October 2019

I-N10 (NP)



Signalment (JPC #1956324): Aged poodle


HISTORY: One of several small dermal masses

HISTOPATHOLOGIC DESCRIPTION: Haired skin and subcutis (2 sections): Expanding the dermis, elevating the epidermis, and surrounding and widely separating adnexal structures is a 1 x 0.5cm, unencapsulated, well circumscribed, multilobulated proliferation of epithelial cells arranged in lobules forming adenomeres on a scant to moderate fibrovascular stroma. Epithelial cells undergo orderly maturation from peripheral basaloid reserve cells (flattened to cuboidal epithelial cells with scant amounts of eosinophilic cytoplasm, round to oval nuclei with finely stippled chromatin and 1 to 2 distinct nucleoli) to central polygonal cells with abundant vacuolated cytoplasm and similar round nuclei (sebaceous differentiation). Lobules are centered on compressed, ectatic ducts (dilated up to 1.5 mm) that are lined by keratinized stratified squamous epithelium. The mitotic rate is 1 per 10 HPF and is confined to the basaloid reserve cells. Within the remaining dermis, apocrine glands are occasionally mildly dilated; lymphatics are mildly ectatic and collagen fibers are separated by clear space (edema).


MORPHOLOGIC DIAGNOSIS: Haired skin and subcutis: Nodular sebaceous hyperplasia, focal, poodle, canine.


SYNONYM: Senile sebaceous hyperplasia



Signalment (JPC #2147441): Age and breed unspecified dog




HISTOPATHOLOGIC DESCRIPTION: Haired skin: Expanding the dermis and subcutis, elevating the overlying epidermis, and compressing adjacent adnexa is a 1.0 x 0.75cm, partially encapsulated, well circumscribed, multilobulated, densely cellular neoplasm composed of polygonal cells arranged in islands and trabeculae supported by a fine fibrovascular stroma. The majority of cells (approximately 80%) are basaloid reserve cells characterized by variably distinct borders, scant to moderate amounts of granular eosinophilic cytoplasm, and round to oval nuclei with finely stippled chromatin and 1 to 3 nucleoli. The remaining 20% of neoplastic cells are characterized by multifocal individual or small aggregates of polygonal cells with distinct cell borders, abundant vacuolated eosinophilic cytoplasm, and centrally located, round nuclei with finely stippled chromatin and 1 or 2 distinct nucleoli (sebaceous differentiation).


The mitotic figures average 1 per 40x HPF and are confined to the basaloid reserve cells. There is multifocal single cell necrosis, large cystic spaces (up to 1 x 3 mm) filled with eosinophilic cellular and karyorrhectic debris (cystic degeneration), and few foci of ductular differentiation. Multifocal neoplastic cells and macrophages contain melanin. Multifocally within the mass and in the adjacent dermis are small aggregates of lymphocytes and plasma cells.


MORPHOLOGIC DIAGNOSIS: Haired skin and subcutis: Sebaceous epithelioma, breed unspecified, canine.



·      Sebaceous gland proliferative lesions are derived from basal cells capable of multiple differentiation paths sometimes within the same tumor; classified according to the level of cellular maturation (but tumor classification based on basal differentiation correlates poorly with biological behavior):

·      Hyperplastic lesion: Nodular sebaceous hyperplasia

·      Neoplastic lesions:

·      Sebaceous adenoma

·      Ductal adenoma

·      Sebaceous epithelioma (low grade malignancy), common epithelial skin tumor in the dog

·      Sebaceous carcinoma

·      Meibomian glands: Specialized sebaceous glands of the eyelid, develop analogous neoplasms to sebaceous glands



·      Unknown



·      Nodular sebaceous hyperplasia:

·      Single or multiple raised, yellow-orange, single or multi-lobulated waxy to hyperkeratotic mass; most often on the head, eyelids, limbs, and trunks of aged animals

·      Predisposed breeds: Poodle, Cocker Spaniel

·      Sebaceous epithelioma:

·      Solitary, firm, nodular or fungiform, or plaque-like mass frequently ulcerated

·      Low-grade malignancy, rarely may metastasize to local lymph nodes

·      Head, neck, ears, and dorsum are common sites

·      Common in dogs, particularly Lhasa Apsos and Shih Tzus



·      Nodular sebaceous hyperplasia:

·      Multiple multilobulated, small (usually <1cm)

·      Epidermis is frequently hyperplastic and hyperkeratotic and may be ulcerated

·      Sebaceous epithelioma:

·      Solitary, raised, smooth, greasy to hyperkeratotic

·      Occasionally cauliflower-like, red to orange

·      Frequently pigmented and/or ulcerated



·      Nodular sebaceous hyperplasia:

·      Well-demarcated, multilobulated, intradermal mass composed of lobules arranged around distended keratinized sebaceous ducts and hair follicles

·      Lobules surrounded by a single peripheral layer of basaloid reserve cells

·      Well-differentiated sebocytes predominate

·      Sebaceous epithelioma:

·      Basaloid reserve cells predominate

·      Multiple, large, irregular islands of epithelial basaloid reserve cells with variable margins

·      Sebocytes are found individually or as small aggregates

·      Higher mitotic rate

·      Foci of ductal differentiation as horn cysts

·      Variable melanization

·      Lymphatic invasion occasionally found at periphery



·      Sebaceous adenoma (if eyelid, Meibomian adenoma): Sebocytes predominate, lobules not arranged around a distended duct, degeneration and drop-out (cystic degeneration) of central zones of mature sebocytes common

·      Sebaceous ductal adenoma (Meibomian ductal adenoma): Haphazard arrangement of predominantly ducts admixed with fewer basaloid reserve cells and sebocytes

·      Sebaceous carcinoma (Meibomian carcinoma): Marked pleomorphism; high mitotic activity; variable cytoplasmic lipid content

·      Basal cell carcinoma: Low grade malignancy without adnexal differentiation

·      Meibomian epithelioma: Low grade malignancy; similar to sebaceous counterpart; frequently pigmented; differentiate from melanoma



·      Seen occasionally in cats

·      Rarely reported in other domestic animals

·      Occur in humans



1.    Hargis AM, Myers, S. The Integument. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier Mosby; 2016:1034.

2.    Kiupel, M, ed. Surgical Pathology of Tumors of Domestic Animals: Volume 1. Epithelial Tumors of the Skin. Gurnee, IL: Davis-Thompson Foundation, 2018:125-146; 232.

3.    Mauldin EA, Peters-Kennedy J. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed, St. Louis, MO: Elsevier; 2016:717-720.

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