I have to get Mohs surgery on top of scalp and am concerned about the size. Can someone help explain what to expect?

First, I understand your concern.  I'm a female and I definitely would not want my head shaved.  At my office, we never shave the scalp, but surgeons vary on this subject.  You should give your doctor's office a call and check their policy.  In general, the scalp heals very well, the stitches are camouflaged by the hair and in the end there is a thin scar that is difficult to find.  
Best,
Kristy Fleming, MD 

While a BB-sized BCC of the scalp could be very small, it could represent the tip of the iceberg. In general, the best person to answer your questions is the Mohs surgeon performing the procedure. All I can do is tell you what I do. Hair does need to be shaved from the operative site as it can make its way into the field. I usually start by shaving about 1 cm around the visible tumor. I then begin by treating the site with electro-dessication and curettage(burning and scraping). Most BCC's are soft and mushy and scrape out fairly easily, normal skin is a lot firmer and resists being scraped out. This then gives me a good idea of how deep and wide the defect will be. It also reduces the number of stages of Mohs surgery necessary to clear the tumor.( I must tell you that many Mohs surgeons do NOT do this and for various reasons. Since payment for Mohs is, in general, by number of stages, reducing the number of stages reduces reimbursement). Mohs surgery can then be performed. Once tumor has been totally removed, you will be left with a defect, let's say the size of a quarter as an example. I will show this to my patient and go over options, let heal or repair. I go over these in detail explaining what needs to be done and what to expect as a result. Let's say that I explain that the quarter sized defect can be simply removed by excising the wound in fusiform fashion(banana or football shaped) and then sewn closed. The resulting closure wound will then be between 3 to 4 times as long as the width of a quarter and, because the tension of scalp skin is usually significantly high, the scar would be subject to stretch-back(widening somewhat to get back closer to the size of the original fusiform excision). Not pretty. Other repairs can be performed such as local flaps(grafts are NOT appropriate in your situation). However, there is no guarantee that the flap will take, and you may be left with a "T" or "Z" shaped or curvy scar, and with hair going in different directions from normal. Not attractive for short hair. The other option is to let this heal by itself, called second intention healing. With proper wound care it would take the wound 3 to 4 weeks to totally heal and it would most likely heal flat and would contract to about 1/3rd the size of the original quarter, smaller than even a dime. This could then receive hair grafts, if necessary, or excised in fusiform fashion for a smaller scar than if it was done right after the surgery. While this option takes additional time for healing, it almost certainly will give the best possible cosmetic result. However, this is not a popular option for most Mohs surgeons, who generally will not even mention it to their patients because, as one Mohs surgeon told me, "you don't get paid to let it heal". By now you should be well-informed and should know what questions to ask your Mohs surgeon before having the procedure. Use this knowledge wisely.