| Objectives: To clarify the anatomical relations of the dependency anatomical constructions in the way for operation of the transnasal approach, cadaveric heads were dissected under microscope, which were provided the important parameters of microdissection for the extended transnasal approach. The safety limits in bone removal and the methods to protect internal carotid artery and its branches were investigated. The virtual anatomy was investigated via transnasal approach in a virtual-reality (VR) setting, to establish a virtual anatomical model and explore the application value of the VR technology.Methods: The posterior ethmoid sinus, sphenoid sinus, carvernous sinus, intracavernous carotid artery and its branches, cranial nerves and adjacent structures were dissected, measured and photographed under the operation microscope by using 10 adult cadaveric heads. 20 patients were given the lamellar imaging examination and CT angiogram with Discovery Ultra 16. The datum were collected and inputted into the Dextroscope in the DICOM format. Three-dimensional reconstruction and visualization research were carried out via the transnasal approach in the virtual-reality (VR) setting.Results:1. Normal-position posterior ethmoid sinus, 55%; supra-sphenoid ethmoidal cell, 25%; and latero-sphenoid ethmoidal cell, 20%. The rate of posterior ethmoidal canal was 100%, 70% of which seated in ethmoid roof, 20% seated in the mucosae of ethmoid, 10% seated in ethmiodal cells.2. The distance of the medial walls of two eye sockets was (29.2±1.4)mm (27.3～29.2mm), the distance from the superior margin of apertura sphenoid sinus to the cribriform plate was (10.4±1.3)mm(8.7～12.8mm), the distance of the inner margin of the bilateral sphenopalatine foramens was (25.5±2.1)mm(22.2～28.4mm), the distance of the anterior apertures of the bilateral pterygoid canal was (28.3±1.8)mm (24.4～30.5mm).3. The internal carotid artery at the lateral wall of the sphenoidal sinus could be subdivided into two main segments: the parasellar and the paraclival. It included: Type I 55%, with two"C-shaped"bends, which formed forwards and backwards from the internal carotid artery; Type II 35%, with an inverse"L-shape", which formed by the anterior part up-tilted and the posterior part down-tilted; Type III 10%, with the anterior part down-tilted and the posterior up-tilted.4. The rate of meningohypophyseal trunk was 100%. The initiating diameter was (0.8±0.2)mm(0.6～1.4mm), 30% originated from the acme of the posterior bended segment, 50% originated from the medial wall of the anterior part of the posterior bended segment, and 20% originated from the medial wall of the posterior part of the posterior bended segment. Its branches: (1) inferior hypophyseal artery; (2) dorsalis meningeal artery; (3) tentorial artery. The originating diameter of the inferior hypophyseal artery was(0.6±0.2)mm(0.2～1.1mm), 70% originated from the infer-lateral wall of the middle part of the horizontal segment, 20% originated from the lateral wall of the posterior part of the posterior bended segment, and 10% originated from the meningohypophyseal trunk.5. Pituitary glands were closely contacted with ICA, 45%. pituitary glands were not closely contacted with ICA, 45%. The lateral aspect of the pituitary gland was divided longitudinally into superior, middle and inferior thirds. The intracavernous carotid artery coursed along only the inferior third in 45%, along some part of both the inferior and middle thirds in 30%, and along some part of all the thirds in 15%. In 10%, the intracavernous carotid artery coursed along below the pituitary gland. The distance from the left abducens nerve to the middle point of the left internal carotid artery was 2.8±1.8(1.1～3.7) mm , The right was 2.5±1.3(1.1～3.6) mm.6. The skin tissue, skull, sphenoid sinus, maxillary sinus, ethmoid sinus, pituitary, and the carvernous segment of internal carotid artery were reconstructed through the automatic extraction function of the Dextroscope. And they were colored with the Color Mode to differentiate various anatomical structures. Moreover, the reconstructed structures could be combined randomly to observe spatial anatomical relationship. With the Stereo Mode and Three-Plane Mode, the reconstructed structures could be displayed in situ, cut and revolved multi-azimuthally and multi-angularly. Preoperative training could be conducted via simulating the surgical approach.7. By simulating middle turbinectomy approach, bone removal was different, when medial and lateral borders of cavernous carotid arteries were exposed. It was important to open posterior ethmoid sinus and sphenopalatine foramen, controll sphenopalatine artery, drill pterygoid process and reveal pterygoid canal, when lateral border of cavernous carotid arteries was exposed.Conclusions:1. The field of middle turbinectomy approach can get the broadest field by excision of middle turbinate. Optimal bone removal of the anterior region of aperture of sphenoidal sinus is the key point to expose the lateral wall of sphenoidal sinus. Bone removal can be extended to the infer-lateral and supra-lateral areas, when expanding to lateral areas in operation, but avoiding damage of lamina papgracea.2. The extended transnasal approach is suitable for lesion which grows to the medial and anteroinferior lacouna. It is difficult to remove lesion which grows to the lateral and posterosuperior lacouna.3. The relationship of the cavernous carotid arteries to the pituitary is very close. The cavernous carotid arteries can be injured , when operator extend toward the lateral of sellae. The relationship of the cavernous carotid arteries to the lateral wall of the sphenoidal sinus is very close. Operator should apply bone drill and rongeur alternately to avoid injuring cavernous carotid arteries, when removing the lateral wall of the sphenoidal sinus. The main anatomical structures of medial, anteroinferior of cavernous sinus include: internal carotid artery and its branches, abducens nerve below the lateral side of internal carotid artery. The cavernous carotid arteries and cranial nerve can be injured when operator expand to lateral areas in operation.4. By using the Virtual Reality Technology, virtual anatomical models of the transnasal approach can be reconstructed, which disclose the adjacent relations and space allocation about different anatomic structures, and provide the reference for transnasal approach in preoperative anatomic evaluation.5. The surgeon is allowed to observe dynamicly and stereoly the anatomic structures of transnasal approach, especially the anatomic details and heteromorphosis of the lateral wall of the sphenoidal sinus, pituitary and cavernous carotid arteries. Using Virtual Reality technology to simulate transnasal approach can provide the reference for preoperative evaluation and operation planning.
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