Formation of ceroid pigment in subcutaneous implants in mice

Primary extracellular ceroid type lipopigment. A histochemical and ultrastructural study

An extracellular ceroid-type (ECC) lipopigment which appears histologically as wavy hyaline membranes or, less frequently, as an amorphous solid or broadly reticulated mass is described. Its ultrastructure is either amorphous or membranous and consists either of simple linear membrane-like aggregates or elaborated trilaminar membranes. The histochemical profile is, as in histiocytic intracellular ceroid, dominated by autofluorescence, strong hydrophobicity, acid and extraction resistance. Staining for aromatic acid residues and periodic acid-Schiff positivity are strong but variable. Lectin receptors are either absent or sparse. The pigment is found solely within the lipid rich tissue debris, bound to processes marked by necrosis of adipose or steatosed tissues and interpreted as originating de novo extracellularly from liquid unsaturated lipids under the influence of local enzymatic and nonenzymatic lipid oxidation catalysts. A hitherto unknown form of extracellular ceroid is the so-called membranocystic lesion found in Nasu-Hakola's disease, in several other conditions and in annular ceroid in human atheromas.