Misclassification of non-melanocytic lesions
Misclassification of non-melanocytic lesions
Occasionally non-melanocytic lesions display a network, globules, streaks, or homogenous pigmentation potentially leading to the incorrect diagnosis of a melanocytic lesion.
Pigment network
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 lentigo, seborrheic keratosis, dermatofibroma and accessory nipple.
Solar lentigo
Solar lentigines 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 border, accompanied by the occasional presence of a clinical jelly sign fingerprinting, milia-like cysts and 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 structures, typically in which the grid is thickened and the holes are wider than those formed by melanocytic lesions. The grid corresponds to ridge 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 veil and linear irregular 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 network 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 light 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 clues 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 carcinoma
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 vessels and a pink-white shiny background are suggestive of BCC although they can appear on melanomas. That said, the misdiagnosis of a BCC as a melanoma would generally result in a similar, yet conceivably more rigorous management 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 dots, often arranged in peripheral linear tracks {Cameron, 2010 #2342}. The presence of scale and dotted or glomerular vessels 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 dots and globule, 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 histology. 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 sign, and those that are featuring dermoscopic clues as milia like-cysts and comedo-like opening facilitate the correct diagnosis.
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.
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 nevus, 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 structures (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.
Regression structures
Basal Cell Carcinoma
Regression structures and polymorphous vessels usually speak in favor of melanoma but occasionally they can also be seen in BCCs as is the case in the image below.
