In rare cases, children diagnosed with attention deficit hyperactivity disorder (ADHD) actually have a tumor that appears to cause symptoms similar to those of ADHD, according to a small new study. The researchers evaluated 43 children with rare tumors of the adrenal gland, called pheochromocytomas and paragangliomas. (The adrenal glands are located near the kidneys, and produce adrenaline and other hormones.)