An oncocytoma is a tumor

Tumor

A tumor or tumour is commonly used as a synonym for a neoplasm that appears enlarged in size. Tumor is not synonymous with cancer...

 made up of oncocyte

Oncocyte

An oncocyte is an epithelial cell characterized by an excessive amount of mitochondria, resulting in an abundant acidophilic, granular cytoplasm...

s, a special kind of cell

Cell (biology)

The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

s.

Presentation

An oncocytoma is an epithelial tumor composed of oncocytes, large eosinophilic cells having small, round, benign-appearing nuclei

Cell nucleus

In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...

 with large nucleoli.

Oncocytoma can arise in a number of organs.

Salivary gland oncocytoma

The salivary gland oncocytoma is a well-circumscribed, benign neoplastic growth also called an oxyphilic adenoma. It comprises about 1% of all salivary gland tumors. The histopathology is marked by sheets of large swollen polyhedral epithelial oncocytes, which are granular acidophilic parotid cells with centrally located nuclei. The granules are created by the mitochondria.

Symptoms

Salivary gland oncocytomas are most common in ages 70-80, females, the parotid gland

Parotid gland

The paired parotid glands are the largest of the salivary glands. They are each found wrapped around the mandibular ramus, and secrete saliva through Stensen's ducts into the oral cavity, to facilitate mastication and swallowing and to begin the digestion of starches.-Location:The parotid glands...

 (85-90%), and are firm, slowly growing, painless masses of < 4 cm. They may be bilateral.

Thyroid oncocytoma

Thyroid oncocytomas can be benign (adenomas) or malignant (carcinomas). Grossly, oncocytic adenomas are encapsulated, solid nodules with a characteristic brown cut surface. The gross appearance of a minimally invasive oncocytic carcinoma is indistinguishable to that of an adenoma, while widely invasive oncocytic carcinomas are obviously invasive macroscopically and display pervasive vascular invasion with multifocal involvement of the thyroid gland. There are no reliable cytologic features which distinguish oncocytic adenomas from carcinomas and the only criteria for a diagnosis of malignancy is the identification of transcapsular and/or vascular invasion.

Symptoms

Patients with thyroid oncocytomas present with a thyroid nodule, usually with normal thyroid function. If the tumor is big or invasive, there may be other symptoms such as difficulty swallowing or talking.