Objective. Previous investigations of esophageal tissue and serum probes failed to identify a common etiologic agent predisposing to, triggering or causing achalasia. In order to further examine the detailed pathologic processes resulting in achalasia we performed electron-microscopic studies of muscle biopsies taken from the LES high pressure zone in patients undergoing surgery - either Heller myotomy or esophageal resection.Methods. Smooth muscle biopsies with a 20 x 15-mm longitudinal segment of the myenteric plexus from the distal esophagus (lower border of the esophageal incision) in patients undergoing Heller myotomy for achalasia were taken. In patients with end-stage achalasia and megaesophagus with esophageal resection, the complete esophageal body was available. For electron microscopy, ultrathin sections were contrasted with uranyl-acetate and plumbic citrate. The photographs were taken by a digitalized electron-microscope (ZEISS, Leo 905). Results. A striking finding was the large number of mast cells in the region
P2of the smooth muscle layers as well as in the surrounding connective tissue and also in close vicinity to the nerve cells and to the nerve fibres. The smooth muscle cells in these regions were very often stained less intensively, and they showed signs of an acute degenerative process.Conclusion. Our electron microscopic studies suggest that mast cells may play an important role in the pathologic developments resulting in the clinical picture of achalasia. Smooth muscle cells in the vicinity of mast cells revealed signs of an acute degenerative process.