Reticulate eruptions: Part 2. Historical perspectives, morphology, terminology and classification

Reticulate eruptions of vascular origin may represent an underlying arterial, venous, microvascular or combined pathology. In the presence of arterial pathology, individual rings are centred around ascending arterial vessels that supply the corresponding area of skin within an arterial hexagon that clinically presents with a blanched centre. Confluence of multiple arterial hexagons generates a stellate (star-like) pattern. In the presence of a primary venous pathology, individual rings correspond to the underlying reticular veins forming multiple venous rings. Focal involvement of a limited number of vessels presents with a branched (racemosa) configuration while a generalized involvement forms a reticulate (net-like) pattern. 'Livedo' refers to the colour and not the pattern of the eruption. Primary livedo reticularis (Syn. cutis marmorata) is a physiological response to cold and presents with a diffuse blanchable reticulate eruption due to vasospasm of the feeding arteries and sluggish flow and hyperviscosity in the draining veins. Livedo reticularis may be secondary to underlying conditions associated with hyperviscosity of blood. Livedo racemosa is an irregular, branched eruption that is only partially-blanchable or non-blanchable and always signifies a pathological process. Retiform purpura may be primarily inflammatory with secondary haemorrhage or thrombohaemorrhagic, as seen in disseminated intravascular coagulopathy.