Updated: 5/22/2021

Epidermal Inclusion Cyst

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  • Introduction
    • 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
    • Anatomic location
      • the distal phalanx is commonly involved
  • Etiology
    • 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
  • Presentation
    • 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
  • Imaging
    • 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
  • Studies
    • 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
  • Differential
    • Tophaceous gout
    • Foreign body granuloma
    • Sebaceous cyst
    • Pyogenic granuloma
    • Giant cell tumor
    • Ganglion cyst
    • Enchondroma
    • Glomus tumor
  • Treatment
    • 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
  • Complications
    • Wound complications
    • Infection
    • Digital neurapraxia
    • Recurrence
      • recurrence rate is low even with bony involvement
  • Prognosis
    • Excision is curative
    • Malignant transformation has not been reported

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