JPC SYSTEMIC PATHOLOGY

SPECIAL SENSES SYSTEM

April 2024

S-M15 (NP)

 

SLIDE A: Signalment (JPC #1722833): 1-year-old sex unspecified standardbred, equine  

 

HISTORY: This yearling had bilateral scleral masses.

 

HISTOPATHOLOGIC DESCRIPTION: Eye, bulbar conjunctiva: There is focally extensive replacement of the bulbar conjunctiva with pigmented, cornified, stratified squamous epithelium and well differentiated pilosebaceous units in the subjacent dense collagenous stroma. Within the connective tissue underlying the bulbar conjunctiva there are few perivascular lymphocytes and plasma cells and a lymphoid follicle.  Diffusely, there is mild congestion. The epithelium is multifocally hyperplastic, there are moderate numbers of transmigrating lymphocytes and plasma cells, and there is multifocal moderate to abundant melanin pigment within the stratum basale.

 

MORPHOLOGIC DIAGNOSIS: Eye, bulbar conjunctiva: Dermoid, standardbred, equine.

 

SLIDE B: Signalment (JPC #267901): Puppy, sex and breed unspecified

 

HISTORY: None provided

 

HISTOPATHOLOGIC DESCRIPTION: Eye, cornea: Replacing 90% of the corneal epithelium is sparsely pigmented, cornified, stratified squamous epithelium, and the corneal stroma subjacent to this is replaced by an irregular dermis that blends posteriorly and laterally with the corneal substantia propria (stroma). The dermis contains cystic hair follicles predominantly lacking hair shafts; nests of sebocytes; rare apocrine glands; a single hair shaft; and multifocal infiltrates of few neutrophils, lymphocytes, macrophages, and plasma cells. The follicular cysts are up to 500 m in diameter, are lined by cornified, stratified squamous epithelium, and are filled with variable luminal contents including one or more of the following: parakeratotic concentrically laminated keratin, granular cellular debris with multifocal mineralization, individual keratinocytes, few neutrophils, and occasional necrotic debris. Peripheral to the area of cutaneous differentiation there is a focus of mild corneal epithelial hyperplasia. The deep corneal stroma has irregular clefting and clear space (edema).

 

MORPHOLOGIC DIAGNOSIS: Eye, cornea: Dermoid, breed unspecified, canine.

 

CONDITION: Dermoid

 

GENERAL DISCUSSION:

• Dermoids are congenital lesions of the cornea, conjunctiva, or eyelids characterized by focal skin-like differentiation and represent a choristoma, a rest of histologically normal tissue in an abnormal location
• Dermoids may be unilateral or bilateral concurrent with other ocular defects, iris hypoplasia, lacrimal gland aplasia/hypoplasia, or partial or complete eyelid agenesis (coloboma)
• A similarly named, completely different condition, referred to as “dermoid cyst” (also called a dermoid sinus), is a developmental tissue-plane closure defect resulting in islands of ectoderm (often containing hair, keratin, or sebum) within the dermis or subcutis and is seen in dogs, cats, horses, and cattle, most notably Rhodesian ridgebacks
  
  

PATHOGENESIS:

• Unknown
• Defective induction by the invading corneal stromal mesenchyme is speculated
• Dermoids are typically single, random anomalies, although in polled Hereford cattle, they are likely hereditary
• Surgical excision is curative

TYPICAL CLINICAL FINDINGS:

• Usually no clinical signs
• Haired dermoids may induce epiphora, blepharospasm, and keratitis
• Depending on the location, vision may be impaired
• May be bilateral

 

TYPICAL GROSS FINDINGS:

• Skin-like growth, often with hair, on the cornea, limbus, conjunctiva
• Bulbar conjunctiva is most commonly affected

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Typically consists of keratinizing squamous epithelium overlying an irregular dermis containing adnexa (hair follicles and glands) that is more or less identical to normal skin
• The degree of adnexal differentiation varies and there may be only skin features and vestigial hair follicles/glands
• Cartilage, bone, skeletal muscle, or nerves are rarely present
• Along the periphery of the dermoid, the dermal collagen and epidermis blend into the corneal stroma and corneal epithelium respectively

DIFFERENTIAL DIAGNOSIS:

COMPARATIVE PATHOLOGY:

REFERENCES:

1. Brannick EM, Newkirk KM, Schaefer MW. Neoplasia and Tumor Biology. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:345. 
2. Labelle P. The Eye. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:1407, 1411.
3. Mauldin EA, Peters-Kennedy J. Integumentary System. In: Maxie MG, ed. Jubb, Kennedy & Palmer's Pathology of Domestic Animals. Vol 1. 6th ed. St. Louis, MO: Elsevier; 2016:520, 546, 704.
4. Schmidt R, Reavill DR, Phalen DN. Special Sense Organs. In: Pathology of Pet and Aviary Birds. 2nd ed. Ames, IA: John Wiley & Sons, Inc.; 2015:264.
5. Shivaprasad HL. Chapter 11: Eye and Ear. In: Abdul-Aziz T, Fletcher OJ, Barns HJ, eds. Avian Histopathology. 4th ed. Madison, WI: Omnipress; 2016: 524. 
6. 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 Limited; 2016:414, 421-422. 

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