Main

Sir,

Keratoacanthoma is a benign epithelial neoplasm first described by Sir Jonathan Hutchinson1 in 1889 as a crateriform ulcer of the face. Although there are many variants of the disease, it usually presents as a solitary rapidly growing lesion and is associated with sun-exposed skin. Its aetiology is diverse, ranging from ultraviolet exposure, viral infection by human papilloma virus, immunosuppression, and genetic susceptibility.2

Case report

An 84-year-old lady presented to the clinic complaining of a small painless pea-sized nodule of the left lower eyelid near the medial canthus, which began a week earlier. Her history revealed that she spends most of her time outdoors, gardening, and walking. Examination revealed a firm, nontender, ulcerated nodule of 1?cm in diameter. She also had a skin lesion on her forehead suggestive of basal cell carcinoma. A provisional diagnosis of basal cell carcinoma was made. She was scheduled for biopsy a month later but returned to the clinic in under 2 weeks during which the tumour on the left lower eyelid had dramatically increased in size and was now a fungating bleeding mass. An excision biopsy was performed the following day. The lesion was noted to be friable and was surprisingly easily peeled away from its crater-like base in its entirety (Figure 1). Biopsy of the forehead lesion confirmed basal cell carcinoma. Histology of the lower lid lesion revealed a keratoacanthoma-like squamous cell carcinoma. The lesion was completely excised and the patient has made an excellent recovery with no evidence of recurrence to date (Figure 2).

Figure 1
figure 1

Left lower lid lesion. ‘Eschar’ from top of lesion came away easily. Note crater-like base.

Full size image
Figure 2
figure 2

Fully excised lesion. Note skin surrounding the lesion looks healthy. A 0.5?mm margin was excised and confirmed healthy skin on histological examination.

Full size image

Comment

Typical histology of a keratoacanthoma is an overall symmetrical lesion with a central keratotic crater surrounded by layers of well-differentiated epithelial cells that may have cytological atypia forming a distinct lip around the lesion. Difficulty in histological diagnosis occurs when the lesion is not completely excised, when it is tangentially cut or in the presence of cytologic atypia of the epithelial lip; confusing keratoacanthoma with well-differentiated squamous cell carcinoma.2 To date, there is no reliable histological criteria to distinguish squamous cell carcinoma from keratoacanthomas3 in the absence of special immunohistochemical staining for bcl-24 and proliferating cell nuclear antigen.5

Clinically, at least 25% of the keratoacanthomas undergo malignant transformation, particularly in photoexposed areas and in elderly patients. This transformation may occur in a single focus, hence it is essential that the entire lesion is completely excised and serial histological blocks are studied in detail to rule out a small focus of malignant change which may metastasise.6 The remainder of keratoacanthomas may either remain a benign lesion or may spontaneously undergo resolution, the mechanism of which is suggested to be immunologically mediated.7 Owing its ability to undergo malignant change and in the absence of predictive prognostic factors, all keratoacanthomas should be completely excised6, 8 and atypical cases should be treated as squamous cell carcinoma.3