Pinguecula and Pterygium
A pinguecula is a small, yellow-tan bulbar conjunctival nodule typically located at the nasal and/or temporal limbus, often bilaterally (Fig 5-11A). A manifestation of actinic damage (ie, exposure to sunlight) or other environmental trauma, such as that caused by dust and wind, this growth is more common with advancing years. On histologic examination, the stromal collagen shows fragmentation and basophilic degeneration, referred to as elastotic degeneration (also known as pseudoelastosis or solar elastosis). These terms refer to the staining of the degenerated collagen with stains for elastin, such as Verhoeff–van Gieson, even after tissue has been treated with elastase for digestion of true elastin (Fig 5-11B, C).
Figure 5-10 Pyogenic granuloma. A, Clinical appearance at a site of prior strabismus surgery. B, Low-magnification photomicrograph illustrates a pedunculated mass composed of granulation tissue with a “spoke-wheel” vascular pattern. C, High magnification shows a mixture of acute and chronic inflammatory cells. Note the neutrophils (N) both within the lumen of the blood vessels and infiltrating the tissue. Chronic inflammatory cells, predominantly lymphocytes (L), are present in this field.
(Part A courtesy of Gregg T. Lueder, MD; parts B and C courtesy of George J. Harocopos, MD.)
A pterygium is similar to a pinguecula in etiology and location but differs from the latter in its invasion of the superficial cornea as a fibrovascular, wing-shaped growth (Fig 5-12A). Histologic examination typically shows elastotic degeneration, as in a pinguecula, as well as prominent blood vessels that correlate with the vascularity seen clinically (Fig 5-12B, C), fibrosis, and variable degrees of chronic inflammation. A recurrent pterygium may lack the histologic feature of elastotic degeneration and is thus more accurately classified as pannus (discussed in Chapter 6) or a fibrovascular connective tissue response.
In pingueculae and pterygia, the overlying epithelium may exhibit mild squamous metaplasia, for example, loss of goblet cells and surface keratinization. Some studies have demonstrated abnormal expression of Ki-67 (a proliferation marker); dysregulation of tumor suppressor genes such as p53 and p63, and other genes associated with DNA repair; cell proliferation, migration, and angiogenesis; loss of heterozygosity; and microsatellite instability. Thus, as with actinic damage to the skin, there is the possibility of malignant transformation of the epithelium, although this occurs rarely. When conjunctival squamous neoplasia arises, it often overlies an area of preexisting elastotic degeneration; therefore, it is important to examine these specimens histologically when they are excised (see the section “Ocular surface squamous neoplasia” later in this chapter).
Figure 5-11 Pinguecula. A, Clinical appearance adjacent to the nasal and temporal limbus. B, Histologic examination demonstrates the acellular, amorphous, slightly basophilic material in the stroma (asterisk) and thick, curly fibers (arrows) indicative of elastotic degeneration. C, With Verhoeff–van Gieson stain for elastin, the basophilic material stains black (asterisk).
(Parts A and C courtesy of George J. Harocopos, MD; part B courtesy of Hans E. Grossniklaus, MD.)
Liu T, Liu Y, Xie L, He X, Bai J. Progress in the pathogenesis of pterygium. Curr Eye Res. 2013; 38(12):1191–1197.
Figure 5-12 Pterygium. A, Clinical photograph. B, Histologically, a focus of elastotic degeneration is present (arrow), as well as prominent blood vessels (arrowheads), with surgically induced hemorrhage. C, In this case, the conjunctival and corneal portions of the pterygium are evident. Note the prominent blood vessels in the conjunctival portion (asterisk) and destruction of Bowman layer by ingrowth of fibroconnective tissue (arrowheads) in the corneal portion.
(Part A courtesy of Hans E. Grossniklaus, MD; parts B and C courtesy of George J. Harocopos, MD.)
Excerpted from BCSC 2020-2021 series: Section 4 - Ophthalmic Pathology and Intraocular Tumors. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.