hamartoma

A hamartoma is a focal malformation that resembles a neoplasm in the tissue of its origin. This is not a malignant tumor, and it grows at the same rate as the surrounding tissues. It is composed of tissue elements normally found at that site but that are growing in a disorganized mass. They occur in many different parts of the body and are most often asymptomatic and undetected unless seen on an image taken for another reason. Hamartomas result from an abnormal formation of normal tissue, although the underlying reasons for the abnormality are not fully understood. They grow along with, and at the same rate as, the organ from whose tissue they are made, and, unlike cancerous tumors, only rarely invade or compress surrounding structures significantly.
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Hamartoma /ham·ar·to·ma/ a benign tumor-like nodule composed of an overgrowth of mature cells and tissues normally present in the affected part, but [more]Hamartoma - Community and Resources

Noun
1. a focal growth that resembles a neoplasm but results from faulty development in an organ
(hypernym) growth

[ham-ar-TOE-ma]
A benign (noncancerous) growth made up of an abnormal mixture of cells and tissues normally found in the area of the body where the growth occurs.