Ryosuke Tomio, Masahiro Toda, Agung Budi Sutiono, Takashi Horiguchi, Sadakazu Aiso and Kazunari Yoshida
Extended endoscopic transnasal surgeries for skull base lesions have recently been performed. Some expert surgeons have attempted to remove tumors such as chordomas, meningiomas, and pituitary adenomas in the clival region using the transnasal approach and have reported abducens nerve injury as a common complication. There have been many microsurgical anatomical studies of the abducens nerve, but none of these studies has described an anatomical landmark of the abducens nerve in the transnasal approach. In this study the authors used cadaver dissections to describe Grüber's ligament as the most reliable landmark of the abducens nerve in the transnasal transclival view.
The petroclival segment of the abducens nerve was dissected in the interdural space—which is also called Dorello's canal, the petroclival venous gulf, or the sphenopetroclival venous confluence—using the transnasal approach in 20 specimens obtained from 10 adult cadaveric heads.
The petroclival segment of the abducens nerve clearly crossed and attached to Grüber's ligament in the interdural space, as noted in the transnasal view. The average length of the dural porus to the intersection on the abducens nerve was 5.2 ± 1.0 mm. The length of the posterior clinoid process (PCP) to the intersection on Grüber's ligament was 6.4 ± 2.6 mm. The average width of Grüber's ligament at the midsection was 1.6 ± 0.5 mm.
Grüber's ligament is considered a useful landmark, and it is visible in most adults. Thus, surgeons can find the abducens nerve safely by visualizing inferolaterally along Grüber's ligament from the PCP.
Shigeo Ohba, Masahito Kobayashi, Takashi Horiguchi, Satoshi Onozuka, Kazunari Yoshida, Takayuki Ohira and Takeshi Kawase
Although gross-total resection (GTR) is a preferable treatment for skull base meningiomas, subtotal resection (STR) with or without radiation therapy can be considered as an alternative treatment for patients at considerable surgical risk. The long-term prognosis of such patients might be related to the biological activity of the tumor. This study examined predictors of progression-free survival (PFS) and sought to determine the optimal treatment strategies, focusing on the pathobiological findings of skull base meningiomas.
This study included 281 patients with skull base meningiomas (mean follow-up period 88.4 months). Risk factors for tumor progression were examined using a multivariate analysis. The PFS and overall survival (OS) rates were evaluated using the Kaplan-Meier method. The functional outcomes of the patients were measured using the Karnofsky Performance Scale (KPS).
The 10-year PFS and OS rates were 66.4% and 97.4%, respectively. Overall, 83.3% of patients achieved a favorable outcome, that is, an improved or unchanged KPS score. The extent of resection, additional radiotherapy, histological grade, MIB-1 index, and p53-positive rate were significantly associated with PFS. The PFS of patients undergoing STR without radiation therapy was significantly shorter than that of either those undergoing STR with radiation therapy or GTR, while no statistical difference was observed between the latter 2 groups. Among the patients undergoing STR with pathobiological risk factors (histological grade, MIB-1 index, and p53-positive rate), the PFS of the patients who received radiation therapy was better than that of those who did not receive radiation therapy. Among the patients undergoing STR without such risk factors, the PFS was not significantly different between patients who received radiation therapy and those who did not.
For patients with skull base meningiomas, a GTR is desirable and additional radiation therapy after STR may contribute to a longer PFS. Additional radiation therapy should be recommended, especially for patients with pathobiological risk factors, but not necessarily for those without such risks.