FFinalistSouthampton · 2027
Dermatology
AKT · Dermatology/Benign lesionslow yield

Epidermoid cyst

Keratin-filled cyst lined by epidermis

Overview

A common benign cyst lined by epidermis and filled with keratin. A mobile, dome-shaped dermal nodule with a central PUNCTUM, classically discharging foul cheesy keratin if squeezed. Often mislabelled "sebaceous cyst". Only needs treatment if symptomatic, inflamed or infected.

Recognise

  • Smooth, mobile, firm dermal nodule with an overlying central punctum (the blocked follicular opening)
  • Discharges cheesy, malodorous keratin if it ruptures; can become red, hot and tender if inflamed/infected
  • Common on the trunk, face, neck and scrotum

Red flags

  • Recurrent inflammation/abscess; multiple cysts (consider Gardner syndrome — with intestinal polyposis)

Differentials & how to tell them apart

Lipomasoft, lobulated, deeper, NO punctum and does not discharge keratin
Pilar (trichilemmal) cystscalp, no punctum, often multiple/familial
Abscessacutely red, hot, tender, fluctuant — an inflamed cyst can mimic this
Dermatofibromafirm, dimples on pinching, no punctum

Clinical image

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Epidermoid cyst — clinical imagesDermNet

Investigations

Clinical diagnosis. Histology after excision if atypical.

Management

Reassurance; complete excision (cyst wall and all) only if symptomatic

  1. 1Reassure asymptomatic cysts. Inflamed/infected → treat the infection (antibiotics ± incision and drainage) first, do NOT excise while acutely inflamed.Gate: Excise a cyst only when it is QUIESCENT and remove the entire cyst wall — operating on an acutely inflamed cyst, or leaving wall behind, leads to recurrence
  2. 2Definitive treatment of a troublesome cyst = complete excision of the sac when settled.
Reassurance / no treatment — asymptomatic cysts need nothing
Antibiotics ± incision — if secondarily infected/abscess
Complete surgical excision — when quiescent — remove the whole cyst wall to prevent recurrence

Key points

"Sebaceous cyst" is a misnomer — most are epidermoid (keratin), not sebum. The central punctum is the recognition clue. Multiple cysts + bowel polyps = Gardner syndrome.

Monitor & prognosis

Recurrence if wall incompletely removed.

Benign; recurs if the cyst wall is not fully excised.

Source: NICE CKS; DermNet