When the diagnosis of pericarditis has been arrived at it is desirable to determine the exact nature of the disease, for whilst cases of pericarditis due to foreign bodies are incurable and in the interest of the owner the animals should be slaughtered, pericarditis due to cold or rheumatism may be successfully treated. Rheumatism generally affects the synovial membranes even before it produces pericarditis, and this indication, supplemented by the history of the case usually ensures one against mistakes regarding the initial cause.
It is much more difficult to distinguish pericarditis due to a foreign body from pericarditis due to carcinoma and from the forms of pseudo-pericarditis produced by lesions in the neighbourhood of the heart. When considering the latter we shall deal with this particular point.
Prognosis. The prognosis is always fatal.
Lesions. When the foreign body is very thin and sharp, the reticulum may not become attached to the diaphragm. In such cases its passage has been rapid and the tissues have healed.
Usually the reticulum, diaphragm and pericardium are united by a mass of fibrous tissue as thick as a man’s arm. It resembles a fibrous sleeve surrounded by an œdematous zone, usually of slight extent. This mass of new fibrous tissue is traversed by a sinuous tract resulting from the irritant action of the foreign body on the surrounding tissues. All writers describe this fibrous sleeve, which, however, only occurs in cases where a very long foreign body has occupied a considerable time in passing from the reticulum to the cavity of the chest.
In very exceptional cases the sinuous tract is ramified, possibly as a result of displacements of the foreign body.
The orifices of the tract are to be found, one in the reticulum, the other in the pericardium. On the side of the reticulum there is never more than one opening, and in many instances the tract is already closed on that side, either by exuberant granulations or by a cicatrix.
On the contrary, the fistula is more frequently open in the pericardial cavity. Its walls are of very varying appearance, depending on their age: they may be red, greyish, soft or hard, and when the lesion is of old standing they may have been converted into a sclerotic tissue.
Fig. 176.—Appearance of the lesions in a case of fatal pericarditis. P, inflamed pericardium, distended with exudate and adherent to the neighbouring pulmonary lobes; 1, posterior lobe; 2, cardiac lobe; 3, anterior lobe; Fp, pleural false membranes.