Ch22 Fibrous Papule
Membranous Loops

Buster (the plight of feral cats)

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F1Ch22 (104478): The lesion is polypoid. Rete ridges are irregularly represented; in areas they are effaced.At this magnification, the dermis near the epidermis is more homogeneous (more uniformly acidophilic without a clearly defined pattern of collagen bundles) than in the deeper portions of the lesion. There is perifollicular fibrosis with abnormal “mantle” patterns. Vessels in the polypoid portion are ectatic and have widened walls. Some of the patterns overlap with those of a fibro-follicular hamartoma.

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F2CH22 (104478): The epidermis shows hyperkeratosis and effacement of the rete ridges. The granular layer is prominent. There is mild melanocytic hyperplasia. There is a basal layer, but above this layer, the cells mostly show the features of cells of the superficial unit There are three blue arrows centrally, they identify a membranous loop; cells are entrapped in the loop. A papillary dermis is not represented as a defined unit. Vessels in the upper portion of the dermis are ectatic; there is mild endothelial hyperplasia. The pattern of collagen bundles is abnormal; there is hyperplasia of cells among the collagen bundles. Some of the cells have an enlarged, irregular nucleus.

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F3Ch22 (104478): A smugdy, thickened basement membrane shows focal defects. Collagen bundles extend to the basement membrane. The collagen bundles form ill-defined concentric patterns about the dilated vessel. Some of the cells near the dermal-epidermal interface contain melanin deposits in the cytoplasm. Green arrows identify two cells. One cell is a balloon cell of the type commonly seen in the epidermis over a fibrous papule. The deeper cell is less distinctive but probably represents an earlier stage of the ballooning process. There is some evidence of individual cell dyskeratosis.

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F4Ch22 (104478): Dilated vessels are clustered. Their widened walls appear somewhat homogeneous at this magnification.

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F5Ch22 (104478): At higher magnification, there are concentric fibrous lamellae about the vessels. Abnormal collagen bundles separate the two vessels.

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F6Ch22 (104478): In areas, the perivascular lamellae become confluent and hyalinized. There is endothelial hyperplasia.

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F7Ch22 (104478): The perivascular deposits are laminated and focally homogenized. Spindle cells (fibroblasts?) and lymphoid cells are entrapped among the lamellae. One spindle cell to the left of the lumen has lavender cytoplasm; it may represent a mast cells.

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