Equine Corneal Stromal Invasive Squamous Cell Carcinoma: Clinical and in Vivo Confocal Microscopic Features of 7 Cases.

Abstract

OBJECTIVE: To describe the clinical and in vivo confocal microscopy (IVCM) characteristics of horses with corneal stromal invasive squamous cell carcinoma (CSI-SCC). ANIMALS STUDIED: Retrospective study of 7 horses with histopathologically confirmed unilateral CSI-SCC. PROCEDURES: Horses with corneal CSI-SCC were examined by laser scanning IVCM. Signalment, clinical findings, and histopathology results were compared with IVCM findings. RESULTS: Clinical ocular lesions in all horses included a heavily vascularized, opaque, gray or tan, anterior or midstromal opacity invading the cornea from the limbus. The corneal epithelium overlying the stromal opacities was intact and the abnormal corneal regions were markedly thickened. Crystalline, white, linear, branching stromal opacities emanated from the leading edge of the corneal lesions in 2 horses. Polygonal neoplastic epithelial cells, with prominent anisocytosis and pleomorphism, were visible in the corneal stroma by IVCM and appeared enlarged and hyperreflective. Islands and cords of neoplastic epithelial cells that occasionally branched could be followed by IVCM as they transversed the corneal stroma. The islands of neoplastic cells were occasionally arranged as circular whirls of cells grouped around concentric layers of hyperreflective cells or amorphous materials within a dark cyst-like space consistent with keratin pearls. Dense accumulations of blood vessels and leukocytes were present within and around the neoplastic cells. CONCLUSIONS: This report demonstrates the unique ability of IVCM examination to provide a rapid and noninvasive method for the presumptive diagnosis of CSI-SCC and to contribute to the formulation of diagnostic and therapeutic clinical plans for individual horses.