Fig. 1

Focal brain lesion in an alpaca (Vicugna pacos): macroscopic and light microscopic findings. a Transverse section through the frontal lobes: The right frontal lobe contains a focal lesion that extends immediately to the leptomeninges of the lateral and medial sites (white arrowhead). The lesion is characterized by the loss of normal brain architecture within cortex and medulla. It consists of firm whitish-beige tissue (diamonds) as well as small areas of soft beige tissue (asterisks) and shows multifocal brownish discoloration (arrow). Bar: 1 cm. b By the microscopic examination, the firm whitish-beige tissue is identified as vascularized fibrous connective tissue (diamond) and the soft beige areas represent liquefactive necrosis (asterisk). The multifocal brown discoloration is attributed to the presence of sheets of siderocytes (arrow) revealed by hematoxylin–eosin (HE) staining. Bar: 200 µm. Upper inset: The fibrous connective tissue is highlighted in red color using a picrosirius red stain. Bar: 200 µm. Lower inset: The siderocytes are marked in blue color with a Prussian blue stain. Bar: 20 µm. c The area of liquefactive necrosis is infiltrated by moderate numbers of gitter cells (arrowheads) as shown by HE staining. Bar: 20 µm. Inset: Areas of necrosis and scar tissue formation are bordered by proliferated astrocytes (circle). An intralesional vessel (arrowhead) shows moderate perivascular edema (asterisk) visualized by HE staining. Bar: 40 µm. d The necrotic area contains aggregates of clear needle-like spaces consistent with cholesterol crystals (asterisks) surrounded by multinucleated histiocytic giant cells (arrowheads) as demonstrated by HE staining. Bar: 20 µm