A 28-year-old primigravida presents on postpartum day 5 with severe breast engorgement, localized erythema, and a palpable hard lump in the upper outer quadrant of the left breast. She is febrile (38.5°C) and has purulent discharge from the nipple. Breastfeeding is extremely painful. What is the most appropriate investigation to confirm the diagnosis and guide management?

Explanation

## Diagnosis: Puerperal Mastitis with Suspected Abscess The clinical presentation—fever, localized erythema, hard lump, purulent nipple discharge, and severe pain on postpartum day 5—is highly suggestive of **lactational breast abscess** (complication of untreated or inadequately treated mastitis). ## Investigation of Choice: Breast Ultrasound **Key Point:** Breast ultrasound is the gold standard for detecting and characterizing lactational breast abscess in the postpartum period. ### Why Ultrasound? 1. **Real-time imaging** — Identifies fluid collection, size, and location with high sensitivity (>90%). 2. **No radiation** — Safe in lactating mothers; no risk to breastfeeding. 3. **Guides intervention** — Allows ultrasound-guided needle aspiration or drainage if abscess is confirmed. 4. **Differentiates** — Distinguishes simple mastitis (no fluid) from abscess (fluid collection). 5. **Cost-effective** — First-line imaging in postpartum breast pathology. ## Management Algorithm ```mermaid flowchart TD A[Postpartum fever + breast lump + purulent discharge]:::outcome --> B[Clinical diagnosis: Lactational mastitis/abscess]:::action B --> C[Ultrasound breast]:::action C --> D{Fluid collection present?}:::decision D -->|Yes| E[Ultrasound-guided aspiration/drainage]:::action D -->|No| F[Antibiotics + supportive care]:::action E --> G[Send fluid for culture & sensitivity]:::action G --> H[Targeted antibiotic therapy]:::action ``` **High-Yield:** In lactational abscess, ultrasound shows a **hypoechoic or anechoic fluid collection** with or without internal echoes, often with surrounding edema. **Clinical Pearl:** Aspiration of pus should be sent for **culture and sensitivity** to identify causative organism (usually *Staphylococcus aureus*, increasingly MRSA) and guide antibiotic selection.