Answer: Adenoid cystic carcinoma

Histology: The lesion shows skin with underlying glandular tumor infiltration. The tumor appears to be infiltrative and ill-defined in size. This tumor shows features typical of adenoid cystic carcinoma; it show the glands growing in a cribriform pattern, the cells are relatively bland in appearance, and often grow in gland-like spaces filled with homogeneous eosinophilic material. This tumor has a well-known tendency for invasion into perineural spaces which also correlates with its pattern of spread. Most of the glandular spaces which are observed are not true glandular spaces but instead represent cavities containing reduplicated basal lumina material produced by the tumor cells.

Discussion: In the external ear canal almost any type of adnexal tumor can involve the skin of this region. The four major categories of tumors of adnexal tumors of the ear include: adenoma, benign mixed tumor, syringocystadenoma papilliferum and adenocarcinoma. The clinical presentation may be similar for all these tumors, however, the malignant tumors are usually ulcerated and sometimes painful. The adenoma of the external ear canal is an encapsulated tumor composed of glandular proliferations lined by apocrine cells. The cells are bland and mitotic figures are rare. Pleomorphism, necrosis, and other evidence of aggressive behavior is lacking. Typical benign mixed tumors of the external ear canal have an appearance similar to those occurring in other salivary glands. They are well-circumscribed lesions and bland in appearance. The adenocarcinoma of the xternal ear canal is usually a well-differnetiated adenocarcinoma that may at times be difficult to distinguish from adenoma. Pleomorphism, some cytologic atypia, the lack of myoepithelial layer, and lack of necrosis and invasive growth pattern are helpful in making this distinction. The tumor in this case has the classical appearance of an adenoid cystic carcinoma. This tumor does have a tendency to infiltrate in the perineural regions which can lead to local recurrence. This tumor can be associated with distant metastasis.