Section: Skin and soft tissue Sub-section: Benign skin and soft tissue] Curriculum:
Sebaceous Cyst
Definition
- Benign encapsulated subepidermal cyst filled with keratin and lined by stratified squamous epithelium
- Also known as Epidermoid cyst and Epidermal Inclusion Cyst
- Sebaceous cyst is a misnomer because the cyst is not filled with sebum nor do they arise from sebaceous glands.
Incidence
- Early adulthood, M > F 2:1
- Patients with Gardner syndrome develop lots of lesions
Aetiology
- Occlude pilosebaceous unit
- Creates a cyst filled with keratin and lipid-rich debris
- Causes
- Congenital: Implantation during embryology
- Traumatic / surgical implantation
- Epidermal inclusion cyst where skin is ‘tucked in’ then continues to produce keratin which becomes trapped
- Occlusion of the pilo-sebaceous unit
Pathophysiology
- Rupture
- Incites an inflammatory reaction (? in response to trapped keratin)
- ± Secondary infection
- Smooth dome shaped fixed to under surface of epidermis ± punctum
- Face, scalp, neck & trunk
- Lined with keratinised squamous epithelium & granular cell layer, filled with keratin
- Multiple lesions associated with Gardner’s Syndrome (variant of FAP)
Pilar Cyst
a.k.a. Trichilemmal Cyst
Definition
- Slow gorwing subcutaneous cyst derived from the root sheath of the hair follicle and is most commonly located on the scalp
Risk
- Often strong family hx (AD inheritance)
- Can occur sporadically or in the setting of a hereditary predisposition with autosomal dominant transmission
- Frequently multiple (70%)
- Arise in middle age
- 90% occur on scalp
Pathology
- Have a palisaded peripheral layer without a granular layer
- Contains Eosinophilic hair keratin
- May have calcification
- Filled with amorphous material
Dermoid Cyst
Definition
- Congenital Hamartomatous Tumour
- Present from birth
- Seen along embryonic fusion lines
- On the face, scalp, and spine and contain epidermal and dermal tissues. The most common locations include the anterior fontanelle, the upper lateral region of the forehead near the eyebrow and the submental region
Types:
- Cutaneous: Most common on forehead
- At outer eyebrow “external angular dermoid”
- Neck
- Floor of the mouth
- Testicular / penile
- Intracranial
- Along embryological lines of closure
- Histologically similar to epidermal cysts BUT contain skin appendages
- Teeth, cartilage, bone
Treatment
- Excision
Milia
- Definition
- Subepidermal keratin cysts that arise from the pilosebaceous units or eccrine sweat ducts
- Clinical
- Firm, white papules, 1 to 2 mm in diameter, most frequently located on the face