Marco Ferrari, Marco Ravanelli, Davide Lancini, Alberto Schreiber, Davide Mattavelli
As illustrated in the previous chapter, the transnasal approach to the parapharyngeal space can be divided from a surgical viewpoint into two corridors (medial and lateral), having the lateral pterygoid plate as a watershed. By running laterally to this landmark or removing it, wide exposure of the far-lateral portion of the upper parapharyngeal space is obtained. Given its trajectory, the lateral parapharyngeal approach lies midway between the medial parapharyngeal approach and the infratemporal approach, thus representing the most extended corridor toward lateral infracranial spaces.
This approach was well described in pioneering anatomical studies,1–6but only isolated cases of its application for removal of tumors of the upper parapharyngeal space have been reported.7,8When compared to the medial parapharyngeal approach, which addresses the petrous portion of the temporal bone and prevertebral musculature, the lateral corridor is directly oriented toward the carotid and the jugular foramina. This anatomical trajectory has two major implications: (1) resection of the eustachian tube is not necessary unless a wide exposure of areas behind it is required and (2) an exceedingly complex network of neurovascular structure fills the deep portion of the corridor, including the mandibular, glossopharyngeal, vagus, spinal accessory, and hypoglossal nerves, as well as the internal carotid artery, the internal jugular vein, the ascending pharyngeal artery, the middle meningeal artery, and the maxillary artery. The posterolateral limit of the space consists of the stylomandibular tunnel, which is enclosed between the posterior portion of the condylar process of the mandible, the stylomandibular ligament, and the inferior surface of the external auditory canal. The target area can be reached with a different perspective by a transcervical–transparotid approach to the parapharyngeal space, so that the combination of the two approaches (multiportal surgery) can find an indication in selected multicompartmental lesions of the skull base and adjacent areas.9–12
This chapter includes three modular variants of the lateral parapharyngeal approach: the first is the least extended corridor that is harvested laterally to the lateral pterygoid plate, extending the dissection performed along the third corridor of the infratemporal fossa to reach the lateral prestyloid compartment and the stylomandibular tunnel; the second lateral parapharyngeal corridor is obtained by removing both pterygoid plates with a lower transpterygoid approach and dissecting the upper parapharyngeal space passing below the eustachian tube and related muscles; and the third and most extended corridor is harvested by removing the eustachian tube to achieve complete exposure of the upper parapharyngeal compartment, from the nasopharynx, medially, to the stylomandibular tunnel, laterally.
Fig. 24.1 Sagittal view of the parapharyngeal space. This sagittal cadaver picture shows with a lateral-to-medial perspective the left upper parapharyngeal space. White dashed lines show the compartmentalization of the parapharyngeal space in upper, middle, and lower. V3, mandibular nerve; IX, glossopharyngeal nerve; X, vagus nerve; XI, spinal accessory nerve; XII, hypoglossal nerve; APA, ascending pharyngeal artery; CCA, common carotid artery; ECA, external carotid artery; FA, facial artery; IAN, inferior alveolar nerve; IJV, internal jugular vein; LN, lingual nerve; LPP, lateral pterygoid plate; LSM, levator scapulae muscle; MPM, medial pterygoid muscle; OA, occipital artery; PAA, posterior auricular artery; phICA, parapharyngeal tract of the internal carotid artery; PhB, pharyngeal branch of the vagus nerve; PhPl, pharyngeal plexus; SCG, superior cervical ganglion; SGM, styloglossus muscle; SHL, stylohyoid ligament; SHM, stylohyoid muscle; SPF, stylopharyngeal fascia; SPM, stylopharyngeal muscle; StyP, styloid process; TLF, thyrolingual-facial venous trunk.Fig. 24.2 Sagittal view of the upper parapharyngeal space and adjacent skull base. This sagittal cadaver picture shows with a lateral-to-medial perspective the upper parapharyngeal space and adjacent skull base. V2, maxillary nerve; V3, mandibular nerve; IX, glossopharyngeal nerve; X, vagus nerve; XI, spinal accessory nerve; XII, hypoglossal nerve; bET, bony portion of the eustachian tube; BP, base of the pterygoid process; C1, first cervical nerve; C2, second cervical nerve; IJV, internal jugular vein (displaced posteriorly and laterally); JuB, jugular bulb; Lab, labyrinth; LVPM, levator veli palatini muscle; LWMS, lateral wall of the maxillary sinus; MFP, periosteum of the middle cranial fossa; MMA, middle meningeal artery; phICA, parapharyngeal tract of the internal carotid artery; PhB, pharyngeal branch of the vagus nerve; PhPl, pharyngeal plexus; PPF, pterygopalatine fossa; SCM, superior constrictor muscle; SiS, sigmoid sinus; TPAt, transverse process of the atlas; TVPM, tensor veli palatini muscle; VA, vertebral artery; VN, vidian nerve.
Due to the complexity and functional relevance of neurovascular structures within the parapharyngeal space, high expertise, in-depth preoperative assessment, precise planning of surgery, intraoperative neuromonitoring, availability of hemostatic materials, ability to convert the surgical approach, and readiness of neuroradiologist in the event of major vascular injuries are essential requirements for such a complex surgical procedure.
The reader is encouraged to identify the position of the mentioned neurovascular structures to fully understand the limitations and potentialities of the lateral parapharyngeal transnasal approach.
Fig. 24.3 Axial CT anatomy of the upper parapharyngeal space and the jugular foramen. The panel includes two axial CT scans passing through (a) and immediately below the jugular foramen (b). The lateral portion of the upper parapharyngeal space lies lateral to the plane passing through the lateral pterygoid plate (LPP). The trajectory parallel to the lateral pterygoid plate leads to the area of the jugular foramen, which includes the styloid process (StyP), internal jugular vein (IJV), and lower cranial nerves. The stylomandibular tunnel, which houses the internal maxillary artery (IMA), can be identified between the styloid process and the condylar process (ConP) of the mandible. The parapharyngeal tract of the internal carotid artery (phICA) runs in a vertical direction in the medial portion of this region. However, this artery can show remarkable medial or lateral kinking toward the posterior pharyngeal wall or nodal level II, respectively. LPM, lateral pterygoid muscle; MPM, medial pterygoid muscle; PhPl, pharyngeal plexus.Fig. 24.4 MRI anatomy of the prestyloid compartment of the upper parapharyngeal space. The panel includes one coronal T2-weighted (a) and three T1-weighted axial MRI images (b–d). The white dotted lines depict the position of the axial images. As seen in a coronal plane, the internal jugular vein (IJV) and the facial nerve (VII) run on the posteromedial and posterolateral surfaces of the styloid process (StyP), respectively. The stylohyoid, styloglossus (SGM), and stylopharyngeal muscle (SPM) arise from the styloid process together with some ligamentous/fascial structures. The stylopharyngeal fascia (SPF) lies from the styloid process to the levator veli palatini muscle (LVPM), making up the posterior limit of the prestyloid compartment of the parapharyngeal space (also called “true parapharyngeal space”). The anterior boundary of this space is the interpterygoid fascia, which extends from the condylar process of the mandible (ConP) to the tensor veli palatini muscle (TVPM). The lateral portion of the upper prestyloid compartment houses the parapharyngeal process of the parotid gland (PG). In the retrostyloid compartment, also called “carotid space,” the lower cranial nerves (X*) lie in the interface between the internal jugular vein and the parapharyngeal segment of the internal carotid artery (phICA). DM, digastric muscle; IMA, internal maxillary artery; LoCM, longus capitis muscle; LPM, lateral pterygoid muscle; MaP, mastoid process; MPM, medial pterygoid muscle.Fig. 24.5 Coronal MRI anatomy of the upper parapharyngeal space. The present contrast-enhanced T1-weighted coronal MRI, which passes through the foramen ovale, shows the relationship between the eustachian tube (ET), the mandibular nerve (V3), the lateral pterygoid muscle (LPM), and the medial pterygoid muscle (MPM). The tensor veli palatini muscle (TVPM) is inserted on the anterior plate of the eustachian tube, while the levator veli palatini muscle (LVPM) lies more inferiorly and runs parallel to the tubal lumen (TuL). Three white dotted lines (A–C) show the position of images composing ▶Fig. 24.6. V2, maxillary nerve; FoPl, foraminal plexus.Fig. 24.6 (a–c) Axial MRI anatomy of the jugular and carotid foramen and related structures. The panel includes three axial CISS (constructive interference in steady state) MRI images; their positions are represented in ▶Fig. 24.5. The area of the jugular and carotid foramina is exceedingly complex due to the convergence of the internal jugular vein (IJV), the parapharyngeal segment of the internal carotid artery (phICA), the lower cranial nerves (X*), and the hypoglossal nerve (XII) in their passage across the skull base. While passing through the jugular foramen, the lower cranial nerves have a trajectory from superomedial to inferolateral. The hypoglossal nerve runs across the skull base caudally to the lower cranial nerves, following a posteromedial-to-anterolateral direction. Both lower cranial nerves and hypoglossal nerves pass between the internal carotid artery and the internal jugular vein. The white dotted (A) and dashed (B) lines depict the orientation of images composing ▶Fig. 24.7. V3, mandibular nerve; ATN, auriculotemporal nerve; ConP, condylar process of the mandible; IAN, inferior alveolar nerve; LN, lingual nerve; LPM, lateral pterygoid muscle; LVPM, levator veli palatini muscle; MMA, middle meningeal artery; MPM, medial pterygoid muscle; PG, parotid gland; TVPM, tensor veli palatini muscle.Fig. 24.7 (a, b) Sagittal and parasagittal MRI anatomy of the jugular foramen. Two CISS (constructive interference in steady state) MRI images show the anatomy of the parapharyngeal segment of the internal carotid artery (phICA), the internal jugular vein (IJV), and the lower cranial nerves (X*) while crossing the cranial base. The orientation of the images of the present panel is depicted in ▶Fig. 24.6. V3, mandibular nerve; IAC, internal auditory canal; iIMA, infratemporal tract of the internal maxillary artery; LPM, lateral pterygoid muscle; MMA, middle meningeal artery; PPF, pterygopalatine fossa; TM, temporal muscle.Fig. 24.8 (a–f) Sagittal MRI anatomy of the retrostyloid compartment of the upper parapharyngeal space. The panel contains six sagittal CISS (constructive interference in steady state) MRI images passing through the upper parapharyngeal space, from lateral (a) to medial (f). In the medial portion of the upper parapharyngeal space, the parapharyngeal segment of the internal carotid artery (phICA) is separated from the upper (UpLP) and lower head of the lateral pterygoid muscle (LoLP) by the mandibular nerve (V3) and the eustachian tube (ET). The lateral portion of the upper parapharyngeal space houses the internal jugular vein (IJV), the lower cranial nerves (X*), and the hypoglossal nerve, which are separated from the lateral pterygoid muscle by the styloid process (StyP) and related muscular and ligamentous/fascial structures. Notably, the roof of the infratemporal fossa (or deep masticatory space) is the greater wing of the sphenoid bone (GW), while the roof of the parapharyngeal space consists of the petrous portion of the temporal bone. VII, facial nerve; AFB, acoustic-facial bundle; Co, cochlea; DTN, deep temporal nerve; FOv, foramen ovale; h, horizontal tract of the petrous segment of the internal carotid artery; IAC, internal auditory canal; IMA, internal maxillary artery; IOF, infraorbital foramen; ION, infraorbital nerve; JuB, jugular bulb; LSC, lateral semicircular canal; MMA, middle meningeal artery; peICA, petrous segment of the internal carotid artery; PPF, pterygopalatine fossa; SiS, sigmoid sinus; TM, temporal muscle; TuL, tubal lumen; v, vertical tract of the petrous segment of the internal carotid artery.Fig. 24.9 (a–f) Axial MRI anatomy of the retrostyloid compartment of the upper parapharyngeal space. The panel contains six axial CISS (constructive interference in steady state) MRI images passing through the upper parapharyngeal space, from cranial (a) to caudal (f). The internal jugular vein (IJV) is formed by the confluence of the sigmoid sinus (SiS) and the inferior petrosal sinus (IPS) in the area of the jugular bulb (JuB). The vein is surrounded by several neurovascular structures: the medial wall is adjacent to the lower cranial nerves (X*) and the hypoglossal nerve (XII); the lateral wall is close to the facial nerve (VII); the anterior wall faces the posterolateral surface of the parapharyngeal (phICA) and the vertical (v) petrous segment of the internal carotid artery (peICA). All these neurovascular structures are enclosed within the retrostyloid compartment of the upper parapharyngeal space. The mandibular nerve (V3) and most of its branches run in the interface between the infratemporal fossa and the prestyloid compartment of the upper parapharyngeal space. The middle meningeal artery (MMA), the auriculotemporal nerve (ATN), the inferior alveolar nerve (IAN), and the lingual nerve (LN) can be identified along a plane parallel to the posterior surface of the lateral pterygoid muscle (LPM). ARCM, anterior rectus capitis muscle; Co, cochlea; h, horizontal tract of the petrous segment of the internal carotid artery; IMA, internal maxillary artery; LoCM, longus capitis muscle; MPM, medial pterygoid muscle; PBF, pharyngobasilar fascia; PG, parotid gland; PSC, posterior semicircular canal; ToT, torus tubarius; TVPM, tensor veli palatini muscle.Fig. 24.10 (a–d) Coronal MRI anatomy of the jugular foramen. The panel contains four coronal CISS (constructive interference in steady state) MRI images passing through the jugular foramen, from posterior (a) to anterior (d). The jugular foramen and the hypoglossal canal (HyC) arise from the superolateral and inferomedial sides of the jugular tuberculum (JuT), respectively. The lower cranial nerves (X*) and the internal jugular vein (IJV) run in the medial and lateral portions of the jugular foramen, respectively. As a result of these trajectories, the hypoglossal nerve (XII) and the lower cranial nerve converge behind the parapharyngeal segment of the internal carotid artery while exiting from their respective canal/foramen. IAC, internal auditory canal; IPS, inferior petrosal sinus.
Endoscopic Dissection
Nasal Phase
Anterior and posterior ethmoidectomy.
Transethmoidal sphenoidotomy.
Type D endoscopic medial maxillectomy.
Skull Base Phase
Transpterygomaxillary approach.
Infratemporal fossa approach (third corridor).
Step 1: Removal of the interpterygoid fascia.
Step 2: Removal of the stylopharyngeal fascia and muscles attached to the styloid process.
Step 3: Opening of the pterygoid fossa.
Step 4: Removal of the medial pterygoid plate.
Step 5: Removal of the lateral pterygoid plate.
Step 6: Removal of the medial pterygoid muscle.
Step 7: Removal of the carotid sheath.
Step 8: Sectioning of the mandibular nerve.
Step 9: Sectioning of the middle meningeal artery.
Step 10: Removal of the tensor veli palatini muscle.
Step 11: Opening of the tubal lumen.
Step 12: Inferior, posterior, and superior sectioning of the torus and dissection of the eustachian tube from the skull base.
Step 13: Sectioning of the eustachian tube.
Step 14: Sectioning of the levator veli palatini and superior constrictor muscles.
Step 15: Styloidectomy.
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