Dr. Greene’s Answer:
Hemihypertrophy, also called hemihyperplasia, is a greater-than-normal asymmetry between the right and left sides of the body. This difference can be in just one finger; just one limb; just the face; or an entire half of the body, including half the brain, half the tongue and the internal organs, or any variation in between. Someone with hemihypertrophy might have acne on only one side of the face. The skin is often thicker, and there may be more hair on the head, on the larger side. Rarely, children can have crossed hemihypertrophy (one leg and the opposite arm are larger than their partners).
Theories abound as to the cause of hemihypertrophy- perhaps it is increased blood flow or decreased lymph drainage, or nerve or hormone abnormalities. To date, not enough research has been conducted to choose between the theories. We don’t know the cause, but we do know that hemihypertrophy is usually not inherited. People with hemihypertrophy can go on to have healthy, normal children (Genetic Counseling, 1993; 4:119–126).
Hemihypertrophy is a key warning to be on the lookout for several kinds of cancers. Sadly, hemihypertrophy is often not looked for and not diagnosed until after the cancer has been discovered.