Ch16L4 Reticular Dermis

Buster (the plight of feral cats)


F1Ch16 (R5256): The epidermis shows mild, compact hyperkeratosis; rete patterns are partially preserved. The rete ridges are composed of small keratinocytes of the basal unit type. The epidermis, away from the rete ridges shows an inconspicuous basal unit; mostly, only a basal layer is represented; the epidermis, away from the rete ridges, consists of an hyperplastic superficial unit. There is mild melanocytic hyperplasia, as evidenced by an increased number of “clear cells” in the basal layer. The upper portion of the dermis shows solar elastosis; in general, solar elastosis is a marker for the upper portion of the reticular dermis. A normal papillary dermis is not represented; the domain of the papillary dermis consists of a fibrous mat of coarse collagen bundles. The mat is hypocellular, but there is an increased number of small cells, some of which are dendritic in outline even at this magnification, irregularly spaced at a short distance from the basal layer of the epidermis. The coarse fibrous mat continues to the left along the infundibulum of a follicle. It extends to form the adventitia of dilated vessel, near the right-hand margin of the field. There are spotty, mild perifollicular infiltrates of lymphoid cells.

The lesion is a thin fibrous papule. The affected anatomic unit is papillary dermis; the normal fibrous stroma of the papillary dermis is not represented. The abnormal fibrous component also affects the perifollicular connective tissue sheath, and the adventitia of a vessel; on the basis of the extent of involvement, it is reasonable to characterize a fibrous papule as a fibrous dysplasia of the adventitial dermis. In normal skin, the fibrocytes of the adventitial dermis would appear to have special qualities; the special attributes combine to qualify the components of the adventitial dermis as stroma. In this approach, stroma is ideally suited to offer sustentacular functions for related epithelium. An alteration in the character of the papillary dermis may find expression in the character of the overlying epidermis. The epidermal changes over a fibrous papule are variable from mild to marked. In the more extreme expressions, the changes have a lichenoid quality but are distinguished by their cell-poor character (with the lymphocyte as the deficient component). For some examples, lymphocytic infiltrates are a prominent component of a dermal, rather than an cellular interface reaction.


F2Ch16 (R5256): The epidermal changes are mild. The rete ridges are effaced and the basal unit consist of only a basal layer. There is mild melanocytic hyperplasia (an increased number of basal “clear cell.” There are mild vacuolar changes at the dermal- epidermal interface; there are scattered dyskeratotic cells in the basal layer with some loss of nuclear polarity. The patterns are those of cell-deficient lichenoid reaction; they qualify as a variation of pathologic apoptosis affecting cells of the basal layer. There is hypertrophy of cells of the epidermal superficial unit with an accentuation of the granular layer and mild, compact hyperkeratosis. The epidermis sits upon a band of fibrous tissue that lacks the qualities of a normal papillary dermis. Focally, the basement membrane is slightly coarsened; the lichenoid reaction has an lupus erythematosus-like quality. The fibrosing reaction is distinctive; collagen bundles are coarsened and somewhat hyalinized; they are loosely spaced in a clear matrix. There is hyperplasia of small, bipolar fibroblasts. Some of the cells among collagen bundles near the dermal-epidermal interface are dendritic in outline. The fibrosing reaction extends along the follicle to the right. It involves the adventitial dermis.


F3Ch16 (Q4225): This is a second example of a fibrous papule. Rete patterns of the epidermis are irregular in distribution. A follicle at the margin of the lesion has an infundibular plug. In contrast to lesion R5256 (above), the fibrosing reaction is less confined; it involves the domains of both the adventitial dermis and the upper portion of the reticular dermis. The immature follicles of the lesion have sebaceous components. Collagen bundles of the reticular dermis are coarse and streaked.


F4Ch16 (Q4225): The epidermis show partial effacement of the rete ridges. There is mild hykeratosis and a mild increased prominence of the granular layer. The fibrosing process involves the papillary dermis, the perifollicular sheaths, the adventitia of vessels, and the upper portion of the reticular dermis. The prominence of the changes in the reticular dermis suggests the possibility that this is a connective tissue nevus of the tuberous sclerosis syndrome - the features overlap with those of a shagreen patch.


F5Ch16 (Q4225); The epidermal response has mild lichenoid qualities; for a “basal unit,” there is only a basal layer. There is mild hyperplasia of the epidermal superficial unit (the component of keratinocytes committed to terminal differentiation). Near the dilated follicle on the left, a multinucleated giant cell is present in a defect at the extremity of the thin rete ridge. Nuclei of this giant cell are arranged in a ring-like fashion; a melanocytic giant cell cannot be ruled out. The basal layer of the epidermis shows hyperplasia of “clear cells.” Collagen bundles of the dermis are streaked and some are more brightly acidophilic.


F6Ch16 (Q4225): The epidermal pattern has features of a mild lupus  erythematosus-like lichenoid reaction. Many of the cells in the superficial unit of the epidermis show peri- nuclear vacuoles; this is a common feature of the epidermal reaction in a fibrous papule. A basal unit is represented only in areas in which the rete ridges are represented; between the rete ridges, the basal unit consists of only a basal layer. Blue arrows identify dendritic cells that by location and cytologic features are interpreted as melanocytes. From the left, the second blue arrow identifies the cytoplasm of a dendritic cell is pigmented (a nucleus is not represented in the cell in the plane of this section). Focally, collgen bundles abut upon the epidermis in basement membrane-like patterns. There are mild vacuolar changes at the dermal-epidermal interface. A delicate fibrous mat, that might be characterized as papillary dermis (stroma) is not represented. The basement membrane is thickened and hyalinized.


F7Ch16 (Q4225): The patterns are as previously described. Blue arrows identify basal dendritic cells that are interpreted as melanocytes. The second and third arrows from the left identify a lacuna containing two dendritic cells. Basement membrane patterns are irregular in character and distribution.


F8Ch16 (Q4225); The material separating follicular epithelium from the collagenous component of the lesion has basement membrane-like qualities; it is laminated and hyalinized; there is also some accentuation of basement membrane patterns at the dermal-epidermal interface on the left. This field is representative of a margin of the lesion.


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