Piero Nicolai, Alberto Schreiber, Marco Ravanelli, Davide Mattavelli, Alberto Deganello
The pterygopalatine fossa is a narrow space bounded by the pterygoid process posteriorly, maxillary sinus anterolaterally, and perpendicular process of the palatine bone anteromedially. This space is the watershed between the sinonasal cavity, infratemporal fossa, and orbital cavity, and houses several neurovascular structures, including the maxillary nerve and the pterygopalatine ganglion with their branches together with the pterygopalatine tract of the internal maxillary artery with its collateral vessels. In view of its supposed origin at the base of the pterygoid process, juvenile angiofibroma is particularly prone to extend within the pterygopalatine fossa and toward adjacent compartments.1Furthermore, sinonasal or nasopharyngeal tumors can reach the pterygopalatine fossa passing through the sphenopalatine foramen or invading its bony boundaries. More rarely, primary neurogenic, vascular, or other lesions can be found in this area. The transnasal endoscopic approach to the pterygopalatine fossa has been employed to resect juvenile angiofibromas,2vidian and maxillary nerve schwannomas,3– 6fibro-osseous lesions,7hemangiomas,7sinonasal or nasopharyngeal malignancies with lateral extension,7and other rarer lesions.
The pterygopalatine fossa can be dissected through the maxillary sinus in a layer-by-layer fashion. The most important bony landmarks are the infraorbital canal, which marks the position of the pterygomaxillary fissure (i.e., the transition between the infratemporal fossa and the pterygopalatine fossa),8and the sphenopalatine foramen, which serves as the starting point to remove the perpendicular process of the palatine bone and the posterior maxillary wall. This step is preferably performed keeping the periosteum intact to protect the neurovascular structures of the pterygopalatine fossa. Inferomedially, the subperiosteal dissection demarcates a triangular area that corresponds to the pterygomaxillary junction, where the maxilla fuses with the pterygoid process. The periosteum is then incised and the underlying fat is meticulously removed to expose the neurovascular structures. After skeletonizing the pterygopalatine tract of the internal maxillary artery and its collaterals, they are removed to analyze the nervous structures, which lie in front of the pterygoid process and cranial insertion of the lateral pterygoid muscle.
Fig. 15.1 Lateral to medial view of the pterygopalatine fossa as seen from the pterygomaxillary fissure. The drawing shows the left pterygopalatine fossa (red area), inferior orbital fissure (blue area), and their nervous content.Fig. 15.2 Position of the pterygopalatine fossa as seen through the transantral window.
The complete removal of fat and neurovascular structures allows identification of the different pathways of communication of the pterygopalatine fossa with adjacent compartments. Specifically, the vidian canal, foramen rotundum, inferior orbital fissure, and pterygomaxillary fissure connect the pterygopalatine fossa with the foramen lacerum, middle cranial fossa, orbital cavity, and infratemporal fossa, respectively.
Fig. 15.3 (a–d) Axial CT anatomy of the pterygopalatine fossa. The panel includes four axial CT scans passing through the pterygopalatine fossa (PPF). The pterygopalatine fossa lies between the posterior wall of the maxillary sinus (PWMS) anteriorly and the pterygoid process posteriorly. The base of the pterygoid process houses the foramen rotundum (FRo) and the vidian canal (VC), while the caudal portion is formed by the medial pterygoid plate (MPP) and the lateral pterygoid plate (LPP). The pterygopalatine fossa is a crossroad region, which is connected with the nasal cavity, orbital cavity, and infratemporal fossa through the sphenopalatine foramen (SPF), inferior orbital fissure (IOF), and pterygomaxillary fissure (PMF), respectively. Caudally, the pterygopalatine fossa ends blindly with the pterygomaxillary junction (PMJ). DPC, descending palatine canal; GPC, greater palatine canal; ION, infraorbital nerve; LPC, lesser palatine canal; PVC, palatovaginal canal; SpS, sphenoid sinus.Fig. 15.4 Angiography of the internal maxillary artery. The panel includes an anterior-to-posterior (a) and lateral-to-medial angiograms (b) of the right internal maxillary artery (IMA). The terminal branches of the external carotid artery (ECA) are the superficial temporal artery (STA) and the internal maxillary artery, which is formed by the condylar, infratemporal, and pterygopalatine tracts. The internal maxillary artery gives origin to the middle meningeal artery (MMA) and other collateral branches before ending with the sphenopalatine artery (SPA) and descending palatine artery (DPA). DTA, deep temporal artery; IOA, infraorbital artery.Fig. 15.5 Coronal MRI anatomy of the pterygopalatine fossa and adjacent areas. The panel includes two series of T2-weighted (a, c, e) and T1-weighted (b, d, f) MRI images, from anterior (upper images) to posterior (lower images). The position of the images composing this panel is showed in ▶Fig. 15.7: the upper, middle, and lower images correspond to A, B, and C, respectively. The pterygopalatine fossa is a narrow space enclosed between the maxillary sinus (MS) and the perpendicular process of the palatine bone (PPPB) anteriorly and pterygoid process posteriorly. The pterygoid process, which is formed by the base (BaP) along with the medial pterygoid plate (MPP) and the lateral medial pterygoid plate (LPP), serves as the cranial insertion of the medial pterygoid muscle (MPM) and the lateral pterygoid muscle (LPM). The condylar tract of the internal maxillary artery (cIMA) runs around to the mandibular condyle, whereas the infratemporal tract (iIMA) passes between the upper head of the lateral pterygoid muscle (UpLP) and the lower head of the lateral pterygoid muscle (LoLP). V2, maxillary nerve; HaP, hard palate; TVPM, tensor veli palatini muscle; VC, vidian canal.Fig. 15.6 Sagittal CT and MRI anatomy of the pterygopalatine fossa. The panel includes two sagittal CT scans (a, b) and a constructive interference in steady state (CISS) MRI scan passing through the pterygopalatine fossa (PPF) (c). The position of the images composing this panel is showed in ▶Fig. 15.7: a corresponds to D, whereas the b and c to E. The foramen rotundum (FRo) ends anteriorly in the cranial portion of the pterygopalatine fossa and is separated from the superior orbital fissure (SOF) by a bony bridge called the maxillary strut (MSt). Cranially, the pterygopalatine fossa continues into the orbital cavity through the inferior orbital fissure (IOF), which is transversally closed to the orbitalis muscle (OrM), also called Müller’s muscle. In the caudal portion, the pterygopalatine fossa ends with the greater palatine canal (GPC) and the lesser palatine canal (LPC) medially and the pterygomaxillary junction (PMJ) laterally. V2, maxillary nerve; BaP, base of the pterygoid process; GPA, greater palatine artery; Ha, hamulus; LPA, lesser palatine artery; LPP, lateral pterygoid plate; MeC, Meckel’s cave; MPP, medial pterygoid plate; peICA, petrous tract of the internal carotid artery; PWMS, posterior wall of the maxillary sinus.Fig. 15.7 (a, b) Axial and coronal MRI and CT anatomy of the areas adjacent to the pterygopalatine fossa. In the axial T1-weighted MRI scan (a), the white dashed lines (A–C) depict the position of images composing ▶Fig. 15.5, while the white dotted lines (D, E) depict the position of the images composing ▶Fig. 15.6. The pterygopalatine fossa (PPF) is surrounded by a number of anatomical areas. It is adjacent to the maxillary sinus anteriorly, infratemporal fossa posteriorly and laterally, sinonasal tract medially, orbital apex superiorly, and palate inferiorly. ACP, anterior clinoid process; DPC, descending palatine canal; IOF, inferior orbital fissure; LPM, lateral pterygoid muscle; LPP, lateral pterygoid plate; MPM, medial pterygoid muscle; MPP, medial pterygoid plate; OC, optic canal; PMF, pterygomaxillary fissure; PMJ, pterygomaxillary junction; SOF, superior orbital fissure; SPF, sphenopalatine foramen; TM, temporal muscle.Fig. 15.8 Axial and sagittal MRI and CT anatomy of the infraorbital nerve. The panel includes an axial T1-weighted contrast-enhanced fat-saturated MRI (a), a curved CISS (constructive interference in steady state) MRI (b), and a sagittal CT scan (c). After arising from the maxillary nerve (V2), the infraorbital nerve (ION) tilts laterally and enters the infraorbital canal (IOCa), forming the shape of a bayonet. The medial edge of the posterior end of the infraorbital canal mostly corresponds to the level of the pterygomaxillary fissure (PMF; white dotted line), thus serving as a guide to distinguish the limit between the pterygopalatine fossa and the infratemporal fossa. BaP, base of the pterygoid process; FOv, foramen ovale; GW, greater wing of the sphenoid bone; LPM, lateral pterygoid muscle; LPP, lateral pterygoid plate; TM, temporal muscle.
Endoscopic Dissection
Nasal Phase
Horizontal uncinectomy.
Type A–B endoscopic medial maxillectomy.
Facultative: Type C–D endoscopic medial maxillectomy.
Facultative: Vertical uncinectomy.
Facultative: Anterior ethmoidectomy.
Facultative: Posterior ethmoidectomy.
Facultative: Middle turbinectomy.
Facultative: Septectomy.
Skull Base Phase
Step 1: Removal of the mucosa of the maxillary sinus.
Step 2: Exposure of the descending palatine canal.
Step 3: Removal of the posterior wall of the maxillary sinus.
Step 4: Removal of the anterior periosteum of the pterygopalatine fossa.
Step 5: Removal of the fat of the pterygopalatine fossa.
Step 6: Partial removal of the vascular compartment.
Step 7: Complete removal of the vascular compartment.
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