_Prognosis_.--After the pouch is formed, it steadily increases in size, since the swallowed food first fills and distends the sac before the overflow passes down the esophagus. When a pendulous sac becomes filled with food, it presses on the subdiverticular esophagus, and produces compression stenosis; so that there exists a "vicious circle." The enlargement of the sac produces increasing stenosis with consequent further distension of the pouch. This explains the clinically observed fact, that unless treated, pulsion diverticula increase progressively in size, and consequently in distressing symptoms. The sac becomes so large in some cases as to contribute to the occurrence of cerebral apoplexy by interference with venous return. Practically all cases can be cured by radical operation. The operative mortality varies with the age, state of nutrition, and general health of the patient. In general it may be said to have a mortality of at least 10 per cent, largely due to the fact that most cases are poor surgical subjects. Recurrences after radical operation are due to a persistence of the original causes, i.e., bolting of food; stenosis, spasmodic or organic, of the esophageal lumen; and weakness in the support of the esophageal wall, which, unsupported, has little strength of its own. _Symptoms_.--Dysphagia, regurgitation, a gurgling sound and subjective bubbling sensation on swallowing, sour odor to the breath, and cough, are the chief symptoms. With larger pouches, emaciation, pressure sensation in the neck and upper mediastinum, and the presence of a mass in the neck when the sac is filled, are present. Tracheal compression by the filled pouch may produce dyspnea. The sac may be emptied by pressure on the neck, this means of relief being often discovered by the patient. The sac sometimes spontaneously empties itself by contraction of its enveloping muscular layer, and one of the most annoying symptoms is the paroxysm of coughing, waking the patient, when during the relaxation of sleep the sac empties itself into the pharynx and some of its contents are aspirated into the larynx. There are no pathognomonic symptoms. Those recited are common to other forms of esophageal stenosis, and are urgent indications for diagnostic esophagoscopy. _Diagnosis_.--Roentgenray study with barium mixtures, is the first step in the diagnosis (Fig. 101). This is to be followed by diagnostic esophagoscopy. Malignant, spasmodic, cicatricial, and compression stenosis are to be excluded by esophagoscopic appearances. Aneurysm is to be eliminated by the usual means. The Boyce sign is almost invariably present, and is diagnostic. It is elicited by telling the patient to swallow, which action imprisons air in the sac. The imprisoned air is forced out by finger-pressure on the neck, over the sac. The exit of the air bubble produces a gurgling sound audible at the open mouth of the patient.