Etiology: Tumors arise from the holocrine glands at the base of the external ear canal. Malignant tumors are locally invasive but not metastatic.
Incidence: Spontaneous tumors are uncommon.
Clinical Signs: This tumor may appear as a firm, subcutaneous mass at the base of the ear. The overlying skin may exhibit signs of hair loss or ulceration (A.).
Pathology: Grossly, tumors are circumscribed and often ulcerated. Histologically, the mass is composed of sheets of epithelial cells with abundant, vacuolated cytoplasm. There are trabecular and acinar patterns within the mass; many of the acinar structures contain keratinized material and debris (B.). Leukocytic infiltration and foci of necrosis are often present.
Diagnosis: Diagnosis can be made upon necropsy and histopathologic examination of tissue.