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Epidermal Naevus ; Inflammatory linear verrucous epidermal nevus

Prurigo Nodularis

Acanthomas - [ Epidermolytic acanthoma;Acantholytic acanthoma; Melanoacanthoma ]

Clear cell acanthoma

Large cell acanthoma

Warty Dyskeratoma

Seborrheic Keratosis

Verruca vulgaris; Palmoplantar wart; Verruca plana ; Epidermodysplasia verruciformis ; Condyloma acuminatum

Actinic Keratosis

Bowen's disease

Basal Cell Carcinoma

Squamous Cell Carcinoma

Verruciform Xanthoma

Keratoacanthoma was first described in 1889 by Jonathan Hutchinson.  He described the lesion as  'crateriform ulcer of face'.

Keratoacanthoma is a controversial cutaneous tumour that usually occurs in elderly patients. Males are more often affected than females.

Keratoacanthomas often occur spontaneously as a single rapidly growing tumour on sun-exposed skin.  Multiple keratoacanthomas are rarely seen. Keratoacanthomas may also develop after trauma, laser resurfacing, radiation therapy, and at the donor site after skin grafting.

This lesion grows rapidly to the size of 1-2 cm over a period of one to two months and tend to resolve spontaneously after several weeks to months leaving an atrophic scar.

Macroscopic features:

The lesion presents as solitary  nodule with a central keratin plug.

Microscopic features:   

Keratoacanthoma is an exoendophytic, symmetrical lesion characterized by deep bulbous lobules of keratinizing  well differentiated squamous epithelium  with  central keratin  filled crater.
There is marked acanthosis with hyperkeratosis and little or no parakeratosis.
In early lesions there is marked atypia and mitotic figures on the base of the lesion.
Cells in the centre of the tumour have a "glassy"  appearance.
There is lipping of edges of normal epidermis that extends over the central keratinous crater.
Prominent inflammatory cell infiltrate is present around the lesion. This tumour does not extend below the level of sweat glands.
The regressing lesion is characterized by loss of crateriform appearance, band of fibrosis, granulomatous infiltrate, and less cytological atypia.
Perineural and vascular invasion may be present.
Microabscesses are common at the advancing edge of these lesions.

Differential diagnosis:

The histologic differential diagnosis of keratoacanthoma is principally with  well differentiated squamous cell carcinoma .
The following features favour the diagnosis of  keratoacanthoma over squamous cell carcinoma.
-  Rapidly growing lesion with a characteristic low power appearance of a crateriform lesion with central keratinous plug.
- Cytological pleomorphism is  less common.
- The cytoplasm has a glassy, pale eosinophilic appearance.
- There is an abrupt transition between the lesion and adjacent epidermis and a sharp outline between the tumour nests and stroma.
- Absence of stromal desmoplasia
- Presence of intraepithelial elastic fibres and intracytoplasmic glycogen.

Rare variants:
Giant keratoacanthoma ;
Keratoacanthoma centrifugm marginatum (multinodular keratoacanthoma) ;
Subungual keratoacanthoma  ;
Multiple Keratoacanthoma.

Gross examination of the skin specimen

Reporting of biopsies taken for Inflam matory Skin Diseases

Lichenoid (Interface)Tissue Reaction Pattern

Psoriasiform Reaction Pattern

Vesiculobullous Reaction Pattern

Spongiform Reaction Pattern

Vasculopathic Reaction Pattern

Lichen planus-like lesions

Lichen Nitidus

Bullous Pemphigoid

Dermatitis Herpetiformis

Hailey-Hailey Disease 

Erythema Nodosum

Folliculitis

Impetigo

Furuncle(Boil)

Carbuncle

Toxic Shock Syndrome

Lassa Fever

Leishmaniasis

Legionellosis

Leprosy

Malaria

Marburg Virus Disease

Meningococcal Infection

Microsporidia

Mycobacterium Leprae Inf.

Mycobacterium Avium Intracellulare

Mycobacterium ulcerans Inf.

Mycoplasma pneumonia

Necrotizing Enteritis (pig-bel)

Nocardiosis

Norwalk Virus related Diarrhea

Onchocerciasis

Shigellosis

Skin infections- (Histo-pathological patterns)

Staphylococcal Infection

Streptococcal Infection

Strongyloidiasis

Subacute Sclerosing Panencephalitis

Syphilis

Tetanus

Toxic Shock Syndrome

Toxoplasmosis

Trachoma

Trichinosis

Trichosporonosis

Trichuriasis

Tuberculosis