In its most pronounced form a dilated stomach appears to occupy the greater part of the abdominal cavity, and in such cases the pylorus is almost always found to be the seat of a localised scirrhous growth which has reduced the outlet to a narrow channel. The disease is often, but not invariably, adherent to the under surface of the liver, and the walls of the viscus are peculiarly thin and transparent. The clinical history indicates that for the first five or six months the gradual contraction of the pylorus was accompanied by a compensatory hypertrophy of the muscular wall of the stomach, the forcible contractions of which were plainly visible through the abdominal parietes. As soon, however, as the general nutrition became seriously impaired the contractile power rapidly failed, and the signs of atony and dilatation made their appearance.
A moderate degree of gastrectasis often accompanies those varieties of carcinoma which produce a rigid patency of the pylorus. In such it may usually be observed that the dilatation is confined to the central and cardiac portions of the organ, and that in addition to the increase of cubic capacity the muscular coat is considerably hypertrophied. This latter condition points to the existence during life of some obstruction to the passage of food into the intestine, and since no obvious obstruction is apparent after death, it must have arisen from destruction of the muscular tissue of the pyloric segment by the new growth. A parallel to this is to be found in the dilated and hypertrophied state of the lower oesophagus which ensues from paralysis of the cardiac sphincter.
In addition to these two main factors in the production of gastric dilatation, viz. stenosis and paralysis of the pylorus, there are probably several others which aid the process in an adventitious manner. In the first place, every case of carcinoma is accompanied by a diffuse chronic gastritis. As a rule the inflammatory mischief merely affects the mucous membrane ; but if the pylorus is contracted or the growth has undergone extensive ulceration, it often spreads to the muscular tunic and impairs the contractile power of the tissue. Secondly, the incompetency of the pyloric valve which results from its infiltration by a soft growth must permit of the constant regurgitation of fluids and gas from the duodenum, which not only distend the stomach, but continually stimulate its secretory and motorial apparatus, and thus induce fatigue. Lastly, adhesions between the stomach and neighbouring viscera not only trammel the gastric movements, but are apt to twist the pylorus or upper part of the duodenum and thus to produce a severe form of mechanical obstruction.