Neurosecretory cells of the lamina propria of the appendix and their possible relationship to carcinoids.

Carcinoid tumours of the appendix are generally thought to be derived from enterochromaffin cells; in-situ abnormalities of these cells are, however, rarely observed in the mucosal epithelium. One hundred appendices, removed consecutively at surgery, were stained with an alcian blue-PAS diastase-lead haematoxylin sequence and, in 69, cells were found in the lamina propria with a cellular and architectural morphology identical to those of an archetypal appendiceal carcinoid tumour. These cells appeared to contain neurosecretory granules, were diazo-positive and showed argentaffinity. They were further characterized by the localization of cytoplasmic neurone specific enolase and the presence of neurosecretory granules was confirmed by electron microscopy. These cells are designated subepithelial neurosecretory cells (SNC). It is suggested they are an integral component of the subepithelial nervous plexus and are in progenitors of appendiceal carcinoid tumours. A neuroectodermal origin of the SNC-and hence appendiceal carcinoid tumours-is proposed.