Exceptions to the algorithm

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The two-step dermoscopyDermoscopy is a non invasive diagnostic method.algorithmIn mathematics and computer science, an algorithm (Listeni/ˈælɡərɪðəm/ AL-gə-ri-dhəm) is a self-contained sequence of actions to be performed. Algorithms can perform calculation, data processing and automated reasoning tasks. aims to differentiate between melanocytic and non-melanocytic lesions and to determine if a melanocytic lesion is benignThis glossary term has not yet been described. or malignantThis glossary term has not yet been described.. While algorithms serve as guidelines that apply to the majority of cases, one should remember that every rule has exceptions. The recognition of the exceptions is essential for the maintenance of high diagnostic precision.

Misclassification of non-melanocytic lesions

Occasionally non-melanocytic lesions display a network, globulesThis glossary term has not yet been described., streaks, or homogenous pigmentation potentially leading to the incorrect diagnosisThis glossary term has not yet been described. of a melanocytic lesion.

Pigment networkGrid-like pattern consisting of interconnecting pigmented lines surrounding hypopigmented holes.

The reticular network reflects a pigmented basal layer, with its grid representing the pigmented rete ridges and the holes representing the lesser pigmented suprapapillary plates. Whenever there is a corrugated and pigmented basal layer, whether its’ pigment lies within keratinocytes or within melanocytes, a corresponding reticular network appears on dermoscopy. Apart from melanocytic lesions, this structure could be seen in a solar lentigoThis glossary term has not yet been described., seborrheic keratosisThis glossary term has not yet been described., dermatofibromaThis glossary term has not yet been described. and accessory nipple.

Solar lentigo

Solar lentiginesThis glossary term has not yet been described. not uncommonly display a reticular network. Differentiation from a melanocytic lesion is usually based on the network being regular, faint and delicate, demarcated with a sharp border or a moth-eaten borderThis glossary term has not yet been described., accompanied by the occasional presence of a clinical jelly sign fingerprinting, milia-like cystsThis glossary term has not yet been described. and comedo-like openings[[Comedo like openings]]. A distinct type of lentigo is the ink-spot lentigo showing a unique dark brown thickened network that ends abruptly, commonly appearing following sun burns.

Seborrheic keratosis

Pigmented seborrheic keratoses occasionally demonstrate network-like structuresThis glossary term has not yet been described., typically in which the grid is thickened and the holes are wider than those formed by melanocytic lesions. The grid corresponds to ridgeThis glossary term has not yet been described. and the holes to the sulci or fissures. The grid can thicken to create a cerebriform appearance, formerly known as the “fat finger”. As with solar lentigines, the network- like structures of seborrheic keratosis end abruptly. When there is a blue white veilThis glossary term has not yet been described. and linear irregularlinear vessels with multiple bends vessels, the observer might mistake the lesion for a melanoma. Gray granularity observed in inflamed or regressed lesions might further add to the diagnostic difficulty.

Dermatofibroma

Dermatofibromas classically reveal on dermoscopy a delicate, tan-colored peripheral network, surrounding a central scar-like area. The delicate networklight brown, thin network lines corresponds to the “dirty feet” histologic appearance of the pigmented basal layer. At the inner edge of the network, circles are commonly seen, representing the widened rete ridges at the edges of the scar. The scar like area can display vessels, and under polarized lightThis glossary term has not yet been described. can show white lines overlying a pink background. As this pattern, along with a clinical dimple sign represent the prototype of dermatofibromas’ appearance, the two step algorithms specifically emphasizes it as an exception. Thus, when the above pattern is observed, a dermatofibroma can be diagnosed with certainty during the first step.

Supernumerary nipples

The areolar basal pigmentation of the nipple results in a dermoscopic delicate network, occasionally leads to the misdiagnosis as nevi or dermatofibromas. Diagnostic cluesThis glossary term has not yet been described. for supernumerary nipples are their clinical appearance as soft papules present along the milk-line, typically with a stable history.

Dots and globules

Although dots and globules are commonly observed in melanocytic lesions, they can appear in a variety of non-melanocytic lesions, including dermatofibromas, seborrheic keratoses, pigmented Bowen’s disease, basal cell carcinomas and cutaneous metastasis.

Dermatofibroma

As noted above, the inner edge of the network of dermatofibromas tends to show ring-like globular structure. This feature’s presence is probably related to the elongated rete ridges overlying the central scar-like area. A combination of clinical and dermoscopic clues including the dimple sign and central scar-like area featuring crystalline structures and occasional vessels are an aid to diagnosis.

Basal cell carcinomais the most common skin cancer, and one of the most common cancers in the United States.[1] While BCC has a very low metastatic risk, this tumor can cause significant disfigurement by invading surrounding tissues

The dermoscopy of pigmented basal cell carcinomas reflects the histologic pigmented tumor islands. Basal cell carcinomas can display and blue-gray non-aggregated globules and small and focused brown dots typically arranged in a “buckshot scatter” pattern. White shiny streaks, arborizing vesselsanalytic term is branched vessels; Bright red sharply in focus large or thick diameter vessels dividing into smaller vessels; BCC and a pink-white shiny background are suggestive of BCC although could appear on melanomas. That said, the misdiagnosis of a BCC as a melanoma would generally result in a similar, yet conceivably more rigorous managementThis glossary term has not yet been described. strategy.

Seborrheic keratosis

Globules are not a common finding in seborrheic keratoses. However occasionally they are present, reflecting the epidermal pigmented horn cyst or comedo-like openings. The presence of a sharp border, ridges and sulci and milia-like-cysts are an aid to the correct diagnosis. A more challenging dermoscopic variant is the clonal seborrheic keratosis in which variable-sized pigmented globular structures are aggregated throughout the lesions, occasionally leading the observer to expand the differential diagnosis to include a melanoma or a BCC.

Pigmented Bowen’s disease

Pigmented Bowen’s disease can display brown focal dotsThis glossary term has not yet been described., often arranged in peripheral linear tracks {Cameron, 2010 #2342}. The presence of scale and dotted or glomerular vesselsThis glossary term has not yet been described. are an aid to the correct diagnosis.

Cutaneous metastasis

Tumors metastasizing to the skin can acquire melanin from epidermal melanocytes or become colonized with melanocytes leading to pigmented structures as irregular dotsAny distribution of dots other than dots as described for regular and globuleThis glossary term has not yet been described., not uncommonly having the appearance of an atypical melanocytic lesion.

Pigmented streaks

Pigmented streaks are linear projections present at the periphery of the lesion. In melanocytic lesions they correspond to confluent junctional melanocytic proliferation but can be seen in variety of non-melanocytic lesions.

Seborrheic keratoses

Seborrheic keratoses display pigmented bulbous rete ridge on histologyThis glossary term has not yet been described.. In the same manner as this histologic feature could reflect a thickened network when present in the center of the lesion, its’ present at the periphery could result in corresponding dermoscopic streak-like structures. In seborrheic keratoses the streaks tend to be thick and occasionally branched. This structure leads to the description of the starburst-like seborrheic keratosis. Clinically distinguishing the stuck-on lesions, those with a negative wobble signThis glossary term has not yet been described., and those that are featuring dermoscopic clues as milia like-cysts and comedo-like openingRound to oval keratin filled clefts facilitate the correct diagnosis.

SteaksSEB.jpg
Basal cell carcinoma

BCC’s at times show thick streak- like structures arraigned radially, connecting to a common base. This is usually a variant of the leaf like structure of spoke-wheel structure.

StreaksBCCjpg.jpg
Pigmented Bowen’s disease

Irregular peripheral streaks corresponding to pigmented dendritic melanocytes are occasionally seen in pigmented Bowen’s disease, a rather rare variant of Bowen’s disease. Scale, ulceration and dotted or glomerular vessels are a clue to correct diagnosis.

Cutaneous metastasis

If epidermal melanocytes or melanin colonize skin metastasis at the periphery of the lesions, streaks could form in the same manner they are formed in melanocytic lesions.

Homogenous blue pigmentation

Due to Raleigh scattering, the shorter wavelengths (blue) are scattered, while the longer wavelengths (red) are mostly absorbed. Owed to this phenomenon, melanin and hemoglobin located deep in the dermis appear blue. Although the classic example of homogenous blue pigmentation is the blue nevusThis glossary term has not yet been described., this feature can appear in malignant melanocytic lesions (primary and metastatic melanoma) and in non-melanocytic lesions including Basal cell carcinomas, tattoos, cysts and vascular lesions.

Tattoos

Foreign material such as asphalt (traumatic tattoo) lead (pencil lead tattoo) or carbon ink (radiation tattoo) can create a homogenous blue lesion occasionally confused with a blue nevus. History is the main key to the correct diagnosis.

Basal cell carcinoma

Pigmented nodular BCC’s rarely appear as homogenous blue lesions. This feature, when present, probably results form a coalition of large ovoid nests.

Epidermal Cysts

Epidermal cysts occasionally have faint blue homogenous appearance. This results from the deeply located keratinous material covered by epithelial lining. Clinically the lesions generally feature as dermal bluish or yellowish nodules. The overlying epidermis occasionally features a punctum.

Vascular lesions

When angiomas and angiokeratomas are located deep in the dermis, occasionally the distinction between the vascular structuresThis glossary term has not yet been described. (lacunas) are not clear. Due to Rayleigh scattering these lesions can appear as homogenous blue or red blue lesions.

Dermatofibromas

Special variants of dermatofibromas such as hemosiderotic and aneurysmatic can display homogenous blue pigmentation due to hemosiderin deposition and large deep vascular channels. The dimple sign and a delicate peripheral network are an aid to the correct diagnosis.

Misclassification of melanocytic lesions

When melanocytic lesions do not display clear-cut melanocytic features, or on the contrary show features associated with non melanocytic lesionsThis glossary term has not yet been described., the diagnostic process could result in their misclassification as non-melanocytic.

Melanomas mimicking Basal cell carcinomas

When a melanoma expresses a pink background, crystalline structures and/or arborizing vessels, it could be misdiagnosed as a basal cell carcinomais the most common skin cancer, and one of the most common cancers in the United States.[1] While BCC has a very low metastatic risk, this tumor can cause significant disfigurement by invading surrounding tissues. Of the features noted above only arborizing vessels are considered specific for basal cell carcinomas, having a PPD of 94%. However, this feature has been described infrequently in melanomas, challenging the dermoscopic distinction of the two entities and having the final diagnosis made by the pathologist.

Melanomas mimicking benign non-melanocytic lesions

Melanomas occasionally display features seborrheic keratoses such as milia-like cysts and comedo-like openings. One should remember not to rule out a melanocytic lesion by noticing non-melanocytic structures. Adhering to the algorithms’ first step by deciding whether a lesion is melanocytic based on the presence or absence of a network, globules, streaks or a homogenous blue pattern, would help avoiding this misclassification.

Melanomas mimicking dermatofibromas

The gestalt pattern of melanomas and dermatofibromas can be similar, thus to achieve high diagnostic accuracy it is imperative to notice specific structure which support the global pattern. As stated above, contrary to dermatofibromas, melanomas generally do not show vessels and crystalline structures within the scar-like areas and lack a dimple sign. However, whenever an atypical dermatofibroma is suspected a reasonable management strategy would be to biopsy the lesion.

melanomas mimicking lichen planusThis glossary term has not yet been described.-like keratosis

Both melanomas and LPLK’S can feature pigmentation and extensive regressionThis glossary term has not yet been described. structure making their distinction occasionally challenging. A clue to lplkThis glossary term has not yet been described.’s diagnosis is a seborrheic keratosis or solar lentigo at the periphery of the lesion and rather coarse blue gray granules in contrast to the fine granularity associated with melanoma. In addition, both lesions can at times exhibit a pink structureless pattern with remnants of a pigment networkGrid-like pattern consisting of interconnecting pigmented lines surrounding hypopigmented holes., and the definite diagnosis is rendered though histologic examination.

Melanomas mimicking pyogenic granulomas

Both amelanotic melanomas and pyogenic granulomas can present as red evolving nodules, occasionally ulcerated or eroded. Pyogenic granulomas can exhibit vascular structures, further adding to the confusion .Considering the dismal consequences of missing a nodular melanomaThis glossary term has not yet been described., it is strongly suggested that all pyogenic granulomas would be removed and sent to histologic examination.

Discussion

As the human decision making is an intricate process, its’ reduction into a stepwise linear process can result in oversimplification leading to the incorrect diagnosis. Confusing a melanoma with a malignant non-melanocytic lesion (ie BCC or pigmented Bowen’s disease) would frequently result in similar management. However, confusing a malignant lesion with a benign lesion could have dismal consequences. It is essential to integrate history and clinical features with the algorithmic process and diagnostic clues in order to reduce diagnostic errors.

Table 1- Features and mimickers

Feature Differential DiagnosisThis glossary term has not yet been described. Mimickers
Negative Network MelanomaThis glossary term has not yet been described. Ridges of Seborrheic keratosesThis glossary term has not yet been described.
Spitz/Reeds Globular Structures of dermatofibromas
Severe Dysplastic neviThis glossary term has not yet been described.
CMN
Streakslines, radial (always at periphery) Reed nevus, melanoma, recurrent nevus Melanoma Leaf-like areasBrown to gray/blue discrete linear or bulbous structures coalescing at a common off center base creating structures that resemble a leaf-like pattern. of BCC
Spitz/Reeds nevusThis glossary term has not yet been described. Ridges (fat-fingers) of seborrheic keratosesThis glossary term has not yet been described.
Pigmented periphery of BowenThis glossary term has not yet been described.'s disease
Pigmented periphery of cutaneous mets
Network NeviThis glossary term has not yet been described. Fingerprinting of solar lentiginesThis glossary term has not yet been described.
Melanoma Cerebriform pattern of seborrheic keratoses
Solar lentigoThis glossary term has not yet been described.
Ink spot lentigo
DermatofibromaThis glossary term has not yet been described.
Accessory nipple
MastocytosisThis glossary term has not yet been described.
GlobulesThis glossary term has not yet been described. NevusThis glossary term has not yet been described. Lacuna
Melanoma Ovoid nests
Clonal Seborrheic keratosisThis glossary term has not yet been described. Blue-gray ovoid nests
Cutaneous metastasis Pigmented cysts
Comedo-like openings[[Comedo like openings]]
Peppering/granularityThis glossary term has not yet been described. Melanoma Blue-gray dots of BCC
Lichen planusThis glossary term has not yet been described.-like keratosis Linear brown dots of pigmented Bowen’s disease
Pigmented actinic keratosisActinic keratosis (also called solar keratosis and senile keratosis; abbreviated as AK) is a pre-cancerous patch of thick, scaly, or crusty skin. These growths are more common in fair-skinned people and those who are frequently in the sun. They usually form when skin gets damaged by ultraviolet (UV) radiation from the sun or indoor tanning beds. AKs are considered potentially pre-cancerous; left untreated, they may turn into a type of cancer called squamous cell carcinoma. Untreated lesions have up to a 20% risk of progression to squamous cell carcinoma, so treatment by a dermatologist is recommended.
Nevi (focal and limited)
VesselsThis glossary term has not yet been described. Various melanocyticThis glossary term has not yet been described. and non-melanocytic lesions Small ulcerations as in superficialThis glossary term has not yet been described. BCC
Linear brown/red dots of pigmented Bowen’s disease
Red globules of BCC
Background vesselsThis glossary term has not yet been described. in normal skin and sun-damaged skinThis glossary term has not yet been described.
BlotchDark structureless areas Melanoma Subcorneal hemorrhage
Clark's neviThis glossary term has not yet been described. Thrombosed angiomangiomas are benign tumors derived from cells of the vascular or lymphatic vessel walls (endothelium) or derived from cells of the tissues surrounding these vessels.[1][2] Angiomas are a frequent occurrence as patients age, but they might be an indicator of systemic problems such as liver disease. They are not commonly associated with malignancy.
Blue nevusThis glossary term has not yet been described. Black lamella
Reed's nevi Exogeneous pigmentation
Heavily pigmented seborrheic keratoses
Heavily pigmented BCC
Venous angiomas
Shiny-white streakslines, radial (always at periphery) Reed nevus, melanoma, recurrent nevus Melanoma Negative networkSerpiginous interconnecting broadened hypopigmented lines that surround elongated and curvilinear globules.
Spitz nevusThis glossary term has not yet been described. White lines of scalp nevi
BCC Wickham striae
Dermatofibroma Rail lines (pyogenic granulomaThis glossary term has not yet been described.)
Scar
Circles-white Actinic keratoses Milia-like cystsThis glossary term has not yet been described.
SCC Lobules of sebaceous hyperplasiaThis glossary term has not yet been described.
White clods of BCC
Lacunes of lymphangiomas
White globules of balloon cell nevi
Folliculitis
Molluscum
Circles-brown Dermatofibroma Curved lines of solar lentigines and seborrheic keraotoses
Bowen's disease Comedo-like openings
Facial melanomaThis glossary term has not yet been described.
Facial nevi
Facial solar lentigines
Angulated linesstreaks Melanoma of sun-damaged skin Spoke-wheel areas
Pigmented actinic keratosis Fingerprinting
Lichen planus-like keratosis Prominent network of congenital neviThis glossary term has not yet been described. and Clark's nevi
Prominent lines of ink spot lentigo
Lattice like pattern of acralAcral melanoma is a type of skin cancer that occurs on fingers, palms, soles, and nail beds. nevi