In other cases practically no new growth of bone occurs or else only at the margin of the effusion; the blood is then more rapidly absorbed and the periosteum settles flush with the bone.
The formation of the bony ring becomes comprehensible when one considers that the haemorrhage originates in the torn vessels of the highly vascular osteogenctic tissue which lies next to the connective tissue layer of the periosteum. The bleeding not only elevates the periosteum but also a portion of the osteogenetic zone. Hence arises the new growth of bone which is most marked at the margin and forms the wall which, at times totally, at limes (with large effusions) only partially, covers the swelling. The periosteal growth begins usually by the end of the first week; up to this time no wall is palpable. The retrogression of the tumor follows sometimes quickly and sometimes slowly. The absorption of the blood may occur quickly without the distinct forma tion of new bone; in other eases the absorption of the effusion and the resolution of the tissues takes several weeks, usually six to eight and sometimes even much longer.
The bone is either unchanged after the healing of a cephahrmatoma or else presents a slight periosteal thickening.
Complications.—Cephahematomata do not always progress so smoothly. Occasionally the bloody contents of the swelling become infected. The infection usually occurs from an external wound; in rare cases its cause is unknown: sometimes, however, it is the result of an incision into the mass. Abscess formation then occurs, which is a serious matter because the purulent. inflammation may extend to the denuded bone or to the soft parts of the skin, Nvhoso movable, wide meshed cellular tissue furnishes opportunity for the spreading of the pus and the extension of the inflammation. Both these complications can become very dangerous; the first by causing an osteitis and extension to the meninges and the second by causing sepsis.
Accompanying cephabematomata there is found, very rarely, an effusion of_blood on the under surface of the cranial bone, thus sepa rating the Jura from it (eephalwmatoma internum). This may occur either with or without a fracture of the bone; in the latter case the blood flows to the under surface of the bone through a congenital fis sure. Signs of increased intra_cranial pressure may then possibly arise,
which, however, may be caused in like manner by a simultaneous cere bral or meningeal hemorrhage.
Pathology. —In children dying immediately after birth, the skin over the eephahematoma is cedematous and richly besprinkled Nvith hemorrhages. The periosteum is elevated, darkly discolored and also full of small hemorrhages; between it and the bare, rough bone the dark fluid is gathered and a few clots of fibrin cling to the walls.
In cases in which the child dies some time after birth, there are signs of a periosteal growth of new bone either at the margin of the effusion, or later, also on the inner surface of the whole roof of the tumor; this is soft at first, offering no resistance to the knife; but later it becomes hard and then colloid masses or irregular lamella of new bone are found over the bone.
With cephakematoma internum similar anatomical changes are found with the addition of the signs of a fracture or else evidence to show that the blood has trickled through a pre-existing fissure. In some cases there are also cerebral haemorrhages. With complications, condi tions are encountered, often extensive, corresponding to the clinical picture.
are caused by a tearing of the vessels of the subperiosteal zone, with the pouring forth of blood and the resultant elevation of the periosteum. The bursting of a vessel is as a rule, caused by stasis and hyperemia (M. Runge).
Because the vessels are easily torn and the periosteum is loosely connected with the bones of the skull in the newborn, stasis readily leads to the formation of a cephabematoma. This simple explanation of Runge's makes it easy to understand just why the parietal bone and especially the right parietal bone should so often be the seat of cephal tematoma. This is clue to the preponderance of L. O. A. positiolis, with which the right parietal bone presents, so that stasis and the bursting of vessels take place oftenest over it. Whether, in this event, only small htemorrhages or a cephalirmatoma ensues depends princi pally upon the size of the ruptured vessels.