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.