A 32-year-old multiparous woman (G3P2) undergoes emergency lower-segment cesarean section for failure to progress at 8 cm cervical dilation. Intraoperative findings include a lower-segment incision, intact bladder, and no obvious placental abnormality. The uterus is closed in two layers. Estimated blood loss is 900 mL. At 6 hours postoperatively, the patient reports persistent lower abdominal pain and mild vaginal bleeding. Abdominal examination reveals a firm, tender uterus. Hemoglobin on post-op day 1 is 8.2 g/dL (preoperative 11.5 g/dL). Lochia is moderate and foul-smelling. Ultrasound shows a heterogeneous echogenic collection within the uterine cavity measuring 4 × 3 cm. What is the most likely diagnosis?

Explanation

## Diagnosis: Retained Products of Conception (RPOC) with Intrauterine Infection ### Clinical Features Pointing to RPOC **Key Point:** The combination of: - Foul-smelling lochia (indicates infection/necrotic tissue) - Heterogeneous echogenic collection on ultrasound (retained clot, placental fragments, or decidua) - Persistent lower abdominal pain and tenderness - Significant hemoglobin drop (3.3 g/dL) despite moderate vaginal bleeding - Firm uterus (rules out atony) ...is diagnostic of **retained products of conception (RPOC)**, likely with secondary intrauterine infection. ### Pathophysiology ```mermaid flowchart TD A[Incomplete placental separation or retained fragments]:::outcome --> B[Intrauterine collection]:::outcome B --> C[Impaired uterine contraction]:::outcome C --> D[Continued bleeding from placental bed]:::outcome D --> E[Hemoglobin drop]:::outcome B --> F[Bacterial colonization]:::outcome F --> G[Endometritis/chorioamnionitis]:::outcome G --> H[Foul-smelling lochia + fever]:::outcome G --> I[Uterine tenderness + pain]:::outcome ``` ### Differential Diagnosis Table | Feature | Uterine Atony | RPOC + Infection | Uterine Rupture | Dehiscence | |---------|---------------|------------------|-----------------|------------| | Uterine consistency | Soft, boggy | Firm, tender | Firm initially, then soft | Firm | | Lochia character | Heavy, bright red | Foul-smelling, moderate | Minimal (intra-abdominal) | Minimal | | Abdominal pain | Mild | Persistent, colicky | Severe, acute | Localized | | Ultrasound finding | Empty cavity | Heterogeneous collection | Free fluid, absent uterine wall | Hypoechoic line at scar | | Hemodynamic status | Unstable early | Stable initially, then unstable | Unstable acutely | Variable | | Fever/infection signs | No | Yes (foul lochia) | No (acute hemorrhage) | Possible | ### Why the Uterus Is Firm **Clinical Pearl:** A firm uterus **rules out atony**. The uterus contracts around the retained products, creating a firm but tender organ. This is a key distinguishing feature from simple atonic PPH, where the uterus is soft and boggy. ### High-Yield: Ultrasound Findings in RPOC - **Heterogeneous echogenic collection** within the uterine cavity (as seen here) - Thickened endometrium (>8 mm) - Absence of gestational sac (post-delivery) - May show cystic or complex areas representing clot, placental tissue, or fluid ### Management of RPOC **High-Yield:** The standard approach is: 1. **Confirm diagnosis** with transvaginal ultrasound (more sensitive than transabdominal) 2. **Administer antibiotics** (broad-spectrum: ceftriaxone + metronidazole or amoxicillin-clavulanate) for endometritis 3. **Perform uterine evacuation**: - Manual removal under anesthesia (safest for post-cesarean) - Gentle curettage (avoid perforation, especially post-op) - Suction evacuation under ultrasound guidance 4. **Administer oxytocin** post-evacuation to promote contraction and hemostasis 5. **Monitor hemoglobin** and transfuse if Hb < 7 g/dL or symptomatic anemia 6. **Continue antibiotics** for 48–72 hours post-evacuation **Warning:** Aggressive curettage in the immediate post-cesarean period risks uterine perforation. Manual evacuation under direct visualization is preferred. ### Why Other Options Are Incorrect **Uterine atony:** The uterus is **firm**, not soft and boggy. Atony presents with heavy, bright-red bleeding and a boggy uterus. This patient's firm uterus and foul lochia point away from simple atony. **Uterine rupture:** Rupture causes acute, severe abdominal pain, hemodynamic instability, and free intra-abdominal fluid on ultrasound. The lochia would be minimal (blood pooling in the abdomen). This patient is stable with moderate lochia. **Dehiscence of cesarean scar:** Scar dehiscence may occur but is rare at 6 hours post-op and typically presents with acute pain, fever, and purulent drainage from the incision. Ultrasound would show a hypoechoic defect at the scar, not an intrauterine collection.