The distinctive features of internal pachymeningitis, therefore, so far as they are at present known, are those which would depend upon a primary cerebral irritation, followed by those of compression of the brain—persistent, often severe, headache, with contracted pupils, and occasionally motor and sensory disturbances; afterward, coma, dilated pupils, and involuntary discharges from the bowels and bladder.
The DURATION of the disease is exceedingly variable, extending from a few days to more than a year. According to a table made from carefully observed cases by Huguenin, 74 per cent. of patients die within thirty days; 18 per cent. live from one to six months; 4 per cent. live from six months to one year; and 4 per cent. live over one year.
PATHOLOGY.—A difference of opinion has existed among pathologists concerning the true nature of hemorrhagic effusions of the inner surface of the dura mater, especially as to whether the membrane in which they are enclosed is formed by a deposit of fibrin from the effused blood itself, or whether the disease consists essentially in an inflammation of the dura, followed by a pseudo-membranous deposit into which blood is afterward extravasated. The latter explanation, offered by Virchow, has been generally accepted, but Huguenin, whose opportunities for observing the disease were unusually good, believes that the first stage of hæmatoma is not the formation of connective tissue, but simply an extravasation of blood.
The disease begins with hyperæmia of the dura mater in the area of distribution of the middle meningeal artery, followed by the formation upon its inner surface of an extremely delicate membrane in small patches of a yellowish color and studded with innumerable bloody points. If the membrane be carefully raised, it is found to be connected with the dura by very delicate blood-vessels, and to contain an immense number of very wide and thin-walled vessels, much larger than ordinary capillaries.6 At a later stage we find the membranes to be made up of several distinct layers, of which the innermost exhibits the character of the primary deposit, being thin and abundantly supplied with blood-vessels, while those of older formation have become successively thicker and are composed of tough, lustrous fibres of connective tissue almost as dense as that of the dura mater itself. The delicate structure of the false membranes and of the vessels which they contain leads almost inevitably to the effusion of blood, which increases in quantity with the thickness of the whole growth, so that in an advanced stage it is not uncommon to find large pools of blood, partly clotted and partly fluid, constituting what is called hæmatoma of the dura mater. The small bloody points are within the substance of the false membrane; the extravasations are interstitial, the largest being always found between the youngest membrane and the older layers. In some cases serous transudations also occur between the false membranes. In still rarer instances no blood or serum is found between or beneath the layers. Occasionally small quantities of blood escape by leakage through the delicate membrane into the cavity of the arachnoid.
6 See Rindfleisch's Manual of Pathological Histology, New Sydenham Soc.'s translation, 1873, vol. ii. p. 302.
The usual situation of internal pachymeningitis is the vault of the cranium, near the median line, the upper or external layer of the tumor being in relation with the dura mater, to which it is adherent, and the lower or internal with the arachnoid and pia mater. If the effusion be extensive, it spreads downward over the frontal and occipital lobes of the brain, and laterally toward the fissure of Sylvius. In the majority of cases the disease occupies both sides of the median line symmetrically, but it may be limited to one side only. According to Huguenin, 56 per cent. of the cases embrace the surfaces of both hemispheres; 44 per cent., that of one only. Hæmatoma very rarely occupies the base of the cranium. The thickness and consistency of the deposit vary in different cases, depending upon the number of successive exudations, and hence are most marked in cases of the longest duration.
Hemorrhagic pachymeningitis is occasionally met with in young children, but much more rarely than in adults. The disease is usually more acute than in older persons, but the anatomical appearances are essentially the same.7
7 For an able description of the lesions of hemorrhagic pachymeningitis in children see the third edition of Rilliet and Barthez's Maladies des Enfants, by Barthez and Sanné, Paris, 1884, vol. i. p. 152.
PROGNOSIS.—The great majority of cases end fatally. A few instances of recovery are reported in which the diagnosis seems justified by the symptoms. Moreover, it is not very rare to find, on post-mortem examination of those who have died of other diseases, evidence of the former existence of hemorrhagic pachymeningitis. According to Steffen, while the prognosis of simple pachymeningitis in children is frequently good, owing to the favorable conditions for the exit of pus through the open fontanels and sutures, in hemorrhagic pachymeningitis recovery is rare.
DIAGNOSIS.—In a disease whose symptoms are so vague the diagnosis must of necessity be difficult and often impossible. The chief elements for the formation of the diagnosis are the slow and interrupted progress of the affection, persistent headache, tendency to prolonged slumber, and final coma; the absence of paralysis of the cranial nerves, of vomiting, and of general convulsions; the age of the patient, the coexistence of alcoholism, chronic insanity, or acute rheumatism, and traumatism. The diseases for which hæmatoma would be most likely mistaken are acute inflammation of the meninges, apoplexy from cerebral hemorrhage, tumor in the substance of the brain, and necrobiosis from thrombus or embolus. The absence of symptoms characteristic of these affections might lead to a probable diagnosis by exclusion, but in many cases the existence of the disease cannot be determined with certainty. In children it is most likely to be confounded with tubercular meningitis, from which it may be distinguished by the fact that it is most common under the age of two years, the other being rare before that period, and that the characteristic symptoms of tubercular meningitis (prodromic period, vomiting, irregularity of pulse, etc.) are wanting. But the tubercular disease in young infants may closely resemble hæmatoma, a profound coma replacing all other symptoms. Here the existence of tuberculous disease in the parents or other near relatives would point strongly to tubercular meningitis, while the absence of such antecedents would suggest hæmatoma.