What are the differential diagnoses and appropriate management for a 36-week pregnant woman with a history of two previous cesarean sections (c/s) presenting with pain at the incision site and a bulge?

Pain at Incision Site and Bulge in 36-Week Pregnant Woman with Two Prior Cesarean Sections

The most critical differential diagnosis to rule out immediately is uterine scar dehiscence, which represents a life-threatening emergency requiring urgent imaging and potential delivery planning. 1, 2

Differential Diagnoses (Prioritized by Urgency)

Life-Threatening Conditions

Uterine Scar Dehiscence (Cesarean Scar Defect)

• Characterized by disruption of endometrial and myometrial layers with intact serosal layer, distinguishing it from complete rupture where all layers are disrupted 2
• Presents with pain at the incision site and visible bulge due to thinning of the anterior lower uterine segment 1
• The uterine wall may become so thin that the placenta can be seen through it at delivery (termed "uterine window") 1
• Risk is dramatically elevated with two prior cesarean sections, particularly if the current pregnancy has anterior placenta previa (up to 40% risk of complications) 1

Placenta Accreta Spectrum Disorder (PASD) with Uterine Scar Dehiscence

• Two prior cesarean sections place this patient at high risk for PASD, especially if placenta is anterior or low-lying 1
• Often occurs in conjunction with cesarean scar dehiscence, where placental villi overlie the thinned scar tissue 1
• The bulge may represent the thinned uterine wall with abnormal placental attachment 1

Non-Life-Threatening but Urgent Conditions

Incisional Hernia

• Reported occurrence ranges from 0.0-5.6% after cesarean section, though this is typically diagnosed postpartum rather than during pregnancy 3
• Less likely at 36 weeks gestation as most develop months to years after surgery 3

Abdominal Wall Endometriosis

• Typically presents as a painful mass in subcutaneous tissue near the cesarean scar, with pain intensifying during menstruation 4
• Less likely in this case as patient is currently pregnant (36 weeks), and endometriosis symptoms typically improve during pregnancy 4

Wound Seroma or Hematoma

• Would be unusual at 36 weeks gestation unless there was recent trauma 5
• More commonly occurs in immediate postpartum period 5

Immediate Management Algorithm

Step 1: Urgent Clinical Assessment

Assess hemodynamic stability immediately:

• Vital signs (blood pressure, heart rate, temperature) to rule out hemorrhage or infection 2
• Fetal heart rate monitoring to assess fetal well-being 2
• Look for signs of impending rupture: severe pain, vaginal bleeding, abnormal fetal heart rate patterns, maternal tachycardia 2, 6

Step 2: Urgent Imaging (Same Day)

Obtain transvaginal ultrasound with color Doppler as first-line imaging:

• Evaluates the cesarean scar thickness and integrity 1, 7
• Assesses placental location and relationship to the scar 1
• Identifies any fluid collections or hematomas 7, 2
• Sensitivity of 90-95% for detecting abnormal placentation 7

If ultrasound findings are equivocal or concerning, proceed to MRI without IV contrast:

• MRI is superior to CT and ultrasound for detecting myometrial defects with intact serosal layer due to superior soft-tissue contrast 2
• Can be safely performed in pregnancy without gadolinium contrast 1
• Particularly valuable for detecting the precise topography of invasion, including depth and laterality 1
• A bladder flap hematoma >5 cm on imaging should immediately raise suspicion for uterine dehiscence 2

Step 3: Multidisciplinary Planning

If uterine scar dehiscence or PASD is confirmed:

• Immediate consultation with maternal-fetal medicine and obstetric anesthesia 1
• Plan for delivery at a tertiary care center with blood bank capabilities and surgical expertise 1
• Consider delivery timing: at 36 weeks with confirmed lung maturity, delivery should be planned urgently (within 24-48 hours) if dehiscence is confirmed 8, 6
• Prepare for possible hysterectomy if PASD is present 1
• Ensure availability of interventional radiology for potential uterine artery embolization if massive hemorrhage occurs 7

If imaging shows benign findings (incisional hernia, endometrioma):

• Conservative management until term delivery 3, 4
• Plan cesarean delivery with careful surgical approach to avoid the mass 4

Critical Pitfalls to Avoid

Do not delay imaging based on reassuring vital signs alone - uterine dehiscence can be asymptomatic until catastrophic rupture occurs 2, 6

Do not interpret hypodense edema at the cesarean incision site as dehiscence in the first postpartum week - however, at 36 weeks gestation, any thinning or bulging should be taken seriously 2

Never perform digital vaginal examination before imaging if there is any concern for abnormal placentation or vascular abnormalities, as this risks perforation or massive hemorrhage 7

Do not plan trial of labor - with two prior cesarean sections and concerning symptoms, this patient requires planned cesarean delivery at minimum, and possibly earlier intervention if dehiscence is confirmed 8, 6, 9

Presence of gas in the myometrial defect extending from endometrium to parametrial tissue along with hemoperitoneum suggests complete uterine rupture rather than dehiscence and requires immediate delivery 2

Key Clinical Pearls

• The combination of pain and visible bulge at the cesarean scar in late pregnancy is uterine scar dehiscence until proven otherwise 1, 2
• The gradual wedge-shaped transition from scar to myometrium distinguishes dehiscence from infiltrative placental invasion 1
• Two prior cesarean sections dramatically increase risk of both dehiscence and PASD, particularly with anterior placentation 1, 6
• Correlation between imaging findings and clinical presentation is essential for accurate diagnosis 1