The grenz zone.

The grenz zone is a narrow area of the papillary dermis uninvolved by underlying pathology. Historically believed to be a feature unique to granuloma faciale, this feature has also been observed in other cutaneous inflammatory conditions, infectious entities, and neoplastic benign and malignant tumors. This review attempts to enumerate cutaneous entities commonly displaying a grenz zone with an emphasis on histopathological features that help in their differentiation. It also attempts to answer the obvious question of why select entities have this histopathologic feature by ascertaining the defining structure of a grenz zone.