By the term encysted placenta, we mean that state of irregular uterine action after the expulsion of the child, where the lower portion of the uterus, particularly the os uteri internum, is closely contracted, while the fundus contains the placenta enclosed in a species of cyst or cavity formed by itself and the body of the uterus.
Upon examination externally, we find the fundus pretty firmly contracted, but probably somewhat higher up the abdomen than usual; the vagina and os uteri externum, or os tincæ, are usually found dilated, the passage gradually tapering like a funnel to the os uteri internum, or upper end of the canal of the cervix.
Situation in the uterus. This state has been very generally considered to arise from a spasmodic contraction in the circular fibres of the body of the uterus, by which it was as if tightly girded by a cord at its middle, and, from the form it was supposed to take, was called hour-glass contraction of the uterus.
From the observations of later years there is much reason to suppose that the true hour-glass contraction, as now described, is of very rare occurrence, even if it does take place at all; and that, in by far the majority of cases, the stricture is either produced by the upper part of the cervix, as we have already mentioned, or resides in the os uteri externum or inferior portion of the cervix.
Baudelocque was the first who pointed out the neck of the uterus as the real seat of the stricture in these cases: “that circle (says he) of the uterus which is round the child’s neck, according to the general laws of its contraction, must narrow itself much quicker after delivery than the other circles which compose that viscus, because it is already narrower, and its forced dilatation at the instant of the expulsion of the child’s trunk is only momentary, and because it has naturally more tendency to close than the other circles have, since it is that which constitutes the neck of the uterus in its natural state.” (Baudelocque, Heath’s Trans. vol. ii. § 969.)
Dr. Douglas, of Dublin, also investigated this subject, and came to a similar conclusion: he considered that encysted or incarcerated placenta from hour-glass contraction, resulted either from morbid adhesion of the placenta, or from inactivity of the uterus, and does not occur as a primary affection; his observations lead to the conclusion that the stricture in hour-glass contraction “does not form from the middle circumference of the uterus; it is formed by the lowest verge of its thickly muscular substance, at the line of demarcation of its body and cervix.” “Thus, then, it would appear that the upper chamber comprises in its formation the entire of the body of the fundus; whilst the lower chamber engages only the cervix uteri and the vagina.” (Medical Transactions of the Col. of Phys. vol. vi. p. 393.)
The late W. J. Schmitt of Vienna considered that the stricture was produced by the os tincæ, or os uteri externum.
From our own experience we would say that the seat of the stricture varies considerably in different cases; that in the simplest form it is nothing more than a contracted state of the os uteri externum; that in others it is formed by the upper portion of the cervix uteri, or os uteri internum; but in other instances it appears to be formed by the inferior segment of the uterus itself. The contraction in this part of the uterus, which, according to the observations of Professor Michaelis, comes on when the os uteri is fully developed, and, by closely surrounding the head, is one chief means by which prolapsus of the cord is prevented, may easily produce a state of stricture after the birth of the child, and thus retain the placenta; it may, however, be questioned whether this portion of the uterus, when fully dilated by pregnancy, and which then forms its inferior segment, would not become the os uteri internum when the uterus is empty and contracted.
Hour-glass contraction of the uterus is liable to occur where the action of the uterus has been much deranged or exhausted, either by the unusual rapidity or excessive protraction of the labour. In all cases where the child has been rapidly expelled before the uterus has had time to contract regularly and uniformly, the disposition in the os uteri to contract, as pointed out by Baudelocque, will manifest itself. This state may also be induced by great previous distention, as from twins, or too much liquor amnii; by irritation, as by improperly pulling at the cord, by having used too much force in artificially delivering the child, by the introduction of the hand or instruments too cold, &c. The most frequent cause, however, is over anxiety to remove the placenta; the cord is frequently pulled at, and at length the os uteri is excited to contract; in this case we generally find the stricture at the os tincæ, which yields without much difficulty, either by gentle friction with the hand over the fundus, and cautiously pulling the placenta in the axis of the superior aperture, or by introducing the hand and bringing it away.
Adherent placenta. When the placenta is still attached either wholly or in part, there are generally some preternatural adhesions to the uterus, which, by keeping its upper portion distended, give rise to partial contractions below. This condition of the placenta is observed to attend nearly every severe case of hour-glass contraction; in some instances its whole surface appears as if grown to the uterus, forming an adhesion so close and intimate as to be overcome with the greatest difficulty: we have met with cases where the placenta tore up into shreds which still adhered to the uterus as strongly as before; in others, however, the adhesions are of smaller extent, varying from the size of a shilling to that of a crown piece, sometimes there being only one, sometimes two or three in the same placenta.