What are epidermal inclusion cysts?

Epidermal Inclusion Cysts

Epidermal inclusion cysts are benign, encapsulated subepidermal nodules filled with keratin material that form when epidermal cells are implanted into the dermis or deeper tissue layers.

Definition and Pathophysiology

• Epidermal inclusion cysts (also known as sebaceous cysts) are benign cutaneous lesions caused by:
  • Implantation of epidermal cells into dermal or subdermal tissue 1
  • Proliferation of epidermal squamous epithelium 2
  • Most commonly result from trauma or surgery 2
  • Can also develop from blocked hair follicles

Clinical Presentation

• Common locations:
  • Scalp, face, trunk, neck, and back 2
  • Can occur anywhere on the body, including glabrous skin (palms, soles) 3
  • Rarely found in breast tissue 4
• Appearance:
  • Firm, round, mobile nodules
  • Usually painless unless infected or ruptured
  • Size varies from a few millimeters to several centimeters
  • Central punctum (pore) may be visible

Complications

• Infection: Most common complication 1
• Rupture: Can cause significant inflammation 2
• Malignant transformation: Rare but possible transformation to squamous cell carcinoma 2
• Foreign body reaction: Can occur with cyst contents leaking into surrounding tissue 5

Diagnosis

• Clinical examination is usually sufficient
• Suspicious features warranting further investigation:
  • Nodular mass, ulceration, extensive scarring
  • Rapid growth, fixation to surrounding tissues
  • Size greater than 1.5 cm 1
• Imaging:
  • Ultrasound: Useful for confirming diagnosis and evaluating extent
  • MRI: May be needed if malignancy is suspected 2
• Fine-needle aspiration cytology (FNAC): Can be diagnostic in uncertain cases 4

Management

Non-inflamed cysts

• Complete surgical excision with removal of the entire cyst wall
  • Minimum 4-mm margin around the cyst border 1
  • Elliptical incision over the cyst
  • Careful dissection around the cyst wall
  • Removal of entire cyst intact
  • Closure with sutures 1

Inflamed/Infected cysts

• Incision and drainage is the definitive treatment for inflamed epidermoid cysts 1
• Antibiotics are only necessary when:
  • Signs of systemic inflammatory response syndrome (SIRS)
  • Markedly impaired host defenses
  • Extensive surrounding cellulitis
  • Failed initial treatment 1

Antibiotic options (if needed)

• First-line oral options:
  • Dicloxacillin, cephalexin, or clindamycin 1
• Alternative options:
  • Trimethoprim-sulfamethoxazole, doxycycline 1
  • Vancomycin for MRSA coverage 1
• Duration: 7-10 days for uncomplicated infections, up to 14 days for severe infections 1

Post-procedure care

• Cover surgical site with dry dressing
• Keep wound clean and dry
• Monitor for signs of infection
• Follow-up within 7-14 days for wound assessment and suture removal 1

Recurrence

• Recurrence rates range from 2.2-8.3% depending on technique 1
• Main cause of recurrence: Incomplete removal of the cyst wall 1

Special considerations

• All excised tissue should be submitted for pathological examination, especially if:
  • Size >1.5 cm
  • Suspicious features
  • Unusual clinical presentation 1
• Cosmetic considerations:
  • Marker sutures for larger excisions
  • Punch incision or CO2 laser excision for cosmetically sensitive areas 1

Key takeaways

• Epidermal inclusion cysts are common benign lesions
• Complete surgical excision is the treatment of choice for non-inflamed cysts
• Incision and drainage is appropriate for inflamed/infected cysts
• Antibiotics should be reserved for specific situations
• Always consider pathological examination to rule out malignancy