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