DEFINITION A hydrocele (HI-droe-seel) is a fluid-filled sac surrounding a testicle that causes swelling in the scrotum. Hydrocele is common in newborns and usually disappears without treatment during the first year of life. Older boys and adult men can develop…
DEFINITION Hypertrophic cardiomyopathy (HCM) is a disease in which the heart muscle (myocardium) becomes abnormally thick (hypertrophied). The thickened heart muscle can make it harder for the heart to pump blood. Hypertrophic cardiomyopathy often goes undiagnosed because many people with…
DEFINITION Hypercalcemia is a condition in which the calcium level in your blood is above normal. Too much calcium in your blood can weaken your bones, create kidney stones, and interfere with the way your heart and brain works. Hypercalcemia…
DEFINITION Hypereosinophilic (hy-per-ee-o-SIN-o-phil-ik) syndrome (HES) refers to a group of blood disorders that occur when you have high numbers of eosinophils — white blood cells that play an important role in your immune system. Over time, these high numbers of…
DEFINITION Hypopituitarism is a rare disorder in which your pituitary gland either fails to produce one or more of its hormones or doesn’t produce enough of them. The pituitary is a small bean-shaped gland situated at the base of your…
DEFINITION Hypoparathyroidism is an uncommon condition in which your body secretes abnormally low levels of parathyroid hormone (PTH). PTH plays a key role in regulating and maintaining a balance of your body’s levels of two minerals — calcium and phosphorus.…
DEFINITION Hypospadias (hi-poe-SPAY-dee-us) is a condition in which the opening of the urethra is on the underside of the penis, instead of at the tip. The urethra is the tube through which urine drains from your bladder and exits your…
DEFINITION Hypoplastic left heart syndrome is a complex and rare heart defect present at birth (congenital). In hypoplastic left heart syndrome, the left side of the heart is critically underdeveloped. If your baby is born with hypoplastic left heart syndrome,…
DEFINITION Hypoglycemia is a condition characterized by an abnormally low level of blood sugar (glucose), your body’s main energy source. Hypoglycemia is commonly associated with the treatment of diabetes. However, a variety of conditions, many of them rare, can cause…
DEFINITION Hypothermia is a medical emergency that occurs when your body loses heat faster than it can produce heat, causing a dangerously low body temperature. Normal body temperature is around 98.6 F (37 C). Hypothermia (hi-poe-THUR-me-uh) occurs as your body…
DEFINITION Hyponatremia is a condition that occurs when the level of sodium in your blood is abnormally low. Sodium is an electrolyte, and it helps regulate the amount of water that’s in and around your cells. In hyponatremia, one or…
DEFINITION When you have hypochondria, you become obsessed with the idea that you have a serious or life-threatening disease that hasn’t been diagnosed yet. This causes significant anxiety that goes on for months or longer, even though there’s no clear…