S8C9aVA1a-1a: Blue arrows point to areas of fibrinoid necrosis involving the wall and adventitia of a small vessel in the upper portion of the reticular dermis. Neutrophils and histiocytes are present in the inflammatory infiltrates. This is classic leukocytoclastic vasculitis with areas of necrosis in the adventitia and walls of blood vessels. This patterns is indicative of an immune complex disease. There is extravasation of red blood cells. Perivascular spaces are edematous. Neutrophils have infiltrated the wall of the small vessel near the bottom of the field.

Vasculitic Patterns

1. perivenular distribution (often, the epidermis is uninvolved)

a. lymphocytic

b. neutrophilic and leukocytoclastic

c. mixed (“a” & “b”)

d. granulomatous

2. collagenosis

a. neutrophilic (including pyodermas, Sweet’s, and acute folliculitides)

b. histiocytic

c. eosinophilic (flame figures)

3. epidermal pustules

S8C9VA1-1: The practice of pathology is based on a collection of accommodations; both variations in morphologic patterns and prejudices are to be accommodated. For the category of vasculitis, we commonly arrive at a diagnosis of leukocytoclastic angiitis even though certain features, often emphasized as basic requisites for the diagnosis of angiitis, are not represented. More often than not, the diagnosis of angiitis is nothing more than an accommodation for interstitial infiltrates of degenerating neutrophils (a neutrophilic collagenosis with leukocytoclasia). In the above Table, components, that are common in the setting of  vasculitic disorders, are listed. In turn, the categories are broadened to include cytologic variations not often considered in common definitions. It is extremely difficult to make a sharp separation between leukocytoclastic angiitis and neutrophilic collagenosis (neutrophilic dermatitis). Much of what is characterized morphologically as a vasculitis relates to the role of the B lymphocyte in immune reactions. Specifically, the histologic patterns relate to effects produced during the activation of complement and the ensuing cascade of events. In response to the deposition, or formation of antigen-antibody complexes, certain sites are preferentially favored; it is in these sites that significant morphologic events of immune complex disease tend to be expressed.

B-lymphocyte

1. markers:

a. plasma cells

b. secretory products (IgG, IgA, IgM)

c. kappa and lambda light chains

2. domain:

a. cortex of lymph nodes (follicular centers, mantle and marginal zones), and medullary cords; variable representation among T-cells in paracortical zones

b. white pulp of spleen

c. adventitia of blood vessels

d. paratrabecular region of bone marrow (a neoplastic expression)

S8C9VA1-2: Some features which are indicative of a role for B lymphocytes in inflammatory or neoplastic processes are listed in the above Table.

B-lymphocyte

3. markers:

a. transformations to small cells (mantle cells, marginal zone (monocytoid) cells, and small cleaved cells)

b. transformations to large cells (cleaved and non-cleaved, and immunoblastic forms)

c. interplay with other lymphocytes (i.e., T-cells)

d. promotion of the formation of granulomas (antigen-antibody complexes)

e. Dutcher bodies (intra-nuclear inclusions)

f. Russell bodies (secretory products of plasma cells)

g. hyalinosis (perivascular, basement membrane, etc.; deposits of immunoglobulins; “para-amyloid”)