There are several breast implant shapes available. There are two general categories which include symmetrical (round) and asymmetrical (shaped or anatomic). The theoretical advantage of shaped implants is a more natural shape and they better approximate natural breasts in the sitting or standing position. This means that there is more breast tissue at the bottom of the breast and less breast tissue at the top of the breast in the sitting or standing position. The disadvantage of shaped breast implants is related to their potential to shift inside the breast implant pocket. If the shaped implant moves or shift to any large degree then the breast may have a misshapen or bizarre appearance. For example, the breast would be full at the top and small at the bottom if the implant rotated 180 degrees (top goes to the bottom and vice-versa). Because of this problem, special care must be made to prevent implant shifting or rotation when using shaped breast implants. Even when special precautions are taken the implant can still shift or rotate to an unfavorable position. Shaped implants appear natural only if they remain in an exact position because they have an asymmetrical axis. Round breast implants are symmetrical about an axis unlike shaped breast implants. Therefore, round breast implants can rotate around a central axis in the breast pocket and maintain symmetry and a normal appearance. This is a distinct advantage of round breast implants as compared to shaped breast implants. Round breast implants are manufactured in low, moderate and high profile designs. The high profile implants give more projection and have a more narrow base diameter when compared to low profile implants, and this design (high profile) is very popular with patients. This allows a larger breast implant to be placed without being too wide (base diameter too wide) which would encroach on the midline of the chest (between the breasts) and the anterior axillary line (the area below the armpit). The high profile breast implants are especially desirable for cosmetic breast enhancement.