Finger Lesion Is Painful When Bumped

DISCUSSION
This type of cyst is sometimes referred to as an implantation cyst and occurs when epidermal tissue, including sebaceous glands, is implanted into deeper tissue by a penetrating injury and continues to grow. Although this is an utterly common and benign diagnosis, the differential for a “fingeroma” includes digital mucous cyst, pyogenic granuloma, acquired digital fibrokeratoma, calcinosis cutis, tophaceous gout, wart, and giant cell tumor. Had the lesion been of bony origin, it could have represented connective tissue cancer (sarcoma) or even metastatic cancer.

Implantation cysts must be removed completely to prevent recurrence. The size and location of this particular cyst made it conducive to simple excision and primary closure. Larger lesions in more difficult locations often require the expertise of a hand surgeon for disposition.

TAKE-HOME LEARNING POINTS
• “Fingeromas” are quite common but have an extensive differential diagnosis—mostly benign, but occasionally malignant.

• Regarding malignancy, it is helpful to remember that any tissue in the body can undergo malignant transformation and that many types of primary cancers can metastasize to distant areas (including the hands).

• Removal, or at least biopsy, is the best way to differentiate between types of fingeroma lesions.

• Implantation cysts, as seen in this case, result from traumatic implantation of epidermal structures (including sebaceous glands) into deeper tissue, where they continue to grow.

• When in doubt, consider referring affected patients to dermatology or to a hand surgeon.