1 - Milia-like cysts
2 - Comedo-like openings
3 - Exophytic papillary structures
4 - Red Lacunas
5 - Leaf-like areas
6 - Central White patch
Milia-like cysts
Definition
Milia-like cysts are variously sized, white or white-yellowish, roundish structures.
Histopathologic correlates
Milia-like cysts correspond to intraepidermal horn globules, also called horn pseudocysts, representing a common histopathologic finding in acanthotic seborrheic keratosis.
Diagnostic significance
Milia-like cysts are predominantly found in seborrheic keratoses, but are sometimes present also in papillomatous dermal nevi (Unna nevi). Very rarely are a few milia-like cysts observed in melanomas.
Comedo-like openings
Definition
Comedo-like openings refer to brown-yellowish or brown-black, roundish to oval or even irregularly shaped, sharply circumscribed structures. The irregularly shaped comedo-like openings are also called irregular crypts.
Histopathologic correlates
Comedo-like openings correlate to keratin plugs situated within dilated follicular openings. Due to clumps of melanin and clusters of bacteria, these keratin plugs often have a yellowish-brown or dark-brown to black coloration. In seborrheic keratoses, and especially in papillomatous dermal nevi, keratin plugs may also accumulate between papillary exophytic structures, then revealing an oval or even irregular shape.
Diagnostic significance
Comedo-like openings are predominantly found in seborrheic keratoses, but are observed also in papillomatous dermal nevi (Unna nevi).
Exophytic papillary structures
Definition
Exophytic papillary structures are densely packed dome-shaped structures, which are commonly separated by irregular, black comedo-like openings also known as irregular crypts.
Histopathologic correlates
Exophytic papillary structures correspond to finger-like projections reflecting pronounced papillomatosis and acanthosis in seborrheic keratoses or to digitiform papillations in papillomatous nevi containing nests of more or less pigmented melanocytes.
Diagnostic significance
At least to a certain extent, exophytic papillary structures are commonly found in papillomatous dermal nevi (Unna nevi) and also in seborrheic keratosis. They are very rarely observed in melanomas.
Red Lacunas
Definition
Red lacunas appear as more or less sharply demarcated, roundish or oval areas with a reddish, red-bluish or dark-red to black coloration.
Histopathologic correlates
Red lacunas correspond to dilated vascular spaces situated in the upper dermis. Examples of red lacunas with dark-red to black coloration correspond to vascular spaces that are partially or completely thrombosed.
Diagnostic significance
Red lacunas are stereotypical features of hemangiomas and angiokeratomas. Variations on the theme of red lacunas may be occasionally found in subungual and subcorneal hematomas.
Leaf-like areas
Definition
Leaf-like areas are brown, brownish-gray to gray-black patches revealing a leaf-like configuration. Some imagination, as when performing a Rohrschach test, is needed to recognize leaf-like structures when looking at these peculiar outlined areas.
Histopathologic correlates
Leaf-like areas correspond to more or less heavily pigmented, solid aggregations of basaloid cells in the papillary dermis of an otherwise typical superficial or nodular basal cell carcinoma.
Diagnostic significance
Leaf-like areas are a rather pathognomonic finding in pigmented basal call carcinoma especially when associated with arborizing vessels. In some instances, a leaf-like pigmentation at the periphery of an otherwise ‘featureless’ melanoma may lead the diagnosis of pigmented basal cell carcinomas astray, thus representing a major pitfall (false-negative case).
Central White patch
Definition
The central white patch, a pathognomonic dermoscopic finding in dermatofibroma, is a relatively sharp, circumscribed, round to oval, sometimes irregularly outlined, crystal-white area within the center of an otherwise regularly, light to dark-brown pigmented lesion. Occasionally, there are small round to oval-shaped, light brownish dots/globules within these central white patches.
Histopathlogic correlates
Obviously, one may infer that the melanin pigmentation of the epidermal basal layer is reduced in the center of dermatofibromas with central white patches. However, we cannot explain lucidly the impact of the attachment of the fibrohistiocytic proliferation in a given dermatofibroma to the overlying epidermis with regard to this particular dermoscopic and clinical finding.
Diagnostic significance
Central white patches are nearly exclusively found in dermatofibromas representing the dermoscopic hallmark of this entity that, in our estimation, is often more easily diagnosed on clinical grounds.