Galeal Frontalis Myofascial Flap

I. T. JACKSON

Z. POTPARIC

The galeal frontalis myofascial flap is a distally based flap that contains the deep subcutaneous tissues of the forehead. It is usually elevated from the coronal flap by subcutaneous dissection, thereby creating a vascularized myofasciodisposal flap that is either placed intracranially, or used for coverage of the orbits or the nose or both. Recently, as a result of careful injection studies, the pericranium also has been included, as to do so increases the vascularity of the flap.

INDICATIONS

The goals in intracranial reconstruction with the galeal frontalis flap are to provide separation between the nasopharynx and brain, to obliterate dead space, to prevent cerebrospinal fluid (CSF) leakage (particularly if the dura is lacerated), and to provide vascularized coverage for bone grafts. The flap is used for reconstruction of defects after resection of anterior skull-base malignancies, trauma involving the anterior cranial fossa, and when a Le Fort III advancement is combined with frontal advancement. In the case of an old CSF leak, the flap is used in precisely the same way. Together with a skin graft, it also can be used as a vascularized soft-tissue bed for coverage of the orbits and the nose. Finally, it is an excellent material for packing the frontal sinus following trauma. In this situation, bone can be packed on top of it to fill this area completely (1). The flap should not be taken from a previously irradiated area or from an area to be irradiated.

ANATOMY

The key to the anatomy of the galeal frontalis myofascial flap is an understanding of the layers of the forehead skin and the scalp. These are histologically composed of the following five layers: (a) skin, (b) subcutaneous tissue, (c) frontalis muscle and its aponeurotic extension, (d) subgaleal fascia, and (e) cranial periosteum.

The subcutaneous fat tissue as well as the subgaleal loose connective tissue are called the subgaleal fascia; these layers vary considerably in thickness in different areas of the forehead as well as in different persons. The subgaleal fascia consists of several well-vascularized parallel connective tissue sheets that glide over one another. Histologically, three superimposed layers may be distinguished: a well-vascularized superficial layer underlying the galea frontalis muscle, a middle relatively avascular layer, and a deep loose areolar layer overlying the cranial periosteum. The layers that were originally included in the galeal frontalis myofascial flap are (a) partial-thickness subcutaneous fat, (b) galeal frontalis muscle, and (c) superficial layers of subgaleal fascia (2). As mentioned, the pericranium has now been added (3).

The blood supply to the galeal frontalis flap is entirely from the supratrochlear and supraorbital vessels (Fig. 9.1). Both divide into larger superficial and smaller deep branches, either within or shortly after exiting from the orbit around the supraorbital rim. Deep branches have a short axial course in the cranial direction, traveling just on top of the periosteum and within the layers of the subgaleal fascia. As the larger superficial branches exit from the orbit, they first pierce the orbicularis oculi and corrugator muscles. For a short distance, they travel within the substance of these muscles and the frontalis muscle. They then pierce the frontalis muscle and become superficial to it and to the galea, coursing within the subcutaneous fat.

As they course toward the crown of the scalp, they become more superficial, travelling just below the dermis and hair follicles. Only a few anastomoses between the paired vessels cross the midline. At the level of subcutaneous tissue, dissection of the flap violates the axial blood supply and determines distal flap viability. Continuous axial vessels within the flap may range from 3 to 7 cm (4). The supraorbital artery provides the major blood supply, as the supratrochlear artery is transected more proximal to the flap because of its more superficial course. Volumes of galeal frontalis flaps, with sizes in the 9- × 14-cm range, vary from 15 to 30 cc (3).

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