JSUR Journal

Introduction

Endoscopic approaches are now widely used in the management of skull-base neoplasms, including pituitary tumors, Olfactory Neuroblastomas (ONB), chordomas, and chondrosarcomas. Surgical treatment planning for such neoplasms requires consideration of the tumor extension and the risks of subsequent skull-base defects, postoperative Cerebrospinal Fluid (CSF) leakage, meningitis, brain abscess, and pneumocephalus [1,2] Because insufficient repair is associated with postoperative complications, reliable skull-base reconstruction after endoscopic surgery is necessary [3,4]. Reconstruction of anterior skull base defects with additional rigid structural support is essential to prevent graft migration due to intracranial pulsation and gravity and to reduce the possibility of frontal lobe herniation [5-7]. To the best of our knowledge, no previous study has investigated postoperative complications following endonasal endoscopic reconstruction with an autologous rigid buttress in ONB patients. This study aims to evaluate the results of endoscopic reconstruction using an anatomical multilayered approach with a rigid buttress and vascularized flap in ONB patients.

Methods And Materials

Patient Data

In this retrospective cohort study, we reviewed the records of ONB patients who underwent endoscopic endonasal surgery with endoscopic rigid reconstruction between May 2015 and December 2021. The diagnosis of ONB was histologically confirmed in all cases. We reviewed patient data including age, sex, diagnosis, surgical procedure, repair technique, length of follow-up, and the presence of postoperative complications. The final cohort included 12 patients. This study was approved by the Institutional Ethics Committee of Chang Gung Memorial Hospital. All cases were jointly managed by the same surgical team, which consisted of otorhinolaryngology and neurosurgery services and an experienced primary surgeon. The otorhinolaryngologist resected tumors located in the nasal cavity and paranasal sinuses, and the neurosurgeon resected dural, olfactory bulb, and intracranial tumors. All patients were evaluated preoperatively using enhanced computed tomography and/or magnetic resonance imaging and positron emission tomography (Figure 1). Biopsied tumor samples were analyzed by a pathologist.

Figure 1: Preoperative and postoperative computed tomography scans. Pre-operative coronal view (A) and pre-operative sagittal view (B) identified a tumor located in the right nasal cavity with frontal base invasion. The orbital wall bone was also eroded and the periorbita laterally displaced. (C,D) Post-operative computed tomography scans showing the rigid bone reconstruction in place, in good anatomical alignment with no encephalocele or flap dislodgement, and restoration of the orbital cavity after tumor resection.

The arrows indicate the fat graft. The arrowheads indicate the bone graft.

Surgical Procedures and Reconstruction Techniques

We identified and completely resected the tumor attachment. The cribriform plate, dura, olfactory bulbs, and tracts were resected depending on the extent of the tumor via navigation assistance. The skull base was then reconstructed. We harvested approximately 2.5 × 2.5 cm of the fascia lata, depending on the defect size, and subcutaneous fat from the thigh before reconstruction. An autologous fat graft was used to eliminate intracranial dead space and prevent the fascia graft from being dislodged into the space. For the first layer, a piece of autologous fascia lata was placed as the subdural inlay, and the margin was extended circumferentially about 0.5 cm beyond the edge of the dural defect. For the second layer (extradural onlay), another piece of autologous fascia lata larger than the bony defect circumferentially was placed outside the dural defect but inside the bony edge (in the epidural space). For the third layer of reconstruction, we used an autologous perpendicular plate, vomer bone chips, or septal rigid cartilage, placing the material over the fascia but inside the bony defect (Figure 2). An important step in our technique was the insertion of both the second layer of fascia and bone graft into the space between the dura and edges of the bony defect. This layer-by-layer anatomic repair ensured closure of the defect and provided rigid support for the frontal lobe. We then inspected the repair to ensure the absence of CSF leakage and brain pulsatility before proceeding to the next step of positioning the flap by Valsalva maneuver. Following bone graft placement, the defect was covered with a vascularized nasoseptal flap. Each layer was then secured with fibrin sealant (Tisseel, Baxter International Inc., Deerfield, IL, USA) to ensure closure and adjacency of the reconstruction layers. Finally, the nasal cavity was supported with a piece of Nasopores (Polyganics, Groningen, The Netherlands) to ensure the nasoseptal flap remained in place.

Figure 2: Intra-operative photographs. (A) The extent of skull base defect after tumor resection. (B) The fat graft was placed in the subdural resected cavity and embedded in the bony or dural border of the defect. (C) The first layer of autologous fascia lata was inserted as an inlay graft inside the dural edge. (D) The second layer of autologous fascia lata was inserted as an extradural onlay graft inside the bone edge. (E) Rigid buttress bone graft was inserted between the onlay fascia lata and bone edge. (F) Diagrammatic representation of the autologous rigid reconstruction of an anterior skull base defect layer by layer in sagittal view. (OB: olfactory bulb; FL: fascia lata; D: dura; B: bone; NSF: nasoseptal flap; F: Fat)

Postoperative Management

Lumbar drainage was initially inserted in one patient (patient 1) to prevent postoperative CSF leak (for monitoring only). We then considered that this additional procedure to prevent CSF leakage was not necessary. Therefore, midway through the study period we revised our protocol to exclude the lumbar drainage, which facilitated earlier mobilization of the patients. The patients were kept on a prophylactic antibiotic regimen consisting of a third-generation cephalosporin or a penicillin-based antibiotic (a beta-lactamase) from 1 day before until 7 days after the surgery.

Results

The clinical characteristics of the patients are shown in Table 1. Of the 12 included patients, 4 (33.3%) were male and 8 (66.6%) were female. Eleven patients had complete reconstruction with a bone graft, and 1 patient had incomplete reconstruction due to inadequate bone reconstruction. The mean patient age was 50.9 years (range, 27-78 years), and the mean postoperative followup period was 24.8 months (range, 7-57 months). The mean Body Mass Index (BMI) was 22.3 kg/m². Three patients with Kadish stage D tumors and lymph node invasion underwent neck dissection surgery. Hyams tumor grading revealed a grade II tumor in 5 patients, grade III tumor in 6 patients, and grade IV tumor in 1 patient. The mean hospital stay for the 9 patients without neck dissection was 8.8 days, compared to 17.3 days for the 3 patients with neck dissection. All patients underwent postoperative endoscopic examination upon return to the otolaryngology clinic. No cases exhibited persistent crusting at the repair site, and there were no cases of postoperative meningitis, mucocele formation, or tension pneumocephalus. Four patients underwent radiation therapy, and 4 patients underwent chemoradiation therapy. One patient (patient #9) had vomer bone erosion leading to inadequate rigid reconstruction, which was managed with complete bed rest for 5 days. The patient did not undergo a second reconstructive surgery. Endoscopic examination was performed by an otolaryngologist every month after surgery in patients treated using the Valsalva maneuver to check for CSF leakage. In a total of 26 months of follow up, no leakage was noted among these patients. In the total patient cohort, we observed no CSF leakage, encephalocele, or central nervous system infection. The mean defect width was 1.56 cm, and the mean defect length was 1.97 cm. The cancer recurred in 3 patients during the follow-up period, as follows: Patient #2, inferior right nasal septum metastasis 23 months after tumor resection; patient #3, lumbar spine bone metastasis 55 months after radiotherapy; patient #4, right lower section of the inferior turbinate metastasis 26 months after concurrent chemoradiotherapy.

Discussion

Our study had described the experience and results of endoscopic reconstruction using an anatomical multilayered approach with a rigid buttress and vascularized flap in ONB patients. ONBs are rare, anatomically complex neuroendocrine malignancies that are thought to arise from the nasal olfactory epithelium. Due to this site of origin, they have a tendency to extend directly into the central nervous system through the cribriform plate and anterior skull base. No uniform treatment algorithm has been established for patients with ONB; however, multidisciplinary management including surgery alone or surgery with radiotherapy is generally preferred [8-11]. While surgical resection can be the sole therapy for early tumors, combination treatment is the preferred method for later tumors at most institutions [12]. The 5-year overall survival rate is 86-100% in patients with Kadish stage A and B tumors and 70.8-76% in patients with Kadish stage C and D tumors [13-15].

The Era of Endoscopic Surgery for Patients with ONB

En-bloc resection through a craniofacial approach has been the traditional technique used in the management of ONB. However, this procedure results in a large facial wound and requires a long hospitalization and intense postoperative care [2,16,17]. The endonasal endoscopic approach avoids the facial incision, extensive osteotomies, and frontal lobe retraction and is therefore less invasive with better preservation of function. The endonasal endoscopic approach is also reported to achieve better survival and local control rates [16,18,19]. A meta-analysis of 36 studies with 609 ONB patients suggests higher disease-specific survival and lower rates of CSF leak and intracranial complications in patients undergoing endoscopy compared to those undergoing craniofacial surgery [16]. The origin of the olfactory neuroblastoma is the olfactory neuroepithelium located in superior nasal vault and cribriform plate. Given this presumed origin, the appropriate surgical margin is considered to be resection of the dura and the olfactory apparatus. Our present retrospective study reveals no association between the recurrence site and reconstructed tissue. We had also reviewed the literature regarding tissue reconstruction and tumor recurrence. According to Florent Carsuzaa et al.,[20] the rate of local recurrence after surgery for malignant sinonasal tumors was about 30-50%. To date, few studies have addressed tumor recurrence in reconstructed tissue in ONB patients.

Common Complications Of Endonasal Endoscopic Surgery

The complications of endonasal endoscopic surgery, including nasal obstruction, CSF leak, meningitis, pneumocephalus, and intracranial hypotension, may be troublesome and are often related to inadequate reconstruction [6,21,22]. Surgical site mobility may require further CSF diversion techniques or revision surgery, resulting in delayed treatment. Postoperative CSF leakage has been reported in 1-8% of anterior skull base reconstructions [5,23,24].

Differences in Endonasal Endoscopic Reconstruction Techniques

Multilayer reconstruction to establish watertight closure is the gold standard for skull base defects  [4,25,26] A number of reconstruction materials have been proposed, including abdominal fat, nasal turbinate mucosa, turbinate bone, septal cartilage, temporalis fascia, a pedicled nasoseptal flap, and an alloplastic plate [27-32] Most case series of skull base reconstruction techniques include pituitary adenomas, which are generally extra-arachnoidal tumors with smaller defects and lower rates of postoperative CSF leak. A summary of anterior skull base reconstruction techniques excluding pituitary adenomas is shown in Table 2. The bilayer button technique for skull base reconstruction has been proposed, however the alignment has been shown to be unsuitable for firm repair. Luginbuhl et al. applied the bilayer button technique in smaller defects by sandwiching the dural edge.[33] The gasket technique, which uses a rigid buttress, is one of the most common cranial base reconstruction methods. Garcia-Navarro et al. described use of the gasket technique with vomer bone or MEDPOR (Porex Corp, Newnan, Georgia, USA) in 46 patients, reporting a postoperative CSF leakage rate of 5.2%. [34] Most of their enrolled patients had craniopharyngioma, and lumbar drainage was placed in 32 patients. However, the surgical defect in patients with ONB may be wider, thus requiring multiple layers of reconstruction. The development of new reconstruction techniques and materials should improve the complication rates.

ONB: Olfactory Neuroblastoma; LD: Lumbar Drainage; CSF: Cerebrospinal Fluid; NR: Not Reported; RT: Radiation Therapy; CCRT: Concurrent Chemoradiotherapy; NSF: Nasoseptal Flap

Table 2: Literature review of cases of anterior skull base reconstruction excluding pituitary lesions.