Rachitic subjects occasionally present at the autopsy, brains of abnormal size and density when there have been no clinical symptoms during life. Whether this hypertrophy of the brain is to be regarded as identical witb the above-described form is not decided. In fact, the clinical as well as the pathological picture of hypertrophy- of tbe brain is so imperfectly known that there is very rarely any question of making a differential diagnosis at the bedside.
8. Defects tin the skull and the rertebral column with protrusion of the nerre subctanre (Cerebral and spinal hernia). It bas, already been emphasized that the highest degrtes of separation, or rather imperfect closure of the braincap and of the medullary tube, produce marked malformations of the central nervous system. Such cases are to be regarded as curiosities. More practical interest attaches, how-ever, to those cases in which separation and failure to close of the central nervous system and its bony envelope are confined to circum scribed areas. Failure of the skull to ossify may manifest itself in the substitution of connective tissue membranes for bony portions of the skull (cranial defects, Heubner, Engstler); indeed, ossification may be entirely absent and there may be merely a membranous skull (Stilling).
a rule, however, failure of the bony envelope to close is associated with marked changes in the central nervous system itself and protru sion of individual portions of the brain and cord through the abnormal openings. We then have to deal with herni of the brain and spinal cord.
(a) Hernia of the brain teephalocele).—Protrusion of the brain substance may take place through an artificial opening in the skull (trephining, injuries) or through defects due to disease (nieningocele spuria, Billroth). The hernia represents a pulsating, cystic, pressible tumor and usually requires surgical treatment (Bayerthal).
A more important condition from the pediatric standpoint is congenital hernia of the brain.
Intermediate between the above-mentioned forms of acrania and anencephalus, which are to be regarded as the most extreme examples of separation of the skull, and hernia of the brain, i8 exencephalus, a condition in which a variable portion of the brain escapes through a large opening in the misshapen skull (Muscatello). Other develop mental disturbances of the brain are also present and the child is not viable (Lyssenkow).
The difference between true hernia of the brain (cephalocele) and exancephalus is that in the former condition the defect in the skull is circumscribed. By far the greater portion of the brain is normal, and the cerebral functions as well as the viability of the infant do not ap pear to be materially impaired. The contents of the hernial sac consists either of cerebral substance with a cystic and dilated portion of the ventricle (encephalocystocele) or a meningeal protrusion containing fluid (meningocele).
Of the two, encephalocystorele is the more frequent and more im portant form of brain hernia. Its most frequent seat is the nape of the neck (eephalocele occipitalis) and the hernia contains altered cere bellar substance and the distorted fourth ventricle. Another seat is the root of Om nose (c. nasofrontalis, c. naso-orbitalis) or the sagittal suture (c. sagittalis); in these eases the contents consist of cerebral substance, and the cavity of the cyst communicates with one of the ventricles. The tumors are usually, but not always situated in the median line. The dura becomes attached to the periosteum at the edge of the bone defect. The cerebral substance, as in hydrocephalus, exhibits every degree of contraction down to a mere membrane COV ered with nerve cells. The vessels are numerous and dilated. The ex ternal coverings either consist of norrnal skin or represent attenuated glistening membranes, sometimes exhibiting scars from intra-uterine processes of repair, The tumors range in size from that of a walnut to that of a child's head. The consistency is soft, elastic and usually fluctuating; sometimes the turnor is transparent; the structure is often lobulated and harder portions can be felt here and there. When the child cries or the tumor is compressed, pulsation and distention are often, although not always, present. The defect in the bone can often be felt.
Clinical symptoms are not necessarily present in every ease and are particularly apt to be wanting when the hernia occupies the anterior or the upper portion of the skull. The nmst important syniptorns are idiocy, nystagnms, strabismus and atrophy of the optic nerve. Other malformations, particularly in the central nervous system, are frequently present (hydromyelia, spina bifida, etc.).