Epidermoid Cyst
An epidermoid cyst, also called an epidermal inclusion cyst or infundibular cyst (and often loosely called a "sebaceous cyst"), is the most common benign cyst of the skin. It is a sac lined by fully keratinizing stratified squamous epithelium, sitting in the dermis or subcutis and filled with degenerated keratin packed in onion-skin layers.
Follicular Origin and Epidermal Implantation
- Origin in the infundibulum: Most epidermoid cysts arise from the follicular infundibulum. When the opening becomes blocked by sebum, scale or minor injury, shed skin cells cannot escape to the surface; they become trapped and gradually expand into a cyst.
- Traumatic implantation: Some epidermoid cysts appear on the palms, soles or other hair-free areas after a penetrating injury pushes epidermal cells down into the dermis, where they keep multiplying and wall themselves off inside an epithelium-lined sac.
Cyst Rupture and the Foreign-Body Inflammatory Reaction
- Keratin buildup: Over time, the cells lining the cyst keep breaking down and releasing keratin, cholesterol and degenerated lipids, so pressure inside the cyst rises.
- Spontaneous or traumatic rupture: When the pressure gets too high, or the cyst is squeezed or rubbed, the wall tears and keratin spills into the surrounding dermal connective tissue.
- Sterile foreign-body granulomatous reaction: The immune system treats keratin in the dermis as a foreign body and mounts an intense acute inflammatory response with neutrophils, macrophages and multinucleated foreign-body giant cells. The cyst becomes swollen, red and very painful. This is sterile inflammation, and it is often mistaken for a bacterial abscess.
At Haute-Derma, we tailor treatment to the state of the cyst (intact versus ruptured/inflamed). Using 20–50 MHz high-frequency skin ultrasound and digital dermoscopy, our doctors map the cyst's depth, wall thickness and any inflammatory hypervascularity around it. For quiet cysts, we favor micro-incision complete sac extirpation through a minimal (2–3 mm) opening, removing the entire wall to eliminate the risk of recurrence. If the cyst is acutely inflamed or ruptured, treatment focuses first on micro-injections to settle inflammation, relieving pressure inside the cyst and tissue recovery with 595 nm Vbeam laser and Pincer Biomodulation, before the remaining cyst wall is removed completely.
Histopathology and Dermoscopic/Ultrasound Diagnostic Criteria
Characteristic Microscopic Findings
Under the microscope, an epidermoid cyst shows these classic epithelial features:
- Cyst wall: lined by fully keratinizing stratified squamous epithelium, with a spinous layer, a well-developed granular layer (stratum granulosum) and an inner cornified layer.
- Cyst lumen: filled with keratin arranged in concentric, onion-skin layers (lamellated concentric keratin flakes). It contains no hair shafts and no purely liquid sebum.
- Foreign-body reaction (after rupture): the cyst wall is broken and surrounded by a dense inflammatory infiltrate containing foreign-body giant cells, plasma cells, histiocytes and reactive fibrosis.
Dermoscopy and High-Frequency Skin Ultrasound (20–50 MHz)
Haute-Derma's non-invasive imaging lets us characterize the cyst before any procedure:
- Dermoscopy:
- Central punctum (pore sign): a small gray-brown or dark yellow dimple at the top of the bump, marking the follicular opening plugged with keratin.
- Off-white/yellowish area: reflects the dense keratin mass beneath a thinned epidermis.
- Telangiectatic vessels: fine, slightly branching capillaries around the base of the cyst, caused by pressure.
- High-frequency skin ultrasound (20–50 MHz, the gold standard):
- Shape: a well-defined, round or oval hypoechoic mass in the dermis or subcutis.
- "Snowflake" (pseudotesticular) pattern: the hypoechoic area contains many small, mobile bright echoes (hyperechoic foci), which are rolled-up flakes of keratin.
- Posterior acoustic enhancement: caused by the ultrasound beam passing through semi-liquid keratin.
- Doppler flow: no blood flow inside the cyst (avascular). If the cyst is inflamed or ruptured, Doppler shows marked hyperemia in the surrounding rim.
Clinical Presentation
- Primary lesion: a dome-shaped papule or subcutaneous nodule with a smooth surface and firm, rubbery feel. It moves slightly over deeper tissue but is usually tethered to the overlying skin at the punctum.
- Common sites: face, neck, chest, upper back, scrotum/genital area and behind the ears (areas rich in sebaceous glands and hair follicles).
- Cyst contents: when squeezed or nicked, the cyst releases thick, creamy white-yellow keratin with a strong, characteristic odor caused by lipid breakdown and saprophytic bacteria.
Clinical and Histologic Comparison
| Epidermoid Cyst | Trichilemmal (Pilar) Cyst | Dermoid Cyst |
|---|---|---|
| Distinct granular layer in the cyst wall | NO granular layer (trichilemmal keratinization) | Granular layer + skin appendage structures |
| Punctum usually visible at the top | Punctum very rarely present | No punctum |
| Face, neck, back, chest | 90% on the scalp | Midline (around the eyes, nose) |
| Layered, onion-skin keratin; foul-smelling | Dense, uniform, sticky keratin | Keratin, fat, hair, sebum |
| Hypoechoic + "snowflake" bright spots | Uniformly hypoechoic, thick wall, calcification | Complex mixed-echo cyst |
Complete Sac Micro-Excision and Reconstruction at Haute-Derma
Our treatment of epidermoid cysts pursues two goals at once: removing the entire cyst wall to prevent recurrence, and achieving the best cosmetic result without an unsightly scar:
Ultrasound Mapping and Inflammation Control (Inflamed Cysts)
- Non-inflamed cyst: proceed directly to micro-excision.
- Inflamed or ruptured cyst: we never perform a wide excision right away. Instead, triamcinolone acetonide (5–10 mg/ml) is micro-injected around the cyst wall and the punctum is nicked to release inflammatory fluid. A 595 nm Vbeam Perfecta laser calms the vascular reaction. Only after 7–14 days, once the cyst wall has localized and the inflammation has settled, do we move on to Step 2.
Minimal-Incision Micro-Extirpation of the Intact Sac
- Micro-incision: the doctor uses a microsurgical blade or a 2–3 mm punch to make a minimal opening right at the punctum.
- Expressing the keratin: the dense keratin is gently pressed out through the opening to shrink the cyst.
- Grasping and removing the whole sac (sac extirpation): fine microsurgical forceps are used to free the cyst wall from the surrounding connective tissue and draw the entire sac out intact. Removing 100% of the cyst wall is what keeps the cyst from ever coming back.
- Closing the micro-incision: the cavity is closed with ultra-fine (6-0 to 7-0) monofilament intradermal sutures, avoiding a coarse linear scar.
Biological Repair of the Cavity and Scar Prevention
- Molecular regenerative therapy: Haute-Derma's proprietary Pincer Biomodulation technique is applied to the base of the emptied cavity to stimulate collagen production, fill the tissue defect and prevent a depressed scar.
- Vbeam laser and dressings: 595 nm Vbeam laser stabilizes the microcirculation at the incision, and a sterile hydrocolloid patch protects the wound for 5–7 days.
