A 28-year-old primigravida at day 5 postpartum presents with severe bilateral breast pain, erythema, and a palpable firm nodule in the left breast. She is exclusively breastfeeding. Temperature is 38.5°C. On examination, the left breast shows localized induration with tenderness over the upper outer quadrant. What is the investigation of choice to confirm the suspected diagnosis?

## Clinical Presentation Analysis The patient presents with classic features of **puerperal breast abscess**: - Day 5 postpartum (peak incidence: days 2–6) - Localized firm nodule with erythema and tenderness - Fever (38.5°C) indicating infection - Upper outer quadrant involvement (most common site) ## Investigation of Choice: Breast Ultrasound with Colour Doppler **Key Point:** Breast ultrasound is the gold standard for diagnosis and management of postpartum breast abscess in lactating women. ### Why Ultrasound is Superior | Feature | Advantage | |---------|----------| | **Safety** | No radiation; safe in lactating women | | **Sensitivity** | 88–95% for abscess detection; can differentiate cellulitis from abscess | | **Colour Doppler** | Demonstrates increased vascularity and can guide aspiration/drainage | | **Real-time guidance** | Enables ultrasound-guided needle aspiration or catheter drainage | | **Cost-effective** | Readily available, quick, non-invasive | | **Differentiation** | Distinguishes simple mastitis (no fluid collection) from abscess (hypoechoic/anechoic collection) | ## Diagnostic Criteria on Ultrasound 1. **Hypoechoic or anechoic collection** within breast tissue 2. **Posterior acoustic enhancement** (suggests fluid) 3. **Irregular margins** with surrounding edema 4. **Colour Doppler:** Hyperemia at periphery 5. **Size:** Typically >2 cm for true abscess **Clinical Pearl:** Ultrasound can differentiate **mastitis** (no fluid collection, diffuse edema) from **abscess** (discrete fluid collection requiring drainage), which changes management. **High-Yield:** Ultrasound-guided needle aspiration of the collection can be therapeutic (drainage) and diagnostic (culture and sensitivity for organism identification). ## Management Implication Once abscess is confirmed: - Ultrasound-guided aspiration or catheter drainage - Culture for organism (usually *Staphylococcus aureus*, including MRSA) - Antibiotics (empirically: amoxicillin-clavulanate or cephalexin; modify based on culture) - Continue breastfeeding from unaffected breast; affected breast may be expressed and discarded if antibiotics are safe [cite:Williams Obstetrics 26e Ch 65]