DermaDiagnosis

Growing Lesion Impedes Finger Flexion

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For several years, a 45-year-old man has had an asymptomatic lesion on the volar aspect of his fourth finger. The lesion is growing and increasingly “in the way.” That, coupled with the patient’s concern about cancer or other serious disease, leads him to request referral to dermatology. There is no history of similar lesions anywhere on his body. Additional questioning reveals that several months prior to the lesion’s manifestation, the patient sustained a puncture wound to the same finger. Initially, the affected area was only a millimeter or two in size. X-rays ordered by his primary care provider did not indicate any bony abnormality, nor did they shed any light on the lesion itself. An impressive 2.6 cm in diameter, the lesion is prominent in vertical elevation as well. Motor and sensory function are found to be intact, although the bulk of the lesion prohibits full flexion of the finger. The lesion is opaque to attempted transillumination. No surface changes are apparent in the overlying skin. Skin lines are intact and parallel. The lesion is quite firm but compressible. The decision is made to excise the lesion, employing a digital block and tourniquet. A football-shaped ellipse of skin with 50° angles on the ends is removed from the surface, revealing a glistening white, smooth mass that comes out intact, with very little blunt dissection. Motor function is again assessed and found to be intact. The large angles in the ends of the ellipse allow the wound edges to be pulled together with interrupted vertical mattress sutures and no leftover redundant skin. The lesion is submitted intact for pathologic examination.

The most likely diagnostic explanation for this lesion is:

a) Ganglion cyst

b) Implantation cyst

c) Wart

d) Acquired digital fibrokeratoma

ANSWER

The correct answer is implantation cyst (choice “b”). This type of cyst is typically caused by trauma (eg, a puncture wound), and its contents are in stark contrast to those of ganglion cysts (choice “a”), which are thick and clear.

Warts (choice “c”) are essentially an epidermal process, not subcutaneous. They almost always disrupt normal skin lines, which often curve around the wart—a finding that was missing in this case.

Acquired digital fibrokeratomas (choice “d”) are benign solid tumors frequently seen on fingers. However, they are more epidermal than intradermal and demonstrate a diagnostic feature called an epidermal collarette (missing in this case).

DISCUSSION

Sometimes called implantation dermoid cysts, these sacs have a well-defined white cyst wall and cheesy, often odoriferous contents. Although common on hands and fingers, they can occur in almost any location and as a result of many types of trauma.

This includes surgical trauma, which effectively implants surface adnexal tissue (eg, the sebaceous apparatus) where it can continue to produce and accumulate its cheesy contents over time. Patients often forget the trauma that caused the cyst, but it is still worth inquiring into.

Merely emptying the sac can confirm the diagnosis; however, this almost always results in recurrence. Fortunately, implantation cysts are usually easily removed with minimal risk to hand function.

As with almost any tissue removed from the body, the specimen needs to be sent for pathologic examination. In addition to the differential items already noted, a number of rare or unusual conditions can present in a similar fashion, including eccrine carcinoma and a variety of sarcomas.

This patient recovered from his surgery without complication. Pathologic examination confirmed the benign nature of the lesion.

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