Equine cutaneous habronematidosis

Clinical history: A 4-year-old Quarter Horse stallion was unsuccessfully treated for a circumscribed and ulcerated lesion of unknown duration located lateral to the prepuce. Microscopic description: The superficial and deep preputial dermis contains multifocal to coalescing, well-demarcated eosinophilic granulomas characterized by a central area of abundant eosinophilic necrotic debris mixed with degenerate eosinophils surrounded by numerous epithelioid macrophages and occasional multinucleated giant cells (foreign-body type), rimmed by ill-defined layers of fibrous connective tissue. In the center of the granulomas, there are cross-sections of degenerate nematode larvae. The adjacent dermal collagen is expanded by dense inflammatory infiltrate composed mainly of eosinophils and a few lymphocytes and plasma cells. The dermal microvasculature is prominent, with hypertrophic reactive endothelial lining. There is also vascular proliferation amidst perpendicularly oriented plump fibroblasts embedded in collagen (granulation tissue). In addition, there are numerous shrunken, hypereosinophilic, fragmented or hyalinized collagen bundles, occasionally surrounded by degranulated eosinophils.