Munro's microabscess is an abscess (collection of neutrophils) in the stratum corneum of the epidermis due to the infiltration of neutrophils from papillary dermis into the epidermal stratum corneum. They are a cardinal sign of psoriasis where they are seen in the hyperkeratotic and parakeratotic areas of the stratum corneum. Munro microabscesses are not seen in seborrheic dermatitis.
It is named for William John Munro.
References
Munro's microabscess Wikipedia(Text) CC BY-SA