—The dura has a duplicate anatomical character. Its outer surface, having the structure of periosteum, functionates as such; its inner surface, being lined with endothelium, partakes of the nature of a true serous membrane. When the former texture is mainly at fault we have pachymeningitis externa, or endocranitis, which is rarely a primary, but usually a propagated lesion met with after injury or external infection. It may lead to infiltration with purulent products, and, if speedy exit for pus be not provided, to involvement of the pia within. Extradural suppuration without external injury is very rare, but should there have been a subdural hemorrhage with external lesion the blood clot may become infected and break down. Pachymeningitis externa is most common after chronic lesions of the cranial bones—i. e., caries and necrosis. Symptoms are not characteristic and often not distinguishable. When chronic there will be local tenderness, evidence of the presence of pus, with focal symptoms.
Treatment.
—The treatment is always surgical, save possibly in certain cases due to syphilis, where delay may be justifiable for the purpose of testing the action of antispecific drugs.
Pachymeningitis Interna.
—Pachymeningitis interna is often confounded with chronic hydrocephalus. It is frequently the occasion of a firm, membranous exudate upon the internal surface of the dura, which forms in time a new membrane rich in small and extremely friable vessels, from which hemorrhages easily occur, thus giving rise to the condition of pachymeningitis hæmorrhagica. Trifling hemorrhages will produce little or no disturbance; when of greater extent they may give rise to localizing brain symptoms. These extravasations may absorb or undergo fluidification—i. e., produce localized or cystic collections of fluid. The condition sometimes occurs after other acute infections, especially pneumonia, pleurisy, typhoid, whooping-cough, etc. Recovery is possible, but usually at the expense of adhesions, which lead to subsequent complications.
The symptoms of pachymeningitis hæmorrhagica are headache, which will increase in intensity with every new escape of blood, usually localized in the vertex, with more or less paralysis following each new extravasation. The final result may be atrophy. Absence of disturbance in the cranial nerves points to lesions in the convexity rather than basal or ventricular. In chronic cases there is optic neuritis, and toward the end coma, usually coming on slowly. Dennis has recommended trephining under these circumstances, and has practised it with great benefit.
Treatment.
—The treatment should be in a large degree surgical, for little short of eradication will bring about the desired result.
Leptomeningitis.
—This term refers to inflammation (i. e., infection) of the pia mater, in whose texture we encounter tissue quite different from that composing the dura, and in which, when inflamed, distinction as between the arachnoid and pia has disappeared. Leptomeningitis suppurativa is an exceedingly common expression of intracranial infection, and may result not merely by extension, but as a primary infection. When begun it spreads rapidly, the fluid contained within the meningeal cavities, mixed with pyogenic agents, helping to disseminate the active agents to the ultimate limits of the membranous involvement. Consequently basilar meningitis usually extends down the spinal canal. Next to injury the most frequent cause is middle-ear disease, with its infectious complications and extensions. Next to this come sinus phlebitis and endocranitis. Infection from the teeth and the nasal cavity may occur. It is also known to result from panophthalmitis: in traumatic cases, when primary, it sets in early, even from four to thirty-six hours after injury. So rich is the pia in loose connective tissue that even from the outset the inflammation may assume the phlegmonous type. The cerebrospinal fluid, as well as that of the ventricles, becomes cloudy, contains numerous flocculi, and is often blood-stained.