Pilomatrixoma - also known as "Pilomatricoma" or "calcifying epithelioma of Malherbe" - is a relatively rare benign tumor of the skin.
The root word is generated by the prefix pilo meaning "hair", the word matrix indicating the formation in a substrate of tissue, and the suffix oma meaning "tumor".
Pilomatrixomas grow slowly, and are most common in the face and neck region. They are also found at times on the scalp, eyelids, and arms. The cells of the pilomatrixoma are differentiated toward (microscopically similar to) hair cells, and become fibrotic and calcified forming a subdermal mass. It is generally asymptomatic, and is found by palpation. It presents and a firm, solitary nodule usually less than three centimeters across. About a quarter of them are inflamed at presentation.
It has an increased incidence in children under ten years old, usually in the first two years of life, but is being increasingly recognized in adults with a second peak of incidence between the ages of 50 to 65 years old. Most cases are reported to have occurred in caucasians, and there is a slightly increased incidence (ratio 1.5:1) in females.
Multiple lesions of this type have been observed in association with myotonic dystrophy. Family members also seem to have an increased incidence, indicating a probable genetic predisposition. There is also a malignant form called Pilomatrix carcinoma which is a much more rare condition.
There is no associated mortality with pilomatrixomas, but very large tumors can cause considerable pain or limitation of motion depending upon their location.
Author's note: I saw one of these just a few days ago - the final pathology report spurred me to write the tumor up. The freshly-excised tumor was a yellowish, gristly, gritty little hard-rubbery mass. No wonder people are happy to have them out!
Author's additional note (12/30/02): I just spoke with the pathologist today about a tumor I had removed last week. He reports a Pilomatrixoma with malignant characteristics! Apparently this is one of only 30 or so known cases of malignant pilomatrixoma!