Marco Ferrari, Marco Ravanelli, Davide Mattavelli, Alberto Schreiber, Francesco Doglietto
As seen from the transnasal perspective, the lower third of the clivus almost corresponds to the sphenoidal floor and the most superior portion of the posterior nasopharyngeal vault.1The resection of the lower third of the clivus is most frequently combined with other corridors through the midclivus or craniocervical junction (illustrated in Chapters 11 and 13, respectively). However, for the purpose of providing the reader with a modular understanding of transclival approaches,2this chapter specifically focuses on the surgical route through the lower third of the clivus. This corridor has been adopted alone or in combination with other transnasal endoscopic approaches for treating chordomas,3–6meningiomas,7chondrosarcomas,4,8nasopharyngeal carcinomas,9cholesterol granulomas,10craniopharyngiomas,10aneurysms,11–13and other rare lesions of the lower clivus and adjacent areas.10,14–17
The lower transclival corridor is bounded by the occipital condyle, the hypoglossal canal, and the jugular tubercle bilaterally, the midclivus superiorly, and the craniocervical junction inferiorly. Differently from other transclival approaches, the lateral boundary does not include the internal carotid artery, since the petrous and parapharyngeal tracts run more laterally compared with the paraclival and parasellar portions.
Even though it is theoretically possible to reach the inferior third of the clivus without opening the sphenoid sinus, an extended transrostral sphenoidotomy is recommended to get oriented with the bony landmarks of the sphenoid sinus. The most important bony landmarks of this route are located in a vertical fashion along the lateral boundary of the transclival corridor. From cranial to caudal, the jugular tubercle, the hypoglossal canal, and the occipital condyle can be easily recognized based on the type of bone: the jugular tubercle and the occipital condyle are mostly made of the medullary bone, while the hypoglossal canal is formed by thick cortical bone. The posterior projection of the tail of the inferior turbinate can be adopted as a landmark to identify in advance the position of the hypoglossal canal.
Fig. 12.1 Structure of the clivus and relationship with respect to nasopharynx, palate, and prevertebral muscles. This illustration shows the architecture of the clivus, which is subdivided in upper, middle, and lower segment, as shown by the black dashed lines. From an anterior-to-posterior perspective, the lower portion of the clivus is contiguous to the nasopharynx.Fig. 12.2 Axial view of the lower clivus. This axial cadaver cut passes through the sphenoidal floor and shows the anatomy of the lower third of the clivus. BA, basilar artery; IT, inferior turbinate; LoC, lower clivus; MS, maxillary sinus; NaP, nasopharyngeal posterior wall; NS, nasal septum; peICA, petrous tract of the internal carotid artery; Po, pons; Vo, vomer.
After incising the clival dura, meticulous dissection of the rhomboid arachnoid membrane allows us to expose the medulla oblongata, the cranial portion of the spinal cord, and related neurovascular structures.18In particular, the vertebral arteries and their branches can be analyzed from the entrance into the cisternal space through the suboccipital cavernous sinus to the vertebrobasilar junction.19,20
Transnasal transclival approaches provide unparalleled exposure of the median posterior cranial fossa, ventral surface of the brainstem, and neighboring neurovascular structures, which prompted pioneering groups to employ these routes to manage several challenging lesions of the skull base and adjacent areas. However, two major drawbacks have emerged: (1) the transnasal trajectory is unfavorable to cross the cranial nerves and (2) reconstruction is challenging as a consequence of high cerebrospinal fluid pressure and several geometrical-anatomical features of the defect (i.e., size, inclination, presence of cranial nerves and major vessels close to the bony edges of the craniectomy). In fact, although multilayered reconstruction with vascularized local or regional flaps is the recommended strategy, a non-negligible rate of postoperative cerebrospinal fluid leak has been reported.
Fig. 12.3 Sagittal CT and MRI anatomy of the lower clivus and adjacent areas. The panel includes four sagittal images: a median CT and constructive interference in steady state (CISS) MRI (a, b) and two paramedian CISS MRI (c, d). The lower clivus (LoC) lies posterior to the nasopharyngeal posterior (NaP) wall and the nasopharyngeal vault (NaV). Therefore, when the clival recess (CR) is well pneumatized, the plane parallel to the sphenoidal floor can be used as landmark to define the limit between the midclivus (MC) and the lower clivus. The lower clivus is located above the odontoid process (OP), anterior arch of the atlas (Ar), and other structures of the craniocervical junction. Posteriorly, the inner cortex of the lower clivus is covered by the basilar plexus (BaP), which is adjacent to the vertebral arteries (VA), medulla oblongata (MOb), and upper spinal cord (SCo). Laterally and inferiorly, the lower clivus continues into the jugular tubercle and occipital condyle (OCo). XI, spinal accessory nerve; XII, hypoglossal nerve; AIPA, anteroinferior petrous apex; ARCM, anterior rectus capitis muscle; C1, first cervical nerve; C2, second cervical nerve; C3, third cervical nerve; CS, cavernous sinus; DoS, dorsum sellae; IPS, inferior petrosal sinus; LMAt, lateral mass of the atlas; LCoM, longus colli muscle; LoCM, longus capitis muscle; MSi, marginal sinus; PhR, pharyngeal raphe; pICA, paraclival tract of the internal carotid artery; peICA, petrous tract of the internal carotid artery; Po, pons; SeF, sellar floor; SeT, sella turcica; SpR, sphenoidal rostrum; SpS, sphenoid sinus; SuPA, superior petrous apex; TSe, tuberculum sellae; Vo, vomer.Fig. 12.4 (a–d) Coronal MRI anatomy of the lower clivus and the craniocervical junction. The panel includes four coronal constructive interference in steady state (CISS) MRI scans, from anterior (a) to posterior (d). The lower clivus (LoC) has an inferior, median protuberance called pharyngeal tubercle (PhT), where the pharyngeal raphe (PhR) is attached. The longus capitis muscle (LoCM) and anterior rectus capitis muscle (ARCM) are inserted on the lateroinferior surface of the lower clivus. Laterally, the lower clivus continues, from cranial to caudal with the anteroinferior petrous apex (AIPA), jugular tubercle (JuT), and occipital condyle (OCo). The intracranial face of these bony structures is covered by the inferior petrosal (IPS) and marginal sinuses (MSi), which are connected to the basilar plexus (BaP). Ar, anterior arch of the atlas; Ax, axis; BA, basilar artery; CR, clival recess; FCB, fibrocartilago basalis; HyC, hypoglossal canal; LCoM, longus colli muscle; LMAt, lateral mass of the atlas; MeC, Meckel’s cave; OP, odontoid process; PCJ, petroclival junction; peICA, petrous tract of the internal carotid artery; Po, pons; SPS, superior petrosal sinus; SuPA, superior petrous apex.Fig. 12.5 Axial CT and MRI anatomy of the lower clivus. The panel shows an axial CT (a), an axial MRI (b), and a coronal MRI scan (c) passing through the lower clivus. The white dotted lines in c depict the position of a and b cuts. The lower clivus (LoC) is located posterior to the nasopharyngeal posterior wall (NaP). It extends laterally into the jugular tubercles (JuT) and occipital condyles. Laterally, the jugular tubercle is adjacent to the nervous compartment of the jugular foramen (nJuF). Both the midclivus (MC) and lower clivus are closely contiguous to the fibrocartilago basalis (FCB) that fills the foramen lacerum. V3, mandibular nerve; BA, basilar artery; DoS, dorsum sellae; ET, eustachian tube; LoCM, longus capitis muscle; LVPM, levator veli palatini muscle; MeC, Meckel’s cave; MMA, middle meningeal artery; peICA, petrous tract of the internal carotid artery; Po, pons; TuL, tubal lumen; v, vertical portion of the petrous tract of the internal carotid artery.Fig. 12.6 Axial and paracoronal MRI anatomy of the hypoglossal nerve. The panel contains an axial T1-weighted, contrast-enhanced, fat-saturated MRI (a), an axial constructive interference in steady state (CISS) MRI (b), and a paracoronal CISS MRI passing through the hypoglossal nerve (c). The hypoglossal nerve (XII) arises from the medulla oblongata (MOb) and runs in the cisternal space passing behind the ipsilateral vertebral artery (VA) with a posterior and lateral course with respect to the lower clivus (LoC). Then, the nerve enters the hypoglossal canal (XII), also called the anterior condylar canal, which contains a venous plexus and a small arterial branch coming from the ascending pharyngeal artery. Together with the venous plexus of the hypoglossal canal, the inferior petrosal sinus (IPS) and marginal sinus (MSi) drain into the system of the jugular bulb (JuB) and internal jugular vein. ASA, anterior spinal artery; LoCM, longus capitis muscle; phICA, parapharyngeal tract of the internal carotid artery.
Endoscopic Dissection
Nasal Phase
Inferior turbinectomy.
Posterior septectomy.
Paraseptal sphenoidotomy.
Transrostral sphenoidotomy.
Expanded transrostral sphenoidotomy.
Facultative: Vertical and horizontal uncinectomy.
Facultative: Type A endoscopic medial maxillectomy.
Facultative: Anterior ethmoidectomy.
Facultative: Posterior ethmoidectomy.
Facultative: Transethmoidal sphenoidotomy.
Skull Base Phase
Step 1: Incision of the posterior wall of the nasopharynx.
Step 2: Incision of the longus capitis muscle and the pharyngeal raphe.
Step 3: Removal of the sphenoidal floor and anterior cortical bone of the lower third of the clivus.
Step 4: Removal of the posterior cortical bone of the clivus.
Step 5: Incision of the periosteum and dura of the lower third of the clivus.
Step 6: Removal of the anterior pontine membrane and the rhomboid membrane.
Step 7: Medialization of the vertebral artery.
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