Head case: Mohs scalp excisions require refined touch

Williamsburg, Va. - The intricacies of scalp excisions and subsequent repairs require careful attention to detail to maximize therapeutic and cosmetic outcomes of Mohs surgery, an expert says.

Successful Mohs surgery of the scalp requires both surgeons and histotechnicians to understand the subtleties of scalp anatomy, says Michael J. Wells, M.D., associate professor of dermatology, Texas Tech University Health Sciences Center, Lubbock, Texas.

For example, one difficulty in processing scalp tissue is that when the periosteum is removed, "It's very thin and prone to come out of the parallel plane. So it can be tough to cut complete sections if it's not done carefully," he says. Otherwise, "The processing of scalp tissue is pretty similar to most other tissue associated with Mohs surgery."

Procedurally, Dr. Wells says, "Most of what you're going to undermine when either closing or working with the scalp is located down below the arteries and nerves, below the galea, which is the strong aponeurosis that makes up much of the scalp."

Because it's a fairly bloodless plane, he says, "It's easily undermined."

Subgaleal area

The space below this aponeurosis consists of loose areolar or connective tissue, also called the subgaleal plane.

"Many times," Dr. Wells says, "that's where physicians will work to try to close these defects, because this area is devoid of much of the vasculature and nerves that supply the scalp."

The subgaleal area makes an ideal dissection plane for defects larger than 1 cm, he says. If defects measure larger than 3 cm, he says, "They will likely require more than a side-to-side closure."

However, he says that because the galea is a thick, inelastic, fibrous band of tissue, "It can make closure very difficult. So, one must mobilize tissue from areas where the skin is thinner and looser. That's usually referred to as the hatband area."

Other methods that have been used to stretch the galeal area include the buried pulley (or figure eight) stitch or towel clamps, Dr. Wells says.

Additionally, he says, "If pre-op tissue expanders are to be used, one must plan for weeks in advance."

As for complications of scalp surgery, he says that due to the calvarium's convex shape, "Blood vessels don't contract as well. Bleeding is a lot more common on the scalp."

Similarly, Dr. Wells advises that Mohs surgeons keep in mind the need to preserve hair follicles for cosmesis.

"Another problem when working on the scalp is that when you get down into bone, it doesn't always heal well by secondary intention. Sometimes, you must perhaps remove the outer table of the calvarium or (bore) into the space between the two plates to allow the tissue to granulate."

Closure techniques

Besides secondary intention, closure techniques for the scalp include simple layered closure, rotation closure and transposition closure.

"When I use a rotation closure," Dr. Wells says, "I believe in back-cuts. They help mobilize the flap into position. And if one closes the back cut first, it helps push the flap into position."

Most texts do not adequately discuss the importance of back-cuts when it comes to closing large defects on the scalp, he says.

However, Dr. Wells says the technique is "a gem for many people to use on scalp closures when they're having a hard time closing, especially with a rotation flap."

In one case involving a large scalp defect that extended down to the bone, he says, "We used a double rotation or O to Z flap, since the area of exposed bone doesn't granulate well; but when we moved the tissue into place, we still had a large secondary defect from one of the flaps."

Rather than attempting to close it and creating too much tension at the edges of the flaps, "We actually planned to allow the area to heal by secondary intention, by undermining in the more superficial but vascularized plane above the galea. The other option would be putting a graft over the remaining secondary defect. This will probably result in alopecia in this area of the second intention healing," but this didn't matter because the patient in question already was bald on the crown (area of the secondary defect), he says.

Additional closure methods include interpolation/axial flaps, full-thickness and split-thickness grafts, and free flaps. The latter require microvascular reanastomosis, Dr. Wells says.

Tumors

Tumors that involve the calvarium also require careful handling, he says.

Strategies here include removal of the superior table and radiation.

"Especially if there's perineural or lymph node involvement," Dr. Wells says, "many people believe adjuvant radiation should be used for squamous cell carcinomas."

Many times, he says, "People think of the bone in the scalp being one dense structure." In removing the superior table, he says physicians must consider that the skull consists of various layers, starting with thickened lamellar bone.

"There's a top portion and a bottom portion, and in between is trabecular or marrow-type bone," he says. If one removes the top table of bone, Dr. Wells says, "One can remove tumor extending into the periosteum as well as allow the blood vessels that traverse through the calvarium to be exposed, which promotes granulation and healing."

This strategy involving removing the exposed bone is a way to remove the superior table without getting into the intracranial cavity, Dr. Wells says. DT

Disclosure: Dr. Wells reports no relevant financial interests.

For more information:

www.ttuhsc.edu

www.mohssurgery.org