🧬 Vet’s 2025 Guide to Equine Epidermoid Cysts (Epidermal Inclusion Cysts)

By Dr Duncan Houston BVSc

1. What Are Epidermoid Cysts?

Epidermoid cysts—also known as epidermal inclusion cysts—are benign skin lesions that form when skin cells become trapped under the surface, creating a firm, expandable sac often containing keratin. They’re uncommon but notable in horses for their appearance and potential to cause small abscesses or discomfort.

2. Causes & Risk Factors

• Trauma: Penetrating wounds, sheath trauma, or prior surgery can trap epidermal cells beneath the dermis.
• Congenital: Rare cases arise from developmental inclusion of skin tissue.
• Breed or location predisposition: Common on the sheath, trunk, or distal limbs after lacerations or healing mishaps.

3. Clinical Signs & Presentation

• Firm, round, smooth nodules under the skin.
• The cyst may be asymptomatic or can enlarge, causing mild irritation.
• Occasionally, inflammation or rupture leads to a draining tract and mild swelling.

4. Diagnosing Epidermoid Cysts

• History & physical exam: Recurrent nodules in healed wound sites.
• Ultrasound: Reveals a well‑defined sac containing echogenic material.
• Fine needle aspiration: Yields white, cheesy keratin cells.
• Excisional biopsy: Offers definitive diagnosis and removes the lesion.

5. Treatment Options

5.1 Conservative Management

• Leave asymptomatic cysts alone if small.
• Monitor for growth, discomfort, or infection.

5.2 Surgical Excision

• Local anesthetic and aseptic technique required.
• The cyst should be removed in its entirety—including capsule—to prevent recurrence.
• Best for large, irritating, or draining cysts.

5.3 Postoperative Care

• Apply antibiotic ointment and bandage initially.
• Administer NSAIDs to reduce inflammation.
• Keep the surgical site clean and dry; monitor healing.

6. Prognosis & Recurrence

Epidermoid cysts are benign with an excellent prognosis. Complete surgical removal typically prevents recurrence. Incomplete excision may lead to regrowth or persistent draining tracts.

7. Complications to Watch

• Infection from leakage or secondary bacteria.
• Surgical complications—bleeding, swelling, slow healing.
• Cyst recurrence if capsule remnants remain post-excision.

8. Prevention Tips

• Promptly treat wounds, cleansed and debrided.
• Ensure clean suturing for sheath or skin surgery sites.
• Regular monitoring of healed lacerations or surgical scars.

9. Ask A Vet Support 🩺

At Ask A Vet, we help you monitor skin nodules, decide if excision is needed, plan aseptic surgical removal, guide post-op care, and set reminders for follow-up checks. Use our app to share photos, receive treatment plans, and access veterinary oversight—no visit required. Download the Ask A Vet app today for personalized skin health care in 2025 and beyond! ❤️

10. Quick Reference Table

11. FAQs

❓ Can epidermoid cysts turn cancerous?

No—cysts are benign, not pre-malignant, but biopsy confirms nature and guides care.

❓ Should I biopsy every skin lump?

Yes—any new or changing lesion should be aspirated or biopsied to rule out abscesses or tumors.

❓ How long does surgical removal take to heal?

Generally 2–4 weeks with careful wound care; deeper or infected cysts may need longer.

12. Final Thoughts

Epidermoid cysts are benign, rarely problematic—but prompt diagnosis and proper excision prevent complications and improve healing. With Ask A Vet, owners receive expert guidance at every step—from assessment to post-op—helping maintain skin health and peace of mind in 2025. Download our app now to access telehealth support for cysts and skin care! ❤️