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Incarcerated Uterus

The uterine fundus (F) is trapped within the sacral hollow. The cervix (C) is anteriorly and superiorly displaced.
The fetal head was difficult to visualize as it was deep within the pelvis within the sacral hollow (arrows).


In this 19 week gestation the uterine fundus is incarcerated (trapped) within the sacral hollow. The cervix is anteriorly and superiorly displaced and may simulate a small non-gravid uterus. The fetal head is often difficult to image as it is deep within the sacral hollow.


Retroversion or retroflexion of the uterus is a relatively common condition in the non-gravid state. In the gravid patient prior to 12 weeks gestation it is said to occur in 11% to 19% of patients. In most patients, retroposition of the uterus early in pregnancy is unassociated with symptomatology. By 14-16 weeks of gestation as the uterus enlarges in size it normally undergoes spontaneous 'reduction' as the uterus becomes an abdominal organ.

Longitudinal sonogram of an early gravid uterus demonstrating retroflexion. This uterus became anteverted as pregnancy progressed

An incarcerated or trapped uterus describes a retroverted or retroflexed uterus that fails to ascend into the abdominal cavity. The uterine fundus is trapped within the sacral hollow as the mid-body and lower uterine segment are stretched superiorly with further uterine growth. Interestingly, the often used term "retroverted" uterus was first used by Hunter in 1754 to describe an incarcerated retroverted gestation. Incarceration of the uterus is uncommon and is said to occur in 1 in 3000 pregnancies. It has been postulated that a deep sacral concavity may predispose to uterine incarceration. Other predisposing factors include: pelvic inflammatory disease, endometriosis, a posterior wall leiomyoma, congenital malformations, such as a didelphic or a bicornuate uterus and previous gynecologic surgery resulting in adhesions. . Uterine incarceration has also been reported in conjunction with placental accreta and placenta increta.

Modified from:Van Winter J, Ogburn PL, Ney JA. Uterine incarceration during te 3rd trimester: a rare complication of pregnancy. Mayo Clin Proc 66:608-613, 1991

The term sacculation if often used when describing a retroverted uterus. One should be aware however that there are two forms of sacculation. When the abnormally positioned (incarcerated) uterus becomes stretched and thin to accommodate the growing fetus it is termed secondary uterine sacculation. This should be differentiated from true uterine sacculation which is defined as diffuse ballooning of some part of the uterine wall in a normally positioned uterus. It occurs only in the pregnant state and disappears as the uterus involutes. Unlike sacculation due to an incarcerated uterus, true sacculation is usually without symptoms and labor may precede normally.

In patients with an incarcerated uterus, the cervix is drawn upward either against or above the symphysis pubis as the uterus enlarges. This results in distortion of the bladder and urethra. The posteriorly positioned fundus may cause pressure against the rectum. As a result, patients often present between the 13th and 17th week of pregnancy with symptoms of bladder outlet obstruction, nonspecific abdominal pain, rectal pressure or constipation. At the time of clinical examination, with advancing gestational age, the cervix and upper limits of the vagina cannot be reached at vaginal examination nor can the cervix be visualized. The vagina becomes elongated and stretched forward and upward, ultimately to the level of the umbilicus. The posterior vaginal fornix is effaced.

Sonographically, a constellation of findings permits the correct diagnosis of a persistently retroverted uterus. First, the products of conception are abnormally positioned deep within the cul-de-sac. The sonographer may first report that biometry or visualization were difficult because the fetus was "too low within the pelvis or standing on its head". Second, the maternal urinary bladder is malpositioned and lies anterior, rather than inferior to the products of conception. A third finding is the visualization of a part of the myometrium which appears to contain a central cavity echo between the urinary bladder and the products of conception. This appearance is due to the anterior displacement and compression of the lower uterine segment and should not be misconstrued as an empty uterus associated with an ectopic or abdominal pregnancy.

Sonogram of a 12 week gestation demonstrating an incarcerated fundus (F) within the sacral hollow. The cervix (C) is drawn anteriorly and superiorly.

Same case as on the left. The maternal urinary bladder (Bl) is drawn superiorly, extending superior to the superior aspect of the visualized uterus. This would never occur with a normally positioned uterus and should be a 'red flag' to the sonologist.

Failure to recognize an incarcerated uterus may result in compromise of the uterine circulation and lead to decidual hemorrhage and subsequent abortion early or arrest of labor or even uterine rupture.

In early second trimester, manual repositioning of the retroverted uterus into an anteverted position can usually be accomplished. If incarceration cannot be reduced manually, the bladder is drained before repeating the attempt with the use of adequate anesthesia. The use of a tenaculum with traction and the knee-chest posture are often helpful. If the retroverted uterus is incarcerated at term, cesarean section is necessary because descent is impeded by the incarcerated fetal parts and uterine displacement. If incarceration is recognized a vertical incision is recommended to facilitate adequate visualization of the pelvic anatomic structures and to decrease the possibility of unrecognized transection of the bladder, endocervical canal or elongated vagina.



Laing FC Sonography of a persistently retroverted gravid uterus. Amer J Roentgenol 136:413-414, 1981

Emery D, Nolan R. Ultrasonography of an incarcerated uterus during pregnancy. Canad Assoc. Radiol J 45:397, 1994

Gibbons JM, Paley WB: The incarcerated gravid uterus. Obstet Gynecol 33:842-845, 1969

Swartz EM, Komins JI: Postobstructive diuresis after reduction of an incarcerated gravid uterus. J Reproductive Med 19:262-264, 1977

Van Winter J, Ogburn PL, Ney JA. Uterine incarceration during te 3rd trimester: a rare complication of pregnancy. Mayo Clin Proc 66:608-613, 1991

Myers DL, Scotti RJ. Acute urinary retention and the incarcerated, retroverted, gravid uterus: A case report. J Reproductive Med 40:487-490, 1995

Smalbraak I, Bleker OP, Schutte MF, Treffers PE. Incarceration of the retroverted gravid uterus: report of four cases. European J Obstet Gynecol Reprod Biol 39:151-155, 1991

Lettieri L, Rodis JF, McLean DA, Campbell WA, Vintzileos AM. Incarceration of the gravid uterus. Obstet Gynecol Survey 49:642-646, 1994

Hoenigl W. Asymptomatic uterine retroversion at 32 weeks gestation: Sonographic features. J Ultrasound Med 18:795-798, 1999

Hill LM, Chenevey P, DiNofrio D. Sonographic documentation of uterine retroversion mimicking uterine sacculation. Am J Perinatol 10:398, 1993

Jackson D, Elliott JP, Pearson M. Asymptomatic uterine retroversion at 36 weeks' gestation. Obstet Gynecol 71:466, 1988

Hunter W. Med Observ Inq 4:400, 1771

Longo LD. Classic pages in obstetrics and gynecology. Am J Obstet Gynecol 131:95, 1978



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Peter W. Callen, M.D.
Professor of Radiology, Obstetrics, Gynecology and Reproductive Science
University of California Medical Center, San Francisco, California