Microsurgical Anatomy Of Endo-Exocranial Communicating Area

The base of the skull can be regarded as a plate consisting of endocranial and exocranial surface. The endocranial surface contains the skull base structure such as frontal lobe, hypothalamus-pituitary gland, cavernous sinus, temporal lobe, brain stem, cerebellum, cranial nerves, et al. The floor of skull base consists of numerous fissures and foramen through which neurovascular structures passes; it also possesses the inherent structures like inner ear, labyrinth, jugular bulb,et al. The exocranial surface of the skull base is made of craniofacial structures and cervicocranial structures like nasal cavity, paranasal sinus, infratemporal fossa, pterygopalatine fossa, parapharyngeal space, et al. Tumors of skull base communicates endocranially and exocranially through above mentioned structures. These structures are located deep inside and have the complex anatomical relationship which makes it neurosurgically challenging. This study was performed from microsurgical anatomical perspective to understand the relationship of endo-exocranial structures and their communicating areas. This study explains the knowledge in identifying the surgical landmarks providing the anatomical basic to perform surgery in endo-exocranial communicating area. Chapter one Microsurgical Anatomy of Cranio-Nasal-Sphenoidal Communicating AreaObjective:To investigate the microsurgical anatomy between anterior cranial fossa with nasal cavity, paransal sinus, sellar region and sphenoid sinus and nasal cavity. To identify the surgical landmarks while performing transfrontal and transsphenoid approaches of this region. Methods:We observe and measure the bony structures of anterior skull base, such as frontonasal suture, foramen cecum, cribiform plate, planum sphenoidale, tuberculum sella, the pituitary fossa, sphenoid sinus, nasal cavity, ethmoid sinus, anterior nasal spine, e.t.c and their relationships were studied. The intracranial, skull base and extracranial structures exposed using three frontal approaches and transsphenoidal approach were observed and studied.Results:Cribiform plate is located at the center of anterior skull base, and lies between the frontal bone, planum sphenoidale, and ethmoidal labyrinth, superior surface being frontal lobe and inferior surface is the roof of nasal cavity. Planum sphenoidale lies on the superior wall of sphenoidal sinus, posterior of which is the chiasmatic sulcus, tuberculum sella and pituitary fossa. Optic nerve lies on the lateral side of planum sphenoidale. Distance from frontonasal suture to foramen cecum was 12.70±1.28mm, frontonasal suture to ethmoidal plate was 35.67±1.12mm, frontonasal suture to limbus sphenoidalis was 51.40±2.98mm,frontonasal suture to tuberculum sella was 54.32±1.89mm, frontonasal suture to dorsum sella was 65.78±1.56mm. Foramen cecum to anterior ethmoidal foramen was 10.98±1.12mm, foramen cecum to posterior ethmoida foramen was 25.11±1.25mm. Distance between anterior nasal spine to the ostium of sphenoid sinus was 42.34±2.23mm,anterior nasal spine to anterior edge of cribiform plate of nasal cavity roof was 41.88±0.24mm, anterior nasal spine to posterior edge of cribiform plate of nasal cavity roof was 52.05±0.45mm.Conclusions:In Cranionasosphenoidal region, cribiform plate and sphenoid sinus are the important structures that communicate anterior cranial fossa with nasal cavity, sellar region with sphenoid sinus and nasal cavity. Surgical landmarks of frontal approach is classified into 3 levels: the first-level landmark includes frontonasal suture,the second-level landmark includes foramen cecum, the third-level landmark includes cribiform plate, planum sphenoidale, limbus sphenoidalis, tuberculum sella, sphenoid sinus e.t.c. Surgical landmarks of transsphenoidal surgery is also classified into 3 levels:the first-level landmark is anterior nasal spine, the second-level landmark is ostium of sphenoid sinus and the third-level landmark is sphenoid sinus. Performing the subcranial approach can broadly expose this communicating region. Chapter two Microsurgical Anatomy of Cranio-orbital Communicating AreaObjective:To investigate the microsurgical anatomy between anterior cranial fossa and orbit, structures of superior orbital fissure and optic canal, to identify the surgical landmark of lateral orbital approach.Methods:We observed the bony structure of orbital roof, optic canal and superior orbital fissure and measured the distance between supraorbital foramen with anterior ethmoidal foramen and optic canal. Relationship between superior orbital fissure, optic strut, carotid groove, foramen rotundum etc was studied.Results:The communication of cranio-orbital area is provided by the optic canal and superior orbital fissure. The structures passing through the optic canal are optic nerve and ophthalmic artery. Orbit is joined to the sellar region by optic canal. Superior orbital fissure is the main channel through which the orbital nerves including occulomotor nerve, trochlear nerve, abducent nerve and ophthalmic nerve passes. Superior orbital fissure connects the orbit to the cavernous sinus of middle fossa. The distance from supraorbital foramen to intraorbital anterior ethmoidal foramen was 30.12±2.35mm, supraorbital foramen to intraorbital posterior ethmoidal foramen was 39.75±1.25mm, and supraorbital foramen to the opening of the orbital canal in orbit was 43.35±1.67mm. Conclusions:Cranio-orbital communicating area is easily damaged by direct injury to the orbital roof, but the main communication occurs at the optic canal and superior orbital fissure.The first-level anatomical landmark of lateral orbital approaches includes supraorbital foramen or supraorbital notch, orbito-frontal foramen; the second-level landmark is superior orbital fissure, anterior clinoidal process, and optic strut. Lateral orbital approach exposes the structures inside the orbit; sellar region, cavernous sinus and lateral portion of middle fossa floor also have the excellent exposure by this approach. Chapter three Microsurgical Anatomy of the Middle Fossa and Infratemporal Fossa and Pterygopalatine Fossa Communicating AreaObjective:To investigate the relationship between middle fossa, infratemporal fossa and, pterygopalatine fossa, lateral wall of cavernous sinus and surgical angle of middle fossa floor. To confirm the surgical landmark of frontotempro-orbitozygomatic approach.Methods:We observed and measured the lateral wall of cavernous sinus, foramen rotundum, foramen ovale, foramen spinosum, middle fossa, infratemporal fossa,pterygopalatine fossa and studied their relationship.Results:Superior orbital fissure and orbit marks the anterior border of middle cranial fossa, temporal fossa on lateral border and posteriorly by petrous part of temporal bone which also separates the middle fossa from posterior fossa; cavernous sinus is situated on both side of sella turcica. The floor of middle fossa contains different foramens, namely, foramen rotundum, foramen ovale, foramen spinosum and foramen lacerum through which it communicates with infratemporal fossa, pterygopalatine fossa and parapharyngeal space. Fronto-orbital artery canal and foramen of spinosum act as the first-level surgical landmark. Superior orbital fissure, foramen rotundum, foramen lacerum, facial hiatus, temporal crest is the second class surgical landmark,the third level landmark includes the maxillary nerve,the mandibular nerve,the middle meningeal artery,pterygoid process and temporal spine.Conclusions:The infratemporal fossa and pterygopalatine fossa are lied below the middle fossa.the middle fossa and infratemporal fossa-pterygopalatine fossa communicating area is connecting with orbital cavity by superior orbital fissure and optic canal,with nasal cavity by spheno-palatine foramen.the fronto-temporo-orbito-zygomatic approach is the appropriate choice of the surgery of tumors of middle fossa-infratemporal fossa-pterygopalatine fossa communicating area. The frontotempo-orbitozygomatic approach provides the multi-angular view of cavernous sinus, sellar region, middle cranial fossa, infratemporal fossa, pterygopalatine fossa. Chapter four Microsurgical Anatomy of Jugular Foramen and Related Endo-Exocranial StructuresObjective:To study the relationship between the neurovascular contents of jugular foramen and its related endo-exocranial structures along with the surgical landmarks of this region.Methods:We observed and measured the structures of cerebellopontine angle region, jugular foramen, craniocervical junction and parapharyngeal space to study the relationship of these structures and to define the surgical landmarks of this region. We followed transjugular process approach for the exposure. Results:Jugular foramen is located at the lateral surface of the foramen magnum and lies in between petrous bone and lateral part of occipital bone. Porus acousticus internus is situated superiorly, jugular tubercle separating from hypoglossal canal inferiorly, petroclival fissure anteriorily,,sulcus of sigmoid sinus posteriorly; connects cerebellopo-ntine angle with parapharyngeal space that is located exocranially. Glossopharyngeal nerve, vagus nerve, accessory nerve and jugular bulb passes from jugular foramen. Surgical landmarks of trans-jugular process approach include mastoid process, stylomastoid process, condylar fossa, digastric muscle, transverse process of atlas and jugular process. Combined with trans-jugular process approach and entering the posterior part of jugular foramen exposes the endo-exo cranial region around the jugular foramen at the same time.Conclusions:Jugular foramen is the main communicating passage between the posterior fossa and parapharyngeal space.the passing structures includes glossopharyngeal nerve,vagus nerve,accessory nerve and jugular bulb.the first-level landmark of trans-jugular pocess includes asterion,mastoid process and transverse process of atlas,the second-landmark is jugular process,condylar fossa,Henry space and digastrics groove,the third-landmark is jugular foramen,carotid canal,hypoglossal canal,styloid process and stylomastoid foramen.