This section is from the book "A Manual Of Pathology", by Guthrie McConnell. Also available from Amazon: A Manual Of Pathology.
Anemia occurs only as a part of a general condition.
Active hyperemia is frequent, being the earliest stage of meningitis. It is also found in death from alcohol, in the infectious fevers, as typhoid and cholera, in certain poisonings, and in delirium of various kinds. The pia is red, and the smaller vessels are injected. The subarachnoid fluid may be increased in amount and cloudy.
Passive hyperemia is rather difficult to recognize postmortem, on account of the hypostasis that occurs. The large veins are distended and tortuous, the arachnoid is cloudy and there may be more fluid than normal. This condition occurs in chronic heart and lung diseases and in venous obstructions.
Hemorrhage into the subarachnoid space from the vessels of the pia may occur in anthrax and in such diseases as scurvy, hemophilia, and in severe infections. The hemorrhages may be numerous and small, or there may be a single large collection of blood between the pia and arachnoid. This latter form is generally the result of some severe injury, or due to the rupture of an aneurysm. The blood, instead of being upon the surface of the brain, may gain entrance into the ventricles.
Small collections of blood may be absorbed and leave nothing but a small, and slightly yellowish area. If the amount has been large, the pigment may be absorbed and leave a clear, serous fluid.
Edema may be present as an increase of the cerebrospinal fluid. A large collection of fluid between the pia and arachnoid is known as an external hydrocephalus. In senile atrophy of the brain there is an accumulation of fluid to fill out the loss of substance - hydrops ex vacuo. The edema may be gelatinous in character in paresis and insanity.
Leptomeningitis or inflammation of the arachnoid and pia may be acute or chronic, and the acute may be classified according to the exudate.
Acute leptomeningitis is an infectious condition due to various organisms. The pneumococcus is the one found in the greatest number of cases, but many varieties have been described. In the epidemic meningitis the Diplococcus intracellulars meningitidis of Weichselbaum has been recognized as the cause. The infecting agent gains entrance either as a result of wounds, by way of the lymphatics, or by direct extension.
Serous leptomeningitis consists of round-cell infiltration of the membranes, with hyperemia and the exudation into the subarachnoid space and ventricles of a serous fluid. This may be slightly cloudy from leukocytes that are sometimes present. This form occurs in children in the course of infectious diseases, as scarlet fever and measles; and in adults after sunstroke. It is probably the beginning stage of an infectious inflammation in which the death of the patient has followed before further lesions have had time to develop.
Fibrinopurulent leptomeningitis is probably a later stage of the preceding. In the subarachnoid space there is a collection of pus and fibrin. This may increase until the sulci are marked out as yellowish bands, and eventually the surface of the brain may be covered by this purulent exudate. The process may be confined to local areas, or involve both hemispheres. If at the vertex, it is known as cortical meningitis; at the base, as basilar meningitis.
The pus may gain entrance into the ventricles, or it may follow along the blood-vessels, particularly the middle meningeal, and involve the cortical substance with degenerative changes in both cells and fibers. Small hemorrhages may be present and discolor the exudate. The termination is usually fatal, but absorption and recovery may take place. There are, however, permanent structural changes, as a rule.
Epidemic cerebrospinal meningitis resembles the above form, except that it has a specific organism, the Diplococcus intracellulars, as its cause. It generally starts upon the convexity of the frontal lobes, and extends backward and downward, involving the basal membranes and those of the cord later on. Death may, however, take place so suddenly that distinct changes may not be noticeable. When recovery occurs, a general fibrous thickening of the pia and arachnoid may take place.
The spinal changes may be more marked than those of the brain, the cord being covered by a thick yellowish layer of pus and fibrin. Occasionally the central canal may contain pus.
Chronic leptomeningitis is an inflammation of the pia, usually secondary to diseases of the brain or dura. There is a hyperplasia of connective tissue and round-cell infiltration. The thickening may be so great as to cause compression of the brain-substance or obliteration of venous channels. Large or small areas may be involved, and adhesions between the pia and the dura or the brain may form.
Tuberculous meningitis is more common in children than in adults, and is generally found upon the basilar surface. This location is so frequent that the term basilar meningitis refers to a tuberculous process. This disease may be primary, but is, as a rule, secondary to tuberculosis elsewhere, particularly of the lung.
Upon the pia over the pons, about the optic chiasm, and along the Sylvian artery are found the miliary tubercles, the characteristic lesions of the process. They may also be noticed in the choroid plexus and the ependyma as a result of extension. The tubercles vary in color from gray to yellow, according to their age.
There is generally some exudate, either serofibrinous or purulent, especially if there has been a mixed infection by the pneumococcus. This may be so thick as to obscure the tubercles.
Most of the tubercles are found around blood-vessels, and consist at first of a cellular infiltration, with some thickening of the vessel-wall. Giant-cells are not as common as in tuberculosis elsewhere. As the disease persists, degeneration and caseation take place.
If the infection has been primary, there may be a single large tuberculous area - a tyroma. Such a mass may be soft from liquefaction necrosis, or fairly firm; occasionally it may be the seat of calcareous infiltration.
Syphilis is found in the pia, usually in the form of gum-mata which may extend and involve the brain or the dura. This form is found as circumscribed, flattened thickenings that generally show necrotic processes.
Another form is characterized by a perivascular round-cell infiltration which may become diffuse. This portion of the pia may become quite thickened and grayish-red in color. Caseation takes place around the edge of the node, and the destroyed portion is gradually replaced by dense cicatricial tissue.
It may occur as a widespread leptomeningitis.
The Pacchionian bodies are numerous small, rounded, projecting structures found along the longitudinal sinus. They consist of fibrous tissue that originates within the arachnoid, but as they grow they force their way at times through the dura and cause a firm union of the membranes. There is also very frequently more or less atrophy of the skull, causing depressions into which these bodies fit. In places the bone may be greatly reduced in thickness. These bodies are found in nearly every adult body, and appear to be of no significance.
Endothelioma and perithelioma are found in the membranes, having originated from the cells of either the lymphatics or the blood-vessels. They may become sufficiently large to cause pressure symptoms, but are usually small. Sarcoma may occur in the form of angiosarcoma or cylindroma. Fibroma, lipoma, and myxoma are occasionally seen. Choles-teatomata are sometimes found in the pia, generally at the base of the brain. Teratomata are rarely encountered. Secondary growths are not infrequent, either by direct extension or by metastasis.
Cysts are rare.
Parasites are unusual, but the echinococcus and the Cysticercus cellulosoe have been observed.