Cesarean scar ectopic pregnancy (CSP) is implantation of the blastocyst in the cesarean scar tissue — in the myometrial defect (isthmocele/niche) — at the anterior lower uterine segment. Incidence is increasing parallel to rising cesarean rates (~1/2000 pregnancies). On US, the gestational sac is seen at the anterior lower segment scar site — thin myometrium toward the bladder (<5 mm) is a critical finding determining rupture risk. Classified into Type I (endogenic — growth toward cavity, risk of accreta spectrum transformation) and Type II (exogenic — growth toward bladder, more dangerous, high rupture and bladder invasion risk). Early diagnosis prevents massive hemorrhage, bladder perforation, and hysterectomy; treatment options are time-dependent.
Age Range
20-45
Peak Age
34
Gender
Female predominant
Prevalence
CSP develops from blastocyst implantation in the myometrial defect (isthmocele/niche) at the cesarean incision scar. During post-cesarean healing, myometrial fibrosis, muscle tissue loss, and a channel or cavity (niche) at the endometrium-myometrium interface form at the incision site — this defect provides a site for blastocyst implantation. Scar tissue shows fibrosis, muscle deficiency, and inadequate decidualization — the control mechanisms present in normal myometrial decidual reaction are insufficient here, so trophoblastic invasion may progress uncontrolled. The two types of CSP differ prognostically: In Type I, trophoblasts grow toward the cavity — as pregnancy advances, transformation to placenta accreta spectrum may develop (accreta/increta/percreta), and in some cases pregnancy continuation under close surveillance has been attempted (high risk). In Type II, trophoblasts grow toward the bladder — thin anterior myometrium (<5 mm) is progressively thinned by the growing sac → uterine perforation, bladder invasion, and massive hemorrhage risk develops. Myometrial thickness measurement therefore has diagnostic and prognostic value. On US, the sac is seen over the scar defect in the anterior myometrium; empty uterine cavity and empty cervical canal support the diagnosis. Color Doppler confirms trophoblastic implantation through neovascularization at the scar site.
Implanted gestational sac in cesarean scar defect at anterior lower segment + thin myometrium toward bladder (<5 mm) + empty cavity and canal — pathognomonic ultrasonographic combination for CSP. Type I/II distinction based on sac growth direction.
On TVUS, the gestational sac is seen in the myometrial defect (niche) at the anterior lower segment, the site of previous cesarean. Uterine cavity is empty, cervical canal is empty — the sac is localized in the isthmus/scar region between these two structures. Myometrial thickness between sac and bladder is measured at the thinnest point — <5 mm is assessed as high rupture risk. Sac shape and growth direction provide Type I/II distinction.
Report Sentence
A gestational sac is seen in the cesarean scar defect at the anterior lower segment with myometrial thickness toward the bladder measuring __ mm — consistent with cesarean scar ectopic pregnancy.
Intense peritrophoblastic vascularity is seen around the sac at the scar site on color Doppler. Neovascularization in scar tissue shows low-resistance arterial flow (RI usually <0.5). This finding confirms implantation and demonstrates vascular density at the scar site. Vascularity intensity reflects trophoblastic activity and correlates with hemorrhage risk. Power Doppler better demonstrates low flow velocities.
Report Sentence
Intense peritrophoblastic vascularity and low-resistance arterial flow (RI: __) is noted around the sac at the scar site.
On T2-weighted MRI, a high signal intensity gestational sac is seen in the scar defect at the anterior lower segment. Myometrial thinning and relationship to bladder wall are clearly evaluated — MRI's multiplanar imaging advantage demonstrates sac growth direction and scar defect depth. Type I/II differentiation can be more accurately performed on MRI. Hemorrhagic areas may be hyperintense on T1-weighted sequences. Contrast MRI evaluates trophoblastic tissue viability through enhancement.
Report Sentence
A gestational sac in the scar defect at the anterior lower segment is seen on MRI, consistent with Type ___ CSP; myometrial thickness __ mm.
Anterior myometrial thickness between the sac and bladder is measured at the thinnest point — <5 mm indicates risk of rupture and bladder invasion. Normal anterior myometrial thickness in this region is >5 mm. Measurement should be careful: shortest distance between sac outer border (trophoblast) and bladder inner surface (mucosa) is measured. Slightly filled bladder improves measurement accuracy — in empty bladder, anterior wall may fold causing falsely thick measurement.
Report Sentence
Anterior myometrial thickness between sac and bladder measures __ mm at the thinnest point.
CT is typically used in emergencies (rupture, massive hemorrhage) or for interventional planning. Contrast CT evaluates hypervascular mass at the anterior lower segment and hemoperitoneum. For uterine artery embolization planning, vascular anatomy is demonstrated — bilateral uterine artery caliber, course, cervicovaginal branching pattern, and potential collateral vessels are identified. In suspected bladder invasion, bladder wall integrity and perivesical fat planes are evaluated.
Report Sentence
A hypervascular mass at the anterior lower segment and pelvic free fluid are seen on contrast CT — should be evaluated for CSP complication.
The uterine cavity and cervical canal are empty — the sac is localized at the scar site between these two structures. The endometrium in the cavity may be thickened from decidual reaction but contains no gestational sac. This finding is important for differentiating from cervical ectopic and miscarriage in process — cervical ectopic sac is below the os, CSP sac is at the scar site.
Report Sentence
The uterine cavity and cervical canal are empty; the gestational sac is localized at the scar site in the anterior lower segment.
Criteria
Sac grows toward cavity, partially implanted at scar, myometrial thickness relatively preserved
Distinct Features
Lower rupture risk, growth toward cavity, risk of transformation to accreta spectrum (accreta/increta/percreta if pregnancy progresses), high-risk pregnancy continuation attempted in some cases — close surveillance and prepared delivery plan required
Criteria
Sac grows toward bladder, myometrium extremely thin (<5 mm), exophytic growth pattern
Distinct Features
High rupture and bladder invasion risk, requires urgent treatment, uterine perforation possible, pregnancy continuation contraindicated — early intervention increases fertility-sparing outcome chance
Criteria
Cases where pregnancy is consciously continued in Type I CSP — placenta accreta spectrum development expected
Distinct Features
Multidisciplinary team management mandatory, serial US/MR follow-up, delivery plan (cesarean + potential hysterectomy), blood product preparation, cesarean hysterectomy possibility discussed
Distinguishing Feature
Cervical ectopic sac is within cervix below internal os; CSP sac is at the anterior lower segment scar above the os — anatomic compartment difference clearly demonstrated on TVUS
Distinguishing Feature
PAS is diagnosed in later pregnancy (2nd-3rd trimester) with diffuse placental invasion; CSP is diagnosed in early pregnancy (1st trimester) with focal scar implantation — localized sac at a single point
Distinguishing Feature
Interstitial ectopic sac is in cornual myometrium with lateral-fundal localization (interstitial line sign); CSP sac is at anterior lower segment scar with midline-anterior localization
Distinguishing Feature
GTD shows snowstorm pattern in cavity and very high β-hCG; CSP has focal gestational sac at scar site and proportional β-hCG — localization and β-hCG level are distinguishing
Urgency
emergentManagement
interventionalBiopsy
Not NeededFollow-up
specialist-referralCSP is treatable with early diagnosis and fertility can be preserved. Treatment options are determined by type and gestational age. Early Type I (<8 weeks, small sac): MTX (systemic single/multi-dose or local injection), US-guided KCl injection, expectant management + serial monitoring (in highly selected cases). Early Type II or large sac: uterine artery embolization + curettage (safe curettage with hemorrhage control), hysteroscopic resection (under direct visualization), laparoscopic wedge resection. Advanced stage or failed treatment: uterus-sparing surgery (scar excision + repair) or hysterectomy (last resort). β-hCG monitoring is mandatory in all treatment modalities — weekly measurements until negative. CSP recurrence risk exists in future pregnancies (5-15%) — should be screened with early US. Scar defect repair (laparoscopic isthmocele repair) may reduce CSP risk in subsequent pregnancies.
The incidence of cesarean scar ectopic pregnancy is increasing with rising cesarean rates. Early diagnosis is critical — untreated, it may progress to placenta accreta, uterine rupture, and massive hemorrhage. Treatment options include methotrexate (early, small), uterine artery embolization, hysteroscopic/laparoscopic excision, or vacuum aspiration (US-guided). Proximity to the bladder carries risk of urological complications.