Introduction: Innovations and technical refinements have expanded the access of endoscopic skull base surgeons beyond sellar region. One inherent concern is the increased risk of cerebrospinal fluid leak. Nasoseptal flap, a vascularized pedicle flap has dramatically reduced the risk of CSF leak. In this study we measure the dimensions of nasoseptal flap theoretically in thin cut CT scan. We further compare these measurements in cadaver studies with the help of neuronavigation.

Methods: Five disarticulated fresh frozen Caucasian adult heads were dissected for this study. CT scans of these cadaver heads were performed and theoretical size of skull base defects and nasoseptal flaps were measured from various landmarks. Finally standard Hadad-Bassagasteguy flap was raised. The flap dimensions were measured using neuronavigation. These were compared on both sides and with the theoretical sizes.

Results: In all specimens, the theoretical flaps were adequate to cover the anticipated defects. However, a 5mm margin between the edges of the mucoperichondreal flaps and the bony edges, required for strong apposition, were not achieved in all instances. The flaps were long enough to cover the inferior aspect of the clival defect, with adequate 5mm margins. The results are summarized in the table below.

Conclusions: Nasoseptal flap plays a significant role in planning of reconstruction after an endoscopic endonasal procedure. However variable anatomy is plausible and the actual flap is always smaller than the theoretical one. Surgeons should consider this individual variation and plan accordingly in each case.

Patient Care: A knowledge of judicious use of nasoseptal flap is of paramount importance in reconstruction of cranial base after endoscopic skull base approach

Learning Objectives: -Theoretical measurements of flaps tend to be longer than that which is practically achievable and might prove to be insufficient. This is true especially in the setting of the co-occurrence of factors such as a very anterior and inferior defect, a combined transsphenoid and transcribriform approach and a small nose. -Extending the dissection to the inferior nasal wall, or once past the vertical attachment of the middle turbinate extending the flap superiorly potentially yields a much wider flap. -alternative options need to be anticipated and explored when a larger exposure is required

References: 1. Hadad G, Bassagasteguy L, Carrau RL, Mataza JC, Kassam A, Snyderman CH, et al: A novel reconstructive technique after endoscopic expanded endonasal approaches: vascular pedicle nasoseptal flap. 2.Kassam AB, Thomas A, Carrau RL, Snyderman CH, Vescan A, Prevedello D, et al: Endoscopic reconstruction of the cranial base using a pedicled nasoseptal flap. Neurosurgery 63:ONS44-52; discussion ONS52-43, 2008 Laryngoscope 116:1882-1886, 2006 3. Pinheiro-Neto CD, Ramos HF, Peris-Celda M, Fernandez-Miranda JC, Gardner PA, Snyderman CH, et al: Study of the nasoseptal flap for endoscopic anterior cranial base reconstruction. Laryngoscope 121:2514-2520, 2011