pilar sheath acanthoma (Monarch Disease Ontology term MONDO_0006907) is a benign, small, papular or nodular skin neoplasm that usually arises above the upper lip. It is characterized by an epithelial proliferation with a central cavity. The cavity wall is lined with keratinocytes. Also known as: Infundibuloisthmicoma, Pilar sheath acanthoma, acanthoma of Pilar sheath, acanthoma of the Pilar sheath.