Pterygium: histological and immunohistochemical aspects

Pterygium represents a triangular conjunctivo-epithelial overgrowth, proliferating from the bulbar conjunctiva and covering the cornea, causing severe vision loss. It is an abnormal growth and differentiation of the conjunctive epithelial structures of the corneal limbus. Chronic exposures to solar ultraviolet radiation, heat and dust, as well as viral agents, are the most common pathogenic entities involved in its evolution. Recent studies linked pterygium with neoplastic proliferation, as ocular limbic stem cells and p53-protein expression are altered.

Our study was conducted on 84 fragments of pterygium, collected after surgery from patients admitted between 2008 and 2009 in the Departments of Ophthalmology of the Emergency County Hospital of Craiova and Hospital of Rovinari. Histological studies were performed by staining with Hematoxylin-Eosin, light green trichromic (Goldner-Szekely technique) and PAS-Hematoxylin. Immunohistochemistry highlighted the T-lymphocytes by using the CD3 antibody, B-lymphocytes by using the CD20 antibody and cells of the macrophage system using the CD68 antibody. The slides were analyzed under a 55I Nikon microscope, resulting pictures being captured with a 5 MP digital camera and digitally retrieved and enhanced using the dedicated NIS-Elements software.

Histology showed the presence of a conjunctivo-epithelial structure, significantly different from the structure from which it developed. In 20% of the cases, the covering epithelium was similar to that of the bulbar conjunctival mucosa. In some cases, when pathogens were more active in the environment, the appearance of the covering epithelium of the membrane appeared pleomorphic, with dysplastic aspects, suggesting significant alteration of cell proliferation and differentiation. In approximately 75% of patients, we identified goblet cells in the surface epithelium. They appeared either isolated or associated in variable numbers, structures resembling intraepithelial glands. These particular cells synthesize and accumulate PAS-positive mucines rich in glycosaminoglycans, and are usually found in conjunctival epithelium. We observed a number of invaginations in the connective tissue underlying the epithelium, mostly formed by goblet cells, this giving the aspect of mucous glands, similar to the "glands of Henle". A highly developed vascular neoformation network, consisting of arterioles, venules and a very large number of capillaries can also be found in the connective tissue. Immunohistochemistry suggested that B-lymphocytes marginally take part in the immune response in pterygium. T-lymphocytes formed the majority of the mass of immune system cell present in connective tissue of the pterygium. Macrophage-type cells were distributed unevenly in the pterygium tissue, as the intensity of the inflammatory process varies depending on antigen levels.

Pterygium shows significant changes both in the epithelium and in the underlying connective tissue. Immune cell infiltrate was diffuse, more abundant in areas with erosion of the covering epithelium.