Equine deep stromal abscesses (51 cases – 2004-2009)–Part 2: the histopathology and immunohistochemical aspect with attention to the histopathologic diagnosis, vascular response, and infectious agents.

This study explores the significance of certain angiogenesis-related factors in the development of equine deep stromal abscesses (DSAs). The researchers targeted angiogenesis factors namely: vascular endothelial growth factor-A (VEGF-A), pigment epithelium-derived factor (PEDF), and interleukin-1 receptor antagonist (IL-1ra). They deduced that decreased VEGF-A expression could be the reason for slow vascularization and delay in resolution of fungal DSAs.

Study Methodology

• The researchers used paraffin-embedded biopsy samples from 51 DSAs. These biopsies were taken during full-thickness penetrating keratoplasty or split-thickness lamellar keratoplasty surgeries at the University of Florida Veterinary Medical Center between 2004 to 2009.
• They conducted histopathologic and immunohistochemical analyses on these samples and tested for associations between the findings.
• Statistical calculations, including prevalence calculation and tests for association with qualitative data analysis, were used to evaluate the collected data.

Study Results

• Fungal hyphae were found histologically in about 47.1% (24 out of 51) of the DSA cases.
• Most fungal DSAs showed suppurative keratitis (inflammatory condition of the cornea) and little to no vascularization infiltrating the abscess.
• All three angiogenesis-related factors (VEGF-A, PEDF, IL-1ra) were expressed in DSA tissue to varying degrees.
• The presence of VEGF-A and PEDF had a negative association with the presence of fungal hyphae implying that cases positive for these two factors were unlikely to have fungal hyphae.

Study Conclusions

• The researchers suggested that abnormally decreased expression of VEGF-A might be the reason for the slow vascularization process and delay in resolution of fungal DSAs.
• PEDF and IL-1ra were not seen to have significant influence on the vascularization process.
• They also proposed that clinical and histopathologic characteristics of DSAs can indicate the potential cause of an equine DSA with an unknown etiology.