Acute and chronic complications of cesarean delivery: An update for the general radiologist

Acute complications of C-section classically include 5 , 11 : • Infections (endometritis, wound infection, abscess formation) • Hemorrhage and hematomas • Uterine dehiscence • Uterine rupture • Injury to adjacent organs (bladder, ureters, bowel) Infections (endometritis, wound infection, abscess formation) Hemorrhage and hematomas Uterine dehiscence Uterine rupture Injury to adjacent organs (bladder, ureters, bowel) In the acute setting, US and CT are the most commonly employed modalities. US may be performed using a transabdominal or transvaginal (TVUS) technique. A systematic outer to inner approach has been proposed, in which evaluation starts at the level of the abdominal wall and progresses towards the uterus [13] . Contrast-enhanced CT is recommended in order to optimize visualization of the uterus as well as to better appreciate infectious collections or hematomas and document active bleeding. However, because of the hemodynamic changes associated with pregnancy superimposed on those caused by surgery, resulting in relative fluid overload, optimal enhancement is not always straightforward to achieve and specific adjustments may help in improving image quality [5] . Some modifications, including high concentration, high volume, and high rate of contrast injection followed by saline flush, appear to be useful but have become standard in modern CT scanners. Although the protocol must be tailored to the specific clinical question in each individual patient and designed in order to obtain diagnostic images while minimizing radiation exposure in a population of relatively young women, some considerations can be made to guide general practice. An initial unenhanced scan followed by arterial and venous phase scans is usually appropriate; a delayed scan can be added when deemed necessary and is mainly required for the evaluation of the urinary tract (outlining any dilatation or injury) or when active bleeding is suspected, particularly to identify subtle extravasation of contrast [14] . When injury to the bladder is suspected, it is preferable to obtain a dedicated CT cystography because intravenous contrast excreted by the kidneys in the delayed phase of a conventional abdominopelvic CT may not exert enough pressure to detect bladder rupture [15] . Depending on local practice, an alternative could be represented by conventional cystography, which is based on fluoroscopy and delivers a reduced radiation dose to the patient. While its sensitivity and specificity in detecting and characterizing injury may be comparable to that of CT cystography [16] , the latter offers superior anatomical detail (especially for the delineation of possible fistulous tracts) and can be conveniently performed following the standard phases without transferring the patient. Of note, conventional cystography can be a valuable option in the longitudinal monitoring of bladder injuries. Infections are among the most common acute complications of C-section; C-section is associated with a risk of endometritis that may be approximately 10–20 times higher compared with vaginal birth [17] . Endometritis remains mostly a clinical diagnosis with aspecific imaging findings. US is often performed first: sonographic findings include enlargement of the uterus, thickening and heterogeneity of the endometrium with increased vascularity on Doppler interrogation, and presence of fluid and/or gas within the endometrial cavity [18] . Recently, two new findings have been investigated to improve diagnostic accuracy in puerperal endometritis, known as subserosal hypoechoic rim sign (presence of a hypoechoic band between the myometrium and serosa reflecting inflammatory edema or pus) and endomyometrial junction indistinctness, with reported high sensitivity and specificity despite non-negligible interobserver variations [19] . CT features are similar to those described for US, namely thickening and heterogeneous enhancement of the endometrium with a variable degree of cavitary distension ( Fig. 2 ); these must be differentiated from normal post-operative changes [18] . CT can detect complications including pyometra, abscess formation, and septic thrombophlebitis. A walled-off collection with peripheral enhancement and internal gas bubbles is consistent with an abscess. Abscesses can form within the pelvis but also along the planes of the abdominal wall in relation to the surgical incision. Septic thrombophlebitis is an infrequent but possibly underestimated complication of C-section, which can involve the ovarian veins or other deep veins of the pelvis [20] . CT or MRI demonstrate enlarged veins with enhancement of their walls, containing an internal thrombus, often with surrounding inflammatory stranding [5] . In very rare cases, infection may progress to peritonitis ( Fig. 3 ). Fig. 2 Endometritis following C-section. (a) Transverse US of the uterus showing a thickened heterogeneous endometrium and an indistinct junction with the myometrium; there are also several hyperechoic foci with posterior acoustic shadowing representing gas bubbles within the endometrial cavity and a hypoechoic band between the myometrium and serosa (arrow). (b) Sagittal CT in venous phase revealing a collapsed endometrial cavity with rare internal gas bubbles and a markedly thickened endometrium (arrow). The cesarean scar is evident in the lower uterine segment as a linear area of hypodensity (circle) and the bladder is catheterized. Fig. 3 Tuberculosis complicating a case of C-section. (a, b, c) Axial CT images approximately 2 weeks after C-section in a young woman presenting to the emergency department with hyperpyrexia (40 °C) showing a large collection in the pouch of Douglas, with abnormal enhancement of the peritoneal leaflets (arrowhead) as well as a further collection in the subcutaneous tissues of the anterior abdomen (arrow); the patient was operated and tuberculous peritonitis was confirmed. (d) MIP coronal reconstruction of the urographic phase of the same CT revealing bilateral hydronephrosis with ureteric strictures due to the enlarged uterus and surrounding collections. (e) MIP coronal reconstruction of the lung apices in the same patient showing multiple tiny miliary nodules. (f) Axial CT scan of the chest revealing an additional pleural tuberculoma on the left (arrow). (g) Surgical picture demonstrating innumerable millet seed-sized nodules along the peritoneal surface of the bowel wall reflecting tuberculous dissemination, (h, i) Axial and coronal CT images of the neck showing a further manifestation of tuberculosis in this patient, who developed a large necrotic lymph node (arrows) extending through the subcutaneous tissues and almost fistulizing to the skin. Endometritis following C-section. (a) Transverse US of the uterus showing a thickened heterogeneous endometrium and an indistinct junction with the myometrium; there are also several hyperechoic foci with posterior acoustic shadowing representing gas bubbles within the endometrial cavity and a hypoechoic band between the myometrium and serosa (arrow). (b) Sagittal CT in venous phase revealing a collapsed endometrial cavity with rare internal gas bubbles and a markedly thickened endometrium (arrow). The cesarean scar is evident in the lower uterine segment as a linear area of hypodensity (circle) and the bladder is catheterized. Tuberculosis complicating a case of C-section. (a, b, c) Axial CT images approximately 2 weeks after C-section in a young woman presenting to the emergency department with hyperpyrexia (40 °C) showing a large collection in the pouch of Douglas, with abnormal enhancement of the peritoneal leaflets (arrowhead) as well as a further collection in the subcutaneous tissues of the anterior abdomen (arrow); the patient was operated and tuberculous peritonitis was confirmed. (d) MIP coronal reconstruction of the urographic phase of the same CT revealing bilateral hydronephrosis with ureteric strictures due to the enlarged uterus and surrounding collections. (e) MIP coronal reconstruction of the lung apices in the same patient showing multiple tiny miliary nodules. (f) Axial CT scan of the chest revealing an additional pleural tuberculoma on the left (arrow). (g) Surgical picture demonstrating innumerable millet seed-sized nodules along the peritoneal surface of the bowel wall reflecting tuberculous dissemination, (h, i) Axial and coronal CT images of the neck showing a further manifestation of tuberculosis in this patient, who developed a large necrotic lymph node (arrows) extending through the subcutaneous tissues and almost fistulizing to the skin. Hemorrhage is another recognized acute complication of C-section. Bleeding can originate from the uterus, especially in cases of uterine atony, from the lower portion of the genital tract as a consequence of trauma, but also from extrauterine sources [14] . Hemorrhage can lead to the formation of hematomas, which tend to occur in predictable locations. When bleeding does not originate from uterine or ovarian vessels, the following types of hematomas can form: subcutaneous hematomas, rectus sheath hematomas, and subfascial hematomas ( Fig. 4 ). Rectus sheath and subfascial hematomas occur as a consequence of laceration of inferior epigastric vessels [11] . Subfascial hematomas are extra-peritoneal collections of blood that form posterior to the rectus abdominis but anterior to the peritoneum; they are continuous with the prevesical space [5] . A large amount of blood can accumulate within this potential space so they are critical to recognize. Rectus sheath hematomas develop within the substance of the muscle and tend to occur in an infraumbilical location when related to the incision. This makes them more dangerous because the aponeurosis of the transversus abdominis and internal oblique is lost below the arcuate line of Douglas, with possible involvement of the prevesical space or rupture into the peritoneal cavity [14] . Bladder flap hematomas are instead found between the bladder and lower uterine segment ( Fig. 5 ) [21] . Smaller hematomas can be treated conservatively, while larger hematomas may require percutaneous drainage or surgical evacuation. It is important to underline that operative management of bladder flap hematomas requires opening of the peritoneum [5] . On US, hematomas appear as heterogeneous complex collections, generally with hyperechoic areas [11] . When acute, hematomas are hyperdense (70–90 HU) on non-contrast CT [5] . Contrast-enhanced scans can instead depict active bleeding as extravasation of contrast material in the arterial phase, with further pooling in the venous and delayed phases ( Fig. 6 ); this may require endovascular treatment [14] . Hematomas can also be complicated by infection. While acknowledging that it may not be easy to differentiate a sterile from an infected hematoma on CT, some indicative signs of superinfection include: (1) presence of gas bubbles within the collection; (2) development of well-defined and often thick walls displaying rim enhancement; (3) evidence of inflammation/edema within surrounding tissues. Fig. 4 Schematic representation of the various possible locations of hematomas (or collections) complicating C-section with selected examples. (a) Sagittal CT showing a subcutaneous collection (dashed arrow) in a patient who recently underwent C-section as shown also by the hypodense linear scar (arrowhead). (b) Sagittal CT showing a rectus sheath hematoma (outlined in white). (c) Sagittal CT showing a subfascial hematoma (outlined in red) as well as a small bladder flap hematoma (outlined in white). (d) Sagittal CT demonstrating a larger bladder flap hematoma (> 4 cm; asterisk) between the uterus (ut) and bladder (bl). Note: schematic diagram previously published in 10.26044/ecr2025/C-20586. Fig. 5 TVUS image showing a heterogeneous predominantly hyperechoic bladder flap hematoma, compressing the bladder. Note: figure previously published in 10.26044/ecr2025/C-20586. Fig. 6 Axial CT scan in precontrast (a), arterial (b), venous (c), and delayed (d) phase showing a heterogeneous rectus sheath hematoma with evidence of active bleeding as shown by the presence of a contrast blush that increases in size from arterial to venous to delayed phase (arrow). Note: figure previously published in 10.26044/ecr2025/C-20586. Schematic representation of the various possible locations of hematomas (or collections) complicating C-section with selected examples. (a) Sagittal CT showing a subcutaneous collection (dashed arrow) in a patient who recently underwent C-section as shown also by the hypodense linear scar (arrowhead). (b) Sagittal CT showing a rectus sheath hematoma (outlined in white). (c) Sagittal CT showing a subfascial hematoma (outlined in red) as well as a small bladder flap hematoma (outlined in white). (d) Sagittal CT demonstrating a larger bladder flap hematoma (> 4 cm; asterisk) between the uterus (ut) and bladder (bl). Note: schematic diagram previously published in 10.26044/ecr2025/C-20586. TVUS image showing a heterogeneous predominantly hyperechoic bladder flap hematoma, compressing the bladder. Note: figure previously published in 10.26044/ecr2025/C-20586. Axial CT scan in precontrast (a), arterial (b), venous (c), and delayed (d) phase showing a heterogeneous rectus sheath hematoma with evidence of active bleeding as shown by the presence of a contrast blush that increases in size from arterial to venous to delayed phase (arrow). Note: figure previously published in 10.26044/ecr2025/C-20586. Uterine dehiscence and rupture are rare complications of C-section. Uterine dehiscence is defined as incomplete rupture of the uterine wall, with preservation of the overlying serosal layer, while uterine rupture is characterized by complete separation of all layers of the uterus [5] . Uterine dehiscence can be very difficult to diagnose on imaging because myometrial discontinuity in asymptomatic patients may be considered a normal finding in the first days after C-section [21] . If available, MRI could be a valuable adjunct to the diagnostic process as it can better distinguish the three layers of the uterine wall with an intact serosa appearing as a thin T2-hypointense line [12] . By contrast, rupture creates a more dramatic picture with direct communication between the uterus and peritoneal cavity. US is usually the first modality used when dehiscence or rupture is suspected, although CT can be helpful in selected cases: findings include visible defects in the uterine wall, associated concomitant hematomas, hemoperitoneum or free fluid in the abdominal cavity with possible extension of gas from the endometrium to the peritoneum, as well as intraperitoneal fetal parts ( Fig. 7 ) 5 , 22 . Detection of a continuous pathway leading from the endometrial cavity to an extrauterine collection is pathognomonic for rupture [11] . Fig. 7 Sonographic findings of uterine rupture, including deformed myometrium with hematoma and defect in the uterine wall (solid arrow) as well as intraperitoneal free fluid (asterisk) and intraperitoneal fetal parts (dashed arrow). Note: figure previously published in 10.26044/ecr2025/C-20586. Sonographic findings of uterine rupture, including deformed myometrium with hematoma and defect in the uterine wall (solid arrow) as well as intraperitoneal free fluid (asterisk) and intraperitoneal fetal parts (dashed arrow). Note: figure previously published in 10.26044/ecr2025/C-20586. Injury to adjacent organs is another possible complication related to the surgical steps of C-section. The bladder is the most common organ damaged at time of C-section ( Fig. 8 ) [23] . As stated before, CT cystography is preferred to detect injury as extravasation of contrast in either intraperitoneal or extraperitoneal location. The ureters and bowel can also be injured during the procedure, with the latter possibly leading to perforation. Fig. 8 Intraperitoneal rupture of the bladder after C-section. (a) Sagittal CT image in the urographic phase showing extravasation of contrast from the anterior wall of the bladder. (b, c) Axial CT images in left lateral decubitus (to avoid compression of the inferior vena cava and abdominal aorta by the enlarged uterus) confirm the defect and enable to detect the spread of iodinated urine in the peritoneal cavity; in this case, it was not necessary to perform a proper CT cystography as the lesion could already be identified with the standard abdominal protocol. (d, e) Frontal and lateral projections from a follow-up voiding cystography taken approximately 1 month later revealing healing of the lesion with no extravasation of contrast. Intraperitoneal rupture of the bladder after C-section. (a) Sagittal CT image in the urographic phase showing extravasation of contrast from the anterior wall of the bladder. (b, c) Axial CT images in left lateral decubitus (to avoid compression of the inferior vena cava and abdominal aorta by the enlarged uterus) confirm the defect and enable to detect the spread of iodinated urine in the peritoneal cavity; in this case, it was not necessary to perform a proper CT cystography as the lesion could already be identified with the standard abdominal protocol. (d, e) Frontal and lateral projections from a follow-up voiding cystography taken approximately 1 month later revealing healing of the lesion with no extravasation of contrast.

Michele Imbriani: Validation, Supervision. Elena Siopis: Writing – review & editing, Writing – original draft, Supervision, Resources, Conceptualization. Matteo Laruccia: Writing – review & editing, Supervision. Franco Demaria: Validation, Supervision. Maria Segata: Writing – review & editing, Supervision, Data curation. Silvia Gazzotti: Writing – review & editing, Writing – original draft, Data curation, Conceptualization.

Chronic (or subacute) complications of C-section classically include 5 , 11 : • Postoperative adhesions • Incisional hernias • Caesarean scar defect, also known as isthmocele or caesarean scar niche • Placenta accreta spectrum (PAS) disorders • Caesarean scar ectopic pregnancy • Caesarean scar retained products of conception (RPOC) • Abdominal wall endometriosis Postoperative adhesions Incisional hernias Caesarean scar defect, also known as isthmocele or caesarean scar niche Placenta accreta spectrum (PAS) disorders Caesarean scar ectopic pregnancy Caesarean scar retained products of conception (RPOC) Abdominal wall endometriosis In the chronic setting, MRI is generally preferred to CT and plays an important role in complementing sonographic findings. A standard protocol should include high-resolution T2-weighted (T2w) sequences in sagittal, axial, and coronal planes along the axes of the uterus as well as diffusion-weighted imaging (DWI) sequences (with low- and high b-values and ADC map; at our institution b = 0 s/mm 2 and b = 1000 or 1500 s/mm 2 ) and T1-weighted (T1w) (+/- fat saturation) sequences in selected cases [12] . Specific technical considerations apply to the assessment of PAS disorders, as explained in the dedicated later section [24] . Postoperative adhesions can occur after C-section as well as any type of abdominal or pelvic surgery and lead to bowel obstruction, chronic pain, infertility, and problems with subsequent pregnancies [5] . After the first C-section, 24–73% of women may experience adhesions; this percentage is reported to increase after each subsequent procedure [25] . Adhesions can tether the lower uterine segment towards the anterior abdominal wall leading to abnormal orientation of the uterus that may be more difficult to evaluate on TVUS [5] . On MRI, adhesions appear as T2-hypointense bands, which may form at various sites, most commonly between the uterus and bladder or between the uterus and anterior abdominal wall [12] . Adhesions that form inside the uterus are referred to as synechiae and can be identified as hypointense streaks (reflecting their fibrous content) within the hyperintense endometrial cavity on T2w images [26] . Similarly, incisional hernias (laparoceles) should be considered as potential chronic complications of any type of abdominal or pelvic surgery, including C-section, with a reported occurrence ranging from 0% to 5.6% in this setting [27] . They reflect a defective or incomplete closure of the abdominal musculoaponeurotic fascia, favored by several factors including surgical wound infection, obesity, or conditions that increase intra-abdominal pressure. Of note, incisional hernias can infrequently present acutely, within the first days after C-section, particularly in cases of early fascial dehiscence or local infection ( Fig. 9 , Fig. 10 ). Fig. 9 Laparocele presenting 7 days after C-section on coronal (a), sagittal (b), and axial (c) CT acquired in venous phase. There is an ileal loop (white solid arrow) herniating through a defect in the anterior abdominal wall corresponding to the location of the surgical incision; the affected loop has diminished contrast enhancement and abundant surrounding fluid with small gas bubbles (white dashed arrows), consistent with strangulation. There is also evidence of dilatation of small bowel loops upstream to the hernia with some gas-fluid levels in keeping with obstruction. The uterus still appears enlarged (asterisk) and the endometrial cavity is filled with blood and gas. In addition, there is a small amount of free fluid within Douglas pouch (red solid arrow). The patient was managed with surgical resection of the ileal loop. Fig. 10 Sagittal (a, c) and axial (b) CT images in venous phase revealing a large laparocele presenting soon after C-section, as shown by the enlarged and hyperemic uterus with retained clots within the endometrial cavity (asterisk). The bowel is distended by gas with some loops herniating through the laparocele. Laparocele presenting 7 days after C-section on coronal (a), sagittal (b), and axial (c) CT acquired in venous phase. There is an ileal loop (white solid arrow) herniating through a defect in the anterior abdominal wall corresponding to the location of the surgical incision; the affected loop has diminished contrast enhancement and abundant surrounding fluid with small gas bubbles (white dashed arrows), consistent with strangulation. There is also evidence of dilatation of small bowel loops upstream to the hernia with some gas-fluid levels in keeping with obstruction. The uterus still appears enlarged (asterisk) and the endometrial cavity is filled with blood and gas. In addition, there is a small amount of free fluid within Douglas pouch (red solid arrow). The patient was managed with surgical resection of the ileal loop. Sagittal (a, c) and axial (b) CT images in venous phase revealing a large laparocele presenting soon after C-section, as shown by the enlarged and hyperemic uterus with retained clots within the endometrial cavity (asterisk). The bowel is distended by gas with some loops herniating through the laparocele. Cesarean scar defects develop because of tethering of the endometrium at the site of a previous caesarean scar, creating a niche where blood or fluid may accumulate ( Fig. 11 a-b) [5] . These defects can cause abnormal uterine bleeding, dysmenorrhea, and chronic pain or infertility [28] . Because the exact definition differs among studies, the prevalence of this complication is difficult to estimate, but may be as high as 70–84% [29] . TVUS and MRI can both demonstrate the diagnosis; distension of the uterine cavity with gel or saline facilitates the identification of the defect [30] . This presents as focal thinning or indentation of the myometrium, with a threshold of 1–2 mm generally accepted for diagnosis and most often with a semicircular or triangular shape [31] . On US, the defect may be hypoechoic or anechoic when filled with fluid. On MRI, the niche instead appears hyperintense in T2w sequences; of note, multiple defects may be present, especially following repeated C-sections [12] . MRI is a reliable tool to grade the severity of the defect by comparing myometrial thickness at the level of the scar with that of the adjacent myometrium ( Fig. 11 c): the defect can be considered severe when this ratio is <50% [11] . Fig. 11 Cesarean scar niche. (a) Sagittal T2w MR image depicting a focal defect at the site of the previous cesarean scar. (b) Axial T1w SPIR image revealing that the defect has a high signal, being filled with blood. (c) Sagittal T2w MR image showing a triangular cesarean scar defect; the corresponding width (yellow marker) and depth (pink marker) of the niche can be measured precisely. The severity of the defect can be graded by comparing the thickness of the residual myometrium at the level of the defect (green marker) to that of the normal adjacent myometrium (blue marker). Note: part c previously published in 10.26044/ecr2025/C-20586. Cesarean scar niche. (a) Sagittal T2w MR image depicting a focal defect at the site of the previous cesarean scar. (b) Axial T1w SPIR image revealing that the defect has a high signal, being filled with blood. (c) Sagittal T2w MR image showing a triangular cesarean scar defect; the corresponding width (yellow marker) and depth (pink marker) of the niche can be measured precisely. The severity of the defect can be graded by comparing the thickness of the residual myometrium at the level of the defect (green marker) to that of the normal adjacent myometrium (blue marker). Note: part c previously published in 10.26044/ecr2025/C-20586. PAS disorders occur as a result of abnormal implantation of the placenta to the uterine wall, believed to be caused by a defect at the interface between the myometrium and the endometrium [32] . Several forms of PAS disorders exist based on the depth of trophoblast invasion and the focus is now shifting towards distinguishing between myoadherent and myoinvasive disease [33] . According to the current FIGO classification, grade 1 represents myoadherent placenta with superficial adhesion of placental villi to the myometrium, while grades 2 and 3 denote myoinvasive disease, which may occur with an intact serosa (grade 2) or with involvement of the serosa (grade 3a), bladder (grade 3b) or other adjacent tissue or organ (grade 3c) [24] . The frequency of PAS disorders is rising worldwide and this phenomenon is related to the increasing performance of C-section, which is a major risk factor for PAS disorders in subsequent pregnancies [34] . This may be caused by an alteration of the structural architecture of the uterus induced by surgery, leading to anisotropy and disrupted orientation of its fibers [35] . The diagnosis is generally achieved with US as it has excellent sensitivity and specificity, approaching 91 and 97%, respectively, according to a large meta-analysis [36] . Women are routinely screened for abnormal placentation during the second trimester; however, MRI may be helpful as an adjunct tool especially when sonography is inconclusive or when the placenta is posterior [5] . The following sonographic features are consistent with invasive placentation: (1) visualization of placental tissue beyond the uterine cavity; (2) abnormalities at the placental-uterine interface including loss of the hypoechoic retroplacental (clear) zone; (3) reduced myometrial thickness in the lower segment; (4) abnormal Doppler findings with increased vascularity; (5) abnormal placental structure with numerous large or irregular lacunae, possibly connected to a feeding vessel ( Fig. 12 ) 37 , 38 . For what concerns MRI, it is important to keep in mind that the optimal time to evaluate invasive placentation is between 28 and 32 weeks of gestation [24] . The basic protocol relies on T2w sequences in three planes combined with an axial or 3D T1w sequence; DWI and balanced steady-state free precession (b-SSFP) are also recommended to clarify the degree of invasion and are best performed in the most convenient plane for each individual case [33] . DWI is especially useful to define the border between the myometrium and placenta, which may not be easily discernible on T2w/b-SSFP images as the former becomes congested later in gestation. At low b-values, the placenta and myometrium have similar signal intensities, while at high b-values the placenta retains high signal intensity while the myometrium shows low signal intensity ( Fig. 13 ) [24] . Overall, the placenta should be homogeneous and have a moderately hyperintense signal intensity on T2w images relative to the myometrium, with smooth borders. A combination of the following features in the appropriate clinical context aids in establishing the diagnosis of PAS disorders: (1) intraplacental T2-dark bands; it should be noted that both normal blood vessels and intraplacental bands are hypointense on T2w images while bands remain hypointense on b-SSFP sequences with vessels appearing hyperintense ( Fig. 14 ); (2) uterine-placental bulge; (3) myometrial thinning over the placenta (to < 1 mm or not visible at all); (4) bladder wall interruption; (5) focal exophytic mass breaking through the serosa; (6) loss of T2-hypointense retroplacental line; (7) abnormal vascularization of the placental bed ( Fig. 15 ) [24] . Fig. 12 Sonographic features of invasive placentation. (a, b) TVUS images in B-mode and HD-flow Color-Doppler mode in a case of placenta percreta showing focal myometrial thinning with loss of retroplacental clear zone and multiple abnormal placental lacunae with increased vascularity and internal turbulent flow. (c) 3D US reconstruction of abnormal placental vessels. (d) Further TVUS image in B-mode highlighting that the placenta is also previa, completely covering the internal os and cervix (between yellow markers). (e) Further TVUS image in HD-flow Color-Doppler mode showing bridging vessels and invasion of the bladder by the abnormal placenta. (f) Surgical specimen demonstrating a gravid uterus with frank evidence of placental invasion. Note: figure parts previously published in 10.26044/ecr2024/C-24467. Fig. 13 Utility of DWI in the assessment of PAS. Sagittal T2w (a) and coronal SSFP (b) images revealing a heterogeneous placenta with bulging, bladder tenting, and multiple dark bands. Sagittal T2w (c) image confirming that the myoinvasive placenta is also complete previa. The red line corresponds to the plane of images d-f while the white line to the plane of images g-h. (d-e) DWI images showing that the cervix (dashed arrow) may appear to be surrounded by the placenta at low b-values (solid arrow), while signal loss at high b-values confirms that it is lined by myometrium, excluding invasion at that level, as shown also in the T2-DWI fusion map. (g) DWI image showing that few millimeters cranially the internal os (dashed arrow) is invaded by placental tissue, which retains high intensity, as confirmed by the T2-DWI fusion map (h). Fig. 14 Utility of b-SSFP sequences in the assessment of PAS. T2w (a) and b-SSFP (b) coronal images in a patient with a myoinvasive placenta, demonstrating a bulging aspect and bladder tenting (light blue arrow). Vessels (red arrow) appear hyperintense in b-SSFP sequences while dark bands (white arrow) can be detected in T2w sequences and remain hypointense in b-SSFP sequences, due to fibrin deposition from hemorrhage and infarct. Fig. 15 Placenta percreta complicated by thrombosis after C-section. (a) Sagittal T2w MR image showing a bulky placenta with bladder tenting and dark bands (arrowhead). (b) Sagittal DWI MR image revealing a focal area of suspected invasion of the bladder serosa by the placenta. (c) Axial T2w MR image confirming invasive placentation with evidence of multiple dark bands (arrowheads). (d) Because of the diagnosis of placenta percreta, the patient was managed with balloon occlusion of the hypogastric arteries prior to C-section. (e, f) Arterial phase taken soon after surgery revealing extensive thrombosis of the left external iliac artery extending proximally to the common iliac artery and distally to the popliteal artery; there is also minor thrombosis of the ipsilateral internal iliac artery. (g) 3D reconstruction of the CT scan better depicting the extent of the thrombosis. (h) Surgical specimen of the retrieved thrombus. (i-k) Upon revision of the MR images, a focal nodule characterized by isointensity to the placenta on T2w SPIR images (i) and diffusion restriction on DWI (j) and ADC (k) was noted, consistent with the chorioangioma found on histopathologic examination. Sonographic features of invasive placentation. (a, b) TVUS images in B-mode and HD-flow Color-Doppler mode in a case of placenta percreta showing focal myometrial thinning with loss of retroplacental clear zone and multiple abnormal placental lacunae with increased vascularity and internal turbulent flow. (c) 3D US reconstruction of abnormal placental vessels. (d) Further TVUS image in B-mode highlighting that the placenta is also previa, completely covering the internal os and cervix (between yellow markers). (e) Further TVUS image in HD-flow Color-Doppler mode showing bridging vessels and invasion of the bladder by the abnormal placenta. (f) Surgical specimen demonstrating a gravid uterus with frank evidence of placental invasion. Note: figure parts previously published in 10.26044/ecr2024/C-24467. Utility of DWI in the assessment of PAS. Sagittal T2w (a) and coronal SSFP (b) images revealing a heterogeneous placenta with bulging, bladder tenting, and multiple dark bands. Sagittal T2w (c) image confirming that the myoinvasive placenta is also complete previa. The red line corresponds to the plane of images d-f while the white line to the plane of images g-h. (d-e) DWI images showing that the cervix (dashed arrow) may appear to be surrounded by the placenta at low b-values (solid arrow), while signal loss at high b-values confirms that it is lined by myometrium, excluding invasion at that level, as shown also in the T2-DWI fusion map. (g) DWI image showing that few millimeters cranially the internal os (dashed arrow) is invaded by placental tissue, which retains high intensity, as confirmed by the T2-DWI fusion map (h). Utility of b-SSFP sequences in the assessment of PAS. T2w (a) and b-SSFP (b) coronal images in a patient with a myoinvasive placenta, demonstrating a bulging aspect and bladder tenting (light blue arrow). Vessels (red arrow) appear hyperintense in b-SSFP sequences while dark bands (white arrow) can be detected in T2w sequences and remain hypointense in b-SSFP sequences, due to fibrin deposition from hemorrhage and infarct. Placenta percreta complicated by thrombosis after C-section. (a) Sagittal T2w MR image showing a bulky placenta with bladder tenting and dark bands (arrowhead). (b) Sagittal DWI MR image revealing a focal area of suspected invasion of the bladder serosa by the placenta. (c) Axial T2w MR image confirming invasive placentation with evidence of multiple dark bands (arrowheads). (d) Because of the diagnosis of placenta percreta, the patient was managed with balloon occlusion of the hypogastric arteries prior to C-section. (e, f) Arterial phase taken soon after surgery revealing extensive thrombosis of the left external iliac artery extending proximally to the common iliac artery and distally to the popliteal artery; there is also minor thrombosis of the ipsilateral internal iliac artery. (g) 3D reconstruction of the CT scan better depicting the extent of the thrombosis. (h) Surgical specimen of the retrieved thrombus. (i-k) Upon revision of the MR images, a focal nodule characterized by isointensity to the placenta on T2w SPIR images (i) and diffusion restriction on DWI (j) and ADC (k) was noted, consistent with the chorioangioma found on histopathologic examination. Caesarean scar ectopic pregnancy occurs when the embryo abnormally implants in proximity to or within the caesarean scar, with growth either towards the uterine cavity or towards the bladder and abdominal cavity in an exophytic fashion [39] . In any case, this condition is dangerous as it poses a risk of hemorrhage and uterine rupture [11] . TVUS is generally sufficient for diagnosis and the most frequent clinical presentation is with painless vaginal bleeding [40] . Suggestive findings include an empty uterine cavity, with development of the gestational sac in the lower uterine segment between the bladder and anterior uterine wall, which means at the site of the location of the cesarean scar; Doppler mode can be used to demonstrate blood flow in the ectopic trophoblast, which is useful for the differential diagnosis with miscarriage in progress ( Fig. 16 ) [5] . MRI may be employed in difficult cases, which can demonstrate the abnormal location of the gestational sac as well as thinning of the myometrium between the gestational sac and bladder [41] . Fig. 16 Cesarean scar ectopic pregnancy assessed at 10 weeks of gestation by TVUS using B-mode (a, c) and HD-flow Color-Doppler mode (b, d). The gestational sac is located at the level of the lower uterine segment and blood flow can be demonstrated in the ectopic trophoblast. Cesarean scar ectopic pregnancy assessed at 10 weeks of gestation by TVUS using B-mode (a, c) and HD-flow Color-Doppler mode (b, d). The gestational sac is located at the level of the lower uterine segment and blood flow can be demonstrated in the ectopic trophoblast. Retained products of conception complicate about 1% of all pregnancies and can occur at any site of implantation, including a cesarean scar [42] . Caesarean scar RPOC are typically evaluated with US; their appearance ranges from irregular saclike remnants up to mixed solid and cystic masses ( Fig. 17 a-b) [5] . Demonstration of trophoblastic low-resistance arterial flow on Doppler imaging within the retained material seals the diagnosis, but it should be noted that RPOC may be avascular at times [43] . MRI features are variable and signal on T1w and T2w images depends on the amount of hemorrhage and necrosis ( Fig. 17 c) [12] . The most common presentation is a heterogeneous enhancing intracavitary mass [44] . RPOC should be differentiated from uterine arteriovenous malformations (AVM), in which blood flow tends to be more conspicuous and centered in the myometrium rather than endometrium ( Fig. 17 d-f) [44] . AVM are very rare complications of C-section and may require embolization [45] . Fig. 17 Imaging findings in RPOC and uterine AVM. (a, b) Transvaginal US images in B-mode (a) and Color-Doppler (b) mode revealing a heterogeneous, predominantly hyperechoic mass within the endometrial cavity, displaying increased vascularity and consistent with RPOC. (c) Sagittal T2w MR image in a different patient showing a RPOC within the endometrial cavity (arrow) in a patient who underwent C-section with concomitant evidence of a scar in the lower uterine segment. (d, e) Transvaginal US images in B-mode (d) and Color-Doppler (e) mode showing a heterogeneous lesion with marked vascularity centered on the myometrium, representing an AVM. (f) Axial T1w fat suppressed gradient-echo MR image in arterial phase in a different patient shows another example of uterine AVM, with marked enhancement and evidence of a feeding vessel (arrowhead). Note: parts a, b, and e previously published in 10.26044/ecr2025/C-20586. Imaging findings in RPOC and uterine AVM. (a, b) Transvaginal US images in B-mode (a) and Color-Doppler (b) mode revealing a heterogeneous, predominantly hyperechoic mass within the endometrial cavity, displaying increased vascularity and consistent with RPOC. (c) Sagittal T2w MR image in a different patient showing a RPOC within the endometrial cavity (arrow) in a patient who underwent C-section with concomitant evidence of a scar in the lower uterine segment. (d, e) Transvaginal US images in B-mode (d) and Color-Doppler (e) mode showing a heterogeneous lesion with marked vascularity centered on the myometrium, representing an AVM. (f) Axial T1w fat suppressed gradient-echo MR image in arterial phase in a different patient shows another example of uterine AVM, with marked enhancement and evidence of a feeding vessel (arrowhead). Note: parts a, b, and e previously published in 10.26044/ecr2025/C-20586. Abdominal wall endometriosis is a rare but possibly underestimated complication of CS related to iatrogenic deposition of endometrial tissue into the abdominal wall at time of surgery [46] . Patients typically present with focal pain or mass near the cesarean scar [47] . US demonstrates round or oval implants with a heterogeneous but mainly hypoechoic structure, possibly with small cystic areas and internal vascularity [5] . These may be found within subcutaneous fat, muscle or fascial layers and are best assessed using a high-frequency linear probe ( Fig. 18 ) [5] . However, MRI remains the most sensitive modality for diagnosis [48] . Lesions are characterized by foci of T1 hyperintensity due to hemorrhagic products and typically show contrast enhancement 11 , 49 . Iatrogenic implantation following surgery may also occur on the peritoneal surface ( Fig. 19 ). Fig. 18 Abdominal wall endometriosis after C-section. (a) US image obtained with a high-frequency linear probe outlining a hypoechoic nodule at the level of the anterior abdominal wall, attached to the underlying rectus abdominis. (b, c) Axial CT images in unenhanced (b) and venous (c) phase confirming the presence of the implant, which displays heterogeneous enhancement. Fig. 19 Peritoneal endometriosis following uterine surgery. Coronal (a) and sagittal (d) T2w MR images showing the presence of a hypointense nodule adherent to the peritoneal surface of one bowel loop within the pelvis (white arrow). The nodule is adjacent to a hyperintense peritoneal inclusion cyst (red arrow). Axial T1w (b) and T1w SPIR, SPIR (c) images reveal that the nodule is hyperintense, consistent with hematic contents. Axial CT images in venous phase (e, f) demonstrated two smaller deposits at the peritoneal level in a more cranial position; the largest one was found also on T2w sagittal MR and was also hypointense (g). Abdominal wall endometriosis after C-section. (a) US image obtained with a high-frequency linear probe outlining a hypoechoic nodule at the level of the anterior abdominal wall, attached to the underlying rectus abdominis. (b, c) Axial CT images in unenhanced (b) and venous (c) phase confirming the presence of the implant, which displays heterogeneous enhancement. Peritoneal endometriosis following uterine surgery. Coronal (a) and sagittal (d) T2w MR images showing the presence of a hypointense nodule adherent to the peritoneal surface of one bowel loop within the pelvis (white arrow). The nodule is adjacent to a hyperintense peritoneal inclusion cyst (red arrow). Axial T1w (b) and T1w SPIR, SPIR (c) images reveal that the nodule is hyperintense, consistent with hematic contents. Axial CT images in venous phase (e, f) demonstrated two smaller deposits at the peritoneal level in a more cranial position; the largest one was found also on T2w sagittal MR and was also hypointense (g).

Some general knowledge on how C-section is performed is necessary to master the interpretation of diagnostic images. Although there are several different surgical techniques to carry out a C-section, the basic steps are laparotomy and hysterotomy. Abdominal incision may be vertical or more often transverse and a standard procedure involves opening of the peritoneum [8] . In some cases, in order to improve access and reduce inadvertent damage, a bladder flap is created by dissection of the peritoneal lining that separates the bladder from the lower uterine segment, although recent evidence on the topic is controversial [9] . Uterine incision is done through the lower segment of the organ, most frequently using a transverse approach, although a vertical approach may be preferred in certain scenarios [10] . In the period immediately after C-section, imaging may be requested in case of abdominal pain, fever, persistent heavy vaginal bleeding or malodorous discharge [11] . Despite acknowledging that a degree of overlap exists between physiologic and pathologic changes detectable on imaging after C-section, some general points based on the time elapsed from the procedure are outlined in Table 1 . In summary, the uterus normally appears enlarged soon after C-section and gradually returns to its normal dimensions over several weeks. The cesarean scar is visible in the anterior lower uterine segment, presenting as an oval or linear hypoechoic area with hyperechoic foci representing suture material on US, and as a zone of reduced attenuation and enhancement on CT ( Fig. 1 ) [5] . On MRI, the scar is characterized by “blooming” artifacts visible on T2* and gradient echo (GRE) sequences, due to susceptibility artifacts related to surgical sutures, eventually becoming hypointense in T2-weighted sequences due to its fibrous content, with thinning and retraction of the uterine wall 12 , 13 . Residual debris including clots as well as a small amount of air can be present within the endometrial cavity in the first weeks after surgery; these findings must be differentiated from endometritis in the appropriate clinical setting [11] . Some gas bubbles with accompanying fluid can also be apparent in the subcutaneous tissues around the incision. Subfascial or bladder flap hematomas are generally considered relevant only when > 4 cm in axial dimensions ( Fig. 1 ) [5] . A detailed anatomical description of these hematomas can be found in the later paragraph dedicated to hemorrhagic complications of C-section. Table 1 Expected findings according to time from C-section. Time after C-section Normal findings 1st week Marked enlargement of uterus with increased arterial vascularity Engorgement of pelvic veins Residual air and fluid/blood within the endometrial cavity Hematomas <4 cm in size (especially subfascial or bladder flap) Peri-incisional edema 2nd week Initial involution of uterus with decreased arterial vascularity but some residual hyperemia Ongoing endometrial regeneration Tendency for residual fluid within the endometrial cavity to become more homogeneous 3rd - 6th week Further involution of uterus with restoration of normal volume, anatomy and vascularity No residual air in the endometrial cavity Fig. 1 Normal imaging findings in the first days following C-section. (a) Sagittal CT image showing a small triangular subfascial collection of fluid with a limited amount of internal air (arrowhead); the area of hypodensity visible in the myometrium of the lower uterine segment is expected as a sequela of the surgical incision, representing the cesarean scar (arrow). (b) Axial CT image in arterial phase revealing an enlarged uterus with prominent vascularity. (c) Sagittal CT image depicting a small bladder flap hematoma (circle; located between the bladder and uterus) as well as minimal residual air within the endometrial cavity. Note: figure parts previously published in 10.26044/ecr2025/C-20586. Expected findings according to time from C-section. Normal imaging findings in the first days following C-section. (a) Sagittal CT image showing a small triangular subfascial collection of fluid with a limited amount of internal air (arrowhead); the area of hypodensity visible in the myometrium of the lower uterine segment is expected as a sequela of the surgical incision, representing the cesarean scar (arrow). (b) Axial CT image in arterial phase revealing an enlarged uterus with prominent vascularity. (c) Sagittal CT image depicting a small bladder flap hematoma (circle; located between the bladder and uterus) as well as minimal residual air within the endometrial cavity. Note: figure parts previously published in 10.26044/ecr2025/C-20586.

To conclude, C-section is infrequently associated with a range of acute and chronic complications that often require imaging for proper evaluation. Because of the increasing use of this procedure, general radiologists should become familiar with expected postoperative findings. US is considered the first-line modality for detecting both acute and chronic complications in patients with a history of C-section and may be sufficient for diagnosis in most cases. Multiphase CT is preferred in the acute setting where MRI has a more limited role. However, MRI exquisitely complements US in the chronic setting providing accurate information on the involvement of adjacent structures and optimizing management in selected patients.

The share of women giving birth via cesarean section (C-section) is steadily increasing worldwide. A recent epidemiological study collecting data from 154 different countries in the time period between 2010 and 2018 reported that 21.1% of deliveries occurred by C-section; this percentage is projected to rise up to 28.5% by 2030 [1] . In Europe, C-section rates varied between 16.0% and 52.2% in 2019 [2] indicating significant geographic inequalities in the use of the procedure. Although C-section can be a life-saving intervention for both the mother and baby, complications can occur in a minority of cases. Historical studies suggest an overall complication rate approaching 15% with emergency procedures implying greater maternal risks compared to elective procedures 3 , 4 . Complications are classically subdivided into acute and chronic [5] : while acute complications present in the intra-operative or post-operative setting, chronic complications may only become evident several years after C-section, most notably at the time of a subsequent pregnancy [6] . Moreover, the World Health Organization (WHO) recommends to reduce rates of C-section at a population level, especially primary ones, considering also that the risk of complications increases with multiple surgeries [7] . Because of the trends presented above, radiologists are now more likely to encounter complications of C-section in their practice, which may require evaluation via transabdominal or transvaginal ultrasound (US), computed tomography (CT), and magnetic resonance imaging (MRI). This review article first provides an overview of the expected findings after C-section, followed by a detailed description of the imaging features associated with acute and chronic complications of the procedure.

All authors declare that they have no conflict of interest.