Imaging Imaging studies are used to define the extent of the tumor and to exclude direct extension from the parotid gland or nasopharynx. The imaging findings are usually non-specific, and cannot give a specific diagnosis. Pathology Tumors are polypoid, identified most often in the posterior canal. It is not uncommon to have ulceration of the surface squamous epithelium. Most tumors are about 1.5 cm in greatest dimension, a limitation of the anatomic site rather than of the tumor type itself. The tumors are separated into three main histologic or microscopic types: *<unk> , NOS *<unk>  adenoid cystic carcinoma *<unk>  mucoepidermoid carcinoma All of the tumors are infiltrative into the soft tissue, benign<unk>  glands, and/or bone. The tumor may expand into the overlying squamous surface epithelium, but it usually does not arise from the surface epithelium. The tumors are cellular, arranged in solid, cystic, cribriform, glandular, and single cell patterns. It is uncommon to see tumor necrosis, but when it is present, it is diagnostic of cancer. The same is true of perineural invasion. Nuclear pleomorphism is usually easily to identify, with the nuclei containing prominent nucleoli. There are usually increased mitotic figures, including atypical forms. There are usually areas of stromal fibrosis. Ceroid (cerumen or ear wax) is not seen in malignancies, although it is seen in benign tumors. The specific features of each tumor type can help with the separation into adenoid cystic carcinoma or mucoepidermoid types. Immunohistochemistry Immunohistochemistry will help to show the biphasic appearance of the tumor, highlighting the basal or the luminal cells: * Luminal cells: positive with CK7 and CD117 * Basal cells: positive with p63, S100 protein and CK5/6 Differential diagnoses It is important to exclude a tumor which is directly extending into the ear canal from the parotid salivary gland, especially when dealing with an adenoid cystic or mucoepidermoid carcinoma. This can be eliminated by clinical or imaging studies. Otherwise, the histologic differential diagnosis includes a<unk>  adenoma (a benign<unk>  gland tumor) or a neuroendocrine adenoma of the middle ear (middle ear adenoma).
Ceruminous adenocarcinoma
Adenosquamous carcinoma
Anaplastic carcinoma
Squamous cell carcinoma
Adenoid cystic carcinoma
Ceruminous adenoma
Adenocarcinoma
Squamous cell papilloma