Some like to make demarcation lines as to where it starts, but it's not really that easy, probably easier to measure hair line, frontal third, mid section and then crown as approximate regions. The crown opens on all sides, from the frontal, sides and dropping down the back, some cultures almost have a double size when it thins on top and then drops down, almost potentially doubling the surface area.
A small crown can easily be almost a circle say 6x6, and for easy measuring, but for those in to their maths comes the PI equation, this calculation is designed to give the values of a circle.
This makes it much harder to treat a crown, where to start, how many grafts to use and where to place them because the probability is the surface area can increase easily by just a little thinning, for example if the crown opened by 1cm more all the way round the surface area has dramatically altered.
This is why, and this goes for the frontal sides receding down also it is important to bite into the existing hair a little to ensure for future loss to some degree; rather than only place in the obviously thin area only for a year or two's time the thinning progress and being left with an island of hair.
The crown also because of design and surface can have an insatiable appetite or need for hair, the placement differs from the frontal areas so needs more to give the same appearance of thickness, and because of this it could need a good 1/2 again compared to the frontal/mid. Generally someone s donor cannot give this (like mine now using beard and body) so a thinner look form a HT or lower density placed is common in the crown.
IF you start working in the crown first then we must be mindful not to "back load" the HT, using most of the resources available only in the crown and not enough to address frontal loss and being able to balance the look of a natural if thinning head of hair.
So, from the hairline back to a line drawn between the two temporal angles measures an area of roughly 50 cm2. The top of the head, from behind the frontal area to the front border of the crown may be about 150 cm2. The crown, as we pointed out can vary widely in size, but in a Class 6 or 7 can be as large as 175 cm2. Even if we transplant a minimal density (15 FU) to a fully bald crown (175 cm2) we have used roughly 2600 FU. If we transplant a higher density, 40 FU, then we have used 7000 grafts, this is more than the average person has available in their donor area and this is just in the crown.
Wow, impressive post Stephenl, very educational. I thoroughly concur with the difficult aspect of defining just where crown starts and how the crown region eats up more grafts than top and front.
For simplicity sake, we use a grid diagram of the hairloss area. It's to give us a rough estimate of the area that's in need. We split the grid in half - top half is around 100cm2 and another 100cm2 for the crown.
As Stephenl mentioned of the way hairs lay at the crown, dense packing in the crown is often necessary to eliminate the see through skin look (approx. 60-70fu per cm2) but most patients do not have the donor supply. Most doctors will not plant at that density to save donor for future. Generally, we'll address the crown when the thinning is really bothersome for the patient but we do not dense pack. In fact, we'll likely plant at half of what is needed. Of course we address each patient on an individual basis.
I,ve measured my loss from behind the frontal 50cm and its measures roughly 100cm,so thats a total of about 150cm of diffuse loss, being that i,m nearly 40 would it be wise to go for full coverage,or go for good density on the front 100cm and then beef up the final third, leaving grafts for any potential loss in the future?
Another question i have is whats the optimal FU per cm to give the appearance of good density?i was thinking 50 to 60 depending on the individual patient
If you have diffuse hairloss it would be very wise to take finasteride for at least 6 months prior to an HT. The native hairs usually get stronger during this period and you risk less shockloss.
Personally I would always invest in the frontal area first. For a good density 50 to 60 grafts per cm2 is usually enough to get good coverage and density. This density is used in zone 1 and 2, but lowered gradually towards zone 3.
The crown is sometimes also reffered to as the black hole. It takes tremendous amounts of grafts to get a full look.