Complications of Caesarean delivery part 2: Non-pregnant and pregnancy-related complications

Introduction With the rise in Caesarean deliveries, complications related to the procedure are increasingly encountered. Sonography has an indispensable role in the assessment of these complications and is often the first-line investigation of choice. Topic description: Part 2 of this pictorial review summarises the non-pregnant and pregnancy-related complications of Caesarean deliveries.

Non-pregnant complications include Caesarean scar defects, scar endometriosis and malpositioned intrauterine devices. Complications related to future gestations include scar ectopic pregnancy, abnormal placentation and intrapartum uterine dehiscence or rupture. Key sonographic features of these conditions are illustrated. Pitfalls, mimics, limitations and indications for cross-sectional imaging are discussed.

Sound knowledge of the sonographic features of common non-pregnant and pregnancy-related complications of Caesarean delivery will facilitate accurate diagnosis, timely management and improved patient outcomes.

Ultrasound, Caesarean section, ectopic pregnancy, placenta accreta

Global data show a doubling in lower segment Caesarean delivery (CD) births in the past two decades from 16.0 million in 2000 to 29.7 million in 2015. 1 Although CD is potentially life-saving with valid elective indications, the procedure is not without risks. Compared to vaginal delivery, CD is associated with higher postpartum maternal morbidity including major puerperal and wound infections, thromboembolic events, 2 as well as high risks for fertility and future pregnancies in the long-term. 3 In addition, acute subfascial and bladder flap haematomas at the incision sites, Caesarean scar defects and scar ectopic pregnancies are complications unique to CD. Imaging plays an important role in the assessment of these complications; in particular, ultrasound is indispensable in obstetrics and gynaecology as both a screening and diagnostic tool. Part 2 of this pictorial review illustrates the key sonographic features of common non-pregnant and pregnancy-related complications unique to and associated with CD. Sonographic pitfalls, mimics, limitations and indications for cross-sectional imaging are also discussed. All images were acquired at a single high-volume specialised women and children’s hospital. Non-pregnant complications Caesarean scar defects and dehiscence The intact Caesarean section scar, if visible, is seen as a thin hypo- or hyperechoic line in the myometrium (Figure 1). Mild retraction of the anterior uterine border is considered nonpathological (Figure 1), whereas a defect in the posterior myometrial border constitutes a scar defect. A common complication is the development of a Caesarean scar defect (synonyms: scar niche, isthmocele), with reported prevalence ranging from 24% to 70% on transvaginal ultrasound (TVUS) and 56% to 84% on sonohysterography in women with one or more previous CD. 4 Scar defects are associated with abnormal postmenstrual spotting, scar pregnancies and uterine rupture in subsequent pregnancies. 5 Criteria for scar defect on sagittal TVUS include an anechoic space in the myometrium at the hysterotomy site with a depth of at least 2 mm and overlying residual myometrial thickness of less than 5 mm (Figure 2). 6 Gel sonohysterography and hysterosalpingo-contrast sonography with saline medium (HyCoSy) have higher sensitivity and can better characterise these defects (Figure 2). 5 Scar dehiscence is reserved for defects spanning 80% or more of the myometrium depth (Figure 3). 7 Abdominal wall scar endometriosis Although scar endometriosis is a rare complication of open abdominal surgery, CD accounted for more than half the cases in several publications. 8 The most common presentation is catamenial pain and/or mass at the abdominal scar. 8 Ultrasound is the first-line modality for suspected anterior abdominal wall scar endometriosis and can exclude other focal lesions such as incisional hernias. Sonographic features are varied, but typical findings are of a solid inhomogeneous hypoechoic mass with irregular/ill-defined margins located in the skin, subcutaneous and/or muscle layer, and some vascularity is usually present (Figure 4). 9 Echotexture depends on composition of haemorrhage and fibrotic tissue. 9 Other reported sonographic findings include hyperechoic inflammatory ring, single vascular pedicle entering the mass and dilated peripheral feeding vessels. 9 Further evaluation with magnetic resonance imaging (MRI) may be required if sonographic features are inconclusive. In particular, scar endometriosis may be indistinguishable from hypertrophic surgical scars (keloids) and desmoid tumours on ultrasound. 9 Treatment is with wide surgical excision. Displaced intrauterine contraceptive devices CD is not known to increase risk of intrauterine contraceptive device (IUCD) complications (e.g. perforation, expulsion)10,11; however, IUCDs can occasionally become lodged within or perforate through the Caesarean scar defect (Figure 5), causing pain and/or abnormal uterine bleeding. Three-dimensional TVUS is increasingly replacing two-dimensional TVUS for IUCD assessment. Properly positioned IUCDs are located in the upper endometrial cavity with the arms extending laterally into the fundus. Pregnancy-related complications Scar ectopic pregnancy Caesarean scar pregnancy is a rare form of ectopic pregnancy involving implantation on or within the hysterotomy scar. The entity is associated with placenta accreta spectrum (PAS) and high risk of uterine rupture. TVUS is the primary diagnostic modality but may be supplemented by MRI in a minority. 12 Sonographic features of scar pregnancy include an empty uterine cavity, gestational sac implanted at the previous Caesarean scar with thin or absent myometrium between the gestational sac and bladder, and presence of high‐velocity, low‐resistance peritrophoblastic arterial flow (Figure 6). 12 Mimics of scar pregnancy include cervical ectopic pregnancy, low intrauterine pregnancy and miscarriage in progress. 13 Scar pregnancy is located at the level of the internal os, whereas cervical pregnancy is below the internal os within a ballooned/barrel-shaped cervical canal. 12 Distinguishing between scar pregnancy growing into the uterine cavity and a low intrauterine pregnancy is difficult, more so later in gestation. 14 For scar pregnancy and miscarriage in progress, the most useful sign is the sonographic ‘sliding sign’ which will be negative in scar pregnancy and positive in miscarriage in progress as the products of conception have detached from the implantation site. Additionally, miscarriage in progress will show an irregular elongated gestational sac with less florid vascularity (Figure 7). Placenta accreta spectrum and placenta previa CD is an established risk factor for abnormal placentation with potential for life-threatening postpartum haemorrhage. An anterior low-lying placenta on antenatal US in a patient with previous CD is highly suspicious for placenta previa and/or PAS. 15 Thorough assessment of the placenta and follow-up TVUS at 32 weeks’ gestation are recommended to confirm a low-lying placenta (placenta less than 2 cm from the internal os) or placenta previa (placenta completely covering the internal os) (Figure 8). 15 Sonographic features of PAS include loss of the hypoechoic retroplacental clear zone, retroplacental myometrial thickness less than 1 mm, placental bulge, focal exophytic mass, interruption of the hyperechoic bladder wall and abnormal placental lacunae on greyscale ultrasound (Figure 8). 16 Doppler features include placental and uterovesical hypervascularity, bridging vessels across and exiting the myometrium and placental lacunae feeder vessels (Figure 8). 16 MRI complements ultrasound in assessing depth and extent of myometrial invasion, especially in posterior placentation and suspected placenta percreta. 15 On MRI, myometrial invasion with loss of the normal T2-hypointense placental-myometrial interface, focal placental or uterine bulging and T2 dark intra-placental bands are suggestive of PAS and should be confirmed on at least two planes. Intrapartum uterine dehiscence and rupture Intrapartum uterine rupture is a rare but catastrophic event. Patients present with pain, vaginal bleeding and may be clinically unstable. The tear tends to occur at the CD scar and may be associated with trauma. Point-of-care ultrasound may be performed in the emergency setting but definitive diagnosis and management is with emergency laparotomy. Sonographic findings include haemoperitoneum, uterine wall defect, extrauterine fetal parts, protruding amniotic sac and anhydramnios. Intrapartum uterine dehiscence, on the other hand, is often clinically occult. Sonographic findings include thinned myometrium, haematoma at the dehiscence and prolapsed amniotic sac or fetal parts (Figure 9).

of ultrasound and indications for cross-sectional imaging Ultrasound has a limited role in the assessment of bowel adhesions, which are best assessed on CT. In addition to the previously discussed indications, cross-sectional imaging is also useful when ultrasound findings are inconclusive. The most appropriate imaging modalities for common non-pregnant and pregnancy-related CD complications are summarised in Table 1. Table 1. | Timing | Category | Pathology | First-line imaging | Additional imaging | Definitive diagnosis | |---|---|---|---|---|---| | Late | Scar-related | Caesarean scar defect | TVUS or sonohysterography | NA | TVUS | | Displaced intrauterine device | TVUS (preferably 3D) | NA | TVUS | || | Abdominal wall scar endometriosis | High-resolution US | MRI if uncertain | Surgical excision | || | Bowel | Adhesions | Abdominal radiography | CECT | Laparotomy | | | Future gestation | Abnormal placentation | Placenta previa | Antenatal TAUS + TVUS | NA | US | | Placenta accreta spectrum | Antenatal TAUS + TVUS | Optional pelvic MRI | US +/−MRI | || | Ectopic pregnancy | Scar pregnancy | TVUS + TAUS | Optional pelvic MRI | US +/−MRI | | | Haemorrhagic | Intrapartum uterine dehiscence | TVUS + TAUS | Pelvic MRI | Laparotomy | | | Intrapartum uterine rupture | Immediate management +/−point-of-care TAUS | NA | Laparotomy | 3D: three-dimensional; CT: computed tomography; CECT: contrast-enhanced CT; MRI: magnetic resonance imaging; NA: not applicable; US: ultrasound; TAUS: transabdominal ultrasound; TVUS: transvaginal ultrasound.

Ultrasound imaging plays an important role in the assessment of CD-related complications at various stages following delivery. Scar defects and IUCDs are best assessed on TVUS, while incisional endometriosis may require MRI for confirmation. During antenatal ultrasound, it is important to assess for abnormal placentation and scar ectopic pregnancies in all patients with previous CD. Sound sonographic knowledge will facilitate accurate diagnosis, timely management and improved patient outcomes. Acknowledgments The authors would like to thank all the sonographers at our institution. Declaration of conflicting interests: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article. Funding: The author(s) received no financial support for the research, authorship, and/or publication of this article. Ethics approval: Ethics approval was waived by the Centralised Institutional Review Board at Singapore Health Services (SingHealth) for this educational pictorial review of anonymised patient images. Guarantor: ET. Contributorship: LCL and HELT conceived the study. ET, TSET and LCL researched literature. ET wrote the first draft of the manuscript. All authors reviewed and edited the manuscript. All authors approved the final manuscript and were in agreement of the submission. ORCID iDs: Eelin Tan https://orcid.org/0000-0002-9521-2190 Timothy Shao Ern Tan https://orcid.org/0000-0001-9297-4598

- 1.Boerma T, Ronsmans C, Melesse DY, et al. Global epidemiology of use of and disparities in caesarean sections. Lancet 2018; 392: 1341–1348. [DOI] [PubMed] [Google Scholar] - 2.Koroukian SM. Relative risk of postpartum complications in the Ohio Medicaid population: vaginal versus cesarean delivery. Med Care Res Rev 2004; 61: 203–224. [DOI] [PubMed] [Google Scholar] - 3.Keag OE, Norman JE, Stock SJ. Long-term risks and benefits associated with cesarean delivery for mother, baby, and subsequent pregnancies: systematic review and meta-analysis. PLoS Med 2018; 15: e1002494. [DOI] [PMC free article] [PubMed] [Google Scholar] - 4.Vaate AJMB de, van der Voet LF, Naji O, et al. Prevalence, potential risk factors for development and symptoms related to the presence of uterine niches following Cesarean section: systematic review. Ultrasound Obstet Gynecol 2014; 43: 372–382. [DOI] [PubMed] [Google Scholar] - 5.Bij de Vaate AJM, Brölmann HAM, van der Voet LF, et al. Ultrasound evaluation of the Cesarean scar: relation between a niche and postmenstrual spotting. Ultrasound Obstet Gynecol 2011; 37: 93–99. [DOI] [PubMed] [Google Scholar] - 6.Jordans IPM, de Leeuw RA, Stegwee SI, et al. Sonographic examination of uterine niche in non-pregnant women: a modified Delphi procedure. Ultrasound Obstet Gynecol 2019; 53: 107–115. [DOI] [PMC free article] [PubMed] [Google Scholar] - 7.Regnard C, Nosbusch M, Fellemans C, et al. Cesarean section scar evaluation by saline contrast sonohysterography: SCSH after Cesarean section. Ultrasound Obstet Gynecol 2004; 23: 289–292. [DOI] [PubMed] [Google Scholar] - 8.Hirata T, Koga K, Osuga Y. Extra-pelvic endometriosis: a review. Reprod Med Biol 2020; 19: 323–333. [DOI] [PMC free article] [PubMed] [Google Scholar] - 9.Gidwaney R, Badler RL, Yam BL, et al. Endometriosis of abdominal and pelvic wall scars: multimodality imaging findings, pathologic correlation, and radiologic mimics. RadioGraphics 2012; 32: 2031–2043. [DOI] [PubMed] [Google Scholar] - 10.Boortz HE, Margolis DJA, Ragavendra N, et al. Migration of intrauterine devices: radiologic findings and implications for patient care. RadioGraphics 2012; 32: 335–352. [DOI] [PubMed] [Google Scholar] - 11.Bala S. Malposition and expulsion of immediate postplacental intrauterine devices [3P]. Obstet Gynecol 2019; 133: 171. [Google Scholar] - 12.Royal College of Obstetricians and Gynaecologists. Diagnosis and management of ectopic pregnancy [Internet]. London: Royal College of Obstetricians & Gynaecologists, 2016. www.rcog.org.uk/en/guidelines-research-services/guidelines/gtg21/ (accessed 17 January 2021). [Google Scholar] - 13.Timor-Tritsch IE, Monteagudo A. Unforeseen consequences of the increasing rate of cesarean deliveries: early placenta accreta and cesarean scar pregnancy: a review. Am J Obstet Gynecol 2012; 207: 14–29. [DOI] [PubMed] [Google Scholar] - 14.Jurkovic D, Hillaby K, Woelfer B, et al. First-trimester diagnosis and management of pregnancies implanted into the lower uterine segment Cesarean section scar. Ultrasound Obstet Gynecol 2003; 21: 220–227. [DOI] [PubMed] [Google Scholar] - 15.Royal College of Obstetricians and Gynaecologists. Placenta praevia and placenta accreta: diagnosis and management (green-top guideline no. 27a) [Internet]. London: Royal College of Obstetricians & Gynaecologists, 2018. www.rcog.org.uk/en/guidelines-research-services/guidelines/gtg27a/ (accessed 10 October 2020). [Google Scholar] - 16.Collins SL, Ashcroft A, Braun T, et al. Proposal for standardized ultrasound descriptors of abnormally invasive placenta (AIP). Ultrasound Obstet Gynecol 2016; 47: 271–275. [DOI] [PubMed] [Google Scholar]