The pleura and pericardium have both been recorded as points of outlet. The pus can even sink down into the inguinal or lumbar region. Spontaneous external opening is said to occur most frequently on a level with the second rib to the left of the sternum.
DIAGNOSIS.—The differential diagnosis between abscess and other mediastinal growths will be considered in the section on Mediastinal Tumors.
TREATMENT.—The exploratory puncture is to be recommended if a fluctuating tumor appear presenting the general symptoms of abscess. Rest, local sedative applications, and the relief of pain are positive indications. Petit, Agnew, and others have applied the trephine to the sternum in search of pus, with a satisfactory result. It is, however, generally conceded that it is better to wait until pointing occurs, as the area of the sternum is so limited that in all probability matter forming behind it would speedily make its way to the surface in an intercostal space at one of the margins of the bone. If the abscess be deeper or due to scrofulous or syphilitic caries of the sternum, the matter which forms may escape into the neck or through perforations of the bone. The latter may be congenitally present or due to disease. Caries, necrosis, or fracture of the bone may make trephining obligatory, or the same indication may prevail if a dependent flow of pus sufficient to drain the cavity is not otherwise obtainable.6
6 Chassaignac, Traité de la Suppuration, tome ii. p. 330.
A similar line of treatment would be indicated if there was no tendency to external pointing, and evacuation into the viscera seemed threatened.
Excision of the whole or part of the sternum for abscess, cancer, or other causes seems to have been fairly successful. Heyfelder7 had collected, in 1863, 18 established cases, in which there were 17 recoveries and 1 death.
7 Traité des Resections, traduit de l'Allemand avec Additions et Notes, par le Docteur Boekels, Strasburg et Paris, 1863.
Adhesions usually prevent a double pneumothorax, even when the sternum and ribs have been resected. Unilateral pneumothorax is not necessarily fatal.
Mediastinal Tumors.
ANATOMY.—The mediastinum is the space which the two pleural sacs leave between them in the antero-posterior plane of the chest, and which contains all the thoracic viscera except the lungs. It is subdivided into three parts—the anterior, middle, and posterior mediastinum. A superior mediastinum has also been described. The space between the pleural sacs occupied by the heart enclosed in the pericardium, the vena cava superior, the ascending aorta, the pulmonary arteries and veins, the phrenic nerves with their accompanying arteries, and the bifurcation of the trachea and roots of the lungs with some bronchial glands, takes the name of the middle mediastinum.