

Dermatoscopic pitfalls There are many pitfalls in dermoscopy but the main objective is a) not to miss a melanoma and b) to avoid unneccessary excision of benign lesions. Throughout this course the emphasis has been on developing safe approaches to managing pigmented and non pigmented lesions. You have learned to look carefully at the ugly duckling lesion, look carefully at a lesion that has changed, either on the patient's word or because you have monitored it, and carefully examine any lesion a patient brings to your attention as a concern. If a patient has previously had a melanoma excised you generally adopt a more aggressive biopsy policy with new or changing pigmented lesions. By this stage in the course the pitfals should be fewer in number than at the beginning but experience teaches you that the variation in dermatoscopic morphology of both benign and malignant lesions is considerable and it takes a long time to be visually acquainted with all these variations. In this module I will look at some of the cases that have appeared in the Skin Cancer Society Blog which have caused the experts problems and hopefully you will learn to avoid them when you meet them again in the future. 

  The Pink Nodule We see pink nodules all the time when we examine patients. Most are dermal nevi, neurofibromas or dermatofibromas if they have been present for a long time. A new pink nodule should be carefully examined but one that arises in association with a pigmented lesion or which has flecks of pigment either within it or around the circumference should definately merit our careful examination with a dermatoscope. We are looking at vessels and any pigment we can see and trying to decide if the lesion is a dermal nevus, BCC, dermatofibroma or amelanotic melanoma. 

  The Pink Nodule When it erupts suddenly it merits our attention. The main concern is to avoid missing a diagnosis of amelanotic melanoma. If the vascular pattern is polymorphic with both dot vessels and corkscrew vessels and linear irregular vessels then consider an amelanotic melanoma. The vessels in a dermal nevus will be mainly comma shaped but if there is a mixture of both thick and thin comma vessels then again consider an amelanotic melanoma. The pink basal cell skin cancer will usually have arborising vessels. The pink dermatofibroma may not have much in the way of vessels at all. Unusual skin tumours such as Merkel cell, atypical fibroxanthoma and rapidly growing squamous cell carcinoma may again have a variety of vessels. When lesions grow rapidly looped vessels will often occur and are known as hairpins. If they have a white halo around them made up of keratinocytes then it is likely to be a keratinocytic lesion rather than a rapidly growing nodular melanoma. In practical terms any rapidly growing pink nodule gets biopsied because usually the vascular patterns are not specific enough to allow you to make a definitive diagnosis.

 Consider the following cases. Image 1 This is Harald's analysis "2. a lesion with 2 patterns (lines reticular and structureless), combined asymmetrically, more than one color (light brown and skin colored), needs just one clue to make the diagnosis of a melanoma: the clue here are linear, serpentine vessels that are coiled like a corksrew. Pathologic diagnosis: melanoma arising in a congenital nevus." Image 2 from Greg Canning is of a dermatofibroma on the dorsum of the foot showing both hairpin and dot vessels but this is very unusual site and morphology. 

Image 3 from Cliff Rosendahl has many lessons. It is a merkel cell tumour that was badly mismanaged elsewhere. The lesson is never to physically obliterate an elevated pink lesion if you do not know the pathology but you really should read this case so that you avoid this pitfall if you ever come across it.

  The Pitfall of the Regressed Melanoma A regressed melanoma should be considered when a lesion has a background pink colour, some small grey dots indicating melanin in melanophages and white stuctureless areas suggesting regression with pigment cell destruction. These features should be enough for you to consider a regressed melanoma in your differential diagnosis. Often any remaining network will be found around the periphery of the lesion and it may be distorted or thickened in areas again suggestive of the primary melanoma lesion. View this case in the blog 

  Image 1 This lesion shows obvious regression clinically with the pigmented areas separated by pale whiter areas. Harald Kittlers analysis -"Patterns: > 1 (clods, dots, structureless zone) Color: >1 Clues: gray dots, white structureless area Diagnosis: Melanoma" 

  Image 2 is a fantastic example of regression. There are no real pitfalls here although with all that regression and the peripheral pigment you might just think it was a pigmented BCC but only for a millisecond ! This is Cliff Rosendahl's description using Harald's algorithm. "Pattern - Structuress zones, clods,scrap of lines reticular(extreme NW), peripheral lines radial 

Colours - A Kaleidoscope! 

Clues 1. Peripheral focal lines radial (radial streaming) 2. Eccentric structureless blue, white,pink 3. Peripheral black clods 4. Patch of white lines reticular (negative network in the north) 5. Vessels dots+curved+one helical(corkscrew)dead centre last image 6.Pseudopods (NE) 7. Focal grey dots (due north last image) and finally the "rising hair on the back of the neck" sign!"

  Small melanomas Small diameter melanomas are usually defined as those that are 5mm or less in diameter. You might think that most of these would be thin lesions because it is relatively early in the development of a melanoma. Studies have shown that a third may be in situ and two thirds invasive. With small melanomas it is difficult to use concepts of symmetry and the nature of the border in your clinical assessment and often it is only the dermatoscopic view that alerts you to melanoma features such as blue/grey veils and peripheral dots and globules or streaking. It has been noted that small melanomas tend to occur in younger individuals but there is no difference in the normally found sex ratio. The small melanoma may simply be noted to be an ugly duckling in that it is often much darker than other similarly sized nevi. If a suspected small melanoma is raised it is prudent to just excise it using a small 4mm to 6mm punch rather than following the lesion. Any papular or raised pigmented lesion really should not be monitored. The problem of monitoring is that small nodular melanomas can grow at a rate of 0.5 of a millimetre a month. A small black nevus can be a diagnostic pitfall. The black pigment is so intense centrally that it obliterates the underlying reticular network. This is because of pigmentation in dead keratinocytes in the stratum corneum. These can be removed by tape stripping and the underlying benign network revealed. Some of these lesions lack the surrounding network as a peripheral halo and these are the lesions that can be mistaken for a melanoma and over aggressively excised. Remember the tape stripping!

  Pitfalls presented by the Amelanotic melanoma We have talked about the amelanotic melanoma above in the context of a pink nodule. However some amelanotic melanomas are macular lesions that present as a pink patch. Because they are thin lesions the predominant vessel pattern is a dot pattern. These dot vessels represent the vertical vessels coming from the deeper dermal plexus into the papillary dermis. They are coming up vertically, so looking down on them we see them as dots. They are mainly seen in thin lesions. Obviously dot vessels can be seen in other pink flat lesions, including psoriasis and dot vessels are common on the lower legs as part of venous stasis. Most amelanotic melanomas are better described as being hypo melanotic melanomas in that they usually have some remnant pigmented network, particularly at the peripheries. In these particular cases we are not dealing with regression or at least we are assuming the lesions do not have regressive features such as grey peppery pigmentation dots in the dermis. Sometimes an amelanotic melanoma is incorrectly diagnosed clinically as a superficial BCC and it may be treated with cryotherapy or curette and cautery without histology being obtained. Unless you can diagnose the superficial BCC quite confidently under your dermatoscope it is best to biopsy these lesions and to avoid cryotherapy. Amelanotic melanomas or hypomelanotic melanomas may become that way because they intrinsically lack melanin and melanocytes or because of regression where the melanocytes have been destroyed. If the latter has occurred you would expect to see a grey dot peppering and whitish areas that are whiter than the surrounding skin. All the criteria normally used to diagnose melanoma become irrelevant in a truly amelanotic melanoma but with the loss of pigment the vascular structures become more easily visible and these patterns are what must be learned and recognised. 

Combinations of amelanotic melanoma with another lesion, for example a basal cell skin cancer, are very unusual and as you can imagine extremely difficult to diagnose. The big problem in examining amelanotic melanomas is in using a dermatoscope with a contact plate and exerting too great a pressure, thereby compressing the vascular structures. A gel should be used if you want to examine vessels and should be placed carefully over the lesion to try and avoid any bubbles and then the lesion examined without lifting the dermatoscope and introducing bubbles into the medium. Gel allows you to look at the vessels without putting pressure on them. Polarised light dermatoscopes may give an even better view. Vessels in an amelanotic melanoma do not have keratin surrounding them. This should help you in differentiating an amelanotic melanoma from an SCC or other keratinising tumour. 

 The vascular patterns in amelanotic melanoma have been given a variety of names ranging from pin point or point like, through dotted vessels and hairpin like or linear irregular vessels. But point or looped vessels are just part of the normal vascular structure of the dermal plexus sending vessels into a growing tumour. The thicker the tumour the more the vessels are distorted and looped rather than pinpoint. Dot vessels are a feature of thin lesions. The thicker the lesion the more likely you are to get varying vessels because the loops are distorted more and you may see twisting or corkscrewing and even glomerular like structures. 

In keratinocytic lesions you tend to find the vascular loops most prominent at the periphery of the lesion but in an amelanotic melanoma they are distributed fairly evenly across the surface, more so in early lesions than late ones. Remember again that the older and thicker an amelanotic melanoma is then the more variable will be the vascular morphology. 

  To summarise thin melanomas less than 0.5 of a millimetre will tend to have dot like vessels distributed over the surface quite regularly. Tumours 0.5mm to 2mm in thickness as well as having dot vessels will also have some hairpin vessels. Tumours greater than 2mm in thickness will have more distorted vessels. Once a tumour is more than 3mm thick it cannot get its vascular supply from below and it tends to develop it from the side of the lesion and so vessels grow over the surface and may come sharply into focus and resemble the arborising vessels of a basal cell skin cancer but even then the arborising is not as marked as you see in a BCC. 

 As an aside a logical analysis of vessels was published first in the late 90s by Kreusch in Clinical Dermatology 20; 248-254 titled Vascular Patterns and Skin Tumours. His sequence of questions was basically the following. You ask yourself "Are there arborising vessels in which case it is BCC, Are there crown vessels in which case it is sebaceous hyperplasia, Are there comma vessels which are mainly found in a dermal nevus. Are there nonspecific vessels, which can indicate Kaposi sarcoma or regressive lesions? Are there pinpoint or hairpin vessels? If there is an absence of white halos the lesion may be melanocytic. If they are present it is probably a keratinocytic tumour. Are there any traces of melanin. If we are dealing with just a pink lesion traces of melanin make a melanocytic lesion more likely." 

 Picking up amelanotic melanomas is obviously difficult. You have to have almost a sixth sense as to which pink lesions need to be examined. Certainly any that the patient brings to your attention as being new or any that your eye picks up as being different from any background pink lesions, in any patient who has previously had a melanoma it becomes mandatory to examine any of the pink lesions whether the initial melanoma was amelanotic or not. Also in patients who have dysplastic nevi, any pink lesions need to be carefully examined. If we select patients who are at increased risk and learn to look at their pink non-melanocytic lesions as well as the darker melanocytic ones, then it is likely we are going to see a higher proportion of amelanotic melanomas. Also in any patient who presents with metastatic melanoma without an obvious primary it is important to examine any pink lesions that are still existing on the skin surface.

  In summary if you look at a pink lesion and it seems to have no features at all then back off, put a bit of gel on and look again without pressure because you are probably obliterating the underlying vascular structures. Only then can you confidently exclude an amelanotic melanoma. This is an interesting article from Medscape discussing the use of dermoscopy in diagnosing amelanotic or hypomelanotic melanomas There is also a recent article in the Archives of Dermatology by Scott Menzies on the dermoscopic diagnosis of hypomelanotic and amelanotic melanomas. Download it here 

  Image 1 is an in situ amelanotic melanoma. It has one milium cyst . If you have read the Scott Menzies article you would know that this is not significant. In his study more than 3 milia was an excellent negative predictor of melanoma. 

  Image 2 is a lesion that clinically looks like an amelanotic melanoma arising from a pigmented lesion but the dermoscopy is of a Firoepithelioma of Pinkus (variant of BCC) arising next to a benign melanocytic nevus! 

  Image 3 is of an extensive melanoma in situ on the neck looking like an area of Bowen's disease. However these are dot vessels rather than the glomerular or coiled vessels more typical of Bowen's. Interestingly the inferior area of redness she has on her neck was an area of Bowen's!

  Metastatic melanoma Metastatic melanoma can take various clinical forms. The skin lesions can be a local recurrence or occur within a skin graft applied over a melanoma excision site. Here the lesions will usually present as black nodules and the diagnosis is not difficult. The diagnosis is difficult when you have a solitary blue lesion in the skin and the obvious differential diagnosis is a blue nevus. Dermatoscopically it is very difficult to differentiate these two lesions in these circumstances unless you have a history that the lesion has been present for years. However if you do not have this history then you would be well advised to excise the lesion. If you rely on structures such as a blue white veil, then in a blue nevus this usually occupies the whole of the lesion or at least 7/8 of it, whereas in melanoma it usually occupies a much smaller component. Metastatic melanoma because of its dermal nature often will not have true blue white veil because you do not get the overlying orthokeratosis. A deeply pigmented basal cell skin cancer could come into the differential diagnosis but in the latter there should be no evidence of a pigment network and hopefully you will see some arborising vessels. Metastatic melanoma can often look like a blue nevus or a deep apocrine cyst because of the background blue colour. View this case from the Blog

The Benign Parallel Ridge Pattern of a Small Acral Nevus This is always a potential pitfall. In fact small acral nevi can even be histologically misdiagnosed as melanoma when in fact they are benign. This is one of the areas of the body where histopathologists are particularly wary of using criteria such as pagetoid spread of melanocytic cells into the epidermis as 100% indicating melanoma. There have been cases in the literature of small acral nevi misdiagnosed as melanoma on the basis of a parallel ridge pattern and some mild pagetoid spread. With small acral nevi always have a look at the edges of the lesion because these are more likely to give you an accurate dermatoscopic picture and often will in fact show a parallel furrow pattern. If a small lesion on the foot or hand is very dark and appears to show a parallel ridge pattern, look at it very carefully and make sure it is not a haematoma with subcorneal haemorrhage in the skin. You can always take a blade and very carefully pare it back. You are much more likely to find this clinical scenario in every day practice than a small acral melanoma. View this case in the Blog

Have a look at his case as well 

And this one and lastly This one also from the Blog

Desmoplastic Melanoma The desmoplastic melanoma is both a clinical and a dermatoscopic pitfall. Clinically it is a pitfall because the lesion often is not pigmented. It may have a red slightly scaly superficial appearance but when you feel around the lesion clinically it feels much harder than the surrounding skin and this hardness often extends beyond the overlying confines of the lesion. In some cases though a desmoplastic melanoma may have a superficial spreading melanoma overlying it and this variant can be missed if only a shave biopsy is done of the overlying pigmented lesion. Suspicion of a desmoplastic melanoma clinically is one reason to do punch biopsies if the lesion is large. Generally we do not like punch biopsies in melanoma but you may need the depth of a punch biopsy to pick up the features of a desmoplastic melanoma. The main dermatoscopic features depend on whether there is an overlying superficial spreading component or not. If there is then the main features you will see will be those of a superficial spreading melanoma with an abnormal thickened network, dots and globules that present in nests particularly at the periphery of the lesion and perhaps some radial streaming or peripheral streaking. There may also be multiple colours. However if there is not a superficial spreading component then these lesions can dermatoscopically look quite bland. They usually have a pink colour and if this is also structureless then this in itself should raise suspicion of a melanoma. Desmoplastic melanoma may also show parallel and anti parallel lines called chrysalids. These represent collagen in the dermis on which the melanoma cells are laid out. These lines are seen in polarised dermoscopy and an example is shown in the image below. Desmoplastic melanoma tends to be a clinical rather than a dermatoscopic diagnosis. Not all desmoplastic melanomas look like this one. A considerable number have an overlying superficial spreading type melanoma component and a shave biopsy may badly underestimate the thickness of the lesion.

  The Half and Half Lesion in Dermoscopy The half and half lesion is an interesting lesion in dermoscopy. It is always quite striking. Some lesions like the case below are very suggestive on clinical examination of melanoma and they may also raise the issue of being a combined lesion, but it appears that most of these half and half lesions are in fact just slight genetic variations with the same underlying histopathology. The lesion below has two different networks one of which was much darker and thickened and suggested a melanoma had developed. However the network that appears thicker and darker is actually quite regular and there are no other major features of melanoma in this lesion. So if the other examples below show seborrhoeic keratoses you should also look at the section on combined nevi which we will deal with in module 12 (2). View this case in the Blog

The Recurrent Nevus This situation usually arises because a pigmented lesion has been shaved and been found to be benign but has not been completely removed. When the nevus cells proliferate again in amongst the scar, the cells can individually look quite suspicious both dermatoscopically and histologically and the pathologist usually has to look at the original histopathology again to be convinced there was not a melanoma in the first place. Hence if you are going to examine pigmented nevi then it is best to do an excisional biopsy with small 1mm to 2mm margins than it is to do a shave or even worse to do a punch biopsy that may inadequately sample the lesion. Recurrent pigmentation that is combined to the scar itself is usually benign. The pigmentation that extends on either side of the scar is always worrying. If there is pigmentation and it is diffuse then several punch biopsies are a reasonable way of approaching the situation. Generally these lesions show multi component patterns with atypical network and irregular linear streaking both in the centre and in the periphery of the lesion. There may be vessels within the scar itself but these will often be described as having a stepladder appearance. Usually the pigmentation is concentrated in the centre of the lesion when it is benign. If the pigmentation is most accentuated at the spreading edge then this is a feature suggestive of a recurrent melanoma. When these lesions are examined histologically then with the recurrent nevus the proliferation of melanocytes is usually above the scar. Some of these melanocytes may be seen in the overlying epidermis simulating pagetoid spread but the nevus cells in the dermis do not extend beyond the outline of the scar. If the nevus cells are found outside this outline again it is a feature most suggestive of a recurrent melanoma. View this Blog case

Dr Peter Bourne's excellent presentation on Melanoma diagnostic pitfalls. I want you to download Peter's presentation here at this time and just work your way through it. I will cover some of the topics again later in this module. It looks at a Susana Puig paper on melanoma simulants that has some excellent images and then reviews Scott Menzies paper on amelanotic and hypomelanotic melanomas with some good case examples. When you complete all segments of the Dermoscopy pitfalls module you would be well advised to go over this presentation of Peter's once more. I will link to it again at the end of Module 12.3

Module 12.2 Dermatoscopic Pitfalls

Pigmented lesions in the scalp
This is a difficult area to be able to carefully examine lesions. I recommend you always cut the hair back to allow you to view a lesion properly with your dermatoscope. The scalp is a common site for pink dermal nevi, often quite exophytic. These are no problem but seborrhoeic keratoses, cellular blue nevi, pigmented BCC and melanoma can all occur alongside normal pigmented nevi in the scalp. It is not uncommon for superficial spreading melanoma to reach a considerable size in the scalp before being found. This pattern is usually seen on the frontal scalp whereas nodular melanoma is more common on the occipital scalp.
The frontal scalp is also an area where seborrhoeic keratoses and pigmented solar keratoses are commonly found.
Image 2 below is an example of a lesion that could easliy clinically be taken to be a seborrhoeic keratosis but was in fact a superficial spreading melanoma.Have a close look at the clinical image and see how prominent the follicular openings are.

Malignant blue nevus may arise from a cellular blue nevus in the scalp particularly in the late 50s.This raises the issue of whether to prophylactically excise these lesions in the scalp at an earlier age.

Image 1 shows just such a case in a young girl.

Image 2 Clinically suggestive of Seb K This case could easily have been missed. The lesion was in his hair line and the hair has been cut to better photograph the lesion. It looks like a seborrhoeic keratosis but the dermatoscopic image dispels that diagnosis very quickly!

Image 3 was clinically thought by me to be a malignant melanoma and I even thought so when I put the dermatoscope on it without cutting the hair. It was only when I was doing the incisional biopsy that the penny dropped!
View this case on the Blog






Overcalling Pigmented IEC

Overcalling pigmented IEC as melanoma has been a common occurrence on the blog. Generally it is a pigmented lesion under the dermatoscope without glomerular vascular structures to alert you to its true identity. There is usually varying pigmentation and sometimes a pseudonetwork, which generally puts you off by sending you down the melanocytic pathway. Non-pigmented Bowen’s disease is much easier with its scaly surface and glomerular vessels but in the pigmented variant of Bowen’s often all you get are structureless grey or brown pigmentation irregularly distributed through the lesion and associated with some globules. The distribution of the globules is usually also irregular. The images below illustrate several examples from the blog.







Overcalling the Blue/Grey Veil

Blue/grey veils are regarded as an important sign of a melanoma. Sometimes this is known as a blue/white veil. It is usually described as a ground glass, irregular confluent blue pigmentation, which covers part or all of the lesion. It usually represents melanin in the mid dermis, either in the form of melanin in melanophages or melanoma cells, with compact ortho keratosis of the overlying epidermis. The blue/white veil has been found in about 50% of invasive melanomas and has a specificity of about 98%. It can be a difficult feature to get everyone to agree about. In a melanoma the blue/white veil is usually irregular and non-uniform and this compares with the relatively uniform, steel blue colour seen in blue nevi. The blue in blue nevi is supposed to correspond to the pigmented spindle shaped cells that are found in the dermis in this lesion. In melanomas the blue/white veil is often seen over areas of regression and here the blue colour is due to melanin in melanophages or free melanin in the dermis.


Image 1 from Simon Hosking. This shows a blue grey veil in a seborrhoeic keratosis!

Image 2 from Peter Bourne in the Blog Here the blue grey veil is in a regressed nevus.

Image 3 from Ian McColl The blue grey veil covers the vast majority of the lesion.





Overcalling Peripheral Lesional Nests

Nevi evolve. They usually start with globular structures which slowly evolve into a reticular network. Part of this growing phase of a nevus is development of peripheral nests. Unfortunately peripheral nesting is also a feature of an expanding melanoma. A lesion with irregularly distributed nests, but where their size is constant, in a young person, usually indicates a growing nevus. If the nests are symmetrically distributed around the outside in a sort of starburst pattern, it sometimes signifies a Spitz nevus, again in a younger person. If you have asymmetrically distributed nests and the nests vary in size and density of colour then this is more in favour of the lesion being a melanoma.

One of the commonest pitfalls in dermoscopy is to overcall common growing nevi as Spitz nevi in young people and to under call melanoma when these lesional nests are in an adult. Some of the examples below from the blog will help to illustrate these points.

Image 1 View this Spitz nevus from Image 1a in the Blog and then Image 1b of composite and Image 1c of the composite

Image 2 14 month old boy with this lesion





Undercalling An Inverse Or Negative Network

The negative network is a particularly common feature of melanoma. Instead of having the normal network where the strands of the net itself are coloured and the holes are pale you have the reverse where the strands of the net are white and the holes are coloured. Negative networks are normally seen in the middle of a lesion but they can be seen at the periphery as well. It is not quite known histologically what they represent.

Overcalling a negative network . Dermatofibromas have white lines reticular centrally which may look like an inverse network especially is there is some overlying pigmentation from melanocyte stimulation in the epidermis.



Image 1 a true Inverse network and then Image 2 in the composite and then Image 3 in the composite



Overcalling Annular Granular Structures In Seborrhoeic Keratoses and Solar Lentigines On the Face

In Australia, because of the amount of solar damage we have and the aging of our population, we see many people with pigmented lesions on their faces. Most of these patients will have solar lentigos or early flat seborrhoeic keratoses but some will have lentigo maligna or lentigo maligna melanoma. Some also have pigmented solar keratoses. All of these lesions are characterised to some extent by annular granular structures representing fine pigment dots in between the hair follicles and sebaceous gland openings. If there are a lot of these dots they can obliterate the space between follicles and as such can then form rhomboid structures and sometimes some asymmetrical perifollicular pigmentation, leading to the erroneous diagnosis of lentigo maligna. Because these dermatoscopic features are common to all of these lesions you are virtually obliged to take a shave or punch biopsy of a suspicious area because you do not want to miss a lentigo maligna. Most lentigo malignas take years to develop fully, so you can in fact afford to follow these lesions up with three monthly dermatoscopic monitoring if you wish but most people will do a targeted biopsy early if a bit is worried about a particular lesion and has specifically mentioned it.





Overcalling Dysplastic Nevi

Dysplastic nevi have a variety of dermatoscopic patterns. This has been dealt with in previous modules but it is useful to go over the dermatoscopic patterns. The reticular and globular patterns can essentially resemble non-atypical nevi. The homogenous pattern is relatively nondescript and it tends to present as a pink lesion. The reticular homogenous pattern usually has a net like pattern around the outside and a homogenous structureless pattern in the middle. The reticular globular pattern usually has globules randomly associated with a background reticular pattern and the globular homogenous pattern is a mixture of globules and dark black structureless areas, some of which may be eccentric. The dermatoscopic disorganisation of these lesions is what leads many people to interpret them as being melanoma. An atypical nevus that has all three patterns namely reticular, globular and homogenous, sometimes is known as the multi component pattern which is more worriesome as it may be found in early melanomas.

The atypical nevus with eccentric hyperpigmentation is the one that most resembles melanoma and is the one that really requires histological examination. The eccentric area of hyperpigmentation usually reaches the border of the lesion. Many other patterns of dysplastic nevi are really quite benign but we still have a tendency to overcall them as melanomas.

Undercalling Dysplastic nevi!
The patient with multiple dysplastic nevi can be a nightmare. Unless you have total body photography and you can do side by side comparisons, then you will undercall the developement of melanoma in some of these patients. There is a great case in the blog that I have put up as image 3 here but certainly look at the link to the blog case and read the excellent discussion and input from Joe Triscott, a dermatopathologist.





Overcalling Vulval and Mucosal Pigmentation

Clinically these lesions always look worse than they actually are. You do not expect to see pigmentation on the vulva or on the mucosal surfaces of the skin either on the lips or inside the mouth. We tend to think of pigmented lesions as being sun induced but of course melanocytes genetically can be found in numerous unusual areas of the body.
Mucosal pigmentation is usually macular. If you get a papular lesion then you would have to look at it very carefully. Labial melanotic macules can look quite atypical clinically with varying pigmentation and an irregular edge but under the dermatoscope they will usually show linear pigmented network with sharp cut off edges at the periphery. The Blog has numerous examples of rather unusual labial melanotic macules and it is worth looking at a few of these cases below.

Vulval melanoma is usually seen in elderly individuals generally on the labia majora. The lesions look suspicious because of the varying pigmentation and the irregular edge you expect to see with a melanoma. They can rarely also be multifocal but generally multifocal pigmentation is more a feature of benign vulval pigmentation. Clinically vulval melanotic macules which are benign lesions can be indistinguishable from malignant melanoma in vulval areas especially if it is the flat in situ type. Even dermatoscopically there can be some degree of overlap of these benign lesions and early superficial spreading melanoma so it is important to always do a biopsy and use the dermatoscope to look for the most suspicious area for biopsy. The vulval area heals very quickly so a shave biopsy can be done if you want to sample a reasonably sized area. Vulval melanomas arising in pre-existing nevi have been reported but they are very rare.Image 3 shows an example of ring like structures seen in around 30% of cases of benign vulval pigmentation in a recent series published in the Aug 2008 issue of the Archives of Dermatology. Their other patterns described were as follows-At dermoscopic analysis, 6 different patterns were observed, alone in 60 of 87 lesions (69%) and combined in 27 of 87 lesions (31%). In 28 of 87 lesions (32%), we observed a ringlike pattern characterized by multiple round to oval structures, white to light brown, with hyperpigmented well-defined regular borders arranged in a grapelike manner in some areas (Figure 1). It was found as a single pattern in 21 of 28 lesions (75%) and combined with other patterns in 7 (25%). A structureless pattern characterized by diffuse homogeneous or variegated brown to gray-blue pigmentation—in the absence of typical dermoscopic criteria for melanocytic lesions, such as dots and globules, pigment network, and streaks—was observed in 18 of 87 lesions (21%) (Figure 2A). A globularlike pattern showing aggregated round to oval structures, tan to dark brown, similar to globules of melanocytic lesions, was also found in 18 of 87 melanotic spots (21%) (Figure 2B). The structureless and globularlike patterns were observed alone in 10 of 18 melanotic spots (56%) and combined with other patterns in 8 (44%).

Another cause of vulval pigmentation is pigmented Bowen’s disease. This is usually viral induced from an oncogenic papilloma virus. Dermatoscopically it may have glomerular vessels more typically associated with this lesion but the degree of pigmentation can be surprisingly dark and usually a biopsy is required to make this diagnosis. Dermatoscopically these lesions will not have a pigment network because the pigment is in the keratinocytes.

Extra mammary Paget’s disease is also another vulval disorder that has to be considered in the differential diagnosis but this usually presents as a pink scaly patch rather than a pigmented lesion. Histologically though these lesions show a pagetoid spread of cells in the epidermis and may be misdiagnosed by the pathologist as an amelanotic melanoma if special stains are not done to establish that these pagetoid cells in the epidermis are in fact of adenocarcinoma rather than melanocytic cells. In males genital melanoma usually arise in the glans penis and sometimes can involve the urethral meatus. A reddish brown pigmented patch on the glans penis may have other differential diagnoses including Kaposi’s sarcoma and Bowen’s disease. The dermatoscopic features of Bowen’s disease have been mentioned in relation to vulval Bowen’s and the same oncogenic virus applies. The dermatological features of Kaposi’s sarcoma are vascular but relatively non specific.

Mucosal pigmentation in the mouth is another issue altogether. It is obviously difficult to get a dermatoscope on this to look at it unless it is just inside the labial surfaces. The many causes of oral pigmentation can be viewed at the following website.





Overcalling the combined nevus

It is often difficult for us to consider the possibility that an apparently single lesion is actually two lesions combined. A combined nevus is therefore the association of two benign melanocytic lesions in the one biopsy specimen. The commonest one that we come across is the combination of the blue nevus with another nevus either a common type or congenital. Collision lesions in comparison are two different neoplastic skin lesions casually colliding within the same biopsy specimen. One of the commonest is the combination of a seborrhoeic keratosis and a basal cell carcinoma. Obviously the clinical features of a combined nevus depend on the types of nevi playing a part. Combined blue nevi usually have blue nevus in the middle or as part of a surrounding congenital or common nevus. The dark central part of the blue nevus is fairly obvious. It is generally homogenous blue and it may be surrounded by a reticular or globular pattern depending on the other common nevus component. The tendency with a combined blue nevus is to overcall it as a melanoma because of the darker central portion and the surrounding light reticular or globular network. In contradistinction collision lesions when they occur tend to have a linear separation between the two lesions rather than intermingling. Although the latter is not always the case.




Molluscum contagiosum and Accessory nipple

I put this case in to show you the features of a giant solitary molluscum contagiosum. The white viral sacs in the centre of the lesion may be mistaken for a dermatofibroma while the dot vessels may have you considering an amelanotic melanoma. The case in the blog illustrated by Alex Chamberlain, has an accessory nipple as the dermoscopic differential.

View this case in the Blog

Module 12.3 Dermatoscopic pitfalls

The Many Shades of Blue

Blue is a colour we notice in dermoscopy. It generally indicates melanin either free in the tissues or taken up by melanophages or in nests of melanocytes with all three being in the dermis. However some blue lesions in the skin are due either to foreign bodies or exogenous pigment such as graphite or a marker pen or due to bleeding into cystic structures such as hydrocystomas. Clinically when we see a blue lesion in the skin we usually immediately think it is a blue nevus. We put the dermatoscope on it and if it is a uniform steel blue colour, rounded with well-defined edges and has been there for some time, then we are quite happy to call it a blue nevus. It can sometimes have a blue/grey veil but generally it will cover the vast majority of the lesion whereas in melanoma the same blue/grey veil often only covers a small portion of the lesion. Blue nevi are due to embryonal melanocytes from the neural crest migrating into the skin and proliferating as nests. These cells can be found distributed in a diffuse fashion in the dermis in lesions such as Mongolian spots over the sacrum or nevus of Ota around the eye, or in nests in the dermis either on their own as in the common blue nevus and the cellular blue nevus variant or combined with other nevus cells as part of a combined nevus. Various clinical forms of blue nevi are described including plaque like and agminated forms where there are multiple clustered blue nevi sometimes on an underlying congenital nevus or on a Mongolian spot. Multiple blue nevi may be seen in the Carney syndrome, which is the association of blue nevi with cardiac myxomas.

The clinical differential diagnoses include trichoblastoma, especially arising within a sebaceous nevus, an apocrine hidrocystoma particularly around the eyes and rarely a pigmented intradermal poroma. Sometimes a deeply pigmented Spitz or Reed nevus can look like a blue nevus because of the deep blue colour but the radial streaks of a Reed nevus usually give it away. Metastatic melanoma remains an important differential diagnosis of a blue nevus and one should be aware of any new apparently blue nevi arising in a patient who has had a previous history of a melanoma. Blue nevi like metastatic melanoma often have a halo of erythema surrounding the lesion. It is not present in every case but when it is, it is a useful distinguishing feature.


View the melanoma case here

View the foreign body reaction here
View this great Blog presentation by Ben Cook





The Pink Hue

Just as blue in a lesion tends to attract your eye and your attention so should a pink area in an otherwise dermatoscopically non-specific lesion. The pink colour is usually due to increased vascularity but sometimes individual vessels are not visible. This milky pink hue is an important feature of amelanotic melanoma. When you see it in a lesion, especially if associated with some pale whiter areas of regression and if there is even just a faint remnant of network around the outside of the lesion, it is mandatory that you biopsy it, preferably by an excision biopsy. In a true amelanotic melanoma the vascular structures are often the only thing we have left to allow us to diagnose the lesion. We have already discussed the significance of dot vessels in thin melanomas with a vascular pattern becoming more disorganised into loops and corkscrew vessels as the lesion thickens. This mixture of vessels is sometimes described as being polymorphic.
The pink hue is often an important element of a desmoplastic melanoma. The desmoplastic variant, which does not have an overlying superficial spreading component, can look like a squamous cell skin cancer and has a firm area surrounding it that extends beyond the surface confines of the lesion. Sometimes a milky pink hue in parts of this lesion are the only features dermatoscopically that may allow you to make a diagnosis of desmoplastic melanoma.


The Pink Nevus

Generally this variant of melanocytic nevi is found in individuals with Type 1 or Type 2 skins. The nevi may be macular or papular. Some may have hair growing from them. Pink compound nevi may show the comma vessel typical of compound nevi and this can be quite a reassuring finding. When a patient has multiple pink nevi it is very difficult to follow them up. You often react on clinical clues where a patient says that an individual pink nevus is itchy or they feel in some way that it has changed. It is always prudent to excise these lesions to exclude an amelanotic melanoma.

View this case in the Blog





Undercalling a lichenoid reaction or regression

A lichenoid reaction is characterised dermatoscopically by blue/grey dots in the dermis. This represents melanin in melanophages where melanocytic cells have been destroyed and the melanin taken up by scavenger cells. When you see regression in a lesion it is always worrying. Sometimes all you see is regression and there is really nothing else left. If you biopsy these lesions the Pathologist may well not be able to tell you what the original pathology was and you generally have to approach these on a case by case basis. If there is any residual pigment network or other features such as a pink hue then it is worthwhile doing a biopsy to exclude an underlying melanoma. The degree of regression histologically and the depth of fibrosis can give you some idea as to what the original thickness of the lesion was because this lesion may have already metastasised and all you are seeing is the outline of the regressed lesion in the skin itself. After another few months this skin lesion may completely disappear and the patient subsequently presents with melanoma metastases down the track without any obvious primary lesion. The dermatoscope helps you to see which area you want to selectively biopsy and generally it is better to do an incisional biopsy here, to get the depth aspect of the regression, rather than a shave or a punch although if it is in a cosmetically sensitive area a dermatoscopically directed punch at the most obvious residual network area may be the better way to biopsy..

Small areas of regression within a pigmented lesion always merit sampling of the lesion to exclude melanoma.

Regression or lichenoid reaction is a common phenomenon directed at a variety of skin lesions including solar lentigines, seborrhoeic keratoses,( See Image 2 actinic keratoses and melanocytic nevi as in the halo nevus. When there is evidence of these underlying benign lesions generally biopsy or sampling is not necessary.

View this case from Ben Cook





Seeing only the seborrhoeic keratosis.
We concentrate on what we can easily recognise.

This is a common pitfall in dermoscopy. Seborrhoeic keratoses are exceedingly common and collision lesions are also commonly seen. The crypts, milia, comedonal openings and the like of a seborrhoeic keratosis are quite distinctive dermatoscopically and usually your eye will tend to focus on these and perhaps miss any subtler associated lesion.
The first image below is a beautiful example of this occurring where there is melanoma in association with a seborrhoeic keratosis. Now this is a most unusual combination. Seborrhoeic keratoses can be associated with basal cell skin cancers and with Bowen’s disease but in an example like this it almost appears to be a combined lesion rather than just a collision, which is certainly unusual. The pitfall here would have been to simply notice the seborrhoeic keratosis features and dismiss it as that without noticing the pigment network at the periphery and the dot vessels in the tail of the lesion. If seborrhoeic keratosis features seem to be present in only part of a lesion examine the rest of it very carefully for these other conditions.


For Image 3 see this case Harald Kittler's comments on it were "Orange clods and white dots are in favor of SEBK but convoluted vessels favor SCC (inlcuding IEC) and grey clods could point to SCC or BCC. Contradiction of features= Biopsy
Slightly favor pIEC over sebk"





Pitfalls of Monitoring

Monitoring of nevi is important especially in a patient with multiple pink or dysplastic nevi where there is a personal or a family history of melanoma. It can be virtually impossible to remember what these lesions looked like three months before. You may work on the basis of needing a certain dermatoscopic degree of atypia with clues to melanoma before you actually excise any of these lesions, in which case it does not matter whether you have monitored them or whether you have a photographic record of them or not, provided you examine every nevus each time and when your excisional threshold is triggered you excise the lesion. This technique does not really allow you to pick up new nevi or early melanomas. In the face of a background of dysplastic nevi you are likely only to pick up melanomas when they are Level 2 or 3 rather than at Level 1 and picking them up at this later stage has a significant detrimental affect on prognosis. Hence it is almost mandatory that these patients nowadays be monitored with digital photography, preferably of the total body variety. Some practitioners have their own machines such as a Solar scan or Mole max and there are other commercial ventures for example Mole map, where patients can have their lesions digitally recorded and then serially examined by a Dermatologist with a report going to the referring practitioner.

The pitfalls of monitoring though relate to the type of change that triggers an excision examination of the lesion. If monitoring is in the hands of experts generally up to eight or nine benign lesions are excised for every melanoma picked up on the basis of dermatoscopic change. Nevi can change depending on patient age, the season of the year and the sun exposure in the previous week or so. These factors have to be taken into consideration when examining a change. Slight darkening of a network is not really significant. A significant asymmetrical enlargement of a lesion is significant as is the appearance of other melanoma clues, such as peripheral nests, an eccentric pigmentation, a thickened localised network and peripheral streaking.

You do not monitor papular or raised lesions. If you are suspicious of one of these you excise it. The reason for this is that these lesions will grow at a rate of 0.5 of a millimetre a month or more and over three months you can have a lesion thickening between 1.5mm and 2mm, which has a similarly significant adverse prognostic change. Hence you only monitor new macular lesions not a new papular lesion. Obviously quite a few dysplastic nevi are papular but this admonition on monitoring papular lesions only applies to a new nevus or a change in a pre existing popular nevus.


Case 1 from Hilton Beck



Poor biopsy decisions

This is one of the biggest pitfalls in skin cancer medicine. The important principle is to adequately sample the lesion to give you all the information you need to sensibly excise it with appropriate margins to ensure it is appropriately treated. With pigmented lesions your biopsy has to tell you if the lesion is melanocytic or not and then preferably if it is benign or malignant. The former distingtion is easy for the pathologist but the latter is more difficult without either the whole specimen or a representative sample. eg You may not be sure if a pigmented lesion is a seb k or a lentigo maligna. A punch biopsy may be all you need to say it is not a seb k but actually expecting the pathologist to diagnose the precise melanocytic nature of the lesion on the punch is another matter. It could be a solar lentigo, a lentigo maligna, a pigmented solar keratosis or an invasive melanoma and if you have not sampled the appropriate area then you will not get the true diagnosis. Punch biopsying nevi to see if they are benign or malignant is a nonsense. You fully excise the nevus to allow the pathologist to make that distinction. People have been sued for punch biopsying a nevus, getting a report it is mildly dysplastic, leaving it and having a full blown melanoma erupt because it was a melanoma in the first place. A shave biopsy is used with a large flat lesion where primary excision would be a big proceedure and the diagnosis is uncertain. Dermoscopy should help to minimise some of these diagnostic problems but it does not eliminate them. The following cases from the blog show situations where biopsy decisions could have been better.



Overcalling a Pigmented BCC as a Melanoma

Some pigmented BCCs can be very dark. They may simulate blue nevi or melanoma. Image 2 below is a case in point where there even appears to be radial streaming and various colours. However there is no true network and BCCs are more likely to ulcerate earlier than melanomas. Less than 7% of pigmented BCCs have more than 75% of their surface pigmented so the lesion in Image 2 is quite unusual.




Unusual vessels In BCC

Basal cell skin cancers are usually described as having linear arborising vessels that are in very sharp focus relative to the underlying vascular plexus of the skin. These lesions usually course over the surface of the basal cell skin cancer and each branching gives rise to a smaller vessel. Though this feature is quite sensitive for basal cell skin cancers specificity is not quite as great as some people think. Linear arborising vessels can be seen in other rapidly growing tumours and there are some good examples in the blog of squamous cell skin cancers showing this, as well as atypical fibrous xanthomas and even Merkel cell tumours. However a lot of BCCs also show other most unusual vessel patterns and some of these are shown in the cases below. The reasons for these patternings is not known although the curious lesion in the breast below may be associated with underlying stretch marks in the skin because the vessels almost seem parallel, like the rope ladder vessels seen in a scar. The coral reef like vessels as shown in Peter Bourne’s case below have been replicated in other small BCCs seen on the blog.


Case 2 from Dr Peter Bourne




Unusual Patterns

The use of lasers and IPL machines, especially in the hands of inexperienced practitioners such as beauticians, has given rise to a variety of interesting dermatoscopic patterns. Curious clumped melanin seen in the first case below with the background hypopigmentation, was seen in a patient who had a hair removal laser session. This clumping of pigment is the result of the destruction of melanin in the hair papilla. The clinical picture showing the zebra like striping is due to an IPL damaging not only the hairs but also the overlying melanocytes in the skin because the power setting used was too high. This may take years to gradually re pigment. As new cases present in the blog we will add them to this section of Dermoscopy Consult.

IPL Hair Removal




Difficult cases from the Blog

The last section of this module will deal with difficult cases from the blog. Most of us feel that all the cases in the blog are difficult but in searching through the blog for cases for this module I have often come across some interesting images that I have not used elsewhere and this seemed a reasonable place to put them. You are probably dermoscopied out by this time but the cases below are my personal selection of worthwhile cases to examine and I will add to them as I find more that fit into this category.

1. Try two of a kind Clinically these lesions were quite similar looking but dermatoscopically very different.

2. This case was thought by most to be a BCC but was a melanoma. It has Confocal views as well. All the way from America