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Expanded Endoscopic Endonasal Approaches to the Maxillary Sinus and Medial Middle Cranial Fossa
1108 16:35-16:45
Skull Base/304A
Introduction: Accessing lesions in the posterolateral wall of the maxillary sinus or the medial middle cranial fossa can be achieved through various surgical approaches. The Endoscopic Endonasal Approach (EEA) is advantageous due to its minimal invasiveness, reduced brain manipulation, and decreased retraction. When combined with other approaches, EEA can offer additional benefits for treating lesions in these areas. This study aims to make the comparison between EEA with medial maxillectomy (MM), the prelacrimal approach (PL), the modified Denker’s approach (MD), and the Caldwell-Luc transmaxillary approach (CLTM). Materials and Methods: Three cadavers (six sides) were dissected using CT registration to compare the surgical approaches. For the posterolateral wall of the maxillary sinus, measurements were taken from the medial superior point, medial inferior point, lateral superior point, most lateral point, and lateral inferior point to calculate the exposure area. For the medial middle cranial fossa, the Meckel’s cave, the superior point of the superior orbital fissure, and the foramen rotundum were used to calculate the anteromedial triangle's exposure area. The Meckel’s cave, foramen rotundum, and foramen ovale were used for the anterolateral triangle. Additionally, we analyzed the attack angles to the Meckel’s cave in both axial and sagittal planes. These metrics were assessed for EEA with MM, PL, MD, and CLTM approaches. Results: The CLTM approach provided a significantly larger exposure area of the posterolateral wall of the maxillary sinus (811.42 ± 87.56 mm²) compared to the EEA with MM (304.82 ± 29.18 mm²), PL approach (412.27 ± 31.82 mm²), and MD approach (598.2 ± 49.36 mm²) (p < 0.001). The CLTM approach offered greater lateral and inferior access to this region. For the anteromedial triangle, the exposure area was also significantly larger with the CLTM approach (185.07 ± 21.8 mm²) compared to the EEA with MM (94.47 ± 4.94 mm²), PL approach (103.9 ± 4.8 mm²), and MD approach (117.21 ± 2.8 mm²) (p < 0.001). The anterolateral triangle's exposure areas were nearly identical across all approaches. In terms of attack angles to the Meckel’s cave, the EEA with MM could not access the lateral aspect. Among the PL, MD, and CLTM approaches, the CLTM provided the largest axial and sagittal angles. Discussion and Conclusions: We presented cases of two patients with trigeminal schwannoma. One patient, with a schwannoma involving the middle cranial fossa and infratemporal fossa, underwent EEA combined with MM and CLTM approaches, achieving complete tumor removal without complications. The other patient, with a schwannoma involving the pterygopalatine fossa, middle cranial fossa, and posterior cranial fossa, was treated using EEA combined with MM, PL, and MD approaches, also resulting in complete tumor removal without complications. EEA, when combined with MM, PL, MD, and CLTM approaches, provides different trajectories for accessing the posterolateral wall of the maxillary sinus and the medial middle cranial fossa. These approaches enable safe access to various skull base lesions depending on the unique features of each expanded endoscopic endonasal approach.

Skull Base Reconstruction
1108 16:35-16:45
Skull Base/304A
Addressing dura defects at the skull base is crucial for surgeons specializing in these procedures. Accurate reconstruction is essential to prevent post-operative cerebrospinal fluid (CSF) leaks, central nervous system (CNS) infections, and exposure of the internal carotid artery (ICA). The approach to skull base reconstruction depends on the characteristics of the CSF leak. The size and location of the dural defect are key factors. For isolated dura defects in the sellar region with low-flow or no CSF leak, an inlay dura substitute combined with an onlay mucosal graft from the middle turbinate is usually sufficient. In cases of high-flow CSF leaks in the sellar region, the optimal strategy includes an inlay dura substitute with an onlay pedicled mucosal flap, commonly the nasoseptal flap (Hadad-Bassagasteguy flap). For Rathke’s cleft cysts, post-drainage reconstruction involves marsupialization with a middle turbinate graft within the cystic cavity and sphenoid sinus to reduce recurrence. For suprasellar region dura defects with high-flow CSF leaks, the preferred technique involves an inlay dura substitute with an onlay pedicled mucosal flap. When using the endoscopic endonasal trans-cribriform approach, anterior skull base dura defects are addressed with an inlay dura substitute, onlay fascia lata, and a pedicled mucosal flap. Clival region dura defects are typically reconstructed with an inlay dura substitute, onlay fascia lata, fat graft, and pedicled mucosal flap, with the fat graft reducing pontine encephalocele risk. Large dura defects in the anterior and posterior fossa often require an external lumbar drain. Alternative reconstruction options include extracranial pericranial flap, temporoparietal fascia flap, lateral nasal wall flap (inferior turbinate flap), and rhinopharyngeal flap, depending on the clinical situation. Over the past three years, our skull base team at MacKay Memorial Hospital had three cases of post-operative CSF rhinorrhea. The first patient had a pituitary macroadenoma, the second a giant pituitary adenoma, and the third a metastatic tumor in the sellar region from the lung. Successful revision surgeries, involving meticulous skull base preparation and nasoseptal flap adjustment, were performed seamlessly. Following these procedures, all patients experienced smooth recoveries without further CSF rhinorrhea. Different skull base pathologies require distinct reconstruction approaches. It is essential for the skull base team to conduct thorough pre-operative assessments. Detailed evaluations, combined with precise intra-operative skills, are critical for successful reconstruction outcomes. Additionally, careful post-operative nasal care is vital to minimize the risk of CSF rhinorrhea. Integrating these elements is key to ensuring optimal results in skull base reconstruction.