By this division we shall be able to take into consideration the fundamental causes of all the forms of pleurisy. Starting from the simple primary form, we shall be able to study special varieties of secondary pleurisies, such as tubercular and rheumatic.
Next, we shall examine separately the hemorrhagic variety as distinct from hæmothorax. The localized forms, such as the interlobular, diaphragmatic, and mediastinal, will be studied as varieties caused by their development in different localities.
The simplest plan to elucidate the whole subject of pleurisy is to analyze carefully, in the first place, the unquestionably acute disease, primary pleurisy, and afterward to connect with it the study of the several forms and varieties. Acute primary pleurisy has a sero-fibrinous exudation, and is the most common form of the disease. In it are best defined the usual characteristics of this inflammation. We consider this the principal type of this class, and with it shall study the development and character common to all the varieties of inflammation of the serous membrane of the thoracic cavity.
PATHOLOGICAL ANATOMY OF FIBRO-SEROUS PLEURISY.—The anatomical changes in all forms of pleurisy begin by hyperæmia of the vessels of the serous membrane and of the subserous connective tissue. This is followed by an exudation of a liquid, a pseudo-membranous deposit. In acute primary cases this is first noticed on the costal pleura. The pleura itself shows, by puffiness and oedema with red points and small ecchymosed spots, that the inflammatory process has affected it. In a few hours, in acute cases, there is found a thin deposit of fibrinous lymph of a reddish-yellow tinge, with more ecchymosed spots, resulting from the rupture of fine capillary vessels. The pleura is somewhat thickened and loses its transparency, and is studded with very fine granulations. Under the microscope it is shown that the epithelial cells are swollen, that their number has been largely increased by proliferation, and that they have been detached in great quantities. The granulations are scattered over the pleural surfaces, and separate the pleura from the fibrinous deposit. The connective tissue is loaded with liquid, in which are found in increased quantity leucocytes which have migrated through the walls of the blood-vessels.
Over the surface of the pleura there is a tissue of granulations composed of embryonic cells, which are derived from the proliferation of the elements of the connective tissue. In this tissue of new formation we find new blood-vessels coming from those belonging to the subserous tissue, which advances through small points, even to the free surface of the granulations. These vessels are very thin and brittle. They sometimes rupture and cause ecchymoses of the pleura and of the false fibrinous membranes—sometimes effusions of blood, which, becoming mixed with the serum in the pleural cavity, cause hemorrhagic pleurisies. This new tissue is susceptible of organization, and of transformation progressively into a tissue analogous to that of a cicatrix. Under the plastic exudation we find abundance of embryonic cells, which become elongated and spindle-shaped in the formation of new connective tissue. This is at first tender, but may become dense and fine over circumscribed points, so as to produce bands which enclose and touch the effusion. This is the origin of the organized neo-membranes which are found on the surface of the pleura. It is, moreover, this tissue of granulations which constitutes the bands which unite the parietal to the visceral pleura, the adhesions being produced by the contact and the union of vegetations or neo-membranes developed on the two opposed layers of the pleura. The membranes form the filamentous thin bands which draw obliquely together portions of the pleural sac. These lesions are very often slight and rudimentary in simple acute pleurisy, but are found well developed in purulent pleurisy, especially when it is chronic. These are hyperplastic parenchymatous lesions of the pleura. Acute inflammation of the pleura gives rise to two distinct forms of exudation—the plastic, deposited on the free surface of the serous layers or formed in flakes in the fluid; and the serous, which falls into the dependent portions of the cavity. The plastic may exceptionally exist alone. Their formation together is the rule. Anstie questions whether the serous effusion ever occurs without the fibrinous. The plastic exudation takes the form of granulations more or less prominent, constituting a bed of very irregular rough points. So long as the period of inflammation continues, new plastic deposits are formed over the old ones. They thus increase in thickness. The neo-membranes which play such an important rôle in the natural history of pleurisies increase very rapidly. Little by little, they are transformed into firm, very resisting tissues. They may become fibrous, cartilaginous, or even calcareous in their structure. These false membranes develop more freely at first when the opposing surfaces are kept apart by the effused liquids. The rubbing of the two pleuræ together seems to impede the process of organization. According to Wagner, the lymphatics are dilated and contain a liquid poor in corpuscles. The newly-organized and vascular tissues often become the starting-points of fresh inflammatory processes and of new products.
Exudations are of two kinds—liquid and pseudo-membranous. When the inflammation extends over a limited surface, the fibro-plastic exudation may be the only one; in which case the disease soon terminates with local adhesions. This is dry pleurisy, which is rarely primary in its origin. Ordinarily, the principal lesion of acute pleurisy consists in a sero-fibrinous effusion which collects in the cavity of the pleura; almost always the liquid effusion exists in decided quantity. In it there are suspended fibrinous flocculi, and on the surface of the pleura are found false membranes. The nature of the effused liquids has been thoroughly studied, ample opportunities having been furnished since thoracentesis has been so extensively used. The quantity of liquid is very variable, from a few grammes up to several liters. The terms small, moderate, and abundant are used to designate the quantity—one-half of a liter is considered a small quantity; moderate, one to one and a half liters; abundant effusion, two to two and a half liters; very abundant, when the effusion goes beyond three liters. The liquid is transparent and of yellowish-amber color. It is darker when the fluid has been some time in the chest, and resembles that of bouillon. Sometimes it has a rose tint when the liquid contains a sufficient quantity of red globules, or it may be somewhat opaque when it encloses a large proportion of leucocytes.
The presence of a few red globules does not constitute a hemorrhagic pleurisy, nor does the presence of a small quantity of leucocytes make a purulent pleurisy. It is only when they are very abundant that they severally give those characters to the effused fluid. Dieulafoy states,1 after frequent examinations of aspirated serous fluid of acute pleurisy, simple and frank, that it contains the smallest quantity, from 500 to 600 red globules to the cubic millimeter, while the white globules were from fifteen to twenty times more numerous. In some instances he counted 1500, 2000, and even 3000, red globules to the cubic millimeter without the coloration of the liquid being sensibly modified. He adds that the liquid from the pleura has not a perceptible rose tint unless it contains from 5000 to 6000 red globules to the cubic millimeter. He concludes that there is no tendency to transformation into purulent pleurisy unless the number of red globules reaches 4000 or 5000 to the cubic millimeter. Rindfleisch (ed. 1869, Leipzig) states also that upon their number and that of the proliferated epithelial cells, with the floating flocculi, depends the convertibility of the serous into purulent effusions.
1 De la Thoracentèse par Aspiration dans la Pleurisie aigue, p. 42, Paris, 1878.
Chemical Character of Effused Fluid.—Mehu2 gives the composition of the fluid as closely resembling that of the serum of the blood. He found in it the same elements—water, albumen, fibrinogenous matter, salts, red globules, and leucocytes. The proportion of these principal constituents of the blood was greatly modified in the pleuritic liquid. The quantity of water was always increased. On the other hand, the quantity of substances in solution was greatly diminished. The exudation was really blood-plasma, more or less diluted, in which the relative proportion of the constituent elements varied according to the intensity of the inflammation. It has the same alkaline reaction, and it is spontaneously coagulable, owing to the presence of the fibrin which is in solution in the serum, the proportion of fibrin making it coagulate more or less rapidly. Mehu found the quantity of fibrin to vary from 09.073 to 19.276 to the kilogramme. The same mineral substances were found, but in less quantity, than in plasma of blood. The intensity of the inflammation causes alterations in the composition of the exudations. The more acute the inflammation, the greater is the quantity of albumen and of fibrinogen. The fibrinogenous matter contained in the exudation is coagulated only by contact with the air. One portion of it becomes concrete in the interior of the body in the form of fibrinous flocculi, which float in the fluid, and in the false membranes, which are deposited in successive layers on the surface of the inflamed pleuræ. This coagulation takes place in a manner analogous to that of the coagulation of the fibrin in a drop of blood. These false membranes are almost always found in acute pleurisies, but their development is very variable. Sometimes they are very thin, friable, and readily disappear; again, when the inflammation is intense, they last a long time and cover thickly both pleuræ. Occasionally they envelop the effusion and produce veritable cysts and localized pleurisies. Their color is opaline or semi-transparent when recently formed, but opaque when old. Their consistence varies according to the duration of the disease. At first they are soft, impregnated with fluid, easy to tear or break; later on they become resistant and almost dry. The microscope shows these false membranes to be formed of crossed fibrillæ, with intervals containing white blood-corpuscles, with voluminous, swollen epithelial cells of serous membrane, proliferated and detached.
2 Arch. général de Méd., 1872.