Spectrum of pathology in diffuse neuroendocrine hyperplasia (DPNECH)

(A) Multiple carcinoid tumorlets. Each is ≤5 mm (by definition).
(B) Higher power of carcinoid tumorlet. On this field alone one could not distinguish between ordinary carcinoid (>5 mm) or a tumorlet. This is based on size alone.
(C) Obliterative bronchiolitis is present in some cases. The arrows highlight submucosal fibrosis resulting in partial obliteration. The lower arrow tip is on the smooth muscle of the bronchiole, and the space between the arrows is filled with collagen.
(D) Chromogranin immunoperoxidase stain of bronchiole (compare to normal shown in panel E). Note the clusters of positive cells indicating hyperplasia of neuroendocrine cells.
(E) Chromogranin immunoperoxidase stain of bronchiole (compare to DPNECH shown in panel D). In a normal bronchiole, there are very few positive neuroendocrine cells.