234: DISEASES OF THE BRAIN. 



ETIOLOGY. It is very doubtful whether pachymeningitis occurs, aa 

 a primary and independent disease, from cold and other causes. At 

 all events, it is generally secondary, and as such accompanies fissures, 

 fractures, and especially caries of the cranial bones, particularly of the 

 petrous and ethmoid bones, as well as caries of the upper cervical 

 vertebra. In periostitis of the outer surface of the skull also, pachy- 

 meningitis occasionally occurs, without our being able to distinguish 

 any continuity between the two diseases by changes in the cranium. 



Inflammation of the cerebral sinus, with consequent thrombosis, or 

 even thrombosis of the sinus, with subsequent inflammation of its walls, 

 occurs proportionately often, being most frequent in the sinus lying on 

 the petrous bone, the lateral and petrosalt This is evidently because 

 inflammation and thrombosis of the cerebral sinuses are induced, in the 

 great majority of cases, by caries of the petrous bone advancing to the 

 base of the skull. The numerous patients suffering from tedious 

 otorrhcea, as a result of otitis interna, are constantly threatened, as 

 with a Damocles' sword, by inflammation or thrombosis of these si- 

 nuses. Not unfrequently there are suppuration and breaking down of 

 the thrombus, and then particles of it may enter the efferent veins 

 and lead to embolism and metastatic inflammation. 



ANATOMICAL APPEARANCES. The anatomical changes in mild and 

 chronic cases of pachymeningitis externa are limited to a gradual 

 thickening of the dura mater as a result of proliferation of connective 

 tissue on its outer surface; the dura mater thus becomes firmly 

 attached to the cranium, and subsequently the neoplastic tissue partly 

 ossifies. In acute and severe cases the dura mater is usually reddened 

 by vascular injection and small ecchymoses, is thickened and infiltrated 

 in circumscribed spots corresponding to the point of injury or caries 

 of the cranial bones. Later, this membrane becomes discolored, its 

 tissue is relaxed and softened ; finally, there is suppuration, and, if pus 

 collects between the dura mater and cranium, the inflamed part be- 

 comes detached from the bone. In the latter case the pia mater also 

 is almost always inflamed, and generally to a great extent. Even on 

 autopsy it is often difficult to decide whether the inflammation of the 

 wall of the sinus preceded the thrombosis, or the reverse. If the 

 thromboses be not disintegrated, they adhere firmly to the relaxed 

 rough inner surface of the thickened wall of the sinus, and occasionally 

 extend backward to the torcular Herophili, and in rare cases down to 

 the internal jugulars ; as has been shown by the observations of Lebert^ 

 who has very greatly advanced our more accurate knowledge of this 

 disease. More frequently on autopsy we find the thrombus already 

 broken down, and the inflamed sinus filled with a purulent or sanious, 

 occasionally gray-green and stinking fluid, mixed with flocculi. Along 



