The lateral humps are the areas of the scalp that fall on the sides of the head, joining the sides to the top of the head from the hair line temple back. The lateral hump becomes important in cases of progressive hair loss when the hair in this area begins to part from the mid scalp.
In lower Norwood scale or even medium hair loss stages the lateral humps remain intact. Generally the initial signs of hair loss occur in the temporal area starting to move back creating a larger recession. Lateral humps may still appear to be intact in some cases but the quality of the hair is weak and miniaturised; in this case it is important the area is treated as having no hair.
When treating advanced hair loss with hair transplantation it is important to always examine the lateral humps for the quality of hair and the potential for them to drop further. If the lateral humps are not rebuilt it will give you an unnatural appearance of hair growth, and can leave a hair line and mid scalp rebuilt but isolated from the hair around the sides and back of the head. When designing the hair line the lateral humps need to be taken into consideration with generally a conservative approach to the design. This is due partly to the pattern of hair loss and the fact if the lateral humps have dropped the recipient surface area increases.
The larger the surface area drives the distribution of grafts to ensure a balanced natural cosmetic result can be achieved, not front loaded with a large area of hair loss behind that could be half the scalp. Another important aspect is understanding how the hair angles change when rebuilding the area, going from the top of the scalp angling down to meet the sides. This requires skill and a great deal of understanding the anatomy of the head.