Midline dural filum of the sellar floor: Its relationship to the septum attachment to the sellar floor and the ossification in the sphenoid sinus.

Objectives: It is important to identify and maintain a midline orientation during endoscopic transsphenoidal surgery (ETSS) for sellar lesions to prevent critical injury to the internal carotid artery. Therefore, the preoperative neuroradiological assessment of the bony structures in the sphenoid sinus, including the septum attachment to the sellar floor and its surrounding structures, is essential. It has been reported that the midline filum of the sellar dura can function as a useful intraoperative orientation guide during ETSS. However, the relationship between the midline dural filum and the intrasinus bony structures, such as the sellar floor, the intrasinus septation and the ossification, remains unclear and the mechanisms underlying development of the midline dural filum have also not yet been explored.

Methods: This retrospective study included 160 patients undergoing ETSS to assess both the midline dural filum and the intrasinus bony structures, using video recording reviews. The intrasinus septum and the ossification in the sphenoid sinus were evaluated on the computed tomography images of the bone window.

Results: A midline dural filum was identified in 66 (41.3%) of 160 patients. Attachment of the septum to the sellar midline was found in 61 (39.4%) of 155 patients, after excluding 5 patients with the conchal type of sphenoid sinus, 55 (90.2%) of 61 patients with a septum on the midline and only 6 (6.4%) of the remaining 94 patients without a septum on the midline had a midline dural filum. The relationship between a midline dural filum and a septum on midline was statistically significant (p<0.001), regardless of the number of intrasphenoidal septa. In terms of the types of sphenoid sinus, the midline dural filum was predominantly detected in patients where ossification extended over the midline filum. In patients with the sellar type of sphenoid sinus, 49 (36.0%) of 136 had a midline dural filum, meanwhile, 16 (84.2%) of 19 patients with the pre-sellar type (p=0.039) and all 5 patients (100%) with the choncal type harbored a midline dural filum (p<0.001).

Conclusion: This study clearly verified the importance of the midline dural filum in a large series and evaluated the obvious relationship between the midline dural filum and the bony structures on the sellar floor. Our results strongly suggest that, during developing of the midline dural filum, the sellar dura becomes tethered to the bony elements attached to the sellar surface, such as the septum on the midline and the ossification in both the pre-sellar and the conchal type of sphenoid sinus.