A histopathology term of art referring to the coating of blood vessels in a tumour–e.g., in small cell carcinoma, with DNA from dead cells, which gives the involved vessels a deeply basophilic (dark blue purple) outline on H&E-stained tissue sections. The effect may also be seen in lymphomas and seminomas.
The term is named in honour of John Azzopardi, a pathologist who correctly identified the “schmutz” as degenerated DNA (nucleic acid debris), based on his review of 100 cases of small cell carcinoma, in which he found the basophilic material in one-third of cases. It had been previously regarded as calcium deposits. In the adjacent image, one can appreciate scattered DNA-coated vessels to the left and small dark tumour cells to the right.