Age / Sex : 34 / M

Chief complaint: Left 2^nd finger pain

PMHx: Lt. 2^nd finger crush injury (10YA)

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Courtesy of Sung Hwan Hong, Seoul National University Hospital

Discussion

Diagnosis: Intraosseous epidermal (epidermoid) cyst

Discussion:

Intraosseous epidermal cysts occur most frequently in the distal phalanges of the hand and in the skull, but have been reported in the toes as well. While a congenital etiology with intraosseous inclusion of embryonal epithelial tissue has been proposed, a post-traumatic origin remains the most prevalent hypothesis as many patients do recall an antecedent traumatic event (such as crush injury or amputation). One theory is that intraosseous epidermal cysts are the result of epidermal cysts from subungual soft tissue eroding into underlying bone. Thus, it is not certain whether soft tissue and intraosseous epidermal cysts are two discrete disease entities.

At radiography, the intraosseous epidermoid cyst appears as a circumscribed unilocular osteolytic lesion with thinned or broken cortex. At MR imaging, epidermal cysts characteristically manifest as well-defined round lesions against high-signal-intensity backgrounds with variable low-signal-intensity components on T2- weighted images and bright foci on T1-weighted images. The lack of contrast enhancement can help differentiate epidermal cyst from other solid lesions.

The differential diagnosis of intraosseous epidermal cyst in the distal phalanx includes enchondroma, glomus tumor, aneurysmal bone cyst, tenosynovial giant cell tumor, metastasis and osteomyelitis. Enchondroma remains the most common bone tumor of the hands and feet and is the most frequent lesion seen in the distal phalanx of the digits. Enchondromas often display intralesional calcification and classically involve the proximal part of the distal phalanx. Intraosseous epidermal cysts are typically based at the distal part of the distal phalanx, but lesions originated at the proximal part of the distal phalanx have been also reported.

Intraosseous epidermal cyst should be considered as one of the differential diagnosis in cases of expansile osteolytic lesions of distal phalanx, especially when there is history of blunt or penetrating trauma. Intralesional curettage and bone grafting is the accepted treatment of choice with low risk of recurrence.

References:

1. Simon K, Leithner A, Bodo K, Windhager R. Intraosseous epidermoid cysts of the hand skeleton: a series of eight patients. J Hand Surg Eur Vol 2011;36:376-378


2. Baek HJ, Lee SJ, Cho KH, Choo HJ, Lee SM, Lee YH, Suh KJ, Moon TY, Cha JG, Yi JH, Kim MH, Jung SJ, Choi JH..Subungual tumors: clinicopathologic correlation with US and MR imaging findings. Radiographics 2010 ;30:1621-1636


3. Memon F, Panjwani TR, Patankar H. Intraosseous Epidermoid Inclusion Cyst of Distal Phalanx: A Rare Entity. J Clin Diagn Res 2016;10:RJ01-2


4. Ruchelsman DE, Laino DK, Chhor KS, Steiner GC, Kenan S. Digital intraosseous epidermoid inclusion cyst of the distal phalanx. J Hand Microsurg 2010;2:24-27


5. Chung MK, Park MS, Kim YS, Lee T, Lee KM, Cho BC. An intraosseous epidermoid cyst that originated from the nail bed of great toe with concurrent joint infection: a case report. J Korean Foot Ankle Soc 2016;20:50-53