Answer: Adenoid cystic carcinoma

Histology: The overlying epithelial is characterized by a stratified keratinized squamous epithelium with adnexal structures consist with the external canal of the ear. The underlying tissue is infiltrated by basaloid nests of cells. Within these nests are the formations of glandular and pseudoglandular structures. The pseudoglandular structures are filled with a bluish-gray stromal material. The true glandular spaces are lined by ductal cells with eosinophilic cytoplasm. Some of these ductal cells appear to retain ceruminous differentiation.

Discussion: Adenoid cystic carcinomas can involve the external ear canal. Although involvement of this site may represent direct extension from the adjacent tail of the parotid gland, they can also arise from the external ear as the primary tumor site. It is generally accepted that adenoid cystic carcinoma primary to the external ear canal take origin from the ceruminal glands that populate this region. Despite this unusual origin, adenoid cystic carcinomas of the external ear closely resemble their salivary gland counterparts. They should not be confused with ceruminal gland neoplasms that feature more obvious ceruminous features in the form of apocrine-type epithelial cells with prominent pink cytoplasm. Like their salivary gland counterparts, adenoid cystic carcinomas of the external ear generally follow a protracted but relentless clinical course punctuated by episodes of local recurrences and distant metastases.