S7C10P7-3: Rounded defects have formed in the epidermis at the interface between the superficial and the basal units on the left. The defects contain neutrophils and histiocytes.  The basal layer is hyperpigmented but this, in part, may be a racially related property. To the right of the rounded defects, neutrophils and histiocytes define a boundary at the interface between the basal and the superficial units. The inflammatory cells have migrated to the region in which a cleft will eventually form. Acantholysis, as usually defined in morphologic terms, is not a feature in the area of the epidermis in which the inflammatory cells have formed linear arrays, but this pattern is occasionally encountered in the clinical setting of pemphigus. Other biopsy specimens from such a patient might show more classic patterns.

S7C10P7-4: At higher magnification, a small pustule (neutrophil-rich vesicle) has formed beneath the superficial unit; the rounded defect compresses the cells of the basal unit. Similarly, the neutrophils and histiocytes in the neighboring basal unit do not violate the boundary between the superficial and the basal units; they are confined to the interstitial spaces of the basal unit and spare the superficial unit. The interface is marked with red arrows. To the right, the zone of pallor at the tips of red arrows anticipates a site of impending separation between the basal and the superficial units of the epidermis.

S7C10P7-5: The basic patterns are repeated in this example. Blue arrows identify the boundary between basal and superficial units of the epidermis. Neutrophils and histiocytes define the plane at the level of impending separation; the plane is not supra-basilar, but is higher at the interface between the superficial and basal units of the epidermis.