Epidermoid and pilar cysts (sebaceous cysts) Flashcards
Are epidermoid and pilar cysts sebaceous cysts?
This is a misnomer as neither are of sebaceous origin
What is an epidermoid cyst? Where do they most commonly occur?
These are epidermal or subcutaenous cysts (benign) , which most commonly occur on the face, scalp, neck, back and scrotum.
What are the causes of epidermoid cyst formation? What are the risk factors?
Risk factors :
- Being past puberty
- Having certain rare genetic disorders - Gardner syndrome (subtype of FAP)
- Injuring the skin
Causes: epidermis constantly sheds cells; when these instead move deeper into the dermis and keep multiplying, a cyst forms. This is usually due to disruption of skin or of the hair follicle. The walls are formed by epithelial cells and the inside contains keratin (thick, yellow). They can become infected. They can also be caused by a blcoked pore adjacent to a body piercing.
How common are epidermoid and pilar cysts?
- Most people will probably have one in their lifetime.
- Most frequent in 20-30yrs
- Epidermoid cysts can be seen in Gardner’s syndrome and Nevoid BCC syndrome.
- Pilar cysts occur in 5-10% and over 90% found on scalp. Can have an autosomal dominant inheritance pattern and be multiple
Both are sometimes called sebaceous cysts even though they do not truly originate from the sebaceous glands.
What is the name of a skin cyst of the eyelid?
Chalazion/meibomian cyst
What is a pilar cyst?
AKA trichilemmal cyst; a common cyst that forms from the hair follicle and most commonly occurs on the scalp. These may run in the family.
What are the causes of pilar cysts? What are the risk factors for them?
- Derived from the root sheath of the hair follicle. Origin is unknown but suggested that budding from the external root sheath is a genetic abberation. This is why they predominantly arise in areas of high hair follicle concentration.
- They are solitary in 30% and multiple in 70%.
- They contain keratin and its breakdown products and are lined by walls resembling the external (outer) root sheath of the hair
RF:
- Genetics - inheritance pattern is autosomal dominant if hereditary
- Occur more commonly in women
- No racial predilection
- More common in middle aged population
What is the difference in distribution of epidermoid and pilar cysts?
Pilar cysts - 90% are found on the scalp and 70% of people have multiple
Epidermoid cyst - usually found in areas of little hair; sites most commonly affected (in descending order of frequency) face, trunk, neck, extremities and scalp.
What is the differential diagnosis with these cysts? What is the difference?
- A lipoma tends to be larger and is very soft.
- A neurofibroma is hard and may be multiple.
- An abscess is hot and red and may resemble an infected sebaceous cyst.
- Multiple cysts in a teenager may suggest Gardner’s syndrome.
What is the typical presentation of pilar cysts?
- Skin coloured, smooth, mobile, firm and well-circumscribed nodules
- No punctum is seen
- Occassionally extrude to form a soft, cutaneous horn
- In areas of dense hair follicles - 90% on scalp
- May be red, swollen, tender if ruptured/infected
- Slwo growing nodule (usually in females)
- Rapid growth if infected/malignant
What is the typical presentation of an epidermoid cyst?
- Usually asymptomatic
- Firm, round, mobile, flesh-coloured or yellow to white nodules of variable size
- Visible punctum
- Occur on face, trunk, neck, extremities (in order) but also in genitals, breasts. Sometimes painful during sex/cause problems walking if on genitals.
- May have a discharge of “cheeselike” smelling material
- Rarely become inflammed or infected –> pain, tenderness
What investigations would you do for epidermoid/pilar cysts?
Usually the diagnosis is clear and no investigations are required. In exceptional cases malignancy may be suspected, in which case excision and histology are required.
