Complications of Caesarean delivery part 1: Early complications

Abstract

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 1 of this pictorial review summarises the early complications unique to and associated with Caesarean deliveries.

Discussion

Acute haemorrhagic complications include retained products of conception, subfascial and bladder flap haematomas and, rarely, postpartum uterine dehiscence or rupture and iatrogenic vascular complications. Infective complications include puerperal and wound infections. Key sonographic features of these conditions are illustrated. Pitfalls, mimics, limitations and indications for cross-sectional imaging are discussed.

Conclusion

Sound knowledge of the sonographic features of common early complications of Caesarean delivery will facilitate accurate diagnosis, timely management and improved patient outcomes.

Introduction

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 Given the rising prevalence of this procedure, associated complications are also increasing. 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 implications for fertility and future pregnancies in the long-term. ³ Additionally, 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 (US) is indispensable in obstetrics and gynaecology as both a screening and diagnostic tool. Common symptoms that would instigate imaging in the immediate post-CD period include fever, pain, heavy per vaginal bleeding and acute drop in haemoglobin level.

A combination of transvaginal US (TVUS) and transabdominal US (TAUS) is often required to assess the integrity of the Caesarean section (CS) scar, although TVUS provides better definition of the tissue layers. When predicting scar dehiscence/rupture, TVUS is also more reliable in measuring lower uterine segment (LUS) thickness with better reproducibility and interobserver reliability compared to TAUS, particularly if three-dimensional US is utilised. ⁴ TAUS is useful in evaluating scar defects located in the higher part of the LUS, commonly seen in cases of CS performed in early gestation and/or before labour, while TVUS is better at visualising scar defects in the lowest part of the LUS, seen in cases of CS performed late in the first or second stages of labour. ⁵

Part 1 of this pictorial review illustrates the key sonographic features of common early complications unique to and associated with CD. Sonographic pitfalls, mimics, limitations and indications for cross-sectional imaging are also discussed.

Non-pathological puerperal findings on US

Sound knowledge of the expected puerperal findings on US is essential to avoid mistaking these features for pathology. Echogenic or mixed density clots and debris are expected within the uterine cavity in the initial 24 hours, particularly in the LUS ⁶ (Figure 1), and subsequently fill the endometrial cavity. ⁷ Enhanced vascularity in the myometrium ranging from focal to large areas on colour Doppler US representing prominent uterine vascular channels at the placental implantation site is a common postpartum finding ⁸ (Figure 1). The enlarged uterus returns to its pre-pregnancy state in 6–11 weeks.

Figure 1.

Expected puerperal findings. (a) Sagittal TVUS four days after Caesarean delivery shows avascular echogenic material in in the lower uterine cavity (arrows) representing blood clots and debris. (b) Sagittal TVUS of a different patient 10 days after Caesarean delivery shows isoechoic region at the uterine incision (arrow). (c) Curvilinear echogenic foci at the uterine incision represent surgical sutures (arrowheads). (d) Increased vascularity in the anterior uterine myometrium on colour power angiography Doppler represents prominent uterine vascular channels at the site of previous placental implantation. (e) Sagittal TAUS of a different patient shows air in the endometrial cavity casting ‘dirty’ posterior acoustic shadowing (empty arrowheads). This is an expected finding following Caesarean delivery and uterine manipulation.

Specific to CD, the transverse lower uterine incision can be identified on TVUS as a hypoechoic or isoechoic region in the anterior wall of the lower uterus lying between the uterovesical fold and internal cervical os (Figure 1). Surgical sutures are seen as hyperechoic linear or punctate foci (Figure 1). Gas in the endometrial cavity is an expected finding following uterine manipulation and CD (Figure 1), and only occasionally seen with vaginal deliveries; this usually resolves by postpartum week 3. ⁷

Early complications

Haemorrhagic complications

TVUS is a screening tool in primary and secondary postpartum haemorrhage (PPH). ⁹ The most common cause of primary PPH, uterine atony, does not require imaging for diagnosis. ⁹ Unstable patients and active bleeding may require immediate management and are otherwise better assessed with computed tomography (CT) and/or catheter angiography. The following haemorrhagic complications may be encountered.

Retained products of conception

Retained products of conception (RPOC) refer to intrauterine tissue of placental trophoblastic origin developing after conception and persisting after delivery or termination of pregnancy. It is one of the most common causes of both primary and secondary PPH, occurring most frequently after second-trimester delivery or termination of pregnancy. ¹⁰ Risk factors include failure to progress during delivery, placenta accreta and instrument delivery. The placenta may be intentionally left behind for uterine preservation in eligible patients with placenta accreta spectrum (PAS). ¹¹ The histological diagnosis of RPOC is made based on the presence of chorionic villi indicating persistent placental tissue invading the endometrial decidua basalis. ¹⁰

Distinguishing RPOC from bleeding related to normal postpartum lochia or uterine atony may be clinically challenging. Ultrasonographic evaluation is often helpful in these patients presenting with PPH, where grey-scale findings of a thickened (8 to 13 mm in thickness) endometrial echo complex or discrete echogenic endometrial mass would suggest RPOC (Figure 2). If associated vascularity is present on colour or power Doppler, the positive predictive value for the diagnosis of RPOC increases. ¹⁰ It is, however, important to note that a proportion of RPOC may be avascular (type 0) or minimally vascular (type 1). ¹² Generally, an avascular endometrium with less than 10 mm thickness makes RPOC unlikely. RPOC has to be differentiated from important mimics such as uterine arteriovenous malformation (AVM) and subinvolution of the placental site (discussed in the next subsection).

Figure 2.

Retained products of conception. (a) Sagittal TAUS three days after Caesarean delivery in a patient with placenta accreta shows echogenic intentionally retained products of conception in the anterior myometrium (arrowheads) for uterine conservation. Recent hysterotomy site with echogenic suture is also noted (arrow). (b) Transvaginal colour Doppler volume sampling shows high‐flow, low‐resistance peritrophoblastic arterial flow consistent with retained products of conception. PSV: Peak Systolic Velocity; EDV: End Diastolic Volume; S/D: Systolic/Diastolic Ratio; RI: Resistive Index.

Bladder flap and subfascial haematomas

Haematomas occurring at the incision sites include bladder flap haematomas in the vesicouterine space (Figure 3) and subfascial haematomas deep to the rectus muscle. Sonographic appearance of acute haematomas can vary from cystic with varying levels of internal echoes to an avascular complex solid-cystic or avascular echogenic solid mass ¹³ (Figure 3). Over time, organising haematomas become more anechoic and can contain septations ¹³ (Figure 3). Non-infected haematomas at the uterine incision smaller than 1.5 cm ¹⁴ and subfascial and bladder flap haematomas smaller than 4 cm are considered clinically insignificant. ¹⁵

Figure 3.

Bladder flap haematoma. (a) Sagittal TVUS five days after Caesarean delivery demonstrates an avascular echogenic complex structure in the vesicouterine space representing a bladder flap haematoma (arrowheads). (b) Follow-up TVUS 12 days after Caesarean delivery shows temporal evolution of the haematoma, now seen as a hypoechoic structure with internal septations creating a lace-like appearance (arrowheads).

Postpartum uterine rupture and dehiscence

Uterine dehiscence involves incomplete disruption of the endometrium and myometrium with intact serosa, whereas uterine rupture involves disruption of all three layers. Both uterine dehiscence and rupture are difficult to diagnose and distinguish on US or CT. Moreover, uterine dehiscence may overlap with normal appearances of the uterine incision after CD. On imaging, haemoperitoneum, large bladder flap haematoma exceeding 5 cm and gas extending from the endometrial cavity through the Caesarean defect into extrauterine space should raise suspicion for acute uterine dehiscence and/or rupture. ¹⁵ Additionally, an LUS thickness of <2.5 mm measured on US has been reported to be associated with a uterine rupture rate of >10% with a specificity of about 90%, although there remains no consensus on the LUS thickness cut-off values.^4,16

In clinically stable patients, magnetic resonance imaging (MRI) allows distinction between the two entities by providing precise visualisation of uterine zonal anatomy.

Iatrogenic vascular complications

Patients with vascular complications tend to present with delayed PPH persisting beyond the puerperium.

Acquired uterine AVMs have been reported following CD and tend to occur adjacent to the hysterotomy. ¹⁷ Uterine AVM is seen as an anechoic multicystic or serpentine mass within the myometrium associated with high flow vascularity on colour Doppler. ¹² Mimics of uterine AVM include RPOC and subinvolution of the placental site, which is exceedingly rare. Epicentre of the lesion can help differentiate RPOC from uterine AVM but may be difficult in patients with PAS or scar pregnancy; multiphasic CT and catheter angiography are usually required. Subinvolution of the placental site appears as an enlarged uterus containing dilated, tortuous myometrial vessels at the implantation site; definitive diagnosis is usually made on pathological specimen following hysterectomy.

Uterine artery pseudoaneurysms are a rare but life-threatening cause of abnormal uterine bleeding (Figure 4). Colour Doppler demonstrates ‘yin-yang sign’ within the false aneurysm sac, representing turbulent arterial flow (Figure 4). Multiphasic CT and catheter angiography are required for confirmation, identification of culprit vessel and treatment (Figure 4).

Figure 4.

Uterine artery pseudoaneurysm and haematoma. (a) Sagittal TVUS for investigation of persistent per vaginal bleeding three months after Caesarean delivery shows a heterogeneous echogenic structure anterior to the lower uterus consistent with a haematoma (arrowheads). (b) Colour Doppler interrogation shows ‘yin-yang sign’ (arrow) within the haematoma characteristic for a pseudoaneurysm. The ‘yin-yang sign’ represents turbulent arterial flow within the false aneurysm sac. (c) Multiphasic CT was performed for further evaluation. Axial image in the arterial phase shows an arterially enhancing saccular structure arising from a branch of the left uterine artery (arrow) within the hypodense haematoma adjacent to the uterine incision, confirming the presence of a pseudoaneurysm. (d) Three-dimensional reconstruction of the arterial phase CT images shows the pseudoaneurysm and its parent vessel (arrow). (e) Digital subtraction catheter angiography re-demonstrates the uterine artery pseudoaneurysm (arrow), which was subsequently treated with coil embolisation.

Infective complications

Endometritis

CD is an independent risk factor for puerperal infection. ² Endometritis is a clinical diagnosis based on symptoms and microbiology from high vaginal swab. ⁹ TVUS may be performed to exclude an alternative diagnosis (e.g. RPOC) or when the clinical course is complicated. US features of endometritis including gas, debris and hypervascularity in the endometrial cavity are non-specific and overlap considerably with non-pathological postpartum features (Figure 1).

Superficial wound infections

Superficial abdominal wound infections can be reliably addressed with high‐frequency US, allowing distinction between cellulitis and drainable collections. ¹⁸ Cellulitis is seen as subcutaneous thickening, typically with anechoic fluid intervening between echogenic subcutaneous fat forming ‘cobblestone’ appearance with associated hyperaemia (Figure 5).

Figure 5.

Abdominal wound cellulitis. Ultrasound was requested to assess for underlying abscess at the infected abdominal wound. High-frequency ultrasound of the region of interest in the transverse plane shows linear echogenic surgical suture (arrow) and irregular hypoechoic abdominal incision (arrowheads). Anechoic fluid intervening between echogenic subcutaneous fat forms a ‘cobblestone’ appearance consistent with subcutaneous oedema.

Deep pelvic infections

Pelvic collections such as abscesses and infected haematomas have similar appearances on US, varying from cystic with internal echoes or septations to complex solid-cystic collections (Figure 6). The presence of gas within a collection, identified as echogenic foci casting ‘dirty’ posterior acoustic shadowing, is highly suggestive for infection (Figure 6). In contrast, postoperative seromas typically appear anechoic. When collections are extensive, US may be inadequate due to suboptimal acoustic windows and incomplete delineation; CT is indicated in such cases especially if patients are acutely unwell.

Figure 6.

Superinfected bladder flap haematoma and bladder flap abscess. (a) Sagittal TVUS performed seven days after Caesarean delivery for fever and sepsis demonstrates a complex mass anterior to the uterine incision (arrowheads) containing linear echogenic foci with dirty posterior acoustic shadowing (empty arrowheads) representing gas. The presence of gas within the haematoma is highly indicative of superimposed infection. (b) Contrast-enhanced CT in the sagittal plane confirms the presence of a gas-containing rim-enhancing collection in the vesicouterine space (arrowheads) continuous with the Caesarean scar (arrow). Percutaneous transabdominal drainage of the collection yielded altered blood. B = bladder. (c) Sagittal TVUS performed four days after Caesarean delivery in a different patient shows an avascular gas-containing (empty arrowheads) structure with low-level echoes and surrounding echogenic fat (arrowheads) anterior to the uterine incision. Percutaneous transabdominal drainage yielded purulent fluid consistent with bladder flap abscess.

Limitations of US and indications for cross-sectional imaging

During the puerperium, US has a limited role in the assessment of postoperative ileus, acute pulmonary embolism and ovarian vein thrombosis/thrombophlebitis, all of which are best assessed on CT. US is, however, the modality of choice for suspected lower limb deep venous thrombosis. In addition to the previously discussed indications, cross-sectional imaging is also useful when US findings are inconclusive. The most appropriate imaging modalities for common early CD complications are summarised in Table 1.

Table 1.

Imaging investigations for common early Caesarean delivery complications.

Timing	Category	Pathology	First-line imaging	Additional imaging	Definitive diagnosis
Early	Haemorrhagic	Uterine atony	If unstable: Immediate managementIf stable: TVUS or CT	N.A.	Clinical diagnosis
		Retained products of conception		N.A.	Histopathology (curettage or hysterectomy)
		Incisional site haematoma (bladder flap, subfascial)		CECT	Clinical diagnosis ± drainage
		Uterine dehiscence or rupture		If stable: Pelvic MRI	Laparotomy
		Iatrogenic vascular complications (uterine AVM, pseudoaneurysm)		Multiphasic CT	Catheter angiography
	Infective	Puerperal infection (e.g. endometritis)	TAUS + TVUS	N.A.	Clinical diagnosis ± microbiology
		Superficial wound infection	High-resolution US	N.A.	Clinical diagnosis ± microbiology
		Deep pelvic infection (infected haematoma, pelvic abscess)	TAUS + TVUS or CECT	CECT	Drainage + microbiology
	Thromboembolic	Lower limb deep venous thrombosis	US	N.A.	US
		Acute pulmonary embolism	CTPA	N.A.	CTPA
		Ovarian vein thrombosis or thrombophlebitis	CECT	N.A.	CECT
	Bowel	Postoperative ileus	Abdominal radiography	CECT ± small bowel follow-through	Clinical course + exclusion of mechanical obstruction

AVM: arteriovenous malformation; CT: computed tomography; CECT: contrast-enhanced CT; CTPA: CT pulmonary angiogram; MRI: magnetic resonance imaging; N.A.: not applicable; US: ultrasound; TAUS: transabdominal US; TVUS: transvaginal US.

Conclusion

US imaging plays an important role in the assessment of CD-related complications at various stages following delivery. To summarise, US can screen for causes of PPH and infection during the puerperium and guide further investigations; in particular, vascular complications, uterine rupture/dehiscence and deep pelvic infections often require cross-sectional imaging. Sound sonographic knowledge will facilitate accurate diagnosis, timely management and improved patient outcomes.