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Histopathology
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Figure 2 |
The defining histological feature of Autoimmune Hypophysitis is the infiltration of the pituitary with lymphocytes. As indicated in Figure 1, this infiltration can involve only the anterior lobe, only the infundibulum/posterior lobe, or both. The end result is a loss and/or partial loss of function of the endocrine cells forming the anterior pituitary. Lymphocytes aggregate to form true lymphoid follicles in 18% of the cases, often with germinal centers. This feature can be clearly seen in the cross cut of the pituitary from one of the first patients reported in the literature (by Egloff in 1969), see Figure 1. In addition to lymphocytes, however, other cells are present in the infiltrate, especially plasma cells and eosinophils (Table).
Table 1
| Other Cell Types seen in AH |
Patients
(% of total) |
| Plasma cells |
126 (54) |
| Lymphoid Follicles |
36 (15) |
| Eosinophils |
28 (12) |
| Neutrophils |
15 (6) |
| Macrophages |
16 (7) |
| Histiocytes |
10 (4) |
| Edema |
8(3) |
| Necrosis |
8 (3) |
| Granulomas |
8 (3) |
| Extensive necrosis (necrotizing form) |
3 (1)
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Focal areas of necrosis can be seen, albeit rare (3% of the cases). In even more rare instances, the necrosis is massive and involves the entire pituitary (1%). This necrotizing form, described thus far only in 3 patients, is considered by some authors separate from lymphocytic hypophysitis and by others as part of the pathological spectrum, depending on whether one is a “lumper” or a “splitter”. Granulomas hypophysitis is distinct from lymphocytic hypophysitis. In some cases however, (3%) the two pathological features (lymphocytic and granulomatous) can occur together in a mix lymphocytic/granulomatous form. The histological spectrum of the disease would then go from a pure lymphocytic form at one end, to the lymphocytic/granulomatous form and finally to the lymphocytic/necrotizing form at the other end.
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