Vascularized Outer Table Calvarial Bone Flap
J. M. PSILLAKIS
This is a relatively new flap, and as such, there is considerable controversy about the correct anatomy and operative approach. The reader is cautioned to read the references and the current literature.
The outer table of the calvarium has become an increasingly important donor site for bone grafts in craniofacial surgery (1, 2, 3, 4, 5). It is close to the operative field, it has a membranous origin similar to that of the facial skeleton, there is an inconspicuous donor-site scar, and there is relatively little postoperative pain.
The vascularized outer table calvarial bone flap can be taken from any part of the skull, but in most cases I use the parietal region as the donor area, and the blood supply is carried by the periosteum in continuity with the deep fascial layer of the temporal aponeurosis.
This flap is useful for bone loss in the frontal area, supraorbital region, zygomatic region up to the level of the nose, maxillary area in the middle third of the face, and the mandibular area up to the level of the chin.
The superficial temporal artery continues cranially anterior to the ear at the level of the superficial fascia of the head, more commonly known as the SMAS, and gives off large branches to the parietal and frontal areas. Relatively large perforators of the superficial temporal artery are given off that penetrate into the calvarium primarily at suture lines. There are multiple anastomoses between the superficial temporal system and the middle meningeal arterial arcade within the diploic space.
The periosteum over the frontal parietal region continues with a thin layer over the deep temporal fascia. At the level of the zygomatic arch, proximal branches from the superficial temporal vessels anastomose within the deep temporal muscle. This system irrigates the periosteum even in the absence of large perforating branches from the distal superficial temporal artery. The outer table of the calvarial bone in the frontal parietal region receives numerous small perforators from the vascular network within the periosteum. These perforators do not significantly contribute to the blood supply of the inner table. The inner table is more vascularized by the meningeal vessels. Because of the existence of this random system of anastomosing vessels from the superficial and deep arteries through the temporalis fascia and periosteum, a periosteal flap can be designed using this layer as a pedicle carrying a segment of the outer table of the calvarium (Fig. 198.1). If only the outer table is to be used, it is unnecessary to include the galea and the superficial temporal artery to maintain the blood supply to the bone. If the full thickness of the bone is to be used, it is important to include the galea and the superficial temporal vessels in the flap. The thickness of the calvarium is variable from one region to the other, but a special study performed in 100 cadavers showed that the thickness of the parietal area is 5 mm, with a range of 4 to 6 mm.