JPC SYSTEMIC PATHOLOGY

INTEGUMENTARY SYSTEM

September 2022

I-N09

 

Signalment (JPC #2028098):  Age and breed unspecified dog.

 

HISTORY:  Tissue from a mass adjacent to the ear canal.

 

HISTOPATHOLOGIC DESCRIPTION:  Haired skin, ear canal:  The dermis is expanded by an unencapsulated, well-circumscribed, multilobular neoplasm composed of two populations of cells supported by a dense fibrovascular stroma that frequently blends into multiple irregular islands of cartilage (chondroid metaplasia). The first population is composed of cuboidal to columnar epithelial cells forming islands and well-differentiated tubules with intraluminal papillary projections. Neoplastic epithelial cells have indistinct cell borders, a moderate amount of granular eosinophilic cytoplasm with occasional apical blebbing, an oval nucleus with finely stippled chromatin and 1-2 prominent nucleoli. Tubules are often ectatic and contain amorphous amphophilic to eosinophilic material (secretory product), necrotic cellular and karyorrhectic debris, and hemorrhage.  Multifocally, tubules are surrounded by a second population of myoepithelial cells arranged in thin streams, with indistinct cell borders, small amounts of fibrillar eosinophilic cytoplasm, and elongate nuclei with finely stippled chromatin and indistinct nucleoli. Anisocytosis and anisokarysosis are mild in both populations. There are 3 mitotic figures per 2.37 mm² in the epithelial population and none observed in the myoepithelial population. Within the stroma there are a few lymphocytes, plasma cells, and macrophages, some of which contain intracytoplasmic hemosiderin and/or secretory product. The epithelium is diffusely hyperplastic with acanthosis, moderate orthokeratotic hyperkeratosis and a focal area of ulceration with underlying infiltration of neutrophils, macrophages, plump spindle cells (fibroblasts), edema, and small caliber vessels (granulation tissue). Adjacent ceruminous glands are hyperplastic and ectatic, filled with amorphous amphophilic to eosinophilic secretory product, and surrounded by a few neutrophils, macrophages, lymphocytes, and plasma cells.

 

MORPHOLOGIC DIAGNOSIS:  Haired skin, near ear canal (per contributor):  Mixed ceruminous gland tumor, breed not specified, canine.

 

GENERAL DISCUSSION:   

• Ceruminous glands are modified apocrine glands within the external auditory meatus (EAM) and lower portion of the pinnae; glands consist of secretory epithelium, surrounded by myoepithelial cells and they empty either into follicular infundibula or directly onto the epidermal surface of the external ear 
  1. Can give rise to cysts, cystomatosis, adenomas, complex and mixed tumors (benign or malignant), and adenocarcinomas  
  2. Histologically, appear very similar to epitrichial (apocrine) glands (I-N06), except for characteristic brown-green-orange glassy luminal secretions (cerumen)
• Ceruminous gland neoplasia reported in dogs, cats, a ferret, and Santa Catalina Island foxes
  1. Adenomas are more common in dogs than cats
  2. Adenocarcinomas are more common in cats, particularly aged male cats; most dog ceruminous gland neoplasia are malignant 
  3. Mixed tumors are rare 

 

PATHOGENESIS:

• May represent a continuum from hyperplasia to benign to malignant, but this has never been proven
• May develop secondarily to recurrent bouts of otitis externa

 

TYPICAL CLINICAL FINDINGS:

 

TYPICAL GROSS FINDINGS:

• Adenoma:  Small or large, single or multiple, pedunculated, irregular, lobulated, firm masses; partially or complete occlude the EAM
• Carcinomas:  Locally invasive, expansile masses that are difficult to delineate and often ulcerated; up to 50% metastasizing to regional lymph nodes and the lungs

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Adenoma: Well differentiated cuboidal to columnar deeply basophilic epithelial cells forming tubules, acini, papillary, and ducts projections with minimal pleomorphism and rare mitoses; surrounded by a single layers of myoepithelial cells; ducts may contain cerumen; plasmacytic inflammation within the periglandular dermis with few neutrophils; dysplasia of surrounding glands 
• Adenocarcinoma: Cells are more pleomorphic with large, vesiculate nuclei, prominent nucleolus, and more frequent mitoses; desmoplastic response; locally invasive 
• Mixed tumors: A mixture of benign or malignant epithelial and myoepithelial proliferation with stroma that displays chondroid or osseous metaplasia 

 

ADDITIONAL DIAGNOSTIC TESTS:

   

DIFFERENTIAL DIAGNOSIS:

• Other ear canal tumors: papilloma’s, basal cell tumors, squamous cell carcinomas, undifferentiated carcinomas 
• Ceruminous gland hyperplasia and dysplasia: May be very difficult to differentiate from an adenoma; often concurrent with otitis externa; Cocker spaniels predisposed  
• Inflammatory aural polyps (cats, dogs, horses): Polypoid masses arising from the middle or external ear that can partially fill the external auditory meatus; characterized by a fibrovascular stromal core with variable edema and inflammatory cells, frequent ulceration, and epithelium ranging from squamous, respiratory, or both; depending on orgin, may have pseudoglands lined by respiratory epithelium with many goblet cells (middle ear mucoperiosteum) and/or ceruminous and sebaceous glands (external acoustic meatus) that may be confused with neoplasia
• Ceruminous cystomatosis, ceruminous cysts (cats): Single (cyst) or multiple (cystomatosis) 1-5mm dark colored nodules or vesicles in the EAM or inner pinnae; often both ears affected and can lead to ear canal obstruction 

 

COMPARATIVE PATHOLOGY:

 

References:

1. Kaimio M, Malkamaki S, Kaukonen M, et al. Clinical and genetic findings in 28 American Cocker spaniels with aural ceruminous gland hyperplasia and ectasia. J Comp Pathol. 2021;185:30-44. 
2. Keel MK, Terio KA, McAloose D. Canidae, Ursidae, and Ailuridae. In:  Terio, KA, McAloose, D, St. Leger, J, eds. Pathology of Wildlife and Zoo Animals. San Diego, CA: Academic Press Elsevier; 2018:236.
3. Maudlin E, Peters-Kennedy J. Skin and appendages. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. Philadelphia, PA; Elsevier Saunders; 2016:719.
4. Njaa BL. The Ear. In: Zachary JF, McGavin MD, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Mosby; 2022:1353, 1363-1364.
5. Raskin RE. Skin and subcutaneous tissues. In: Raskin RE, Meyer DJ, eds. Canine and Feline Cytology. A color atlas and interpretation guide. 3^rd Ed. St. Louis, MO: Elsevier; 2016;64-65. 
6. Walsh KA, DeHeer HL, Patel RT. The external ear canal. In: Valenciano AC, Cowell RL, eds. Cowell and Tyler’s Diagnostic Cytology and Hematology of the Dog and Cat. 5th Ed. St. Louis, MO: 2020;167-168. 
7. Welle MM, Linder KE. The Integument. In: Zachary JF, McGavin MD, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Mosby; 2022:1219, 1261.
8. Wilcock BP, Njaa BP. Special Senses. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. Philadelphia, PA: Elsevier; 2016:498-499,507-508.

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