Abstract
Approaches to the pterygopalatine/pterygomaxillary space (PPS) provide the surgeon with a vantage point into the pterygopalatine fossa, infratemporal fossa, and lateral recess of the sphenoid sinus. Pathologic processes in this area include sphenoid encephaloceles, juvenile nasopharyngeal angiofibromas (JNAs), neurogenic tumor, inflammatory lesions, or other skull base neoplasms. To ensure adequate exposure and access to this area, a thorough understanding of the anatomy of the maxillary artery as it traverses this space is critical, and possible control of this vessel and its tributaries, specifically the sphenopalatine artery, is crucial for successful surgery. In surgical management of vascular tumors such as JNA, the surgeon should obtain wide access through all boundaries of the tumor with minimal manipulation of the mass itself to prevent inadvertent bleeding. Preoperative embolization should be considered in all cases to preemptively control its dominant vascular supply. JNAs have a tendency to extend into the many corridors adjacent to the PPS and often may progress posteriorly through the vidian canal.
Keywords
juvenile nasopharyngeal angiofibroma, lateral recess, maxillary artery, pterygomaxillary space, pterygopalatine fossa, skull base
Introduction
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Pterygopalatine/pterygomaxillary space (PPS) approaches are used to treat lesions in areas posterior to the maxillary sinus, including the pterygopalatine fossa and lateral recess of the sphenoid sinus (LSR). Pathologic processes within the PPS are rare; the most common ones are juvenile nasopharyngeal angiofibroma (JNA), neurogenic tumors such as schwannoma, and perineural extension of sinonasal malignancy. A characteristic lesion found within the LSR is the encephalocele, which is commonly associated with idiopathic intracranial hypertension (IIH).
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Endoscopic, endonasal PPS approaches have paved the way for minimally invasive treatment of these lesions, providing excellent visualization and instrument accessibility, as well as reduced morbidity. In contrast, surgeons have traditionally used open transfacial approaches (e.g., midfacial degloving, lateral rhinotomy) with medial maxillectomy and/or subtemporal craniotomy to treat these lesions. Compared with these options, a PPS approach may obviate the need for open incisions, although at times an adjunctive canine fossa incision is a useful complement to the endoscopic approach, especially for posterolateral access.
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Exposure of the pterygopalatine fossa through a PPS approach allows maxillary artery ligation both for management of refractory/recurrent epistaxis and for arterial control during resection of tumors, such as JNA.
Anatomy
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The PPS is bounded by the posterior wall of the maxillary sinus (anterior), perpendicular plate of the palatine bone (medial), pterygoid process of the sphenoid bone (posterior), and body of the sphenoid bone (superior). Inferiorly, it is in continuity with the greater palatine canal. Laterally, it connects with the infratemporal fossa ( Fig. 24.1 ).
Fig. 24.1
Anatomic drawing showing the relationship of the pterygopalatine space to the adjacent sphenoid, maxillary, and palatine bones. Note the course of the maxillary artery and V 2 through the potential space, which can be enlarged by pathologic processes. a., Artery; n., nerve.
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Several foramina provide passageways for neurovascular structures residing in the PPS and thus form the path of least resistance to the orbit, palate, skull base, infratemporal fossa, and nasal cavity for pathologic processes.
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The vascular and neural structures are located anteroinferiorly and posterosuperiorly, respectively, within the PPS. The sphenopalatine artery, a terminal branch of the maxillary artery, is found between the sphenoid and palatine bones and enters the nasal cavity at the sphenopalatine foramen. If access posterior to the artery is necessary (e.g., LSR), then once the artery is identified it can sometimes be retracted down. However, it will often need to be divided and ligated, as simple retraction may increase the risk of arterial avulsion and subsequent hemorrhage.
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The maxillary artery is a terminal branch of the external carotid system. In traditional anatomic nomenclature, it has been referred to as the internal maxillary artery.
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The maxillary division of the trigeminal nerve (V 2 ) and the vidian nerve emanate from the posterior wall of the space, from the foramen rotundum (superomedial) and the pterygoid canal (inferolateral), respectively. They form the pterygopalatine ganglion and branch into the infraorbital nerve exiting through the inferior orbital fissure and the greater and lesser palatine nerves passing through the correspondingly named foramina. Through these terminal branches, the maxillary nerve provides sensation to the cheek skin, lower eyelid, upper lip, nasal sidewall, and hard and soft palate. The vidian contributors traveling with the maxillary branches produce secretory function of the lacrimal, nasal, and palatal glands. The vidian canal is found within the floor of the sphenoid sinus and can often be identified by elevating the mucosa overlying the anterior face of the sphenoid sinus off the bone in an inferolateral direction.
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Posterior to the PPS, pneumatization of the lateral portion of the sphenoid bone can result, forming a lateral sphenoid recess. This is observed in up to 25% to 48% of patients; the bone is extensively pneumatized in 8% of cases. The roof of this space can lie directly beneath the temporal lobe in the middle cranial fossa and is a common location for middle cranial fossa encephaloceles.
Preoperative Considerations
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The need for transfusion should be anticipated given the proximity to the maxillary arterial system and pterygoid venous plexus, especially for vascular lesions such as a JNA. Preoperative angiography and embolization may be necessary with certain pathologic processes such as JNA.
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Neurosurgical consultation should be strongly considered, particularly in the setting of an encephalocele or cerebrospinal fluid (CSF) leak, or if there is intracranial extension of pathology.
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Magnetic resonance imaging (MRI) and computed tomography (CT) should both be performed; image-guided surgical navigation is useful intraoperatively. When an LSR encephalocele is being addressed, intrathecal administration of diluted fluorescein may be necessary to identify or confirm the site of the leak intraoperatively ( Fig. 24.2 ).
Fig. 24.2
Triplanar computed tomography (CT) images showing a large, complex lateral sphenoid recess meningoencephalocele splaying the pterygoid plates. The endoscopic view (lower right) reveals the fluorescein-stained sac, which has been exposed by removal of the posterior wall of the maxillary sinus and bone of the pterygoid root. These bony layers are indicated by white arrows on the axial CT image (lower left).
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Whether a nasoseptal flap will be necessary for skull base reconstruction should be determined. The flap may be raised at the beginning of surgery and tucked posterolaterally (i.e., in the nasopharynx) for the remainder of the procedure to avoid trauma to the flap while the approach is performed.
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The patient should be counseled on the possible sequelae of PPS approaches, including ipsilateral palatal or cheek numbness or dry eye.
Radiographic Considerations
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High-resolution CT images should be obtained using a stereotactic navigational protocol (1-mm axial slices). Neurogenic tumors in the PPS will characteristically enlarge the bony openings as they pass through foramina, which is often visible on CT imaging studies ( Fig. 24.3 ).
Fig. 24.3
Coronal computed tomography (CT) sinus scan showing a right schwannoma involving the enlarged foramen rotundum (white arrow). The black arrow denotes a normal-appearing foramen rotundum.
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MRI will better define soft tissue structures, including perineural spread of a sinonasal or skull base neoplasm ( Fig. 24.4 ). Adenoid cystic carcinoma is notorious for spreading into neural foramina, and perineural invasion may proceed intracranially. The palatine branch of the maxillary nerve innervates the mucosa of the hard palate, which contains minor salivary glands and can also harbor neoplasms.
Fig. 24.4
Axial T2-weighted magnetic resonance image (MRI) showing a right-sided adenoid cystic carcinoma involving V 2 (arrow) and traversing through inferior orbital fissure.
Instrumentation
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0-degree and 30-degree endoscopes
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Standard endoscopic sinus surgical tray
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4-mm diamond choanal atresia bur or 15-degree angled diamond bur
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Extended-length Kerrison rongeurs
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Through-cutting instruments
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Endoscopic clip applier
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Suction monopolar cautery or endoscopic bipolar cautery, to have available for small branches of the maxillary artery
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Endoscopic microscissors
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Blunt dissecting instrument, such as curette or ball-tip probe
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Image-guided surgical navigation system
Pearls and Potential Pitfalls
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A wide maxillary antrostomy allows appropriate exposure of the PPS and provides fixed anatomic landmarks for dissection. For large lesions, consideration should be given to a medial maxillectomy for exposure.
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Use of image guidance is important.
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Specific surgical landmarks of the palatine bone (orbital, pterygoid roots) should be identified.
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A drill should be used when necessary to remove the dense bone of the pterygoid process.
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One should be prepared to extend the approach with a Caldwell-Luc procedure or endoscopic Denker approach (see Chapter 22 ) for expanded access lateral to the infraorbital nerve.
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Any branches of the maxillary artery encountered must be identified and cauterized. They may go into spasm and can cause profuse bleeding postoperatively.
Surgical Procedure
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Undertake the usual preparations for endoscopic sinus surgery:
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Topically vasoconstrict and anesthetize the nasal cavities with pledgets soaked in 4% cocaine, oxymetazoline, or 1:1000 epinephrine.
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Inject 1% lidocaine with 1:100,000 epinephrine into the axilla of the middle turbinate and the region of the sphenopalatine foramen. Intraoral injection of the greater palatine foramen can be performed as well.
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Maxillary artery ligation is often performed as part of pterygopalatine fossa surgery for both access and preemptive vascular control.
Step 1: Wide Maxillary Antrostomy and Sphenoidotomy
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A wide antrostomy is the first key to the procedure. After performing the uncinectomy and the middle meatal antrostomy to enter through the natural ostium, enlarge posteriorly through the region of the posterior fontanelle using through-cutting forceps and a microdébrider. This will expose the orbital process of the palatine bone ( Fig. 24.5 ).
Fig. 24.5
Artist’s depiction in endoscopic view (A) and endoscopic photograph (B) of a widely opened maxillary sinus, with attachment of the middle turbinate posteriorly. The medial wall of the maxillary sinus should be resected to the orbital process of the palatine bone.
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It is important to take the posterior fontanelle flush to the posterior wall of the maxillary sinus.
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Be prepared for bleeding from this maneuver, as branches of the sphenopalatine and descending palatine arteries may be transected. This can typically be controlled with suction monopolar cautery.
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For extended lesions, anterior and posterior ethmoidectomy may be required with identification of the skull base starting in the posterior ethmoid cavity.
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After maxillary antrostomy has been performed, create a wide sphenoidotomy toward the floor of the sphenoid sinus. During this maneuver, it is often necessary to control the posterior septal branch of the sphenopalatine artery, which courses within the mucosal tissues along the anterior face of the sphenoid sinus, inferior to the sphenoid os.
Step 2: Elevation of Mucosa of the Posterior Wall of the Maxillary Sinus and Drilling
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Elevate the mucosa in a submucoperiosteal plane.
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Using a diamond bur and Kerrison forceps, remove the ascending process of the palatine bone and the bone from the posterior wall of the maxillary sinus, thus opening the anteromedial wall of the PPS ( Fig. 24.6 ).
Fig. 24.6
Artist’s depiction (in endoscopic view) of reflection of the mucosa of the posterior wall of the maxillary sinus and use of a suction irrigation drill to thin the wall. The posterior wall of the maxillary sinus is thinned until the fascia of the pterygopalatine fossa is encountered.
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For maxillary artery ligation alone, generally only the posterior wall of the maxillary sinus needs to be taken down.
Step 3: Enlargement of the Window Into the PPS
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The step of enlarging the window into the PPS is not necessary for maxillary artery ligation, although it is often helpful to follow the sphenopalatine artery back to the maxillary artery.
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Enlarge the sphenoidotomy laterally and bring it into communication with the soft tissue of the sphenopalatine foramen and medial pterygopalatine space. It is often necessary to cauterize the sphenopalatine artery where it exits its foramen during this step. Note that there may be several branches.
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Using a drill, Blakesley forceps, and Kerrison forceps, further enlarge the opening into the posterior wall of the maxillary sinus laterally to expose the soft tissue of the PPS.
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Make sure to open widely to prevent complications. Take great care not to perforate the fascia until the bone is widely removed. The contents of the PPS are often under tension and can herniate into the nose; if the artery is damaged, control of the artery is difficult.
Step 4: Incision of the Anterior Pterygopalatine Fossa Periosteum
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Incise the anterior pterygopalatine fossa periosteum with either a sickle knife or a suction monopolar cautery applied at a low setting ( Fig. 24.7 ).
Fig. 24.7
Artist’s depiction of incision of the fascia of the pterygopalatine fossa in endoscopic view. Great care should be used when incising the fascia, because the maxillary artery can be easily injured.
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Once the periosteum is cut, use blunt instruments, such as a J-curette or ball-tip probe, to widely open the remainder of the periosteum.
Step 5: Identification of the Maxillary Artery
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The maxillary artery is generally buried within the pterygopalatine fat and traveling from lateral to medial through the posterior wall of the maxillary sinus.
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Often, pulsations can be visualized to identify the location of the vessel.
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Tease the artery out of the fascia with a blunt instrument, such as a ball-tip probe ( Fig. 24.8 ).
