Microdissection And Virtual Reality 3-dementional Image Study Of The Lateral Skull Base And Related Middle Cranial Fossa

ObjectiveTo investigate the key anatomical structures and communicating avenues between lateral skull base and the related middle cranial fossa and help to select optimal surgical approach.MethodsFifteen cadaveric specimens injected with colored latex and contrast agent were dissected using a frontotemporal-zygomatic preauricular subtemporal infratemporal approach. CT scan was performed before and after the specimen injection; MRI scan was performed before and after the specimen injection and dissection respectively; the DICOM data of the CT and MRI were transferred to and reconstructed in the Destroscope virtual reality system. The important anatomic structures and landmarks were observed and measured in the dissection procedures and virtual reality environment respectively. The results obtained from the microdissection and virtual reality 3-D stereoscopic image studies were demonstrated and compared.Results1The superficial temporal artery, facial nerve, pterygoid muscle, internal maxillary artery, mandibular nerve, pterygoid venous plexus, parapharyngeal space and pterygoid palatine fossa were dissected microscopically. The important structures among them and the communicating avenues between lateral skull base and the related middle cranial fossa were demonstrated and measured. Likewise, the work was carried out based on the 3-D stereoscopic image in the virtual reality environment. The results obtained from the microdissection and virtual reality 3-D stereoscopic image studies have no statistic difference.2 Superior and inferior pterygoid muscle triangles were proposed, the side length and area were measured and the structures through which were described.3 A new bony landmark point"O", the junction point between the temporal-sphenoidal suture and the infratemporal ridge, were described. From the view of the middle cranial fossa, the radial lines from the point"O"to the interior point of the superior orbital fissure, foramen rotundum, foramen ovule, foramen spinosum, are approximately equal with the average length of 23.22mm. Therefore, the above four points distribute on a circle arch with the center of the point"O"and radius of 23.22mm and form a sector to the center point"O".The angle of the sector is 66.07°and the area is 310.71mm2. From the view of the roof of infratemporal fossa, the distances from the point"O"to the important landmarks were measured and described.4 Based on the natural landmarks, one point, two spines, three clefts, four lines, 5 foramens and six regions can be used to describe the lateral skull base.Conclusions1 This study introduces a new landmark point"O", i.e. the junction point between the temporal-sphenoidal suture and the infratemporal ridge. It is a good bony landmark in that the interior point of the superior orbital fissure, foramen rotundum, foramen ovule, foramen spinosum distribute on a circle arch to the center of the junction point. The sector area formed by the above five points is not only a crucial avenue for the communication of tumors between the middle cranial fossa and the infratemporal fossa but also a safe area through which to remove the skull base communicating tumors.2 This study introduces the concept of superior pterygoideus triangle and inferior pterygoideus triangle. They can be deemed as muscle landmarks to describe and localize the internal maxillary artery, buccal nerve and lingual nerve, inferior alveolar nerve and provide anatomic landmarks for lateral skull base surgery.3 The lateral skull base can be summarized to one point, two spines, three clefts, four lines, five foramens, six regions. This facilitates us to describe and understand the complex anatomic relations and provides anatomic landmarks for lateral skull base surgery.4 Frontotemporal-zygomatic preauricular subtemporal-infratemporal approach which can provide an excellent exposure of the lateral skull base and the related middle cranial fossa is optimal to the microdissection study and provide the anatomic knowl- edge for designing the suitable surgical approaches. 5 The numerical data obtained from the virtual reality 3-D image study well consist with that from the dissection study. Virtual reality 3-D image study not only is a helpful supplement to the microdissection study but also has unique advantages,it can be used alone or combined with the microdissection to construct anatomic model, observe and measure the anatomic structures and simulate dissection procedures.