JPC SYSTEMIC PATHOLOGY
SPECIAL SENSES SYSTEM
April 2024
S-M11
Signalment (JPC #2320239): 4-year-old male collie
HISTORY: Dog had a non-movable, non-invasive scleral mass
HISTOPATHOLOGIC DESCRIPTION: Sclera (per contributor): Extending to all margins is a moderately cellular proliferation of plump, loosely-arranged, spindle cells arranged in short, interlacing streams and bundles on a fine fibrovascular stroma. Spindle cells have variably distinct cell borders, a moderate amount of eosinophilic, fibrillar cytoplasm, and an oval to elongate, occasionally vesiculate, nucleus with finely-stippled chromatin and one variably distinct nucleolus. There is mild anisocytosis and anisokaryosis. The mitotic rate is less than 1 per 10 HPF. The spindle cells are often separated by clear space (edema) and infiltrated by numerous lymphocytes, fewer plasma cells, and macrophages. Multifocally, there are numerous small vessels and capillaries (vascularization) that are often lined by hypertrophied (reactive) endothelium.
MORPHOLOGIC DIAGNOSIS: Sclera (per contributor): Scleritis, lymphoplasmacytic and histiocytic, focally extensive, chronic, severe, with fibrovascular proliferation, collie, canine.
ETIOLOGIC DIAGNOSIS: Idiopathic episcleritis
CONDITION: Nodular granulomatous episcleritis (NGE)
SYNONYMS: Nodular episclerokeratitis, nodular fasciitis, nodular scleritis/episcleritis, fibrous histiocytoma, proliferative keratoconjunctivitis, conjunctival granuloma, Collie granuloma
GENERAL DISCUSSION:
- Most prevalent primary scleral disease of dogs
- Nodular tumor-like lesion of the limbus (usually)
- Collies and Shetland sheepdogs predisposed
PATHOGENESIS:
- Cause is unknown, but an immune-mediated reaction is suspected
TYPICAL CLINICAL AND GROSS FINDINGS:
- Clinical spectrum varies: Unilateral to bilateral, nodular to multinodular and episcleral to conjunctival firm, painless, 0.5 – 1 cm nodule(s) +/- corneal edema and vascularization
- Most commonly at bulbar conjunctiva near limbus, but third eyelid and other locations also reported
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Proliferative, non-encapsulated, well circumscribed mixture of histiocytic cells, spindle cells, plasma cells, and lymphocytes; occasionally eosinophils and multinucleated giant cells may be present
- Distinguishing NGE from early necrotizing scleritis (see below) can be difficult, but absence of collagenlysis and discrete granulomas are two important differentiating characteristics
- Lymphocytes may be more numerous at the periphery
- Special stains reveal scant collagen, but abundant reticulin
ADDITIONAL DIAGNOSTIC TESTS:
- Gridley's reticulin stain
DIFFERENTIAL DIAGNOSIS:
- Necrotizing scleritis (idiopathic necrotic scleritis): Coalescing scleral granulomas centered on remnants of denatured, refractile collagen; painful; coalescing true granulomas; collagenolysis, perivascular necrosis, multinucleated giant cells, and eosinophils present; destructive; rapidly-progressive to involve entire sclera +/- uvea and retina
REFERENCES:
1. Labelle P. The Eye. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2023:1428.
2. Wilcock BP, Njaa BL. Special Senses. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. St Louis, MO: Elsevier; 2016:476-477.
