Updated: 12/4/2019

Epidermal Inclusion Cyst

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https://upload.orthobullets.com/topic/6087/images/epidermal inclusion cyst clinical photograph.jpg
https://upload.orthobullets.com/topic/6087/images/epidermal inclusion cyst clinical image.jpg
https://upload.orthobullets.com/topic/6087/images/epidermal inclusion cyst clinical photo.jpg
https://upload.orthobullets.com/topic/6087/images/epidermal inclusion cyst.jpg
  • A painless, benign, slow-growing soft tissue tumor that often occurs in the hand
    • occurs months to years after a traumatic event
  • Epidemiology
    • incidence
      • third most common hand tumor
    • demographics
      • more common in men than women
      • occurs in the third to fourth decade
    • location
      • the distal phalanx is commonly involved
  • Pathophysiology
    • results from a penetrating injury that drives keratinizing epithelium into subcutaneous tissues or bone
    • cells grow slowly to produce an epithelial cell-lined cyst filled with keratin
  • Prognosis
    • excision is curative  
    • malignant transformation has not been reported
  • Symptoms
    • painless mass, most commonly occurring in the fingertip
    • although less common, erythematous, painful lesions have been reported
  • Physical exam
    • inspection & palpation
      • flesh-colored, yellow, or white in appearance
      • well-circumscribed, firm, slightly mobile lesions
        • lesions are firmer than ganglion cysts and do not transilluminate
      • often superficial and tethered to overlying skin
    • range of motion
      • there may be loss of ROM when lesions are large and occur near IP joints
    • neurovascular exam
      • sensory deficits may be evident with 2-point discrimination testing secondary to digital nerve compression
  • Radiographs
    • recommended views
      • AP, lateral, and oblique views of the involved digit or hand
    • findings
      • soft tissue mass may be evident
      • a lytic lesion of the distal phalanx may be present if the cyst erodes into bone
        • may mimic a malignant or infectious process
  • Biopsy
    • indications
      • should be considered before surgical excision to rule out neoplasm or infection if a lytic bony lesion is present in the distal phalanx
  • Histology
    • gross appearance
      • cysts contain a thick, white keratinous material
    • characteristic findings
      • cysts filled with keratin and lined with epithelial cells
  • Tophaceous gout
  • Foreign body granuloma
  • Sebaceous cyst
  • Pyogenic granuloma 
  • Giant cell tumor
  • Ganglion cyst
  • Enchondroma
  • Glomus tumor
  • Nonoperative
    • observation
      • indications
        • not recommended
  • Operative
    • marginal excision
      • indications
        • diagnosis of epidermal inclusion cyst
        • painful lesions
        • loss of function
        • cosmetic concerns
      • technique
        • careful dissection to remove the entire capsule
        • local curettage and bone graft may be required for lesions eroding bone
        • amputation is an alternative with advanced bony destruction in rare circumstances
      • outcomes
        • marginal excision is curative
        • low recurrence rate
  • Wound complications
  • Infection
  • Digital neurapraxia
  • Recurrence
    • recurrence rate is low even with bony involvement

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