Combined naevus

Combined naevi are clinically defined as melanocytic lesions comprising two or more distinct melanocytic naevus components; histologically lesions are determined by the presence of two or more different naevus cell types in one biopsy specimen. They are uncommon representing less than 1% of all biopsied melanocytic naevi. Combined naevi include any combination of melanocytic naevi, the most common is a blue naevus combined with a common brown melanocytic naevus. Given the combination of colours some combined naevi mimic melanoma.

This chapter is set out as follows:

• Although combined naevi are mainly congenital, many are not visible at birth
• Combined naevi can be seen at any age, most commonly presenting in young adults
• There is a slight male predominance 

• Distribution
  • Most frequently affect the trunk and head and neck region,  less commonly the extremities 
     
• Morphology
  • Since combined naevi are composed of distinct naevi, their clinical appearance could be very diverse. In practice, combined naevi are usually small, flat, or minimally raised lesions, often characterised by a small blue area (rarely black or white) in the context of a larger area of brown colour surrounding the blue naevus 
     
• Dermoscopy (hover over terminologies for description)
   
  • Since combined naevi are composed of at least two different naevus types in various combinations, their dermoscopic features are characterised by mostly multicomponent, unspecific, and sometimes random patterns
     
  • Differentiating combined naevi from melanoma:
     
    • Combined naevi - typically, the multicomponent structure of combined naevi exhibit a reasonably symmetrical appearance, which is consistent with already established findings that benign naevi tend to exhibit symmetry. The structureless blue part of the lesion is commonly central or off-centre, usually covering about 30% of the lesion. If located centrally, the blue structureless area is surrounded by another pattern, most commonly a brown globular pattern or pigment network. Benign lesions should lack dermoscopic melanoma-specific features
       
    • Melanoma - should be considered if the blue area is greater than 30% or touches the edge, if blue is combined with a colour other than brown, in chaotic lesions (asymmetry of structures or colour) and those with any dermoscopic melanoma-specific features

• In cases of diagnostic uncertainty lesions should be referred on an urgent skin cancer pathway  
• Lesions are often excised with a 2 mm margin of normal skin to confirm the diagnosis and exclude melanoma