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3. ENDOSCOPIC ANATOMY ALONG THE TRANSNASAL APPROACH TO THE PITUITARY GLAND AND THE SURROUNDING STRUCTURES M. Tschabitscher and R. J. Galzio "The nasal route is impracticable and can be never otherwise", Dandy, 1945 [2]. This assumption of one of the greatest neurosurgeons of the 20th century proved to be wrong. The idea of reaching the pituitary along the preformed route through the nose and the sphenoid sinus goes back to Davide Giordano's [4] theoretical considerations in 1894. Schloffer [13] first practically tried to access the pituitary by reflecting the nose and removing most of what is inside it, i.e. the nasal septum, the turbinates and the ethmoid. Kanavel [8] only reflected the lower half of the nose and thus spared the ethmoid, while Halstead [5] used a sublabial approach. With Hirsch's [6, 7] work the transnasal approach made its first breakthrough in 1909. Quite variable in size and shape and rarely symmetrical, the nasal and paranasal sinuses form a complex system of cavities just above the oral cavity, which is divided into セッ@ separate units by the nasal septum. 3.1 Nasal cavity 3.1.1 Development The nose begins to develop in the 5th week at an embryonic size of about 5 mm with the appearance of the olfactory placode from the ectoderm [1]. From it the olfactory sacs are derived by impression and invagination from the olfactory pits and extend to the roof of the primitive oral cavity. The epithelial lining of the olfactory sacs fuses with the epithelium of the oral cavity to form the oronasal (bucconasal) membrane. Rupture of this membrane in the 6th week of embryonic development gives rise to the primary choanae]. The primitive palate separates the oral and nasal cavities anteriorly. The left and right primitive nasal cavities are divided by the nasal septum, which grows downward from the medial frontal process. At the same time, the palatine processes sprout out from the maxillary processes and grow toward medial and caudal. They continue to grow horizontally as the tongue subsides and make contact anteroposteriorly with the primitive palate. The posterior part remains patent craniocaudally and develops into the pharynx [1]. 3.1.2 Bony skeleton of the nasal cavity The two nasal cavities resemble truncated pyramids. They are enclosed by a roof (= cribriform plate), a floor (= hard and soft palate), a medial wall (= nasal septum), a lateral wall (= ethmoid and maxillary bones + inferior nasal turbinate), a posterior wall (= body of sphenoid bone) and an anterior wall (= external nose). The roof is formed by a number of bony elements. These include the nasal bone, the frontal process of the nasal bone, the cribriform plate of the ethmoid and the most anterior part of the sphenoid body. The floor is composed of the palatine process of the maxillary bone (and the intermaxillary bone [Goethe] = premaxilla) anteriorly, which forms a synostosis with the maxilla early at an embryonic size of 20 mm, and the horizontal plate of the palatal bone. E. Divitiis et al. (eds.), Endoscopic Endonasal Transsphenoidal Surgery © Springer-Verlag Vienna 2003 M. Tschabitscher and R. 22 J. Galzio Fig. 3-1 . Lateral wall of the nasal cavity. 1: inferior nasal turbinate, 2: middle nasal turbinate, 3: superior nasal turbinate, 4: frontal sinus, 5: anterior ethmoid cells, 6: posterior ethmoid cells, 7: sphenoid sinus, 8: pituitary The medial wall is contributed by the nasal septum. It consists of three parts of different tissues: the fibrous columella (pars mobilis) anteriorly, the cartilaginous part (pars cartilaginea) behind it and the bony part (pars ossea), i.e. the perpendicular plate of the ethmoid and the vomer, posteriorly. The lateral wall accommodates three nasal turbinates. In just under 20% of cases there may be 4 (supreme nasal turbinate). The inferior nasal turbinate is a separate bone. Below it the nasolacrimal duct empties into the inferior nasal meatus. The middle and superior nasal turbinates are part of the ethmoid. The anterior margin of the middle turbinate is about 2 cm posterior to the anterior margin of the inferior turbinate. Below it the maxillary sinus, the frontal sinus and the anterior ethmoid air cells open into the nasal cavity through the hiatus semilunaris, wh ich is bordered by the ethmoid bulla and the uncinate process. The tail of the middle turbinate lies approximately at the level of the sphenopalatine foramen (this is important for identifying arterial bleeding sources.) Below the superior turbinate the posterior ethmoid air cells open into the nasal cavity (Fig. 3-1). 3.1 .3 Lining of the nasal cavity The nose is part of the upper airways and is mainly lined by respiratory tract epithelium (= ciliated epithelium with goblet cells and seromucous glands). The nasal vestibulum is an exception because it is lined by multi-layer keratinized squamous epithelium (= facial skin) and olfactory epithelium overlying the superior nasal turbinate and the nasal septum opposite it. The anterior inferior part of the nasal septum accommodates a mucosal recess of variable depth, the vomeronasal organ (Jacobson's organ) (Fig. 3-2). 3.1.4 Vessels and nerves of the nasal cavity Two major arteries supply the nasal cavity, i.e. the ophthalmic and the maxillary artery. The ophthalmic artery supplies the inner nose anterior to the nasal turbinates with its anterior ethmoid branch. Its posterior ethmoid branch carries blood to the superior nasal Endoscopic anatomy 23 Fig. 3-2. Anteriormost nasal segment. 7: mobile part of the nasal septum (columella), 2: inferior nasal turbinate, 3: vomeronasal organ of Jacobson, 4: agger nasi, 5: middle nasal turbinate Fig. 3-3. Posterior nasal segment. 7: inferior nasal turbinate, 2: middle nasal turbinate, 3: superior nasal turbinate, 4: ethmoid bulla, 5: opening of the posterior ethmoid cells, 6: posterior ethmoid cell, 7: sphenoid sinus, +-+ branches of sphenoethmoidal artery turbinate and the anterior half of the middle turbinate. The maxillary artery gives off the sphenopalatine artery in its pterygopalatine segment: this artery supplies the middle and inferior turbinates with its lateral posterior and posterior septal branches from behind and the inferior two thirds of the septum (Figs. 3-3, 3-4). M. Tschabitscher and R. 24 J. Galzio Fig. 3-4. Dissection of the sphenopalatine artery as it passes through the sphenopalatine foramen. The posterior end of the middle turbinate is slightly retracted anteriorly to bring into view the division into a superior and an inferior branch. 1: inferior nasal turbinate, 2: middle nasal turbinate, 3: superior nasal turbinate, 4: sphenopalatine artery, 5: sphenoid sinus The veins generally accompany the arteries and usually form a plexus. The lymphatics draining the areas anterior to the nasal turbinates ultimately empty into the submandibular nodes, those draining the posterior area and the paranasal sinuses into the retropharyngeal and deep cervical nodes at the level of C2. The sensory innervation of the nose is derived from the first branchial arch and thus belongs to the trigeminal system. The ophthalmic nerve basically serves the same territory as the ophthalmic artery. The maxillary nerve supplies the lateral wall of the nasal cavity and the middle and inferior nasal turbinates with its lateral branches. Scarpa's nasopalatine nerve from the medial group of the maxillary nerve passing the sphenopalatine foramen extends to the incisive canal and supplies the gingiva overlying the incisive bone. The terminal and vomeronasal nerves probably are subservient to perception during embryonic development, but are largely lost postnatally. 3.2 Sphenoid sinus The sphenoid sinus, which is derived from two mucosal evaginations at the posterior wall of the nasal cavity, is initially paired. Its development begins in the third month of fetal life Endoscopic anatomy 25 and is completed about the end of puberty. Parts of its wall (conchae sphenoidales) originate from the ethmoid anlage. They enclose the right and left natural openings of the sphenoid sinus. Three sinus types are distinguished by their shape and size: • Concha I type: anterior to the pituitary fossa (3%) (Fig. 3-5); • Sellar type: extending to beneath the pituitary fossa (80%) (Fig. 3-6); • Retrosellar type: extending to the clivus (17%) (Fig. 3-7). The space within the sphenoid body is subdivided by one or several septa [141. (Single septa are not always located in the midline!) The sphenoid sinus roughly resembles a cube, which is subdivided in 2 halves by the septum. These halves are of different size in 65 to 70% of cases. Its walls are composed of 6 parts. The roof is part of the anterior segment of the anterior cranial fossa and extends from the jugum (= planum) sphenoidale to the limbus of the sphenoid. Behind it is the sella turcica with the prechiasmal sulcus in between. Fig. 3-5. Sphenoid sinus - concha I type (mediosagittal section) . 1: clivus, 2: sphenoid body, 3: posterior clinoid process, 4: sellar bridge, 5: anterior clinoid process, 6: posterior ethmoidal cell, 7: sphenopalatine foramen. _ to the sphenoid sinus - .... +-- spheno-occipital synchrondrosis Fig. 3-6. Sphenoid sinus - sellar type. 1: clivus, 2: sphenoid sinus, 3: incomplete septum in the frontal plane, 4: sphenoid ostium, 5: sphenopalatine canal, * optico-carotid recess 26 M. Tschabitscher and R. J. Galzio Fig. 3-7. Sphenoid sinus - retrosellar type. 1: sphenoid sinus, 2: clivus Fig. 3-8. Lateral extension of the sphenoid sinus into the pterygoid process. 1: posterior ethmoid cell, 2: sphenoid ostium, 3: lateral evagination of sinus into pterygoid process, 4: clivus, * spheno-occipital synostosis The floor forms the roof of the choanae anteriorly and the roof of the nasopharynx posteriorly. Medially the pterygoid canal of Vidianus is recognizable as a bulge. (It should not be mistaken for a septal remnant.) Laterally, at the junction with the lateral wall, the maxillary nerve may form another bulge (Figs. 3-8, 3-9). The medial wall is formed by the septum. The lateral wall also forms the bony medial wall of the cavernous sinus. A recess of variable size, optico-carotid recess, is located between the bulge of the optic nerve and that of the internal carotid artery. This recess may be quite deep and extend well into the anterior clinoid process. It should not be mistaken for an Onodi-Grunwald cell. Bone dehiscences of variable age-related extension may be present above the carotid. The lateral wall has paired natural apertures medially and is contiguous with the posterior ethmoid cells. The posterior wall is contributed by the clivus. Endoscopic anatomy 27 Fig. 3-9. Multi-septated sphenoid sinus extending inferiorly into the pterygoid process - frontal section viewed from anterior. 1: foramen rotundum, 2: pterygoid canal of Vidianus, 3: pterygoid process, 4: pneumatized anterior clinoid process, 5: optic nerve canal , 6: planum sphenoidale, * sphenoid sinus 3.2.1 How to reach the opening of the sphenoid sinus The opening of the sphenoid sinus may be reached along two different routes: From the upper choanal border along the posterior pharyngeal wall upwards into the spheno-ethmoid recess (Fig. 3-10). This approach should be strictly medial along the septum, lest a "maxillary fontanel" (that means an accessory opening of the maxillary sinus present in about 10 to 20% of cases) be mistaken for the ostium sphenoidal is. Fig. 3-10. Access to the sphenoid ostium from the upper choanal border. 1: choana, 2: inferior nasal turbinate, 3: nasal septum, 4: superior nasal turbinate, 5: middle nasal turbinate, - sphenoid ostium, + .. maxillary sinus fontanels, * branch of sphenopalatine artery M . Tschabitscher and R. 28 J. Galzio Fig. 3-11. Access to the sphenoid ostium through the center of the middle nasal turbinate. 1: too steep, 2: right, 3: too flat From the anterior nasal spine precisely through the center of the middle nasal turbinate towards posterior. (Care should be taken to avoid an excessively steep and an excessively flat approach. The former would lead into the cribriform plate, the latter deep into the posterior cranial fossa) (Fig. 3-11). 3.3 Ethmoid labyrinth (complex) The ethmoid cells are interposed between the lateral nasal wall and the medial orbital wall. The 5-sided perpendicular plate of the ehtmoid (upper part of the bony nasal septum) Fig. 3-12. Isolated ethmoid. Left - from anterior; right - from above. 1: crista galli, 2:cribriform plate, 3: ethmoid cells, 4: lamina papyracea, 5: perpendicular plate of the ethmoid, 6: middle nasal turbinate, * anterior ethmoid canal (foramen) Endoscopic anatomy 29 divides the ethmoid into two halves. The cribriform plate is horizontal and lies between the frontal bones. The ethmoid cells are suspended from its lateral margin like the side bags of a motorcycle (Fig. 3-12). Between the sagittal borders, i.e. the upper and middle turbinates medially and the lamina papyracea laterally, thin-walled chambers are present. These communicate with one another or open into the nasal cavity. The ethmoid cells are divided in three groups, i.e. anterior, middle and posterior. A factitious perpendicular plane drawn through the anterior ethmoid canal (foramen) helps to distinguish the anterior and middle from the posterior cells. The anterior cells open below the middle turbinate into the middle meatus, the posterior cells open below the superior turbinate into the superior meatus. There is, however, considerable variation (14). 3.4 Sellar region The sphenoid body lies in the center of the cranial base (Fig. 3-13). Atransverse bulge, the sellar tubercle, demarcates the sella turcica anteriorly. Anterior to it the prechiasmal sulcus (12) extends towards the optic nerve canal and demarcates the planum sphenoidale. Sometimes the planum sphenoidale has a right and left extension: medial clinoid process. Ossification of the dura mater bridging from the anterior to the medial cI,inoid processes gives rise to a carotico-clinoid foramen (foramen of Henle), (,.....,10% of cases) (Fig. 3-14). An ossified dural bridge (taenia interclinoidea, sellar bridge) between the anterior and posterior clinoid processes is found in approximately 6% of cases. The sella turcica is bordered posteriorly by the dorsum sellae. Between the dorsum and the sellar tubercle lies the pituitary fossa. Its roof is formed by the sellar diaphragm, a dural fold perforated Fig. 3-13. Sellar region. 1: planum sphenoidale, 2: prechiasmal sulcus, 3: sellar tubercle, 4: optic nerve canal, 5: anterior clinoid process, 6: medial clinoid process, 7: posterior clinoid process, 8: dorsum sellae, 9: carotid sulcus, 10: foramen rotundum, 11: foramen of VESALIUS M. Tschabitscher and R. 30 J. Galzio Fig. 3-14. Variants of the sellar region . 1: optic nerve canal, 2: anterior clinoid process, 3: medial clinoid process, 4: posterior clinoid process, 5: carotico-clinoid foramen of Henle, 6: sellar bridge for accommodating the pituitary stalk. The width of this opening increases with age. The inferior aspect of the diaphragm and the pituitary capsule are separated by an arachnoid invagination: the hypophyseal cistern of Ferner (3). With its lateral extension the diaphragm contributes to the superior wall of the cavernous sinus. Called "Wannenregion" by Lang (9), this region is the key for the access to the cavernous sinus from above posterior to the anterior clinoid process. (It roughly coincides with the 2 triangles of Dolenc + Hakuba.) It is demarcated laterally by the anterior petroclinoid fold. The lateral wall ofthe sella turcica also constitutes the bony medial wall ofthe cavernous sinus. The right lateral wall is significantly steeper than that on the left side (9). In the carotid sulcus the internal carotid artery arches from lateral and posteroinferior towards medial and anterosuperior. Its anterior end comes to lie deep to the clinoid process and medial to the superior orbital notch. 3.5 Suprasellar region Perneczky (11) equated the suprasellar region with an "equilateral pyramid". Its base is formed by the sellar diaphragm. The sides of the pyramid contain the following structures: the lamina terminal is, the anterior aspect of the optic nerve chiasm, the two optic nerves and the anterior communicating artery complex with the Aland A2 segments anteriorly; the optic tract, the internal carotid artery and 3 parallel structures, i.e. the posterior communicating and the anterior choroidal arteries and the third cranial nerve, laterally; and the interpeduncular fossa with the basilar tip and its division into the posterior Endoscopic anatomy 31 cerebral and superior cerebellar arteries as well as the exit of the third cranial nerve posteriorly. The infundibulum and the stalk of the pituitary mark the geometrical axis of the pyramid. The stalk and anterior lobe of the pituitary are supplied by the superior hypophyseal artery from the internal carotid artery [12]. These vessels typically are parallel to the long axis of the stalk thus giving it a unique appearance (Fig. 3-17). Fig. 3-15. The "equilateral pyramid" of the suprasellar region . Geometrical drawing from Perneczky Tschabitscher - Resch: Endoscopic Anatomy for Neurosurgery (by courtesy ofThieme Verlag) Fig. 3-16. Structures found on the sides of the pyramid. 1: optic nerve, 2: optic chiasm, 3: optic tract, 4: lamina terminal is, 5: anterior cerebral artery (A 1), 6: internal carotid artery, 7: pituitary stalk 32 M. Tschabitscher and R. J. Galzio Fig. 3·17. Blood supply of the pituitary stalk. 1: superior hypophyseal artery, 2: internal carotid artery, 3: sellar diaphragm, 4: dorsum sellae, 5: chiasmal branches The posterior pituitary is supplied by the inferior hypophyseal artery from the meningohypophyseal trunk (= truncus carotico-cavernosus posterior) [10). Rarely, it receives blood directly from the intracavernous internal carotid artery. 3.6 Parasellar region The parasellar region more or less corresponds to the cavernous sinus. Correctly we have to subdivide the parasellar area into an extra and intracavernous part. Its roof is formed by the "Wannenregion" described above (Figs. 3-18, 3-19). Fig. 3·18. Roof of the cavernous sinus (Lang's "Wannenregion" ). 1: optic nerve, 2: oculomotor nerve, 3: Lang's "Wannenregion", 4: trochlear nerve, 5: anterior clinoid process, 6: lateral wall of cavernous sinus, 7: temporal lobe Endoscopic anatomy 33 Fig. 3-19. Cavernous sinus opened along the anterior petroclinoid fold. 1: oculomotor nerve, 2: Lang's " Wannenregion", 3: cavernous sinus (opened), 4: trochlear nerve Structures within the roof include, from anterior to posterior, the second cranial nerve, the internal carotid artery (usually with the origin of the ophthalmiC artery), the third cranial nerve and the triangular field of the fourth cranial nerve (Hakuba's triangle) at its Fig. 3-20. Posterior part of sinus roof (opened). 1: ligament of Gruber, 2: abducent nerve, 3: oculomotor nerve, 4: superior cerebellar artery, 5: trigeminal nerve, * canal of Dorello 34 M. Tschabitscher and R. J. Galzio posterior end. The third cranial nerve lies lateral to the posterior clinoid process and medial to the anterior petroclinoid fold. After its long intracranial course the fourth cranial nerve passes between the anterior and posterior petroclinoid folds lateral and posterior to the third cranial nerve and enters the roof of the cavernous sinus to proceed to its lateral wall. 1.5 to 2 cm inferior and medial to the posterior clinoid process the 6th cranial nerve enters the dural port between the periosteum (stratum periostale) and the dura (stratum durale), which accommodates a venous plexus (3). It approaches the cavernous sinus from posterior near the tip of the petrous bone. At this site it is usually crossed by a well developed ligament (superior sphenopetrosal ligament of Gruber). Ossification of this ligament gives rise to an abducent nerve foramen (foramen of Wegner) (Fig. 3-20). Fig. 3-21. Mediosagittal section through sphenoid sinus. For easier distinction the arterial system is shown in red and the venous system in blue. The mucous membrane and the bony sinus wall were preserved to illustrate the bulges formed by the structures lateral to them . 1: pituitary, 2: optic nerve and ophthalmic artery, 3: internal carotid artery, 4: opticocarotid recess, 5: ophthalmic nerve, 6: maxillary nerve Fig. 3-22. View into the cavernous sinus after removal of its medial wall. 1: pituitary, 2: optic nerve, 3: ophthalmic artery, 4: optico-carotid recess, 5: internal carotid artery, 6: ophthalmic nerve, 7: abducent nerve, * superior orbital notch Endoscopic anatomy 35 Fig. 3-23. View into the cavernous sinus from below. 1: pituitary, 2: planum sphenoidale, 3: dura of optic nerve canal , 4: internal carotid artery Fig. 3-24. 1: pituitary, 2: planum sphenoidale, 3: optic nerve (dura of the optic nerve canal opened), 4: ophthalmic artery, 5: internal carotid artery M. Tschabitscher and R. 36 J. Galzio Fig. 3-25. 1: pituitary, 2: pituitary stalk, 3: optic chiasm, 4: optic nerve, 5: ophthalmic artery, 6: internal carotid artery, 7: olfactory nerve, 8: rectal gyrus Fig. 3-26. 1: pituitary, 2: optic nerve, 3: ophthalmic artery, 4: ocu lomotor nerve, 5: trochlear nerve, 6: abducent nerve, 7: ophthalmic nerve The cavernous sinus can be accessed transnasally either through its medial wall (= lateral wall of the sphenoid sinus) (Figs. 3-21, 3-22) or through its floor from anterior and inferior (Figs. 3-23 - 3-26). Endoscopic anatomy 3.7 37 Retrosellar - retroclival region Entry into the posterior cranial fossa through the posterior wall of the sphenoid sinus is most easily gained, when the sinus is of the retrosellar type. After negotiating the mucosa Fig. 3-27. Removal of clivus brings into view the venous plexus between the periosteum and the dura mater. 1: pituitary, 2: optic nerve, 3: ophthalmic artery, 4: internal carotid artery, 5: intracanalicular internal carotid artery, 6: clivus removed and venous plexus Fig. 3-28. 1: olfactory nerve, 2: gyrus rectus, 3: anterior cerebral artery, 4: optic chiasm, 5: pituitary, 6: intra-sinusal internal carotid, 7: intracanalicular internal carotid, 8: basilar artery M. Tschabitscher and R. J. Galzio 38 Fig. 3-29. 1: pituitary, 2: mamillary body, 3: oculomotor nerve, 4: posterior communicating artery, 5: posterior cerebral artery, 6: superior cerebellar artery, 7: basilar tip, 8: anterior choroidal artery and the bone, which is sometimes no more than 1 to 2 mm thick, the very dense venous plexus between the periosteum and the dura is reached . During dissection particular attention should be paid to the 6th cranial nerve. Depending on the optical system used, the basilar artery in the basal cistern and its branches as well as the neighboring cranial nerves are well seen along almost their entire course (Figs. 3-27 -3-29). References 1. Clara M (1966) Entwicklungsgeschichte des Menschen, 6.Aufl. VEB Georg Thieme, Leipzig 2. Dandy WE (1945) Surgery of the Brain. In: Lewis' practice of surgery, vol 12. Maryland W . F. Prior Company Inc., Hagerstown, p 557 3. Ferner H (1960) Die Hypophysenzisterne des Menschen und ihre Beziehung zum Entstehungsmechanismus der sekundaren Sellaerweiterung. Z Anat Entw Gesch 121: 407 -416 4. Giordano D (1894) Manuale di medicina operativa. In: Duplay e Reclus (eds) Trattato di Chirurgia. UTET, Torino, pp 100-103. (quoted from Guiffre R. Neurosurgery 42: 909-912, 1998) 5. Halstead AE (1910) The operative treatment of tumors of the hypophysis. Surg Gynec & Obstet 10: 494-502 6. Hirsch 0, Kotrnetz H (1931) Uber die topographische Beziehungen des Chiasma opticum zur Hypophyse und ihre Bedeutung fUr die Chirurgie des Hirnanhanges. Arch Klin Chirurgie 168: 85-110 7. Hirsch 0 (1909) Eine neue Methode der endonasalen Operation von Hypophysentumoren. Wiener Med Wochenschrift 12: 636-638 8. Kanavel AB (1909) The removal of tumors of the pituitary body by an infranasal route. JAMA 53: 1704-1707 9. Lang J (1988) Klinische Anatomie der Nase, Nasenhohle und Nebenhohlen. Aktuelle OtoRhino-Laryngologie Bd 11. Georg Thieme, Stuttgart New York 10. McConnell EM (1953) The arterial blood supply of the human hypophysis cerebri. Anat Rec 115: 175-201 Endoscopic anatomy 39 11. Perneczky A, Tschabitscher M, Resch KDM (1993) Endoscopic anatomy for neurosurgery. Georg Thieme, Stuttgart New York 12. Schaeffer JP (1924) Some points in the regional anatomy of the optic pathway, with especial reference to tumors of the hypophysis cerebri and resulting ocular changes. Anat Rec 28: 243-279 13. Schloffer H (1906) Zur Frage der Operationen an der Hypophyse. Beitr Klin Chirurgie 50: 767 -817 14. Zuckerkandl E (1893) Normale und Pathologische Anatomie der Nasenhohle und ihrer pneumatischen Anhange. Bd 1, 2. Auf!. Wilhelm Braumuller, Wi en Leipzig