Spontaneous reposition of a posterior incarceration (“sacculation”) of the gravid uterus in the 3^rd trimester

Introduction

Uterine incarceration is a rare complication in pregnancy caused by a persistent retroverted uterus, first described by William Hunter in 1771 [1]. In the case of posterior incarceration the cervix is anteriorly displaced and extremely elongated. The lower uterine segment is overstretched and the uterine fundus is wedged in the pelvis despite increasing volume of the uterine contents (Figure 1). An incarceration means that there is a disturbed polarity. Both a posterior and an anterior incarceration have been described. The posterior incarceration with the sacculation of the anterior wall of the uterus happens in context of a retroflected uterus. A simple sacculation is a kind of diverticulum. These different terms were described by Dierickx et al. [3]. Posterior incarceration is associated with increased foetal mortality and maternal morbidity. Undiagnosed, it may lead to obstetric complications such as spontaneous abortion caused by decreased blood flow to the uterus from mechanical compression of the uterine vessels, preterm labor, uterine dystocia, rupture of the uterus and intraoperative injuries during caesarean section through the altered anatomy [4–6]. Risk factors known to predispose to incarceration of the pregnant uterus include adhesions following pelvic inflammatory disease and surgical procedures, uterine and pelvic anomalies, endometriosis and tumours [7, 8]. The typical sign of posterior incarceration on clinical examination is the non-palpable (“vanished”) cervix. The cervix is displaced anteriorly, the cervix and vaginal canal are elongated and stretched behind the pubic symphysis and unreachable for vaginal examination [5]. Transvaginal measurement of the cervix by ultrasound scan is impossible due to the malposition of the cervix. Pelvic examination reveals a mass in the posterior fornix of the vagina. Common misdiagnosis on ultrasound scan is placenta praevia. The symptoms are non-specific – obstetric and gynaecological (bleeding, miscarriages, contractions), pressure symptoms (lower abdominal pain), gastroenterologic (rectal pressure, tenesmus, constipation) and urologic (hydronephrosis, dysuria, urinary retention) [9]. Some cases were without symptoms, as in our case.

Figure 1:

Schematic diagram of posterior uterine incarceration with sacculation of the anterior wall of gravid uterus (from [2]); blue arrow – cervix; red arrow – internal os of cervix; B – bladder; P – placenta.

In early pregnancy, the aim is to restore the normal polarity of the uterus. Manual reposition in combination with operative methods can be attempted [5]. Some authors describe the coloscopy-assisted manual reposition of the incarcerated uterus [10]. In cases of unsuccessful manual or colonoscopy-assisted reposition an operative intervention via laparoscopy or laparotomy is possible and should be discussed. Incarceration of the gravid uterus in the third trimester is an extremely rare diagnosis – it occurs in approximately one of 3000 pregnancies [4]. Diagnosis of posterior incarceration at term requires caesarean delivery. The internal os of the cervix is located more superiorly than normal, that is why we recommend the median laparotomy with a high corporal incision if it is not possible to restore the normal anatomy [9]. Unrecognised and persistent posterior incarceration with sacculation of the anterior wall of uterus involves the risk of inadvertently incision of the bladder, cervix or vagina during caesarean section [9]. Thus, early and accurate diagnosis is essential for appropriate perinatal management.

Case

The posterior incarceration of the uterus in our 36-year-old primigravida was an incidental finding during prenatal screening at 22 weeks and 5 days of pregnancy. The patient had, except for an anamnestic retroflected uterus, no risk factors and was asymptomatically. Ultrasound examination highlighted the cervix between the bladder and the posterior uterine wall – spindle-shaped in the transabdominal transverse and elongated in the sagittal view. The cervix was not detectable during either vaginal ultrasound or on speculum examination. Posterior incarceration of the uterus was suspected and the diagnosis confirmed by magnetic resonance imaging (MRI) (Figure 2). At the 27^th week follow-up the ultrasound scan results remained unchanged (Figure 3). Non-operative reduction as well as operative intervention via laparotomy were discussed, but declined by the patient who favoured expectative management. The patient remained asymptomatic throughout. At the 31^st week we arranged a follow-up for planning of delivery. The cervix presented remarkably and unexpected normally with a well-configured length of 35 mm (Figure 4). The foetus was in breech position and the placenta located at the front wall of the uterus. In order to plan delivery this was confirmed by MRI (Figure 4). Before we could discuss our findings and make a final delivery plan with the patient in case of persistent breech position, she presented in labour at 36 weeks and 3 days with regular contractions and an 8 cm open cervix. It was decided to perform a caesarean section because of the premature and breech presentation and a healthy male (2830 g, pH 7, 41, APGAR 9/9/10) was delivered. The intraoperative situs of the uterus appeared to be normal.

Figure 2:

MRI (sagittal and axial) at 23 weeks of gestation. Uterus with appearingly cephalic presentation of the foetus, the cervix is elongated between posterior wall of the uterus and bladder (A); spindle-shaped cervix between the bladder and uterus (B); blue arrow and circle – cervix; red arrow – internal os of cervix.

Figure 3:

Abdominal ultrasound (sagittal and transversal) at 28 weeks of gestation, the cervix is elongated between back wall of the uterus and bladder (A), spindle-shaped cervix between the bladder and uterus (B); blue arrow and circle – cervix; B – bladder.

Figure 4:

MRI (sagittal) at 36 weeks of gestation: uterus in the regular position, cervix is normally configured (A), blue circle – cervix; abdominal ultrasound (vaginal) at 31 weeks of gestation, cervix is normally configured with a length of 35 mm (B).

Discussion

This case represents an unusual course of spontaneous reposition of an incarcerated uterus in the third trimester of pregnancy which had previously only been reported in one case [11]. Since posterior uterine incarceration in an ongoing pregnancy is an extremely rare event, the key features such as suddenly “vanished” cervix, “false” placenta praevia have to be highlighted and considered. An undiscovered incarceration may lead to particularly maternal morbidity like hydronephrosis, obstructed labour, uterine rupture or intraoperative difficulties during caesarean section. Therefore, awareness and recognition of the signs and symptoms of an incarcerated uterus during early pregnancy remains important in planning restoration of uterine polarity as well as in the event of persistent incarceration in adapting the surgical approach to caesarean section to avoid intraoperative injury to adjacent organs. Although spontaneous reposition of a posterior incarceration becomes less probable with advancing gestational age, our case demonstrates clearly that the natural course can be surprising and unexpected.