The Extended Nasoseptal Flap for Skull Base Reconstruction of the Clival Region: An Anatomical and Radiological Study

Introduction: The use of the nasoseptal flap has dramatically reduced the incidence of cerebrospinal fluid leak after endoscopic extended skull base approaches. The extended nasoseptal flap adds the nasal floor and inferior meatus mucosa to the septal area. Reconstruction of large clival defects is challenging, and the standard nasoseptal flap is not always sufficient.

Objective: The objective of this study is to analyze in detail the morphology, potential indications, and limitations of the extended nasoseptal flap compared with the standard nasoseptal flap for skull base reconstruction of the clival area.

Methods: Twenty-seven sides of 14 silicon-colored formalin-fixed anatomical specimens were used for dissections. Thirteen 1-mm thick CT scans of the same specimens were acquired before the dissections. Under 0-degree endoscopic visualization, a standard flap in one side and an extended flap in the other side were performed with electrocoagulation to mimic the surgical procedure. Complete drilling of the clivus and exposure of the sella, cavernous sinus, and clival dura mater were performed. Coverage of both flaps was assessed and the flaps were incised and extracted for measurements. The predicted dimensions of the flap according to the measurements in CT scans were compared with the dimensions of the flap after the dissection.

Results: The extended nasoseptal flap has two parts: the septal part and the inferior meatal part. On average, the extended flaps are 20 mm longer craniocaudally compared with the standard flap, and they add 780 mm² of mucosal area for reconstruction. These flaps can cover a clival defect from tuberculum to foramen magnum in 66.6% of the specimens, and from below the sella to the foramen magnum in 92.4%. In most cases, the reconstruction area covers both parasellar and paraclival segments of the internal carotid arteries and cavernous sinus. The lateral limits considered for the inferior coverage area are the medial aspect of the hypoglossal canals and the eustachian tubes. CT scans can predict preoperatively the need or limitation of an extended nasoseptal flap.

Conclusions: The nasal floor and inferior meatus mucosa add a significantly larger area for reconstruction of the clival area up to the foramen magnum. A defect that extends laterally beyond the level of the hypoglossal canals is not likely covered with this variation of the flap. Preoperative CT scans are useful to guide the reconstruction techniques.