Vascular Supply of Local-Regional Flaps in Skull Base Surgery

4 Vascular Supply of Local-Regional Flaps in Skull Base Surgery

Philippe Lavigne and Eric W. Wang

Summary

With the advent of new technologies and better understanding of the anatomy, skull base defects have become increasingly larger and more complex to reconstruct. Several options now exist from avascular free grafts to large axially perfused local-regional flaps. Some of the vascularized options are harvested traditionally through open approaches, but several endonasal options are available. The concept for both remains the same: a watertight closure to reconstruct the barrier separating the intracranial cavity from external spaces and the aerodigestive tract and prevent postoperative complications. Most vascularized flaps arise from external carotid artery branches, except for the pericranial flap which receives vascular supply from branches of the ophthalmic artery, itself a branch of the internal carotid artery. Reconstructive choice depends on the defect location, size, surgical approach, disease process, patient factors, and surgeon’s preference. Ideally, surgeons will be comfortable with several options to offer tailored reconstruction for optimal results.

Keywords: Endoscopic, reconstruction, skull base, vascularized flap

4.1 Key Learning Points

●Reconstruction of skull base defects is needed to create a protective barrier around the cranial cavity.

●Extranasal flap options include: anterior pericranial flap, temporoparietal fascial flap, temporalis muscle flap, facial artery musculomucosal (FAMM) flap, and occipital pericranial flap.

●Endonasal flap options include: nasoseptal flap, inferior turbinate/lateral nasal wall flap, and middle turbinate flap.

●Flap selection depends on the underlying pathology, patient co-morbidities, prior therapy, approach extension, and defect location and size.

4.2 Introduction

Reconstruction of the skull base is critical to re-establish a barrier between the cranial cavity and the sinonasal tract and to prevent postoperative cerebrospinal fluid (CSF) leaks. Failed reconstruction can lead to pneumocephalus, meningitis, abscess formation, and ventriculitis. Significant advances in technology and the advancement of endoscopic endonasal techniques have required endonasal reconstruction of larger and more complex skull base defects. Reconstructive techniques have also evolved, and multiple options are now available to skull base surgeons. The reconstructive algorithm depends on defect size and location, surgical approach, pathologic diagnosis, patient factors, and prior therapy. Small defects (<1 cm) of the ventral skull base can be repaired with >90% success rates with multilayered nonvascularized free grafts.1 Larger dural defects or those that are exposed to high-flow CSF leaks were found to have CSF leak rates of 16.7 and 16.2% with endoscopic endonasal approaches and open craniofacial resections, respectively.² ^, ³ Vascularized tissue was found to significantly reduce CSF leak rates in such high risk defects.⁴ This chapter presents the most commonly used vascularized reconstructive flaps in transcranial and endoscopic endonasal skull base surgery. Table 4.1 presents the major characteristics for each flap.

Table 4.1 Intranasal and extranasal reconstructive flaps for skull base reconstruction

Location	Flap name	Vascular supply	Advantage	Disadvantage/Limitations
Extranasal
	Pericranial flap	Supraorbital and supratrochlear arteries	Large dimension; pliable; technically easy	Risk of injury to frontal branches of facial nerve; delayed endonasal mucosalization; typically large external incision
	Temporoparietal fascia flap	Superficial temporal artery	Consistent vascular anatomy; large dimension; reaches to posterior cranial fossa	Limited reach to anterior cranial fossa; risk of injury to frontal branch of facial nerve; risk of anterior skin necrosis; hair follicle damage; technically challenging
	Temporalis muscle flap	Deep temporal artery	Strong vascular supply; offers significant bulk/volume	Limited arc of rotation; temporal wasting if all the muscle is mobilized
	FAMM flap	Angular artery	No external incision; strong vascular supply	Potential morbidity (trismus, oral cavity harvest site dehiscence); technically challenging; limited reach
	Occipital pericranial flap	Occipital artery	Large reconstructive surface; strong vascular supply	Limited reach to anterior cranial fossa; large flap length to pedicle ratio; additional dissection of neck; access to posterior scalp
Endonasal
	Nasoseptal flap	Posterior nasoseptal artery	No external incision, long vascular pedicle; reaches all areas of ventral skull base	Potential for microscopic tumor invasion with sinonasal malignancy; potential loss of vascular supply with prior endonasal surgery; limits ipsilateral pterygoid access
	Inferior turbinate/Lateral nasal wall flap	Posterior lateral nasal wall artery	Alternative to NSF when not available	Potential for nasolacrimal duct injury; not as versatile as NSF; short pedicle; lateral nasal wall crusting
	Middle turbinate flap	Middle turbinate artery	Low nasal morbidity; alternative to NSF when not available	Small reconstructive surface; short pedicle and limited arc of rotation
Abbreviations: FAMM, facial artery musculomucosal; NSF, nasoseptal flap; PPF, pterygopalatine fossa.

4.3 Extranasal Reconstructive Flaps

For transcranial approaches, vascularized scalp flaps are effective at re-establishing separation of the intracranial space. Preoperative surgical planning of scalp incisions aids in the harvest and preservation of the vascular supply for these reconstructive options. With open approaches, primary repair of the dural defect with suturing of a fascial graft and inset of the flap facilitates a watertight seal. For reconstruction of endonasal skull base defects, extranasal flaps have the advantage of being harvested at distance from the primary pathology. This is most significant for malignant sinus and skull base tumors where involvement of local tissues can jeopardize the vascular supply of a flap or compromise oncologic resection. Furthermore, if the patient has received prior radiation therapy to the nasal cavity or skull base, the flap and its vascular supply are typically beyond the radiation field.⁵

4.3.1 Anterior Pericranial Flap

The anterior pericranial flap (PCF) receives blood flow from the supraorbital and supratrochlear arteries, both branches of the ophthalmic artery. It is the only locoregional skull base reconstructive flap that receives its blood supply from the internal carotid artery (ICA). It can be harvested unilaterally or bilaterally depending on defect size and arc of rotation and can be extended posteriorly beyond the bicoronal skin incision if needed. A standard PCF combines the periosteum and the superficial loose areolar connective tissue. A galeo-pericranial flap also includes the galeal layer but is rarely employed due to increased risk of overlying necrosis. When using anteriorly based scalp flaps, it is advisable to preserve blood supply to the anterior scalp to reduce the risk of skin necrosis, especially in previously irradiated patients. In these patients, the bicoronal scalp incision should be planned to preserve the parietal branch of the superficial temporal artery (STA) for increased vascular supply to the frontal scalp.⁶ PCFs are traditionally utilized for skull base defects from the frontal sinus to the planum sphenoidale. This flap can be inserted intracranially via a frontal craniotomy, and its utility in endonasal surgery is increasingly noted. It can be transferred endonasally below the plane of the skull base (extracranially) through an osteotomy at the nasion (Fig. 4.1). Care must be taken during this step not to twist the pedicle and compromise the vascular supply to the flap. Endoscopic-assisted harvesting of the PCF has been described and has the potential for reduced morbidity.⁷ Disadvantages of the PCF include the external incision and delayed mucosalization of the flap which leads to prolonged nasal crusting, especially with postoperative radiation therapy (see Table 4.1).

Fig. 4.1 (a) Sagittal view of a cadaveric dissection showing transposition of the extracranial pericranial flap (PCF) (b) transferred endonasally through an osteotomy at the nasion to cover a defect of the ventral skull base. (c) Intraoperative view of endonasal endoscopic PCF inseted through a nasion osteotomy to cover an anterior cranial base defect. PCF, pericranial flap; PS, planum sphenoidale; LO, left orbit; RO, right orbit.

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