S7C12P9-1: In this lesion of hydroa aestivale, there is hyperplasia of both the basal and the superficial units of the epidermis. Centrally, the superficial unit shows a plate-like zone of necrosis with increased cytoplasmic acidophilia  and with lysis of the nuclei of dead keratinocytes. In a sense, this is a form of cytopathy. Some of the cells in the neighboring epidermis show dyskeratosis (increased cytoplasmic acidophilia). The basal unit shows inter-cellular edema with scattered, irregular defects in reticulated patterns. The defects contain loosely spaced, degenerating keratinocytes and a sprinkling of inflammatory cells. Perivascular infiltrates of inflammatory cells are prominent in the underlying dermis.

S7C12P9-3: The superficial unit shows a superficial, plate-like area of necrosis in a saucer-like configuration (dying keratinocytes are preserved in ghost outlines). Patterns of necrosis with these qualities are seen in a variety of clinical settings; they are common in early “neurotic excoriations.” They also may be seen in the epidermis in association with a leukocytoclastic angiitis (presumably, as a manifestation of ischemia). The irregular pattern of lysis of the basal unit of the epidermis is not in keeping with classic spongiotic vesiculation as seen in the setting of cell-mediated immunity (as manifested in a lesion such as a contact dermatitis). The irregular, reticulated quality of the pattern implicates a degenerative process affecting keratinocytes in an irregular fashion. Patterns of this type correlate with the form of cytopathy characterized as ballooning degeneration. Some of the neighboring keratinocytes have pale or vacuolated cytoplasm. Some of the keratinocytes are shrunken and acidophilic; these changes, too, are a feature of cytopathy.

S7C12P9-4: This lesion of “hydroa aestivale” shows a single, reticulated vesicle in the epidermis to the right of the follicle. The defect is in the basal unit of the epidermis; the basal layer of the epidermis is interrupted. There are perivascular and interstitial infiltrates of neutrophils and histiocytes in the upper portion of the reticular dermis. In this field, the infiltrates are most prominent beneath the vesicle.

S7C12P9-5: At higher magnification,  the defect is irregularly reticulated (it is partitioned by bridges of compressed keratinocytes, some of which show degenerative changes with increased cytoplasmic acidophilia). The neighboring epidermis has a spongioform quality, and many of the keratinocytes show vacuolization of cytoplasm. Neutrophils are present in the vesicle and in the defects among keratinocytes in the neighboring epidermis. The basal unit is hyperplastic. The superficial unit of the epidermis is thin. The underlying reticular dermis contains interstitial infiltrates of neutrophils and histiocytes. There is evidence of leukocytoclasia.