Ultrastructure of the goblet cell type of adenocarcinoid of the appendix.

Two examples of the goblet cell form of adenocarcinoid were studied with electron microscopy. Mucin was present in the form of large and small vacuoles or small patches of denser mucin granules. A small population of cells had a complement of organelles similar to the more obvious goblet cells but contained little or no identifiable product. Enterochromaffin cells were similar to those seen in normal midgut and in conventional carcinoids of midgut derivation. Enterochromaffin granules and mucin were not mixed with one another. Cell types transitional between mucinous and enterochromaffin were not found. Although study of plasmalemmae was hindered to a degree by artifacts due to tengential sectioning and, possibly, insufficiently rapid fixation, we favor the interpretation that the goblet cell type of adenocarcinoid is composed of two separate classes of cells.