S10C10P8-1:  The pattern in this field is that of a lobular panniculitis. The lobules of fat in, and at the interface with, the dermis show more diffuse interstitial infiltrates of inflammatory cells than do the deeper lobules. In this field, septa are only slightly altered. In the two deeper lobules, the interstitial infiltrates are spotty in distribution and show variations in the density of the infiltrates.

S10C10P8-3: The patterns in this lesion also are prominently lobular, but the septum near the top of the field is also involved. The cells of the interstitial infiltrates are mostly neutrophils. Centrally in the septum, there is a collection of extrasavated red blood cells.

S10C10P8-4: In this field, the lobular panniculitis focally is hemorrhagic. The vacuoles vary in size; they are not associated with flattened, eccentric nuclei. The fat is necrotic; the defects are lipid-filled cysts. Some examples of lobular panniculitis, including so-called Weber-Christian’s disease, may be hemorrhagic.

S10C10P8-5: In this field, the patterns are mostly septal; the infiltrates are band-like at the interface between dermis and the subcutaneous fat. The septum to the left is widened and edematous. Infiltrates spill from the interfaces into the lobules in a “septal panniculitis-like” pattern. The band-like infiltrates (blue arrows) are basophilic; they lack the acidophilia usually associated with granulomatous infiltrates when seen at low magnifications (M. chelonii infection).

S10C10P8-6: The infiltrates are dense and lymphoplasmacytic. Red arrows outline a cluster of cells with plasmacytoid qualities. Histiocytes are loosely distributed; they are not arranged in epithelioid patterns. Centrally, there are defects containing neutrophils. There also are scattered clusters of extravasated red blood cells. This is a poorly organized suppurative granuloma. The combination of features should suggest the possibility of an infectious process (M. chelonii infection).