The pathology of butterfly densities in uraemia.

Seven cases are presented which are considered to throw some light on the pathology of butterfly densities and their pathogenesis. It is shown that reversible butterfly densities may represent pulmonary vascular congestion and readily reabsorbed oedema fluid resulting from fluid retention and increased blood volume (fluid lung). Terminal butterfly densities associated with hypertensive heart failure in uraemia represent variable haemorrhagic and fibrinous pulmonary oedema with secondary cellular changes and organization (uraemic pneumonia). By means of whole lung sections haemorrhagic forms of uraemic pneumonia associated with hypertensive heart disease are shown to be localized to the lung `medulla', and the relevance of secondary lobular boundaries to the pathological anatomy is demonstrated. It is considered probable that the butterfly distribution is not determined by uraemic factors but by a non-specific haemodynamic mechanism which is relevant to all forms of central pulmonary oedema.