6 The Extended Transsphenoidal Approach (Mid-maxillotomy) to the Clivus
Guilherme Henrique Weiler Ceccato, Marcio S. Rassi, Jean G. de Oliveira, and Luis A. B. Borba
Abstract
Lesions located at clivus are challenging considering their complex deep location and close relationship with many critical neurovascular structures. Clivus can be divided into three regions based on their relation with posterior fossa neurovascular structures. Several extensions of the traditional transsphenoidal approach have been described, and here we discuss a variation comprising the removal of anterior and medial wall of maxillary sinus, which enlarges the surgical corridor and exposure of clivus.
Keywords: Keywords: mid-maxillotomy, maxillectomy, clivus, extended transsphenoidal, chordoma, skull base
6.1 Introduction
Lesions located at clivus comprise both neoplastic and non-neoplastic pathologies. The most common pathology in this location is chordoma, representing about 40% of masses in this region.1 However, they represent just 0.1 to 0.2% of all intracranial tumors, and present an incidence of 0.8/100.000 persons.1,2,3 Other pathologies are much more diversified; however, malignant neoplasms are more common than benign ones.1,2 Examples of lesions encountered in this region together with chordoma in the group of malignant neoplasms are chondrosarcoma, metastasis, multiple myeloma, plasmacytoma, lymphoma, and osteosarcoma. Benign neoplastic lesions in this region can be pituitary adenomas and petroclival meningiomas; nontumoral lesions consist of fibrous dysplasia, epidermoid, dermoid, arachnoid or neurenteric cysts, ecchordosis physaliphora, among others.1 However, as clival masses are rare entities, there is scarce epidemiological data in the literature.
Chordomas arise from notochord remnants usually at clivus in midline; chondrosarcomas arise from cartilaginous remnants of petroclival or spheno-occipital synchondrosis and can occur de novo or as a malignant transformation of chordomas.1 These lesions are locally aggressive; however, despite a low rate of metastasizing, they have high rates of local recurrence, usually in the surgical corridor by seeding during removal.4 The prognosis of these lesions is linked mainly with the extent of resection, which includes removal of great amounts of affected bone.3,5
Chordomas usually arise in extradural space and commonly remain confined to this region and present important infiltration of surrounding bone, especially from clivus; but they can also infiltrate dura and extend to intradural space. Therefore, to treat these lesions, a targeted extradural approach, which could clearly face the compromised bone and extradural space and be capable to resect intradural extensions, is required. Anterior approaches, especially extensions of the traditional transsphenoidal approach, can provide good access to clivus and allow the safest and greatest possible resection of clival masses, especially if confined to the midline.
6.2 Anatomical Background
Clivus is formed by occipital and sphenoid bones, and it is separated from adjacent petrous parts of temporal bone by the petroclival fissures and jugular foramina. Dorsum sellae of sphenoid bone forms the upper third of clivus, and the inferior two-thirds are formed by occipital bone. The inferior edge of clivus forms the anterior rim of foramen magnum, which is related to occipital condyles laterally6 (Fig. 6.1).
Clivus can be divided into superior, middle, and inferior regions7,8 (Fig. 6.1). The dural pori of abducens nerves and the glossopharyngeal meatus in jugular foramina are intracranial landmarks to separate the regions.1 The floor of sella and of sphenoid sinus can also be used to approximate the limits between these regions.8
Fig. 6.1 (a) Intracranial and (b) extracranial demonstration of clivus segments, the upper clivus in red, middle in green, and lower in yellow. Intracranial limits between these divisions are the abducens nerve pori located few millimeters below petrous apexes and glossopharyngeal meatus in the upper edge of jugular foramen. (c) Inferior view of skull depicting the muscular insertion points of longus capitis, superior pharyngeal constrictor muscle inferiorly, and the rectus capitis anterior muscles in front of atlanto-occipital joints. (d) Angled view demonstrating the muscular insertions and depicting the choanae, bordered by medial plates of pterygoid process laterally, bony nasal septum medially, sphenoid sinus superiorly, and hard palate inferiorly. Cho, choana; FM, foramen magnum; JF, jugular foramen; LCl, lower clivus; MCl, middle clivus; OC, occipital condyle; Pteryg. proc., pterygoid process; Sphen. Sin, sphenoid sinus; UCl, upper clivus.
Abducens nerves arise from medial aspect of pontomedullary sulcus and run from inferomedial to superolateral. They pierce dura around 3.4 mm below petrous apex and then run toward Dorello’s canal, which is bounded by petrosphenoidal ligament (Gruber’s ligament) superiorly, petrous apex inferolaterally, and clivus inferomedially. The nerve runs upwards until reach cavernous sinus.6
Dura covering jugular foramen has two openings. One is the glossopharyngeal meatus that allows passage of cranial nerve IX and creates an indentation in the superior aspect of jugular foramen. The other is the vagal meatus below, through which the X and XI nerves course.6
The joining point between the lacerum and paraclival internal carotid artery (ICA) segments provides correlation with abducens nerve dural porus.6,9 Also, posterior end of vidian canal opens inferolaterally close to the lacerum ICA, and from an anterior perspective, can delimit the upper and middle clival regions.6,10 From an extracranial point of view, the pharyngeal tubercle can be also a landmark between middle and lower clivus divisions, located approximately 3.9 mm above the tubercle. Other important point is that hard palate is located in the axial plane of foramen magnum.6
Clivus is thicker and wider in its superior aspect and thinner and wider inferiorly. Some studies reported a thickness of 18 mm rostrally and 8 mm inferiorly.11 Other study reported a thickness of 11.34 mm in the middle part of clivus and 5.34 mm in its inferior aspect.12 Width of upper clivus was 16 mm, between abducens nerves pori 20 mm, and between hypoglossal canals 34 mm.11 Anterior angulation of clivus varies between 45 and 67.4 degrees, depending on the study.6,12
On average, upper clivus has a length, between posterior clinoid and abducens dural porus, of 13.2 mm (12–17 mm); middle clivus has a length, between dural porus of VI and IX nerves, of 21.4 mm (19–24 mm); and lower clivus has a length, between glossopharyngeal meatus and hypoglossal canal, of 25.4 mm (23–30 mm).6 However, these measurements are significantly variable, and careful study of preoperative imaging is fundamental for surgical planning.
Lateral limit of upper clival exposure is represented by the cavernous carotids (Fig. 6.2). It was reported that the distance between ICA and midline was of 28.12 mm at a level 10 mm inferior to petrous apex, against 9.94 mm at a level 10 mm superior to it, which depicts the narrower corridor in the upper clivus. Another aspect is that the distance between paraclival carotids and midline is about 10 to 11 mm in the middle clivus, and is about 15 mm at level of foramen lacerum.12
Fig. 6.2 (a) Demonstration of sphenoid sinus with pituitary gland exposed by removal of sellar floor, and the lateral limitation imposed by internal carotid arteries. Upper clivus is located posterior to pituitary gland, middle clivus posterior to sphenoid sinus, and lower clivus just below posterior to nasopharynx. (b) Demonstration of projection of anterior loop of cavernous carotid over anterior face of pituitary gland, narrowing surgical corridor. Also, the other neurovascular structures are demonstrated. ACA, anterior cerebral artery; ICA, internal carotid artery; Ophthal. a., ophthalmic artery; ON, optic nerve; Pit., pituitary gland; Sup. hyp. a., superior hypophyseal artery.
To access upper and middle clivus, the anterior wall and floor of sphenoid sinus must be removed. The floor of sphenoid sinus contains, from medial to lateral, the vomerovaginal, palatovaginal, and vidian canals. The vomerovaginal is a bony groove, and the palatovaginal transmits the pharyngeal nerve and artery, and 2 mm lateral to it lies the vidian canal.6
The dura of upper clivus is easily separated into two layers, and basilar venous plexus, cavernous sinus, and inferior petrosal sinus can be important sources of bleeding in this region (Fig. 6.3). The basilar venous plexus becomes less prominent as it continues caudally toward foramen magnum, where it joins the marginal sinus.
Fig. 6.3 Stepwise dissection of pituitary gland and exposure of upper and middle clivus. (a) Venous plexus around pituitary. (b) Gland covered by its capsule after removal of this plexus. (c) Better demonstration of pituitary exposed between cavernous carotids and the clival recess below, corresponding to the middle clivus bordered laterally by paraclival carotids. (d) Exposure of pituitary superiorly, clival recess and middle clivus bordered by paraclival carotids, and further down, exposure depicting part of lower clivus. ICA, internal carotid artery; ON, optic nerve; Ophthal. a., ophthalmic artery; Paraclav., paraclival; Pit., pituitary gland.
Upper clivus is the smallest of the three clival segments, and it is also called sellar clivus (Fig. 6.4). It is related to dorsum sellae and posterior clinoid anteriorly, and laterally, with the uppermost aspect of the petroclival fissure where abducens nerves travel through Dorello’s canal to reach cavernous sinus. Upper transclival approach provides a route that exposes the interpeduncular cistern and its contends, including basilar bifurcation, posterior cerebral and superior cerebellar arteries, as well as part of posterior communicating artery, laterally, the third nerves, and superiorly, the floor of third ventricle and mamillary bodies (Fig. 6.5). Laterally, this approach can access the medial aspect of cavernous sinus, closely related to the cavernous carotids.10
