Diagnosis: Epidermoid Cyst
A cyst with a white wall and white cheesy contents is characteristic of an epidermoid cyst, and the definitive treatment is incision and drainage without routine antibiotics or cultures. 1, 2
Clinical Characteristics
Epidermoid cysts (often erroneously called "sebaceous cysts") contain cheesy keratinous material with normal skin flora present even when uninflamed 3. The white, cheesy appearance you describe is pathognomonic for this diagnosis 4, 5, 6, 7, 8. The inflammation and purulence that may develop occur as a reaction to rupture of the cyst wall and extrusion of contents into the dermis, rather than as a true infectious complication 3.
Management Algorithm
Primary Treatment
Incision and drainage is the recommended treatment (strong recommendation, high-quality evidence) 1, 2:
- Perform thorough evacuation of the pus/contents
- Probe the cavity to break up loculations
- Simply cover with a dry dressing (easiest and most effective) 3, 1
- Packing with gauze causes more pain without improving healing 1
When NOT to Culture or Use Antibiotics
Gram stain and culture of pus from inflamed epidermoid cysts are NOT recommended (strong recommendation, moderate-quality evidence) 1, 2. Systemic antibiotics are rarely necessary 3.
Exceptions Requiring Antibiotics
Antibiotics are indicated ONLY when 3:
- Multiple lesions present
- Cutaneous gangrene
- Severely impaired host defenses
- Extensive surrounding cellulitis
- Severe systemic manifestations (high fever, SIRS criteria: temperature >38°C or <36°C, tachycardia >90 bpm, tachypnea >24 breaths/min, WBC >12,000 or <4,000 cells/µL) 1
Key Clinical Pitfalls
The most common error is overtreating these lesions with antibiotics and cultures when simple drainage suffices 1. The presence of white cheesy material does not indicate infection requiring antimicrobial therapy—it represents normal keratin accumulation 3.
Another pitfall is confusing epidermoid cysts with true abscesses. While cutaneous abscesses are typically polymicrobial with S. aureus present in only ~25% of cases, epidermoid cysts contain normal skin flora that become inflammatory only after cyst wall rupture 3.