JPC SYSTEMIC PATHOLOGY

SPECIAL SENSES SYSTEM

April 2024

S-N06

 

SLIDE A: Signalment (JPC #2241434): Cocker spaniel

 

HISTORY: Tissue from a cocker spaniel with a long-standing history of otitis externa

 

HISTOPATHOLOGIC DESCRIPTION: Glabrous skin, ear canal: Expanding the dermis and elevating the overlying hyperplastic epidermis is an unencapsulated, well-circumscribed, moderately cellular, polypoid neoplasm composed of cuboidal epithelial cells lining variably ectatic to cystic tubules, occasionally forming papillary projections, supported by a moderate fibrovascular stroma. Neoplastic cells have indistinct cell borders, a moderate amount of eosinophilic granular cytoplasm, and a round to oval nucleus with finely stippled chromatin and one distinct nucleolus. There is 1 mitotic figure per 2.37mm². Diffusely, lumina of tubules are filled with pale, homogeneous, eosinophilic to gray-brown material (cerumen), few sloughed epithelial cells, macrophages, degenerate neutrophils, and necrotic debris. Multifocally within the stroma are few scattered lymphocytes, plasma cells, and macrophages that often contain intracytoplasmic brown material (cerumen). Diffusely, the epidermis is hyperplastic with acanthosis, occasional rete ridges, and mild orthokeratotic hyperkeratosis. There is multifocal epidermal erosion.

 

MORPHOLOGIC DIAGNOSIS: Glabrous skin, external ear canal: Ceruminous gland adenoma, cocker spaniel, canine.

 

SLIDE B: Signalment (JPC #1416286): Cat

 

HISTORY: Both ear canals contained variably sized nodules projecting from the pinna and occluding the canal. The nodules were white to dark blue and firm.

 

HISTOPATHOLOGIC DESCRIPTION: Haired skin, ear canal: Expanding the dermis, focally distorting the auricular cartilage, and elevating the hyperplastic, ulcerated epidermis is an unencapsulated, poorly circumscribed, infiltrative, densely cellular neoplasm composed of polygonal cells arranged in nests, tubules, and acini with multifocal luminal papillary ingrowths supported by moderate fibrovascular stroma.   Neoplastic cells have indistinct cell borders, a moderate amount of finely granular, eosinophilic, often vacuolated cytoplasm, and an irregularly round to oval, occasionally vesiculate, nucleus with finely stippled chromatin and 1-2 magenta nucleoli. There is moderate anisokaryosis and anisocytosis. Mitoses average 2 per HPF. Focally within the subcutis, a vessel contains a cluster of neoplastic cells surrounded by fibrin. The stroma contains multifocal aggregates of many lymphocytes, fewer plasma cells, neutrophils, and macrophages that are often laden with brown material (cerumen). There is focal lymphovascular invasion. Adjacent ceruminous glands are hyperplastic and ectatic, lined by attenuated cuboidal cells, and are variably filled with abundant brown to eosinophilic secretory product (cerumen), necrotic debris, sloughed epithelial cells, macrophages, degenerate neutrophils, and occasionally acicular cholesterol clefts. Multifocally, sebaceous glands are mildly hyperplastic. Diffusely, the epidermis overlying the neoplasm is hyperplastic, with acanthosis and rete ridge formation. There is multifocal mild orthokeratotic hyperkeratosis and epidermal ulceration and erosion.

 

MORPHOLOGIC DIAGNOSIS: Haired skin, external ear canal: Ceruminous gland adenocarcinoma, breed unspecified, feline.

 

GENERAL DISCUSSION: 

• Ceruminous glands are modified apocrine sweat glands within the external auditory meatus; glands are surrounded by myoepithelial cells

• The majority are malignant in cats while the majority are benign in dogs

• Ceruminous gland adenocarcinomas are the most common malignant neoplasm in the external acoustic meatus of both dogs and cats

• Usually occur in the older animal

• Mixed or complex ceruminous gland tumors are morphologically similar to apocrine gland tumors

 

PATHOGENESIS:

• Represents a continuum from benign to malignant

• May develop secondarily to recurrent bouts of otitis externa; inspissation of cerumen may play a role in development
• Adenocarcinomas are locally invasive, expansile, and may metastasize to the regional lymph nodes, lungs, and systemic viscera

 

TYPICAL CLINICAL FINDINGS:

• Head-shaking, scratching at the ear, hemorrhage from the ear canal
• +/- peripheral vestibular signs (head tilt, nystagmus), deafness, Horner's syndrome 

 

TYPICAL GROSS FINDINGS:

• Smooth, nodular or pedunculated, often exophytic mass in the ear canal  

• Difficult or impossible to distinguish from cystic dilation and epithelial hyperplasia (hyperplastic polypoid otitis externa), especially in cocker spaniels  

• Smooth or ulcerated, soft or firm, and brown on cut section

• Adenomas: Usually <1 cm diameter, exophytic, only ulcerated if secondarily infected
• Carcinomas: Larger, more likely to be ulcerated; may invade the surrounding parotid salivary gland, soft tissues, or bone; may form a mass at the base of the ear

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Hallmark: Intraluminal deeply-eosinophilic to brown/orange colloid-like material (cerumen); +/- small brown intracytoplasmic globules in neoplastic epithelium  
• Adenomas: Proliferation of well-differentiated acini and ducts usually surrounded by a single layer of myoepithelial cells; ducts are often cystic, lined by papillary projections, and contain a deeply eosinophilic or orange secretory product; atypia and mitoses are infrequent; seldom exceed 1 cm
• Carcinomas: Not markedly different from adenomas but have less secretion, more cellular anaplasia, may show invasion into an abundant peripheral fibrous stroma or entry into blood vessels or lymphatics  
• Complex/mixed tumors: Infrequent; both epithelial and myoepithelial proliferation, +/- bone or cartilage formation (mixed)

 

DIFFERENTIAL DIAGNOSIS:

• Gross appearance is indistinguishable from hyperplastic polypoid otitis externa; may resemble feline inflammatory polyps
• Carcinomas may be confused with salivary carcinoma when they invade the parotid salivary gland, or bone, and when very anaplastic 
• Other neoplasms of the external ear: Squamous cell carcinoma (most important skin tumor affecting the ear), carcinoma of undetermined origin, histiocytoma (dog), basal cell tumor, chondroma, chondrosarcoma, and rhabdomyomas (cat)

 

COMPARATIVE PATHOLOGY:

• Foxes: Santa Catalina Island subspecies of island fox, occurs at highest known prevalence of a tumor in wild animals; 52% of foxes had ceruminous gland tumors, 34% were malignant
  1. Invaded tympanic bullae and other bones of skull
  2. Metastasized to regional LN or lung
  3. Associated with ear mite (Otodectes cynotis) and chronic inflammation only on the Santa Catalina Island
• Horses: Sarcoids and dentigerous cysts may occur at the base of the ear
• Laboratory rats:  Under certain conditions (especially after long-term administration of some carcinogens), Zymbal's glands (under the mucosa of the ear or in the subcutis ventral to the ear) can become the origin of sebaceous adenomas or carcinomas

 

REFERENCES:

1. Goldschmidt MH, Goldschmidt KH. Epithelial and melanocytic tumors of the skin. In: Meuten DJ, ed. Tumors in Domestic Animals. 5th ed. Iowa State Press: Ames, IA, 2017:115, 119-120. 
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. London, UK: Academic Press; 2018:237-238. 
3. Njaa BL. Tumors of the ear. In: Meuten DJ, ed. Tumors in Domestic Animals. 5th ed. Iowa State Press: Ames, IA, 2017:935-936.
4. Njaa BL. The Ear. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:1363-1364.
5. 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; 2016:507-508.

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