Ch3 Epidermis &  
Adventitial Dermis

Buster (the plight of feral cats)

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F1Ch3 (106049): This is a characteristic configuration of a “fibrous papule.” The epidermis shows some degree of hyperkeratosis with focal effacement of rete ridges. Some of the rete ridges have pointed extremities. The changes along the dermal-epidermal interface share features with the reaction pattern of the lichen planus-like lichenoid category. In this example, immature follicles are regularly distributed and show mixed catagen, anagen, and resting patterns. The epidermis is rarely emphasized in descriptions of this lesion. The most prominent pattern of fibrosis in the dermis is manifested in the adventitial domain - in the domain that abuts upon the epithelium of the epidermis and hair follicles. A compact fibrous matrix extends from the dermal-epidermal interface into the dermis; the vertical dimension of this fibrous domain varies area to area. This same fibrous domain extends along follicles in the pattern of a widened, dense fibrous sheath. Beyond this distinctive fibrous domain, collagen bundles are coarse and loosely spaced; in areas, the patterns might be dismissed as those of the normal reticular dermis, but the bundles are coarsened and some form vertically oriented arrays. The component in the reticular dermis may also represent an expression of a fibrous hamartoma. To the right of the follicle on the left, the collagen bundles form parallel arrays that are vertically oriented; these same bundles are more brightly acidophilic than those in other areas. Ectatic vessels are mostly a feature of the compact fibrous matrix that abuts upon the epidermis. To the right, the neighboring reticular dermis shows solar elastosis.

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F2Ch3 (106049): This is another section of the same lesion as seen Fig. 1. The epidermis shows focal effacement of the rete ridges (green arrows).The compact fibrosis of the “adventitial domain” is less extensive. Although the pattern in the “reticular dermal domain” somewhat resembles that of the normal reticular dermis, it is also abnormal; bundles are more widely spaced and then to show increased acidophilia. In addition, fibrocytes among the bundles are increased in number and individually hypertrophied. Ectatic vessels are mostly a feature near the surface of the lesion but are not confined to the compact “adventitial” component. Immature follicles focally are loosely clustered; they are cut in cross-section. In cross-section, the perifollicular sheaths are concentrically laminated (purple arrows).

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F3Ch3 (106049): To the left, dilated vessels are clustered; they have widened, pale walls. Streaking of the acidophilic collagen bundles is prominent in this same area; the streaked bundles extend to the deep margin of the field. The follicle to the right shows catagen phenomena.

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F4Ch3 (106049): The epidemis shows a prominent granular layer and hyperplasia of the superficial unit; a basal unit is most evident in the irregular rete ridges. Two fiber patterns are evident in the “adventitial domain.” The background pattern is contributed by a pale compact matrix in which collagenous unit fibrils are randomly distributed. Loosely spaced, branching collagen bundles contribute the secondary pattern. These bundles are brightly acidophilic. Most of these bundles are either vertically or horizontally oriented. In either orientation, the bundles tend to form parallel arrays. Many of the vertically oriented bundles extend to the dermal- epidermal interface. At the interface between the “adventitial domain” and the “reticular dermal domain,” the vertically oriented bundles of the “adventitial domain” are in continuity with coarse vertically oriented bundles of the “reticular dermal domain.” There is an irregular hyperplasia of basal clear cells (presumably melanocytes) in the epidermis. Focally, rete patterns are effaced.

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F5Ch3 (106049): A cluster of dilated vessels is represented. Some of the vessels show endothelial hyperplasia; the endothelial cells are hypertrophied and bulge into the lumen. A sheath of pale connective tissue outlines many of the vessels. Near the bottom of the field, the pale sheath contains a loose infiltrate of lymphoid cells.

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F6Ch3 (106049): The superficial unit of the epidermis is hyperplastic; the granular layer is accentuated. The basal unit is represented mostly in the pattern of elongated rete ridges. There is irregular hyperplasia of basal melanocytes.There are focal clusters of distinctive “balloon” cells in the superficial unit of the epidermis. Dilated vessels extend into the dermal papillae. The upper portion of the dermis, including the “adventitial domain” and the “reticular dermal domain,” is hypercellular.

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F7Ch3 (106049): A component, that might be characterized as “papillary dermis,” cannot be histologically defined. The vertically oriented collagen bundles of the “adventitial domain” tend to be laminated about the rete ridges (in a pattern that can be compared to lamellar fibrosis). Melanocytes are irregularly hyperplastic. In the area outlined with yellow arrows, many of the keratinocytes at the interface between the superficial and basal units of the epidermis show evidence of dyskeratosis. In some areas, even basal keratinocytes show features of dyskeratosis (premature keratinization).

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