Chapter 37 Pericranial and Temporoparietal Fascia Flaps
It has been well established that vascularized flaps are the best reconstructive options in preventing postoperative cerebrospinal fluid (CSF) leak in patients with large skull base defects, high intracranial pressure (>30 cm H20), widely dissected arachnoid cisterns, and extensive removal of dura. While intranasal flaps, specifically, the posteriorly based nasoseptal flap has become the workhorse flap in endoscopic skull base reconstructions, there are still occasions where extranasal pedicled flaps are needed for reconstruction.1
Extranasal pedicled flaps may be used in situations where the vascular supply to the nasoseptal flap, or other local regional intranasal flaps, has been compromised or when multiple flaps are needed for the reconstruction. Other potential circumstances when these flaps may be necessary include neoplastic involvement of intranasal tissue that would otherwise be used as a flap or previous use of flaps (e.g., recurrent tumor). In this chapter, we describe two extranasal pedicled flaps: the transpterygoid temporoparietal fascia (TPF) flap and the transfrontal pericranial flap. Indications, contraindications, and surgical technique will be discussed in detail.
37.1 Anatomy of the Frontal and Temporal Scalp
Elevation of the pericranial and temporoparietal flaps requires a thorough understanding of the anatomy of the scalp. The scalp is divided into five layers. From superficial to deep, these layers comprise the following:
Aponeurotic layer includes the galea and frontalis muscle anteriorly, the occipitalis muscle posteriorly, and the TPF laterally.
Subaponeurotic layer comprises of loose areolar tissue.
The periosteal layer on the frontal scalp is contiguous with the superficial layer of the deep temporalis fascia, which overlies the temporalis muscle.
Pericranium is a surgical term defined as a combination of the periosteal and the subaponeurotic layers (i.e., areolar tissue).
37.2 Transfrontal Pericranial Flap
The transfrontal pericranial flap is a regional pedicled flap comprising the ipsilateral anterior pericranium, which is pedicled on the ipsilateral supraorbital (and sometimes the supratrochlear) neurovascular bundle. This flap has been used extensively in skull base reconstruction after anterior craniofacial resection (usually using both sides of the frontal pericranium and their corresponding neurovascular pedicle) with excellent outcomes.2–4
When considering defects after endoscopic skull base surgery, this flap is most useful to reconstruct large anterior skull base defects when intranasal pedicled flaps are not available or when multiple flaps are required (i.e., to cover defects extending from the frontal sinus to the clivus and from orbit to orbit).5
Careful consideration should be given to any patient who has undergone prior open cranial surgery, particularly via a subfrontal approach, a brow lift, or any patient who has suffered orbital rim fractures.
A transfrontal pericranial flap is based on the supraorbital and supratrochlear neurovascular bundles, and therefore, the frontal pericranium can be harvested as two separate flaps. The supratrochlear and supraorbital nerves are cutaneous branches of the ophthalmic division of the trigeminal nerve. The supratrochlear nerve supplies the midline forehead to the hairline and the supraorbital nerve supplies the forehead and scalp extending back to the vertex.6 The supratrochlear and supraorbital arteries are branches of the ophthalmic artery, which branches from the supraclinoid segment of the internal carotid artery as it emerges from the roof of the cavernous sinus.6 The supratrochlear artery emerges through the frontal notch or foramen as part of the neurovascular pedicle. The supratrochlear notch (or foramen), which is medial to the supraorbital notch (or foramen), which lies approximately 22.2 mm from the midline.7
A supraorbital notch (as opposed to a foramen) is most common, being present in approximately 70% of cadaveric specimens. Conversely, a foramen is found in approximately 30% of specimens.7 The arteries ascend in the galea frontalis muscular layer providing branches that supply the pericranium.2 It is important to remember that to avoid injury to the neurovascular pedicle during the elevation of the pericranial flap, the frontalis muscle layer should not be separated from the pericranium closer than 10 mm of the orbital rim.2 Both the supraorbital and supratrochlear arteries anastomose with each other and with the superficial temporal artery, a terminal branch of the external carotid artery, thereby forming anastomoses between the internal and external carotid arterial systems.
37.2.4 Surgical Steps8
The nasal cavity is decongested with cottonoids impregnated with a solution of 1:10,000 epinephrine. This aids with hemostasis throughout the surgery. At the beginning of surgery, the lateral nasal wall is infiltrated with a solution of lidocaine 0.5 to 1% with epinephrine 1:100,000.
Before elevating the pericranial flap, a Draf III frontal sinusotomy (i.e., endoscopic Lothrop) is performed. This helps maintain frontal sinus drainage and will prevent the formation of a frontal sinus mucocele postoperatively. Mark a coronal incision at the vertex of the scalp, extending from one ear to the other ( Fig. 37.1a ). Depending on the goals of resection, the marked incision may be carried inferiorly and anteriorly in the preauricular region to allow increased mobility of the flap. Placing the incision at the vertex prevents transection of anterior branches of the superficial temporal artery supplying the anterior scalp and is cosmetically superior especially if there is some potential future for hair loss (e.g., young males with possible hairline recession).
Inject the marked incision line with a solution of 1% lidocaine with 1:100,000 epinephrine.
Carry the incision down to the cranium from one temporal line to the other ( Fig. 37.1b ).
Lateral and inferior to the temporal line, the incision is carried down to the superficial layer of the deep temporal fascia, which is continuous with the periosteal layer of the cranium ( Fig. 37.1c ).
Minimize bleeding applying Rainey clips at the edges of the incision. Alternatively, any significant bleeding point is cauterized using a bipolar electrocautery.
Elevation of the pericranium attached to the scalp flap prevents desiccation of the pericranial flap and also allows inclusion of the subaponeurotic tissue (loose areolar tissue) in the flap, thus making it more robust ( Fig. 37.1d ).
The scalp is then elevated in an anterior direction to reach and expose the superior orbital rim, paying attention to the fact that the supraorbital neurovascular pedicle may arise from a foramen or a notch ( Fig. 37.1e ). If there is a complete foramen, the supraorbital neurovascular pedicle may be freed via an inverted-V osteotomy performed with a 2- to 3-mm osteotome to prevent traction injury to the pedicle
As previously mentioned, care must be taken near the superior orbital rim to avoid transecting the penetrating branch of the supratrochlear and supraorbital arteries, which may arise 10 mm above the orbital rim ( Fig. 37.1e ).
A high-speed drill is used to open a 1 mm × 15 mm osteotomy at the nasion. This will communicate the coronal approach and frontonasal area with the endonasal anterior skull base resection site ( Fig. 37.3b ).
The flap is carefully transposed through the nasion osteotomy into the nasal cavity avoiding any rotation of the pedicle ( Fig. 37.3c ).
An endonasal bolster is placed to support the flap ( Fig. 37.3d ).
The coronal incision is closed meticulously in a multilayered fashion
Postoperatively, do not apply any pressure dressing over the orbital rim to avoid compression of the vascular pedicle.