Cesarean Section Scar Diverticulum (Isthmocele) – A Comprehensive Radiologic and Clinical Review to Optimize Diagnosis and Management

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Introduction

Cesarean section (C-section) has become one of the most commonly performed surgical procedures in women worldwide. While advances in obstetric care have dramatically improved maternal and neonatal safety, the long-term sequelae of C-sections are increasingly recognized. Among these, Cesarean Section Scar Diverticulum—also referred to as Cesarean Scar Defect (CSD), Isthmocele, Uterine Niche, or Cesarean Scar Pouch—has emerged as a clinically significant entity with implications for gynecologic symptoms and reproductive outcomes. 

Cesarean section scar diverticulum is a pouch-like myometrial defect at the site of a previous cesarean scar, typically in the anterior lower uterine segment. Radiologically, it presents as an indentation, notch, or triangular hypoechoic defect communicating with the endometrial cavity. This review will explore the pathophysiology, epidemiology, clinical presentation, imaging features, differential diagnosis, diagnosis, treatment options, and prognosis of this condition, integrating the most recent high-impact literature to aid clinical practice and exam preparation for physicians.

Pathophysiology

Cesarean section scar diverticulum arises from defective tissue healing at the site of the uterine incision made during a cesarean delivery. Unlike typical wound healing in other tissues, the lower uterine segment undergoes complex remodeling under both hormonal and mechanical influences after childbirth. Poor approximation of myometrial edges, inadequate suturing technique, infection, or tension at the scar site can result in incomplete healing of the hysterotomy.

This leads to a weak, discontinuous myometrial region that allows blood and menstrual debris to collect within a residual pouch. Over time, repeated cyclical bleeding and endometrial infiltration of the scar can enlarge the defect, creating a diverticulum that can retain fluid, menstrual blood, and debris—exacerbating symptoms. The exact molecular and cellular mechanisms remain under investigation.

Epidemiology

The true prevalence of Cesarean section scar diverticulum is difficult to determine due to varying diagnostic criteria and imaging techniques, but it is recognized to occur in a substantial proportion of women who have undergone cesarean delivery. Transvaginal ultrasonography (TVUS) detects niche formation in 24–70% of women after C-section, while saline instillation sonohysterography (SIS) reveals rates as high as 56–84%. 

Although many women remain asymptomatic, approximately 30% of those with niches express clinical symptoms such as abnormal uterine bleeding or pelvic pain. Repeated cesarean deliveries and a retroflexed uterus are among the most frequently identified risk factors.

Clinical Presentation

Cesarean section scar diverticulum is most commonly encountered in reproductive-aged women with a history of one or more cesarean deliveries. Clinical symptoms vary widely:

1. Abnormal Uterine Bleeding

  • Heavy or prolonged menstrual bleeding

  • Postmenstrual spotting lasting several days
    This results from blood accumulation within the scar diverticulum reservoir, which slowly drains into the uterine cavity.

2. Pelvic Pain

  • Chronic pelvic discomfort or dysmenorrhea
    Blood stagnation and local inflammation can induce pain. 

3. Infertility and Subfertility

  • Impaired sperm migration or embryo implantation related to altered uterine environment.

4. Obstetric Complications

In future pregnancies, scar defects may contribute to rare but serious conditions such as placenta accreta, placenta previa, uterine rupture, and cesarean scar ectopic pregnancy. 

Imaging Features

Radiologic evaluation plays a central role in diagnosing cesarean scar diverticulum. The choice of imaging modality depends on symptom severity, clinical suspicion, and resource availability.

1. Transvaginal Ultrasound (TVUS)

★ First-line imaging modality due its accessibility and cost-effectiveness.
Sonographically, a scar niche appears as a hypoechoic or anechoic triangular defect at the anterior lower uterine segment communicating with the endometrial cavity. 

Figure 1. TVUS Image of Isthmocele

Key Findings :

Defect Site: There is a distinct, fluid-filled (anechoic) triangular indentation located at the anterior wall of the lower uterine segment, specifically at the site of a previous Cesarean section scar.

Shape: The defect presents a characteristic "niche" or triangular shape, which is typical for an isthmocele.

Residual Myometrium: The image allows for the assessment of the thickness of the remaining uterine muscle (residual myometrium) between the apex of the niche and the serosal surface.

Fluid Accumulation: The dark (black) area within the niche indicates the accumulation of menstrual blood or mucus, which often leads to clinical symptoms like postmenstrual spotting.

Ultrasound Characteristics Observed:

Hypoechoic/Anechoic Area: The dark pocket within the myometrium signifies a loss of continuity in the uterine wall.

Uterine Orientation: Based on the probe placement at the top of the image, this is a sagittal view of the uterus.

Clinical Significance:

This condition is often associated with:

Abnormal Uterine Bleeding (AUB): Specifically prolonged spotting after a period.

Pelvic Pain: Chronic discomfort in the lower abdomen.

Secondary Infertility: The fluid in the niche may create an inflammatory environment hostile to sperm or embryo implantation.

2. Saline Infusion Sonohysterography (SIS)

SIS enhances niche visualization by distending the uterine cavity with saline, highlighting the depth and morphology of the scar defect. SIS typically demonstrates a more conspicuous pouch than TVUS.

Figure 2. Saline Infusion Sonohysterography (SIS)
Fluid outlines the anterior isthmocele (arrow) better than standard TVUS, showing an elongated pouch within the lower uterine segment.
SIS augmentation reveals the full contour and volume of the diverticulum.

3. Magnetic Resonance Imaging (MRI)

MRI offers superior soft tissue contrast and detailed measurements of defect size and surrounding myometrial integrity, especially when surgical planning is considered or diagnosis is equivocal on ultrasound. 

Figure 3. MRI of Cesarean Scar Diverticulum
Axial T2-weighted MR imaging shows a well-defined hyperintense pouch (arrow) at the anterior lower uterine segment with thinning of the residual myometrium.
Interpretation: MRI confirms the presence and extent of the scar diverticulum and quantifies residual myometrial thickness.

Differential Diagnosis

Accurate diagnosis requires distinguishing cesarean scar diverticulum from other gynecologic conditions:

1. Endometrial Polyps

Typically appear as focal masses within the endometrial canal on TVUS or SIS but do not communicate with myometrial apices.

2. Submucosal Fibroids

Hypoechoic masses indent endometrial cavity but lack the characteristic triangular outpouching seen in niches. 

3. Adenomyosis

Diffuse thickening of the junctional zone without the focal anterior deviation typical for isthmoceles. 

4. Uterine Rupture Dehiscence (in pregnancy)

Acute discontinuity with clinical instability distinguishes it from chronic niches.

Diagnosis

Diagnosis relies on integration of clinical history, gynecologic symptoms, and imaging findings. Although no universal diagnostic threshold exists, the defect in the myometrium at the cesarean scar site is generally considered significant when ≥2 mm in depth on imaging. 

Diagnostic criteria typically include:

  • History of cesarean delivery

  • Anechoic or hypoechoic triangular defect at scar site on TVUS/SIS

  • Confirmation of communication with endometrial cavity

SIS or 3D ultrasonography often enhances diagnostic specificity. MRI is particularly useful when invasiveness or extensive morphological assessment is required.

Treatment Options

Therapeutic strategies are individualized based on symptomatology, desire for future fertility, and defect size.

1. Expectant/Medical Management

  • For asymptomatic or mild cases, observation is often acceptable.

  • Hormonal therapy may mitigate heavy bleeding but does not eliminate the anatomical defect.

2. Surgical Approaches

a. Hysteroscopic Repair (Isthmoplasty)

  • Most common for smaller defects.

  • Excision of scar edges and restoration of normal endometrial contour. 

b. Laparoscopic Repair

  • Preferred for larger defects or when residual myometrium is thin.

  • Laparoscopic resection and multilayer closure improve strength. 

c. Vaginal or Combined Approaches

  • May be utilized depending on surgeon expertise and anatomical factors. 

Figure 4. Laparoscopic Repair Schematic
Illustration depicting surgical resection of the diverticulum and layered closure of residual myometrium.
Interpretation: Surgical repair eliminates the diverticulum and reinforces the uterine wall.

Prognosis

Symptomatic relief after appropriate surgical repair is generally favorable, with significant improvement in bleeding, pain, and reproductive outcomes reported in multiple case series. However, continued monitoring is important as recurrent niche formation and obstetric risks persist, particularly in subsequent pregnancies.

Practice Questions for Physician Trainees (Exam Preparation)

Question 1

Which imaging modality is most sensitive for detecting a small Cesarean scar diverticulum (isthmocele) not visible on standard transvaginal ultrasound?

A) Abdominal X-ray
B) Saline infusion sonohysterography (SIS)
C) Hysterosalpingography
D) Plain CT scan

Answer: B) Saline infusion sonohysterography (SIS)
Explanation: SIS distends the cavity, improving visualization of the defect compared with TVUS. 

Question 2

The most common clinical symptom associated with Cesarean section scar diverticulum is:

A) Acute abdominal pain
B) Abnormal uterine bleeding / postmenstrual spotting
C) Urinary incontinence
D) Vaginal discharge without bleeding

Answer: B) Abnormal uterine bleeding / postmenstrual spotting
Explanation: The diverticulum can trap blood leading to prolonged postmenstrual bleeding. 

Question 3

Which surgical technique is preferred for a large scar defect with thin residual myometrium in a woman desiring future fertility?

A) Hysteroscopy alone
B) Laparoscopic scar resection and multilayer closure
C) Vaginal hysterectomy
D) Expectant management

Answer: B) Laparoscopic scar resection and multilayer closure
Explanation: This approach optimally reinforces uterine integrity in large defects, especially when fertility preservation is desired. 

References

  1. T. G. Kremer, I. B. Ghiorzi, and R. P. Dibi, “Isthmocele: An overview of diagnosis and treatment,” Rev. Assoc. Med. Bras., vol. 65, no. 5, pp. 714–721, 2019. SciELO

  2. T. Manchanda, S. S. Singhu, and A. Dave, “Presentation of isthmocele and its management options: a review,” Ital. J. Gynaecol. Obstet., vol. 35, no. N.1, pp. 98–107, Mar. 2023. gynaecology-obstetrics-journal.com

  3. J. M. Donnez et al., “Gynecological and obstetrical outcomes after laparoscopic repair of a cesarean scar defect,” Fertil. Steril., vol. 107, no. 1, pp. 289–296, 2017. Obstetrics & Gynecology

  4. Cesarean Section Scar Diverticulum, Radiopaedia.org, 2025. Radiopaedia

  5. Isthmocele: An Overview of Diagnosis and Treatment, PubMed, PMID: 31166450, 2019. PubMed

  6. N. Najwa et al., “Uterine Isthmocele: An overview of diagnosis and treatment of a large isthmocele,” Open Access Library Journal, vol. 11, pp. 1–6, 2024. SCIRP

  7. Diagnosis and Management of Cesarean Scar Niche, JOGC, 2025. 

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