This skin lesion is a keratoacanthoma. It is a benign, self-limiting skin lesion that occurs on exposed skin, most frequently on the hands and face. It begins as a small erythematous nodule that rapidly grows over 3 to 4 weeks to reach a
final size of up to 3 cm in diameter. At this stage it macroscopically shows an area of central ulceration filled with a keratin plug. It has characteristics heaped up shoulders around the crater. Subsequent involution occurs over 3 to 4
months often leaving an ugly and irregular pitted scar if not treated surgically. Most keratoacanthomas are single lesions but a small number of patients develop multiple recurrent lesions.
The aetiology of these lesions is unknown. They are more common in men. The rapid growth often raises clinical suspicion of a squamous cell carcinoma. Diagnosis can be confirmed by a biopsy that transects the lesion, including subcutaneous
tissue, as diagnosis depends on its histological architecture rather than cytological features. The important points differentiating a keratoacanthoma from a squamous cell carcinoma are the raised rolled edges with absence of rapidly dividing
neoplastic keratinocytes below the level of the deepest skin appendages.
Treatment is by excision biopsy. This results in a cosmetically more acceptable scar than if spontaneous resolution is allowed to occur. Large lesions at sites where surgery may be difficult can be treated by radiotherapy (600 -1000cGy).
Skidmore R A. Flowers F P. Non-melanoma skin cancer. Med Clin North Am 1998; 82: 1309-1323.