Anterior skull base reconstruction using nasoseptal flap: cadaveric feasibility study and clinical implication [SevEN-001]

Abstract

Background: Pedicled nasoseptal flap (PNSF) has significantly improved the surgical outcomes of endoscopic endonasal approach (EEAs) by reducing cerebrospinal fluid (CSF) leakage. The purpose of this study is to assess the feasibility of using a PNSF for anterior skull base (ASB) reconstruction and to describe a method to compensate for a short flap based on our results.

Methods: In this cadaveric study, ASB dissection without sphenoidotomy was performed using 10 formalin-fixed and 5 fresh adult cadaver specimens, and the sufficiency of the PNSF to cover the ASB was assessed. After the sphenoidotomy, the length by which the PNSF fell short in providing coverage at the posterior wall of the frontal sinus (CPFS), and the extent of the anterior coverage from the limbus (CL) of the sphenoid bone was measured.

Results: Without sphenoidotomy, the mean length of the remaining PNSF after the coverage of the posterior wall of the frontal sinus was 0.67 cm. After sphenoidotomy, the PNSF fell short by a mean length of 2.10 cm, in providing CPFS. The CL was 1.86 cm. Based on these findings, defects resulting from an endoscopic resection of ASB tumors were reconstructed using PNSF without total sphenoidotomy in 3 patients. There were no postoperative CSF leaks or complications.

Conclusions: The use of PNSF for ASB reconstruction may be insufficient to cover the entire ASB defect after removal of large lesions which need total sphenoidotomy. When possible, by leaving some portion of the anterior sphenoid wall for supporting the PNSF, successful ASB reconstruction could be achieved in endoscopic resection of ASB tumors. Additional methods might be needed in some cases of large ASB lesions wherein the anterior sphenoid wall should be removed totally and the ASB defect is too large.

Keywords: Anterior skull base; Nasoseptal flap; Skull base reconstruction; Sphenoidotomy.

Fig. 1

Schematic diagrams illustrating the dissection procedures. a Endoscopic view of right nostril. b Sagittal view of the pedicled nasoseptal flap. OS: sphenoid ostium, MT: middle turbinate, IT: inferior turbinate, S: septum

Fig. 2

Anterior skull base reconstruction without sphenoidotomy. a An illustration of the sagittal view without sphenoidotomy. b A 0-degree endoscopic view of the anterior skull base without sphenoidotomy and (c) the view after covering with the pedicled nasoseptal flap. d Confirmation of the end point of the coverage under navigation. CPFS: coverage at the posterior wall of the frontal sinus, CP: cribriform plate, SS: sphenoid sinus

Fig. 3

Anterior skull base reconstruction with sphenoidotomy. a An illustration of the sagittal view with sphenoidotomy. b A 0-degree endoscopic view of the anterior skull base with sphenoidotomy and (c) the view after covering with the pedicled nasoseptal flap. d Confirmation of the end point of the coverage under navigation. ASBD: anterior skull base distance, CPFS: coverage at the posterior wall of the frontal sinus, CL: coverage from the limbus, PS: planum sphenoidale

Fig. 4

Images from Case 1. A recurrent olfactory neuroblastoma. a Coronal enhanced magnetic resonance imaging (MRI) reveals a recurrent tumor on the frontal base, which was operated upon by an endoscopic endonasal approach from the left nostril. b Enhanced sagittal MRI shows a mass with irregular margins in the left ethmoid sinus extending to the frontal base bone, dura, and sphenoid sinus. c The tumor can be seen extending into the left side of the sphenoid sinus and nasal cavity. d The right lateral side of the sphenoid sinus wall is left intact to support the pedicle of the PNSF. e The PNSF covers the ASB defect through the bony support of the remnant lateral side of the sphenoid sinus wall. f, g Postoperative coronal and sagittal MRI reveals a well enhanced PNSF and coverage of the ASB defect. h, i One year after the operation, the follow-up coronal and sagittal MRI showed well-healing state of the nasal mucosa and no recurrence of the tumor. j An endoscopic view shows a well-harvested PNSF at 2 weeks after the operation. FS: frontal sinus, CP: cribriform plate, SS: sphenoid sinus, PS: planum sphenoidale, PNSF: pedicled nasoseptal flap, ASB: anterior skull base

Fig. 5

Images from Case 2. An olfactory neuroblastoma. a Enhanced coronal MRI reveals a mass with irregular margins on the left side of the upper nasal cavity extending to the frontal base. d The tumor can be seen invading the frontal base and extending to the anterior wall of the sphenoid sinus. b, e A well-enhanced PNSF and coverage state of the ASB defect can be seen in the postoperative coronal and sagittal MRI. c, f The follow-up coronal and sagittal MRI revealed stable disease status and well-healing state of the nasal mucosa 6 months after the operation. ASB: anterior skull base, PNSF: pedicled nasoseptal flap

Fig. 6

Images from Case 3. A meningothelial meningioma. a Coronal enhanced MRI reveals an extradural mass in the frontal base extending into the upper nasal cavity. d Sagittal MRI shows extensive involvement of the tumor in the upper nasal cavity, but not in the sphenoid sinus. b, e Postoperative contrast-enhanced coronal- and sagittal MRI shows a well-enhanced PNSF that covers the ASB defect. c, f The follow-up coronal and sagittal MRI showed small mucocele in the sphenoid sinus without any symptoms 6 months after the operation. ASB: anterior skull base, PNSF: pedicled nasoseptal flap

Fig. 7

a, c A 78-year old male patient with huge olfactory neuroblastoma with extensive ASB defect which was revealed in preoperative enhanced coronal and sagittal MRI. b, d Postoperative coronal and sagittal MRI showed insufficient anterior coverage of PNSF for ASB defect, and loose attachment of PNSF to the skull base despite the support of tissue glue and nasal packing. The patient encountered the CSF rhinorrhea 3 days after the operation. ASB: anterior skull base, PNSF: pedicled nasoseptal flap