JPC SYSTEMIC PATHOLOGY

SPECIAL SENSES SYSTEM

April 2024

S-N04

 

Signalment (JPC #1978468): German shepherd dog.

 

HISTORY: This dog had a unilateral corneal opacification, scleral vascularization, epiphora, and secondary glaucoma. 

 

HISTOPATHOLOGIC DESCRIPTION: Eye: Expanding and effacing the posterior iridal epithelium, compressing and distorting the ciliary body, obliterating the anterior and posterior chambers, adhering to the fragmented anterior lens capsule, and occluding the filtration angle is a 2.0 x 0.75 cm, unencapsulated, well demarcated, densely cellular neoplasm composed of epithelial cells arranged in islands, nests, and abundant intertwining arborizing papillary projections supported by a prominent basement membrane and a thin, often pigmented fibrovascular stroma. Neoplastic cells have variably distinct cell borders, a moderate amount of granular, pale to brightly eosinophilic cytoplasm, and a round to oval, typically hyperchromatic nucleus with a variably distinct nucleolus. Mitoses average 1 per 2.37mm² and there is scattered single cell necrosis. Low numbers of melanophages, neutrophils, and lymphocytes infiltrate the neoplastic stroma. Multifocally, the anterior iris is adhered to the cornea (anterior synechia) by a thin fibrovascular membrane (pre-iridal fibrovascular membrane) that occludes the drainage angle. Multifocally, similar fibrovascular membranes extend through the vitreous (intravitreal membrane) and are adherent to the pathologically detached retina (traction retinal detachment), ciliary body (cyclitic membrane), and lens. Diffusely, the retina is detached except at the optic nerve head and there is diffuse atrophy of the retina with degeneration and/or loss of both inner and outer layers, including vacuolation of the nerve fiber layer with prominent Muller fibers, nearly complete loss of the ganglion cell layer, loss of the outer plexiform layer with blending of the inner and outer nuclear layers, and loss of the photoreceptor layers. There is hypertrophy of the retinal pigment epithelium (tombstoning). Diffusely the sclera is mildly to moderately thin. The cornea exhibits multifocal epithelial hyperplasia and hyperpigmentation; stromal infiltration by few lymphocytes, plasma cells, neutrophils (keratitis), and small caliber vessels (vascularization); and there is a retrocorneal fibrovascular membrane that multifocally contains hematoidin and has contracted resulting in an undulant Descemet’s membrane.

 

MORPHOLOGIC DIAGNOSIS: 1. Eye: Iridociliary adenoma, German shepherd dog, canine.

2. Eye: Fibrovascular membranes, preiridal, cyclitic, intravitreal, and retrocorneal, with diffuse traction retinal detachment and atrophy.   

3. Eye, cornea: Keratitis, lymphoplasmacytic and neutrophilic, chronic-active, multifocal, mild, with corneal vascularization and hyperpigmentation.

 

SYNONYM: Iridociliary adenoma/carcinoma; iridociliary epithelial tumor; ciliary body adenoma/carcinoma

 

GENERAL DISCUSSION:  

• Iridociliary epithelial tumors are of mature anterior uveal neuroectoderm origin, most arise from the non-pigmented inner layer of ciliary or iris epithelium, and most commonly originate at the pars plicata
• Second most common ocular neoplasm in dogs behind melanocytic neoplasia 
• Metastasis is rare, giving no justification for diagnosis of a carcinoma

 

TYPICAL CLINICAL FINDINGS:

• Mass on or distorting the iris
• Secondary hyphema or glaucoma

 

TYPICAL GROSS FINDINGS:  

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:  

• Generally well-differentiated cuboidal to columnar ciliary epithelium with little stroma; arranged in tubules or papillary projections +/- cyst formation; non-pigmented eosinophilic cytoplasm, regular basilar nucleus +/- few melanin laden macrophages
• Abundance of basal lamina oriented toward inside of the eye; PAS positive and helps differentiate this neoplasm from metastatic carcinoma
• Propensity to induce formation of pre-iridal fibrovascular membranes and neovascularization; may cause secondary hyphema and glaucomatous changes

 

ADDITIONAL DIAGNOSTIC TESTS:  

• PAS: Abundant basement membrane basal lamina production in adenomas highlighted by PAS 
• Positive for S100, vimentin, and neuron-specific enolase 
• Adenomas are negative for cytokeratin, but carcinomas are positive 
• Cytology (FNA): Epithelial cells with pink amorphous intracellular material; carcinomas exhibit anisokaryosis, irregularly shaped nuclei, nuclear molding, and distinct cytoplasmic vacuoles

 

DIFFERENTIAL DIAGNOSIS:

Selected intraocular tumors:

• Anterior uveal melanocytoma: Most common primary neoplasm of the globe of the dog
• Metastatic carcinoma: Demonstration of basement membrane by PAS stain is useful in distinguishing ciliary tumors from carcinomas metastatic to the eye
• Medulloepithelioma or Retinoblastoma: Arise from the primitive neuroectoderm of the optic cup; those with at least focal maturation into recognizable photoreceptors are retinoblastomas and the rest are medulloepitheliomas; retinal differentiation is in the form of photoreceptor-like neuroblasts clustered around a central lumen with their apical portions linked by terminal bars reminiscent of the retinal outer limiting membrane and positive staining for retinal S antigen; medulloepitheliomas are the most common intraocular tumor in horses

 

COMPARATIVE PATHOLOGY:  

 

REFERENCES:

1. Deschuillers PL, Raskin RE. Chapter 16: Eyes and Ears. In: Raskin RE, Meyer DJ, & Boes KM eds. Canine and Feline Cytopathology: A Color Atlas and Interpretation Guide. 4th ed. St. Louis, MO: Elsevier; 2022:574.
2. Labelle P. The eye. In: Zachary JF, eds. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:1418.
3. Wilcock BP. Special senses. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. St. Louis, MO: Elsevier Limited; 2016:485-486.
4. Young KM and Teizeira LBC. Eyes and associated structures. In: Valenciano AC and Cowell RL, eds. Cowell and Tyler’s Diagnostic Cytology and Hematology of the Dog and Cat. 5th ed. St. Louis, MO: Elsevier; 2020:153-154.

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