Differential Diagnosis of Pterygium
The key differential diagnoses for pterygium include ocular surface squamous neoplasia (OSSN), conjunctival melanoma, conjunctival lymphoma, pinguecula, and pseudopterygium, with OSSN being the most critical to exclude due to its malignant potential.
Primary Differentials to Consider
Ocular Surface Squamous Neoplasia (OSSN)
- Most important differential - presents with elevated conjunctival lesions, often with leukoplakic or gelatinous appearance 1
- Associated with HPV, significant UV exposure, and chronic inflammation 1
- Critical distinguishing features on AS-OCTA: OSSN shows abnormal "zigzag vessel patterns" with markedly meandering large blood vessels in both superficial and deep layers 2
- In contrast, pterygium demonstrates "straight vessel patterns" (unbending stretched vessels) in the superficial layer with an avascular zone in the deep layer of the pterygium head 2
- Clinical pitfall: Up to 21% of surgically excised pterygiums show mild to moderate dysplasia on histopathology, and 53% harbor features suggestive of OSSN or primary acquired melanosis 3
Conjunctival Melanoma
- Presents as painless, flat or nodular, brown or fleshy-pink lesion on bulbar conjunctiva 1
- Risk factors include significant UV exposure, previous melanoma history, or primary acquired melanosis 1
- Tends to spread to adnexal structures and metastasize 1
- Can be pigmented or nonpigmented 1
Conjunctival Lymphoma
- Unilateral, painless, pink lesion with indolent fleshy "salmon patch" appearance 1
- Most commonly presents on superior or inferior conjunctiva with chronic follicles 1
- Mobile and nonlobulated with intrinsic vessels 1
- Associated with immune deficiency, autoimmune conditions (Sjögren's, Hashimoto's, IgG4-related disease) 1
Pinguecula
- Yellowish, elevated conjunctival lesion that does NOT cross the limbus (key distinguishing feature from pterygium)
- Remains confined to the bulbar conjunctiva
- UV-related degenerative change without corneal invasion
Pseudopterygium
- Results from conjunctival adhesion to cornea following trauma, inflammation, or chemical injury
- Critical distinction: Can pass a probe underneath a pseudopterygium (not possible with true pterygium)
- Does not originate from limbus like true pterygium
Clinical Approach to Differentiation
Red Flags Requiring Biopsy
- Atypical appearance: irregular borders, nodular growth, or unusual pigmentation
- Rapid growth or change in appearance
- Unilateral presentation in older patients (>60 years)
- Vascular patterns: feeder vessels or irregular vasculature suggesting neoplasia
- Location: temporal location more suspicious than nasal
- History of recurrence after multiple excisions 1
Key Examination Features
- Pterygium characteristics: triangular fibrovascular tissue extending from limbus onto cornea, typically nasal (72% of cases), with straight stretched vessels 2, 4
- OSSN features: papillomatous or sessile nodules, leukoplakia, gelatinous appearance, sentinel vessels, meandering vasculature on AS-OCTA 1, 2
- Melanoma features: pigmented or amelanotic lesion with irregular borders and thickening 1
- Lymphoma features: salmon-patch appearance, mobile, fleshy swelling 1
Critical Management Point
All surgically excised pterygiums should be sent for histopathological examination 3. This is essential because:
- 21% show dysplastic changes potentially associated with OSSN 3
- 32% demonstrate melanocytic hyperplasia suggesting primary acquired melanosis 3
- Both conditions have malignant potential requiring appropriate follow-up 3
The traditional view of pterygium as purely benign is challenged by molecular similarities with UV-related malignancies and documented preneoplastic features 5, 6. While pterygium itself doesn't metastasize, concomitant disease is not rare, and the shared UV exposure risk mandates vigilance for other conjunctival malignancies 3.