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Changes in the uterine isthmus during early pregnancy
Changes in the uterine isthmus during early pregnancy JAN Vejprty,
MARSALEK Czechoslovakia
Asplundl and Youssef4 followed up the hysterographic changes in both the isthmus and the canal of the uterine cervix during pregnancy. In a classical monograph on the uterine isthmus and cervix, Asplund claimed that these two uterine segments do not differ in the pregnant and nonpregnant states, although, as a rule, in the pregnant state, they are longer and the isthmus is frequently contracted. Youssef investigated only 2 pregnant women in this respect and found the isthmuses elongated and narrow.
C u R R E N T knowledge on anatomic and histologic grounds provides proof that the structure and function of the uterine isthmus differ from that of the body of the uterus. Hysterographic studies have shown that the isthmus is delimited by two functional sphincters. Asplundl and Palmer2 were the first to investigate changes in the isthmus under physiologic conditions. They proved that the tonus of the isthmic musculature is elevated during the secretory phase, under the influence of progesterone, whereas there is no significant effect on the isthmic mucosa. Youssef3 studied in detail the effect of hormones on the appearance of the isthmus. In the proliferative phase, the isthumus is cylindrical as its musculature is relaxed. The functional sphincters cannot be identified on films or they appear only as slight constrictions of the contrast medium, so that the uterine cavity communicates with the cervical canal in a comparatively broad way. In the secretory phase the isthmus is distinctly narrower, because the tonus of its musculature is elevated and the sphincters are tightly closed. The sharp beginning and end of the ribbon-like x-ray shadow mark the borders of the isthmus on hysterogram. The uterine cervix reacts in the same fashion to hormonal influences, as Asplund demonstrated in his monograph. In our studies we verified this hormonal effect on the isthmic and cervical canal by hysterography.
From the Department Gynecology, Vejprty,
of Obstetrics Czechoslovakia.
Material
and
personal
observations
Under the legal reform in Czechoslavakia, the indications for termination of pregnancy up to the end of the third month have been considerably revised, so that we have been able to undertake hysterography in 27 pregnant women before evacuation of the uterus. The longest pregnancy that we have investigated by hysterography was 16 weeks. Among multiparas only those who did not show badly lacerated cervices were selected. We introduced the Schultze filling cannula into the uterine cervix to a depth of only 0.5 to 1 cm. from the external OS in order to avoid casting a shadow on the canal of the uterine cervix. Although it was noted at bimanual examination that the uterine cervix was soft and edematous and had a livid color, we were surprised, when introducing the filling cannula into the uterine cervix, at the narrow caliber of its canal and at the elevated tonus of its musculature. On hysterograms of pregnancies exceeding 6 weeks, the canal of the isthmus attains the
and 591
592
September 1, 1962 .4m. J. Obst. & Gynec.
Maridek
greatest possible contraction, so that its shadow is only 1 or 2 mm. in width. The canal of the uterine cervix is either of the same width, so that both parts merge almost imperceptibly (Fig. 2), or it is wider and sharply demarcated from the isthmus (Figs. 1 and 3). This change in the configuration of the isthmus must necessarily affect the whole shape of the uterine cavity. In pregnancies of 6 to 8 weeks, the inferior apex of its trigonal form disappears, giving rise to a pentagon-shaped shadow (Fig. 2). Later on, the ball-shaped shadow of the uterine cavity merges abruptly with the ribbonshaped isthmic shadow, which is sometimes as thin as a thread (Figs. 3, 4, and 5). The same finding was seen in both primiparas and multiparas. The behavior of the isthmus and of the uterine cervix is characteristic in cases of abortion. In threatening abortion, the constriction persists unchanged; at the moment of the separation of the ovum, however, the uterine cervix and the isthmus begin to widen. Comment
Under
normal
musculature
of
of the isthmus
conditions, the
body
is governed
the tonus of the of
the
uterus
and
by cyclic changes
Fig. 1. Six weeks’ pregnancy. The uterus tonic and not completely filled. The ovum right half of the uterus. The isthmic narrower and its borders are distinct.
Fig. 2. Seven weeks’ pregnancy. The uterus is hypotonic and ,its cavity is completely filled and has the shape of a pentagon. The isthmic and cervical canals are reduced to a narrow ribbon-like shadow.
is hypois in the canal is
in the hormonal activity of the ovaries.” In the proliferative phase, the canal of the isthmus will assume a cylindrical shape owing to the action of estrogens; the functional sphincters are indistinct, so that the uterine cavity communicates in a comparatively broad way with the uterine cervix. The musculature of the isthmus is found to be relaxed, in contrast to the musculature of the uterine corpus, the tonus of which appears to be elevated so that the radiopaque substance from the uterine cavity leaks into the uterine tube, the isthmus, and the uterine cervix quite easily. In the secretory phase of the menstrual cycle, because of the effect of progesterone, the tonus of the musculature of the uterine corpus is decreased, but that of the isthmus and of the uterine cervix is increased, which manifests itself in the x-ray films as a constriction and elongation of the canals. At the end of the secretory phase,
Volume Number
84 5
2 or 3 days before the onset of menstruation, when the level of the progesterone in the blood is dramatically decreasing and the second rise in the titer of estrogens is reached, the tonus of the musculature of the isthmus relaxes and its canal becomes shorter and wider, The changes in the isthmus and the cervix due to pregnancy are conditioned by hormonal activity of the corpus luteum and of the placenta or trophoblast.6 Estrogen elevates the activity of the isthmic and cervical musculature. Progesterone has the opposite effect. These facts have been verified in a series of experimental studies.‘, 8, g The different effect of these hormones on the isthmic and cervical musculature has also been demonstrated by hysterography. During pregnancy the placenta produces a considerably larger amount of estrogens
Fig. 3. Ten weeks’ pregnancy. The hypotonic uterus has the shape of a ball and the radiopaque substance fills only its inferior part. The internal cervical OS is visibIe as a conical constriction of the cervical canal.
Changes
in uterine
isthmus
in pregnancy
593
Fig. 4. Eleven weeks’ pregnancy. The radiopaque substance fills the space beneath the inferior pole of the ovum. The isthmic canal is narrowed and at the site of the internal cervical OS it merges with the conical shadow of the widening cervical canal.
and progesterone. Progesterone is functionally more important, as active estrogen is converted into inactive estriol. This is why we can demonstrate only the effect of progesterone by hysterography during normal pregnancy. We recognize only three definite radiographic signs of pregnancy: visibility of the fetal skeleton; maximum constriction of the isthmus and, eventually, of the cervix, combined with a simultaneous hypotonia of the musculature of the body of the uterus; and, finally, visibility of the placental sinuses. Constriction of the isthmus or of the uterine cervix is not visible on hysterogram until the sixth week of pregnancy; it can be observed in hysterogram up to the end of the fourth month (Fig. 5). This constriction of the isthmus and the uterine cervix provides excellent natural protection against trauma which otherwise might endanger the ovum. We ascribe to it great diagnostic value, for ( 1) it is an absolutely uniform phenomenon in pregnancy exceeding 6 weeks, (2) it does not occur to such an extent in any other condition, and (3) it is visible during the period when the skeletal parts of the embryo cannot be detected (x-ray evidence of a fetal skeleton having previously represented the only reliable radiographic evidence of pregnancy).
594
September
MariCIlek
1, 1962
Am. J. Obst. & Gynrr.
to use hysterography to establish pregnancy when we have at our disposal simple and harmless methods, such as the biologic tests. Hysterography can mechanically provoke abortion and we must consider the effect of x-rays on mutational changes in the ovum. Summary
The increased production of progesterone in pregnancy causes maximum constriction of the uterine isthmus and sometimes also of the cervical canal beginning with the sixth week of gestation. This change in the isthmus has been observed uniformly up to the fourth month of normal pregnancy. It does not occur in any other condition. It may, therefore, be considered a reliable radiographic sign in early pregnancy.
Fig. 5. Fourteen weeks’ pregnancy. Thr isthmic canal is maximally constricted and its shadow resembles a wire. The radiopaque substance has filled the space beneath the inferior pole of the ovum. The skeleton of the fetus is visible.
We were able to follow the changes in the isthmus and cervix only up to end of the fourth month. There remains one problem to be solved: the time of the actual penetration of the inferior pole of the OVUI~ into the isthmus. This, however, represents another field of investigation. For all practical purposes, radiographic signs of pregnancy are important only in differential
diagnosis.
It
would
be
a mistake
REFERENCES
1. Asplund, J.: Acta radiol. suppl. 91, 1952. 2. Palmer, R.: Bruxelles med. 30: 409, 1950. 3. Youssef, A. F.: AM. J. OBST. & GYNEC. 75: 1320, 1958. 4. Youssef, A. F.: AM. 5. OBST. & GYNEC. 75: 1305, 1958. 5. Palmer, R., and Lacomme, M.: Gynec. & Obst. 47: 905. 1948. 6. Noack, H.: Hormonelle Regulationen in der Friihschwangerschaft, Leipzig, 1958, Georg Thieme Verlag. 7. Knaus, H. H.: Arch. Gynak. 146: 343, 1931. 8. Reynolds, S. R. M., and Allen, W. M.: Am. J. Physiol. 102: 39, 1932. 9. Courrier, R.: Endocrinologie de la gestation. Paris. 1945. Masson et Cie. 10. Borell, M.; and Fernstram, I.: Acta obst. et gynec. scandinav. 32: 7, 1953. 11. Char-vat, J.: Steroid& harmony, Stat. zdravot. naklad. Praha, 1952.
MARSALEK Czechoslovakia
Asplundl and Youssef4 followed up the hysterographic changes in both the isthmus and the canal of the uterine cervix during pregnancy. In a classical monograph on the uterine isthmus and cervix, Asplund claimed that these two uterine segments do not differ in the pregnant and nonpregnant states, although, as a rule, in the pregnant state, they are longer and the isthmus is frequently contracted. Youssef investigated only 2 pregnant women in this respect and found the isthmuses elongated and narrow.
C u R R E N T knowledge on anatomic and histologic grounds provides proof that the structure and function of the uterine isthmus differ from that of the body of the uterus. Hysterographic studies have shown that the isthmus is delimited by two functional sphincters. Asplundl and Palmer2 were the first to investigate changes in the isthmus under physiologic conditions. They proved that the tonus of the isthmic musculature is elevated during the secretory phase, under the influence of progesterone, whereas there is no significant effect on the isthmic mucosa. Youssef3 studied in detail the effect of hormones on the appearance of the isthmus. In the proliferative phase, the isthumus is cylindrical as its musculature is relaxed. The functional sphincters cannot be identified on films or they appear only as slight constrictions of the contrast medium, so that the uterine cavity communicates with the cervical canal in a comparatively broad way. In the secretory phase the isthmus is distinctly narrower, because the tonus of its musculature is elevated and the sphincters are tightly closed. The sharp beginning and end of the ribbon-like x-ray shadow mark the borders of the isthmus on hysterogram. The uterine cervix reacts in the same fashion to hormonal influences, as Asplund demonstrated in his monograph. In our studies we verified this hormonal effect on the isthmic and cervical canal by hysterography.
From the Department Gynecology, Vejprty,
of Obstetrics Czechoslovakia.
Material
and
personal
observations
Under the legal reform in Czechoslavakia, the indications for termination of pregnancy up to the end of the third month have been considerably revised, so that we have been able to undertake hysterography in 27 pregnant women before evacuation of the uterus. The longest pregnancy that we have investigated by hysterography was 16 weeks. Among multiparas only those who did not show badly lacerated cervices were selected. We introduced the Schultze filling cannula into the uterine cervix to a depth of only 0.5 to 1 cm. from the external OS in order to avoid casting a shadow on the canal of the uterine cervix. Although it was noted at bimanual examination that the uterine cervix was soft and edematous and had a livid color, we were surprised, when introducing the filling cannula into the uterine cervix, at the narrow caliber of its canal and at the elevated tonus of its musculature. On hysterograms of pregnancies exceeding 6 weeks, the canal of the isthmus attains the
and 591
592
September 1, 1962 .4m. J. Obst. & Gynec.
Maridek
greatest possible contraction, so that its shadow is only 1 or 2 mm. in width. The canal of the uterine cervix is either of the same width, so that both parts merge almost imperceptibly (Fig. 2), or it is wider and sharply demarcated from the isthmus (Figs. 1 and 3). This change in the configuration of the isthmus must necessarily affect the whole shape of the uterine cavity. In pregnancies of 6 to 8 weeks, the inferior apex of its trigonal form disappears, giving rise to a pentagon-shaped shadow (Fig. 2). Later on, the ball-shaped shadow of the uterine cavity merges abruptly with the ribbonshaped isthmic shadow, which is sometimes as thin as a thread (Figs. 3, 4, and 5). The same finding was seen in both primiparas and multiparas. The behavior of the isthmus and of the uterine cervix is characteristic in cases of abortion. In threatening abortion, the constriction persists unchanged; at the moment of the separation of the ovum, however, the uterine cervix and the isthmus begin to widen. Comment
Under
normal
musculature
of
of the isthmus
conditions, the
body
is governed
the tonus of the of
the
uterus
and
by cyclic changes
Fig. 1. Six weeks’ pregnancy. The uterus tonic and not completely filled. The ovum right half of the uterus. The isthmic narrower and its borders are distinct.
Fig. 2. Seven weeks’ pregnancy. The uterus is hypotonic and ,its cavity is completely filled and has the shape of a pentagon. The isthmic and cervical canals are reduced to a narrow ribbon-like shadow.
is hypois in the canal is
in the hormonal activity of the ovaries.” In the proliferative phase, the canal of the isthmus will assume a cylindrical shape owing to the action of estrogens; the functional sphincters are indistinct, so that the uterine cavity communicates in a comparatively broad way with the uterine cervix. The musculature of the isthmus is found to be relaxed, in contrast to the musculature of the uterine corpus, the tonus of which appears to be elevated so that the radiopaque substance from the uterine cavity leaks into the uterine tube, the isthmus, and the uterine cervix quite easily. In the secretory phase of the menstrual cycle, because of the effect of progesterone, the tonus of the musculature of the uterine corpus is decreased, but that of the isthmus and of the uterine cervix is increased, which manifests itself in the x-ray films as a constriction and elongation of the canals. At the end of the secretory phase,
Volume Number
84 5
2 or 3 days before the onset of menstruation, when the level of the progesterone in the blood is dramatically decreasing and the second rise in the titer of estrogens is reached, the tonus of the musculature of the isthmus relaxes and its canal becomes shorter and wider, The changes in the isthmus and the cervix due to pregnancy are conditioned by hormonal activity of the corpus luteum and of the placenta or trophoblast.6 Estrogen elevates the activity of the isthmic and cervical musculature. Progesterone has the opposite effect. These facts have been verified in a series of experimental studies.‘, 8, g The different effect of these hormones on the isthmic and cervical musculature has also been demonstrated by hysterography. During pregnancy the placenta produces a considerably larger amount of estrogens
Fig. 3. Ten weeks’ pregnancy. The hypotonic uterus has the shape of a ball and the radiopaque substance fills only its inferior part. The internal cervical OS is visibIe as a conical constriction of the cervical canal.
Changes
in uterine
isthmus
in pregnancy
593
Fig. 4. Eleven weeks’ pregnancy. The radiopaque substance fills the space beneath the inferior pole of the ovum. The isthmic canal is narrowed and at the site of the internal cervical OS it merges with the conical shadow of the widening cervical canal.
and progesterone. Progesterone is functionally more important, as active estrogen is converted into inactive estriol. This is why we can demonstrate only the effect of progesterone by hysterography during normal pregnancy. We recognize only three definite radiographic signs of pregnancy: visibility of the fetal skeleton; maximum constriction of the isthmus and, eventually, of the cervix, combined with a simultaneous hypotonia of the musculature of the body of the uterus; and, finally, visibility of the placental sinuses. Constriction of the isthmus or of the uterine cervix is not visible on hysterogram until the sixth week of pregnancy; it can be observed in hysterogram up to the end of the fourth month (Fig. 5). This constriction of the isthmus and the uterine cervix provides excellent natural protection against trauma which otherwise might endanger the ovum. We ascribe to it great diagnostic value, for ( 1) it is an absolutely uniform phenomenon in pregnancy exceeding 6 weeks, (2) it does not occur to such an extent in any other condition, and (3) it is visible during the period when the skeletal parts of the embryo cannot be detected (x-ray evidence of a fetal skeleton having previously represented the only reliable radiographic evidence of pregnancy).
594
September
MariCIlek
1, 1962
Am. J. Obst. & Gynrr.
to use hysterography to establish pregnancy when we have at our disposal simple and harmless methods, such as the biologic tests. Hysterography can mechanically provoke abortion and we must consider the effect of x-rays on mutational changes in the ovum. Summary
The increased production of progesterone in pregnancy causes maximum constriction of the uterine isthmus and sometimes also of the cervical canal beginning with the sixth week of gestation. This change in the isthmus has been observed uniformly up to the fourth month of normal pregnancy. It does not occur in any other condition. It may, therefore, be considered a reliable radiographic sign in early pregnancy.
Fig. 5. Fourteen weeks’ pregnancy. Thr isthmic canal is maximally constricted and its shadow resembles a wire. The radiopaque substance has filled the space beneath the inferior pole of the ovum. The skeleton of the fetus is visible.
We were able to follow the changes in the isthmus and cervix only up to end of the fourth month. There remains one problem to be solved: the time of the actual penetration of the inferior pole of the OVUI~ into the isthmus. This, however, represents another field of investigation. For all practical purposes, radiographic signs of pregnancy are important only in differential
diagnosis.
It
would
be
a mistake
REFERENCES
1. Asplund, J.: Acta radiol. suppl. 91, 1952. 2. Palmer, R.: Bruxelles med. 30: 409, 1950. 3. Youssef, A. F.: AM. J. OBST. & GYNEC. 75: 1320, 1958. 4. Youssef, A. F.: AM. 5. OBST. & GYNEC. 75: 1305, 1958. 5. Palmer, R., and Lacomme, M.: Gynec. & Obst. 47: 905. 1948. 6. Noack, H.: Hormonelle Regulationen in der Friihschwangerschaft, Leipzig, 1958, Georg Thieme Verlag. 7. Knaus, H. H.: Arch. Gynak. 146: 343, 1931. 8. Reynolds, S. R. M., and Allen, W. M.: Am. J. Physiol. 102: 39, 1932. 9. Courrier, R.: Endocrinologie de la gestation. Paris. 1945. Masson et Cie. 10. Borell, M.; and Fernstram, I.: Acta obst. et gynec. scandinav. 32: 7, 1953. 11. Char-vat, J.: Steroid& harmony, Stat. zdravot. naklad. Praha, 1952.