Neurosurgical Techniques EBEN ALEXANDER, JR., M.D., EDITOR
Supratentorial Skull Flaps GuY L. ODOM, M.D., AND BARNES WOODHALL,!V[.D. Department of Surgery, Division of Neurosurgery, Duke University Medical Center, Durham, North Carolina T ~E following illustrations show the scalp and bone flaps commonly used by the neurosurgical service at Duke University Medical Center to expose supratentorial lesions. In planning any skull flap, the most important aspect of the problem is being certain that it is properly placed in order to expose the intracranial lesion with as little trauma to the adjacent brain as possible. Other aspects of the procedure which are extremely important are (1) preservation of blood supply to the scalp flap, (~) avoiding the frontal sinus, (3) avoiding damage to the major venous sinuses, (4) avoiding damage to the branch of the facial nerve to the forehead, and (5) avoiding placing burr holes too far apart. In this series of sketches, burr holes are outlined indicating that the bone is cut with a gigli saw. If a craniotome is used rather than a gigli saw, we have found that in older people in whom the dura adheres to the inner table, it is better to use several burr holes in order to separate the dura from the inner table of the skull and avoid cutting the dura at the bone edge by the craniotome. Often it is useful to connect the burr holes through their outer periphery rather than through their center as shown in the drawings. This modification provides an additional centimeter of exposure throughout the circumference of the bone flap. Unilateral Frontal Flap The incision for the average unilateral frontal (Fig. 1 A) scalp incision is outlined in such a way as to preserve the blood supply from the temporal artery and the branch of the facial nerve to the forehead. The scalp and bone flaps are reflected separately, the scalp anteriorly and the bone laterally onto the temporal muscle. The bone flap should avoid the frontal sinus, unless the sinus is large or it is necessary to obtain a low exposure, as in a hypophysectomy. If the sinus is opened intentionally or unintentionally it should be immediately sealed off with a strip of fascia. If a large bone flap is planned, three burr holes instead of two are placed just lateral to the sagittal sinus to avoid the danger of tearing the dura and a cortical vein while separating the dura from the inner table of the skull (Fig. 1 B). Fro. 1. A. Unilateral frontal scalp flap. Note location of branch of facial nerve and temporal artery. 49~
Supratentorial Skull Flaps 493 FIG. 1. B. Unilateral frontal bone flap.
494 Guy L. Odom and Barnes Woodhall Bilateral Frontal Flap A bilateral frontal flap (Fig. ~ A), also must avoid the branches of the facial nerve on each side and should not enter the frontal sinuses. The scalp is easily reflected forward if the coronal incision is curved slightly forward on each side and at the vertex. Bilateral bone flaps (Fig. ~ B) are hinged on the temporal muscles. We prefer this to removing the frontal bone as a free flap. In order to avoid damaging the sagittal sinus, burr holes are placed near the midline on each side of the sinus and then the bone is cut on one side between the medial, anterior and posterior, burr holes. The cut should be FIo. 2. A. Bilateral frontal scalp flap indicating location of burr holes.
Supratentorial Skull Flaps 495 beveled so that the two flaps can be wired tightly together. After reflecting the flap on one side, the region of the sagittal sinus can be separated from the inner table of the skull just before the opposite flap is elevated. A coronal scalp flap is sometimes helpful even if a unilateral skull flap is planned. It has the cosmetic advantage of keeping the incision behind the hairline; moreover, the opposite skull flap can easily be reflected if additional exposure becomes necessary. This is especially useful in the repair of cerebrospinal fluid rhinorrhea. FIG. ~. B. Bilateral frontal bone flap. The bone overlying the sagittal sinus between the anterior and posterior medial burr holes is removed with rongeurs.
496 Guy L. Odom and Barnes Woodhall Parietal Flap In the parietal region (Fig. 3 A) we have found it is always better to place the medial limb of the incision near the midline. The ends of the anterior and posterior portion of the incision should be the same distance apart as the length of the medial portion of the incision. FIG. 3. A. Parietal scalp flap.
Supratentorial Skull Flaps 497 The scalp is reflected laterally and a free bone flap is removed (Fig. 3 B). In this way, if additional lateral exposure is necessary, bone may be removed beneath the temporal muscle after the scalp incisions have been extended into the temporal region. FIG. 3. B. Parietal skull flap.
498 Guy L. Odom and Barnes Woodhall Temporal Flap The anterior limb of the incision of a temporal flap (Fig. 4 A) is placed no more than 1.5 cm. anterior to the external auditory meatus in order to avoid the branch of the facial nerve. FIG. 4. A. Temporal scalp flap. Note location of facial nerve and temporal artery.
Supratentorial Skull Flaps 499 The incision is extended down to the zygoma in order that as much of the temporal bone as necessary may be removed with rongeurs after the bone flap has been reflected (Fig. 4 B). If mastoid cells are opened they must be immediately plugged with bone wax. FIG. 4. B. Temporal bone flap.
500 Guy L. Odom and Barnes Woodhall Occipital Flap In the occipital region the scalp (Fig. 5 A) and bone flaps are reflected separately. The incision begins just above and lateral to the inion and extends parallel to the midline into the posterior parietal region and curves down into the temporal region. FrG. 5. A. Occipital scalp flap.
Supratentorial Skull Flaps 501 In this position, the scalp flap is reflected posteriorly preserving the blood supply from the occipital artery. The bone flap (Fig. 5 B) is hinged on the temporal muscle and the burr holes should avoid the transverse and sagittal sinuses. FIG. 5. B. Occipital bone flap.