[Anatomical investigation of the venous system in pedicled nasal septal mucosal flap and its application in nasal skull base reconstruction].

Objective: To investigate the distribution and primary drainage sites of the venous drainage system in the pedicled nasal septal mucosal flap, as well as to examine protective measures for the venous system of the nasal septal mucosal flap and its application in repairing the nasal skull base through the anatomical study of the nasal septum mucosal venous system in cadavers. Methods: Gross anatomy dissections were performed on 13 sides perfused fresh frozen cadaveric head specimens. The nasal septum mucosal flap was separated along the perichondrium and subperiosteum, then passed across the vomer, anterior wall of sphenoid sinus, clivus, and towards the anterior edge of vertical plate of palatine bone. Detailed documentation, including photographs, was made to record the morphology, distribution and drainage location of veins of the nasal septum mucosal flap and its pedicle, along with number of sphenopalatine veins. Furthermore, venous injuries resulting from obtaining a pedicled nasal septal mucosa flap were observed. From March 2023 to March 2024, a retrospective analysis was conducted on patients with nasopharyngeal lesions who underwent surgical repair using a modified pedicled nasal septum mucosal flap for venous system protection in the ENT institute and Department of Otorhinolaryngology at the Eye & ENT Hospital of Fudan University. The postoperative endoscopy was employed to assess the viability of the mucosal flap. Results: The veins of the nasal septum mucosa were primarily located in the posterior region, including the vomerine region, anterior wall of the sphenoid sinus, clivus region, and posterolateral wall of the nasal cavity, in a reticular pattern. Perforating veins draining into these bony structures could be observed, although their quantity and morphology varied. Notably, no prominent sphenopalatine veins were identified in 10 specimens examined, while 3 specimens exhibited sphenopalatine veins: one with a small single branch and two with venous bundles. Preservation of the nasal septal vein was possible when dissection was limited to the anterior edge of the wing of vomer. A wider range of dissection increased the risk of veinous injury. In cases where only vascular pedicles at the sphenopalatine foramen were preserved, three cadaveric head specimens retained intact sphenopalatine veins, while drainage veins were completely destroyed in ten other specimens. Fifteen patients with unilateral lesions (8 with recurrent nasopharyngeal carcinoma and 7 with nasopharyngeal radionecrosis) were included in this study. The postoperative reconstructions were carried out using contralateral pedicled nasal septal mucosal flaps. The average follow-up time was 7 months (ranging from 3 to 12 months), and all the nasal septal mucosal flaps survived. Conclusions: The primary location of the drainage vein within the nasal septum mucosa is situated in its posterior region, where it penetrates into adjacent bone structures. Very few sphenopalatine veins pass through the sphenopalatine foramen. Extensive dissection of the pedicled nasal septal mucosal flap may potentially impair the venous system and adversely affect flap survival rates, necessitating further clinical exploration.