SHAPE OF THE HEAD IN VERTEX PRESENTATIONS.
The moulding experienced by the head in passing through the pelvis is of two kinds, one affecting the soft parts, and the other the cranium. The former constitute the caput succedaneum, and the latter the true cranial distortions.
Caput Succedaneum.
This is a tumefaction formed upon the presenting foetal part, and consist ing in an oedematous, sero-sanguinolent infiltration of the sub-cutaneous cellular tissue of the part. The tumor always appears in that portion of the presenting part which corresponds to the pelvic cavity, i.e., on the un compressed part. It therefore varies with the presentations and the posi tions. On the vertex, it forms a tumor which is more or less prominent according as labor has been of greater or less duration, and the membranes have been long or but lately ruptured. The tumor is more or less violet, in color, and upon it, in certain cases, are little ruptured or unbroken vesicles. It is, generally, limited to the skin. Sometimes it extends deeper, down to the periosteum, which it detabhes, and to the bones, the vessels of which are distended with blood. In still rarer cases, the lesions have involved even the interior of the cranium, detaching the dura mater, and inducing congestion of the pia-mater and of the choroid plexuses. It was formerly supposed that the caput succedaneum was only formed during the period of dilatation and after rupture of the membranes. Schroeder and Budin's cases prove that it may sometimes be formed, even when the membranes are intact. Although generally small, from .78 to 1.5 inches in its longest diameter, it is sometimes large, particularly when the labor is long and the membranes are ruptured early. Its presence furnishes valuable data for a retrospective diagnosis of the posi tion. Since it is always formed on the part corresponding to the pelvic cavity, its position varies with the position. Thus, in right positions, the caput will be upon the left lateral part of the head, in the left positions, upon the right side. In anterior positions it will be on the posterior part, and, in posterior positions, on the anterior part—in brief, on that part of the head occupying the front and centre of the pelvis. Thus, in Position 0. L. A., the caput is on the posterior superior angle of right parietal bone. Position O. L. P., " " " " " anterior " " " " " 0. R. A., " " " " " posterior " " " " left Sot " 0. R. P., " " " " " anterior " " " " ti This is the general rule. Nevertheless, when the head, after escaping from the cervix and having rotated, remains a long time in situ, before being expelled, a second caput succedaneum may be formed. This one, however, is always placed on the median line, so that the first caput may be discovered, in front or behind, thus showing the nature of the original position of the head. When labor advances rapidly, the e,aput is either not formed or consists, merely, in a slight discoloration of the tissues. The caput has generally no influence upon the life of the child. It is usually limited to the thickness of the skin and disappears in twelve or twenty-four hours after labor, but, if it extends to the interior of the cranium, it may, of course, become dangerous to the child.
Distortions of the Bones.
Little known or neglected by the older authors, these distortions, which Kuneke calls the plastic phenomena of labor, have only recently been really studied by &add°ldt, Dohrn, Barnes, Hecker,Olshausen, Grossman, Schroeder, Spiegelberg, Perlis, Budin and Labatt. To these authors be long the credit of calling attention to this very interesting point, and of showing that given distortions are distinctive of each presentation. Stadt feldt showed, in 1363, that the shape of the cranium is greatly modified by the different positions of the head, and by its various movements during labor. He holds this to be particularly true of the brow and face
presentations, and in those cases where the bi-parietal diameter of the head traverses the pelvis. This diameter is shortened, but the occipito frontal diameter is elongated from one quarter to three quarters of an inch. Not only does an overlapping of the bones occur, but the borders of the bones are bent inward toward their centre. Ordinarily, the com pression occurs in the diameter 0. F. and in the vertical circumference, and the compensatory change occurs in the diameter B. P. When the pelvis is contracted, depressions and impressions result, and their traces remain either on the parietal or on the frontal bones. Dohrn shows that, the cranium being obliquely placed in the pelvis, the side of the cranium situated in front is more deeply engaged than the posterior one. The latter is, therefore, flattened by pressure against the posterior pelvic wall, while the anterior cranial surface is more spherical. Immediately after labor, the head of a child born with a vertex presentation is oblique. This is due partly to the caput succedaneum, and, partly, to the mutual lateral displacement of the two halves of the cranium. This is convinc ingly proved by the fact that one parietal eminence is placed farther for ward than its fellow. This displacement is due to the pressure exerted by the posterior pelvic walls. If we push a head, the occiput of which is deep in the pelvis, from above downward, toward the promontory, the side turned toward the promontory is depressed in front, near the sagittal suture. If, however, the front part of the head is deeply engaged, the part depressed by the promontory will be near the occiput, i.e., behind. If we place the two fontanelles on the same level, the depression will corre spond with the engagement of the anterior part of the head, and this depression will be more marked on the frontal side, in proportion as the obliquity of the head is more pronounced. Dohrn, on measuring with the cyrtometer, found this cranial depression in thirty-eight out of forty cases. The displacement in the first position of the vertex, O. L. A., averages .2 of an inch, in the second position, O. R. P., .26 of an inch. Olshausen states that the first and most common of the distortions is the depression of the occipital, beneath the parietal bone, and this can be ascertained so soon as labor begins. The same is true of the depression of the frontal, beneath the parietal bones. We may find, almost as frequently, a differ ence in the heights of the two halves of the cranium, (in more than two thirds of all cases). Generally the depression of one half of the cranium is only perceptible on the parietal, but may, more rarely, be seen on the frontal bone. The posterior parietal and frontal bones are depressed twice as frequently as the anterior ones. The depression is rarely suffi cient to produce overlapping of the lateral halves of the frontal. When the overlapping does occur, all of one side of the cranium, particularly the parietal eminence, is carried backward on the side corresponding to the half of the cranium which is anterior. It is much more common to see disparity of form in the temporal fossa'. The fossa which is anterior is the deeper. Finally, it is not rare to see the posterior parietal alone depressed. Only rarely does the frontal, of the same side participate in this flattening. The almost constant depression of the occipital and of the frontal beneath the parietal, shows that the pressure is constantly and early exerted on these bones. Olshausen refers it to the psoas and iliacus muscles, which lessens the transverse diameter of the inlet, although not sufficiently to prevent the descent of the head (Fig. 205).