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Case of the Week #253

28 September 2012 - Case of the Week #253

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Thanks to Dr. Saroona Haroon, The Aga Khan University Hospital (Pakistan), for contributing this case. To contribute a Case of the Week, follow the guidelines on our Case of the Week page.

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(1) The Skin - Nonmelanocytic tumors chapter has now been updated, based on reviews by Christopher Hale, M.D., NYU Langone Medical Center, New York. We plan to have a recent update (since 2010) for all chapters by the USCAP meeting in March 2013, and then to update each chapter every 12-18 months. We also plan to add more images and references to each topic.

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Case of the Week #253

Clinical History:

A 70 year old woman presented with a painless cheek lesion for the past 4 months, which was increasing in size.

Gross images:


Micro images:



What is your diagnosis?




Keratoacanthoma is considered by some to be a well differentiated cutaneous squamous cell carcinoma. It typically (80%) occurs in males, on the sun exposed face, and is associated with inflammatory dermatoses, congenital lesions, genetic diseases and scars. Those affected are usually younger than in classic cutaneous squamous cell carcinoma. Clinically, most cases arises from normal skin, grow rapidly for 4-8 weeks, then regress over 6 months to leave a depressed, annular scar.

Histologically, the early phase is composed of well circumscribed solid lobules of large, pale squamous cells with little keratinization. The follicular infundibulum is distorted, and there is mild atypia. The stable phase, which is often excised, has a central crater filled with keratin, but no granular layer. There are larger and more irregular infiltrating squamous nests and islands, accompanied by a marked inflammatory infiltrate with lichenoid features and eosinophils but no plasma cells. The squamous cells may be deeply infiltrative, with microabscesses of neutrophils and eosinophils approaching the surface. There is also often marked atypia with mitotic figures, atypical mitotic figures at the periphery, perineural invasion and rarely vascular invasion. The regressing (resolving) phase is characterized by a keratin filled crater, but with mature epithelium without atypia. There is flattening of the cup-shape, horizontal fibrosis in dermis, reduced inflammation and perforating elastic fibers (J Cutan Pathol 2012;39:243).

The differential diagnosis includes squamous cell carcinoma, which usually lacks the overhanging edges, the keratin-filled crater and the hemispheric shape. Other diagnoses to consider basal cell carcinoma, nodular melanoma (non-pigmented, Sultan Qaboos Univ Med J 2012;12:360), pilomatricoma and hypertrophic lichen planus.

Most lesions regress, but show persistent crateriform architecture (J Am Acad Dermatol 2012 Apr 19 [Epub ahead of print]). Rare metastases have been reported (but see Semin Diagn Pathol 2009;26:150). Traditional treatment is surgical, but intralesional methotrexate (Can J Plast Surg 2011;19:e15) and topical imiquimod cream (Ann Dermatol 2011;23:357) have also been effective.

Nat Pernick, M.D., President
and Palak Thakore, Associate Medical Editor
PathologyOutlines.com, Inc.
30100 Telegraph Road, Suite 408
Bingham Farms, Michigan (USA) 48025
Telephone: 248/646-0325
Email: NatPernick@Hotmail.com
Alternate email: NatPernick@gmail.com