Post caesarean section complications conundrum: Role of imaging.

Although caesarean delivery is a safe procedure, however, with rising numbers being performed every year globally, increasing number of complications are being encountered by clinicians and radiologists. These complications can be early, occurring over first few days to weeks, or late, which can present months to years later. Also, it must be kept in mind that the normal variations of physiological involution occurring in early postpartum period can mimic pathology in many cases. Clinical history, laboratory parameters, and radiological investigations go hand in hand in identifying acute complications at the earliest, enabling early initiation of treatment. Among radiological investigations, ultrasound is the first line investigation of choice, followed by computed tomography (CT) and magnetic resonance imaging (MRI) in certain conditions which will be described and illustrated further in this article.

Caesarean section (CS) is a widely performed surgical procedure globally. A low transverse incision is generally preferred, termed lower segment caesarean section (LSCS). In modern obstetrics, there are only a few conditions where the lower uterine segment is difficult to access such as in very preterm labor, previous fistula repair, cervical cancer, or adherent placenta, where a vertical upper segment incision is performed, which is known as classical CS. 1 The normal appearance of a healed LS caesarean scar on ultrasound (USS) and MRI is shown in Figure 1. Despite being a relatively safe procedure, caesarean delivery is not free from post-procedural complications. The frequency of such complications has increased in the recent past, owing to the increased number of CS being performed every year. Clinical history, laboratory parameters, and radiological investigations go hand in hand in identifying the post-CS complications at the earliest, enabling early initiation of treatment. Post CS complications can be divided into early, which occur within the first month after CS and late, which can present months or even years later. 2 In this article, we describe the imaging findings of post-CS complications under the following subheadings: early complications, late complications, and complications that can arise in future pregnancies.

Normal findings in the early phase The early phase is defined as the first month of the postpartum period after CS. Normal physiological findings in this period include uterine enlargement, minimal fluid and air foci within the endometrial cavity 2 (Figure 2). The lower segment scar is seen as an oval or triangular, iso- to hypoechoic region between the bladder and uterus on ultrasound. CT reveals an area of low attenuation in the anterior lower segment. A small amount of air can be normally seen in the subcutaneous incision site, endometrial cavity, and urinary bladder. Early complications The two most common complications encountered in the early phase are infection and haemorrhage. 2 Patients who require radiological investigations usually present with fever, lower abdominal pain, bleeding per vaginum, abdominal distension, or hemodynamic instability. The first radiological investigation of choice is an ultrasound scan (USS). Role of ultrasound On USS, we describe an innovative, systematic “outer to inner approach” for detecting early CS complications (Figure 3). Starting from outwards, first, the abdominal wall wound should be assessed with a linear high-frequency transducer to look for any incision site collection or abscess (Figure 3b). Few air foci can be a normal finding in this location. Then, from outer to inner, specific sites should be looked for hematoma formation. The various hematomas in this order are subcutaneous hematoma, rectus sheath hematoma, subfascial hematoma, and bladder flap hematoma (Figure 3c–e). On ultrasound, hematomas have varied echogenicity, ranging from hyperechoic in the acute phase to anechoic in the chronic phase. The isoechoic hematoma in the subacute phase may be missed if not specifically looked for. Larger hematomas may also get secondarily infected and the presence of thick septa and air foci within the hematoma is highly suggestive of infection. Hematomas can be located in the subcutaneous plane at the scar site and superficial to the rectus abdominis muscle. The rectus sheath may be enlarged with hematoma within the sheath. A subfascial hematoma is an extraperitoneal hematoma that forms in the pre vesical space deep to the rectus abdominis muscle, fascia transversalis and superficial to peritoneum. 3 Bladder flap hematoma is also extraperitoneal in location and occurs between the urinary bladder and the lower uterine segment (LUS). 4 Subfascial and bladder flap hematomas should be distinguished as the latter may require a peritoneal incision. Bladder flap hematoma 5 cm indicates the possibility of uterine dehiscence. 5 From the extraperitoneal compartment in the pelvis, an extension of the hematoma may occur into the retroperitoneal space. Next, the uterus is assessed for size, endometrial cavity and scar site. The endometrial cavity should be looked for any retained placenta or blood clots. Both appear as echogenic soft tissue. Color doppler can distinguish between them by demonstrating internal vascularity in the former (Figure 4). Endometritis is more of a clinical diagnosis as sonographic features are non-specific, overlapping with normal findings such as an enlarged uterus with fluid and air within the endometrial cavity. 6 As the presence of air can be a normal finding, correlation with the patient’s clinical presentation is essential. Salpingitis is another complication, which can occur with or without endometritis (Figure 5). The scar site should be specifically evaluated for the intactness, especially in patients with clinical worsening. It is difficult radiologically to differentiate between uterine dehiscence and uterine rupture and the key features are described below. Uterine dehiscence A separation of the endometrium and myometrium with an intact serosa is suggestive of uterine dehiscence. 2,3 In the postpartum patient with clinical deterioration, a bladder flap hematoma greater than 5 cm diameter and large pelvic hematomas should raise the suspicion of scar dehiscence 2,3,6 (Figure 6). The intactness of the serosa is better visualized on MRI or CT (oblique reformatted images perpendicular to the incision scar). In cases of uterine dehiscence, the treatment is usually conservative. Uterine rupture There is complete separation of all the layers of the uterine wall, including the serosa. 6 This results in a communication between the endometrial and peritoneal cavities, hematoma formation, and hemoperitoneum (Figure 7). There is a lack of standardized diagnostic criteria for uterine rupture. However, the demonstration of air between the endometrial cavity and the extrauterine collection in the presence of hemoperitoneum is highly suggestive of rupture. 2,3 Cross-sectional imaging better documents the disruption in all the layers of the uterus (Figure 7). Color doppler should be routinely used for assessment of the surgical incision site, especially in cases of vaginal bleeding. It can diagnose a pseudoaneurysm which shows high velocity, bidirectional flow with classical yin-yang sign and can be managed by angioembolization 6 (Figure 8). The pelvis and abdomen should be evaluated for the presence of free fluid. Echogenic debris within the fluid is suggestive of hemoperitoneum. The ultrasound checklist for early complications is summarized in Table 1. Table 1. EARLY COMPLICATIONS: USS CHECKLISTIncision site: Collection - Hematoma: presence/ absence - If present, look for - Site (subcutaneous/ rectus sheath/ subfascial/bladder flap/ pelvic or retroperitoneal extension) Size Echogenicity (correlates with chronicity) - Thick septa, air foci within hematoma-Present/absent (If present suggests superadded infection) - Endometrial cavity: air foci/ fluid/ echogenic soft tissue (blood clots/ retained placenta) Scar site: focal discontinuity/ pseudoaneurysm Pelvic free fluid, hemoperitoneum | Role of CT Contrast-enhanced CT has various advantages including its ability to provide cross-sectional anatomy, multiplanar reconstructions and fast acquisition. CT is better than USS in the assessment of infected hematomas (by demonstrating air foci, peripherally enhancing thick wall) and extent evaluation of pelvic abscesses 2 (Figure 9). Hematomas in the extraperitoneal location if large can extend to the retroperitoneum. Such large hematomas require cross-sectional imaging for extent estimation before surgical evacuation (Figure 10). While doing CT for evaluation of large pelvic hematomas, the arterial phase should be acquired to look for active contrast extravasation, suggesting active bleeder, which can be embolized by angiography. 7 CT also acts as a problem solver in clinically suspect cases of uterine rupture. In uterine rupture, the endometrial cavity is seen directly opening into the peritoneal cavity, with air foci and blood leaking out and associated hemoperitoneum 2,4 (Figure 7). Role of MRI MRI may play a role in differentiating uterine dehiscence and uterine rupture because of its ability to distinguish uterine layers separately (Figure 7). Serosa will be torn in the latter and intact in the former. Management is conservative in uterine dehiscence, while urgent surgical exploration is needed for uterine rupture. 3 Also, MRI has a role in demonstrating adherence in cases of retained placenta post-CS 8 (Figure 4). Late complications Late complications occur months to years after CS. Patients can present with abnormal uterine bleeding (AUB) and chronic pelvic pain and the common etiologies are abdominal wall endometriosis and caesarean scar defect. The first radiological investigation of choice is ultrasound, followed by MRI in some cases. On USS, abdominal wall assessment should be done first, with a linear high-frequency transducer. USS reveals irregular, solid, hypoechoic soft tissue at the abdominal scar site with or without internal vascularity in abdominal wall endometriosis (Figure 11). MRI can give a definite diagnosis by demonstrating T1 hyperintense areas due to subacute blood products (Figure 11). MRI is the modality of choice to assess the local extent and deep infiltrating endometriotic implants. 6 Then uterine scar integrity should be assessed by transvaginal ultrasound (TVS). Caesarean scar defect (CSD), also known as uterine niche, is the most common and least known late complication of CS. It refers to focal thinning of uterine myometrium at the scar site to which endometrium gets adhered. There is chronic stagnation of mucus and blood in the niche which becomes a hyperemic inflamed zone leading to chronic pelvic pain and AUB. 2 USS shows a triangular hypoechoic defect at scar site 9 (Figure 12). T2 -weighted MRI images help in better assessment of residual myometrial thickness (Figure 12). Grading of CSD can be done by calculating the ratio of myometrial thickness at the CSD site to the adjacent myometrial thickness. 10 If this ratio is less than or equal to 50%, it is categorized as severe CSD. 10,11 As in other surgeries, intraabdominal adhesions are also a common long-term complication post-CS. They can lead to bowel complications, chronic pelvic pain and even infertility adding to the long-term morbidity. Adhered uterus with distorted anatomical relations can also lead to poor visualization of the uterus on TVS. Complications in future pregnancies These complications are usually related to the previous myometrial scar site and include ectopic pregnancy, retained products of conception and abnormalities of placentation. Ectopic pregnancy at the scar site This is a rare form of ectopic pregnancy and is potentially life-threatening. The endometrial and cervical cavities are empty, and the gestational sac is in the lower segment myometrium. 2 On color doppler, there is evidence of arterial, low-resistance peri-trophoblastic blood flow between the bladder and the lower uterine segment 12 (Figure 13) It is important to differentiate a cervical ectopic pregnancy from a scar site ectopic. The cervical ectopic is located in the endocervical canal and not the scar site myometrium with trophoblastic flow seen adjacent to the gestational sac. MRI can be used as a problem-solving tool and reveals the gestational sac located in the myometrium of the lower uterine segment on sagittal T2 -weighted images (Figure 13). Retained products of conception (RPOC) These can occur at the scar site post-termination of the scar site ectopic pregnancy. Ultrasound reveals an irregular cystic area or an echogenic mass with trophoblastic, high-velocity, low-resistance arterial flow 13 (Figure 14). MRI can demonstrate T1 hyperintense blood products at the scar site (Figure 14). Abnormal placentation This includes placenta accreta, increta and percreta, depending on the depth of placental invasion into myometrium. 2 Prior caesarean delivery and placenta previa are the two most important risk factors for an adherent placenta. The mildest form is placenta accreta, in which there is implantation on the uterine wall. Placenta increta indicates a deep myometrial invasion; with extension through the serosa of the uterus in placenta percreta. The placenta appears heterogeneous with numerous placental lacunae, uterine contour bulge, loss of retroplacental clear space, loss of myometrial interface at the scar site and markedly increased vascularity on USS 2,14 (Figure 15) MRI reveals similar findings with heterogeneous placenta and T2 hypointense bands with contour bulge 15 (Figure 15). The loss of myometrial interface with extension into bladder and parametrium is also well seen on MRI. Scar site adherence is a problem peculiar to post-LSCS pregnancies. There is evidence of irregular myometrial interface at the scar site with a markedly heterogenous placenta which is located anteriorly.

Ultrasound is the baseline investigation of choice in imaging both early and late complications following caesarean delivery. Using a systematic checklist approach while doing the ultrasound, allows for a thorough assessment of the case. Red flag imaging findings in the early phase are large bladder flap hematoma and discontinuity of lower uterine segment suggesting uterine rupture, which warrants early laparotomy and uterine repair/hysterectomy. A previous history of caesarean section should always be elicited while imaging a patient with chronic pelvic pain and irregular vaginal bleeding with a special focus on CS defect and abdominal wall endometriosis. Future pregnancy ultrasound scans should carefully evaluate CS scar and look for scar ectopic and adherent placenta. Contributor Information Ankita Dhiman Nair, Email: [email protected]. Smita Manchanda, Email: [email protected]. Shivanand Gamanagatti, Email: [email protected]. Garima Kachhawa, Email: [email protected]. Neerja Bhatla, Email: [email protected].

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