Keratoacanthoma

A keratoacanthoma (KA) is a rapidly evolving tumour of the skin, composed of keratinising squamous cells originating in pilosebaceous follicles and resolving spontaneously if untreated.

This chapter is set out as follows: 

• Sun exposure plays a role
• In some cases the lesion may follow an injury to the skin

• Males are more commonly affected than females
• Lesions grow rapidly

Distribution

• Normally UV-exposed skin 

Clinical features

• Lesions look very similar to well-differentiated SCC, although their behaviour may differ in that:
  • KA grow rapidly over a period of about 12 weeks from a small, firm, rounded, skin-coloured to red papule, in to a very symmetrical dome-shaped nodule with a smooth shoulder of skin and a central keratin core, giving it a volcano-like appearance
  • Lesions start to resolve after approximately three months
  • On rare occasions a keratoacanthoma can appear yellow, looking almost sebaceous in nature 

Dermoscopic features (hover over terminologies for description) are often similar to those of an SCC, and may include:

• A central white keratin mass, which may look yellow if keratin mixes with serum due to erosion or ulceration
   
• Other white//yellow structureless areas
   
• Targetoid hair follicles - these are variably large roundish structures composed of a yellow to light-brown structureless centre and a white outer rim (these structures are sometimes referred to as white or yellow clods or circles), and are found around the central keratin
   
• Peripheral and often radial vessels (ie pointing to the centre), which may be serpentine, arborising, or looped; occasionally glomerular. Click here for more information on Vessel patterns in dermoscopy  

• It can be difficult to distinguish clinically and histologically between a KA and an SCC and so patients should be referred urgently (two-week wait) to Secondary Care - dermatology or plastic surgery (check local pathways)