Introduction

The pterygopalatine fossa (PPF) is a critical region located behind the posterior wall of the maxillary sinus and bordered by the pterygoid plates posteriorly, palatine bone medially, and middle cranial fossa superiorly. It has connections with the infratemporal fossa laterally through the pterygomaxillary fissure, the posterior nasal cavity medially through the sphenopalatine foramen (SPF), the orbit superiorly through the inferior orbital fissure, and the palate inferiorly through the palatine foramina.1 Given this fact, the PPF represents the main pathway for the spread of different inflammatory or neoplastic diseases from the head and neck to the skull base.

24.1 Indications

The endoscopic endonasal transantral approach can be tailored according to the extension of the disease involving the PPF and to the experience of the surgeon. The aim of surgery could be to sample the lesion for diagnostic issue or to treat it with a radical intent.2 The great majority of pathologies involving the PPF can be diagnosed using only clinical and radiologic assessment, performing the biopsy and the complete resection of the lesion during the same surgical procedure. For example, the biopsy of the lesion is strongly contraindicated in case of highly vascular lesions in young male patients for the suspect of juvenile angiofibroma (JA). In the latter, a preoperative intra-arterial angiography with embolization of the hypervascularized component is recommended.

However, the tissue biopsy could be useful for the pretreatment work-up in selected cases of unclear diagnosis, especially when malignant tumor is suspected. For example, when lymphoproliferative disorder, mesenchymal tumor (e.g., sarcoma), or poorly differentiated cancer is suspected, surgery is performed only for a tumor biopsy, obtaining the precise diagnosis that is essential to properly orientate the medical treatments (different protocols of radiotherapy and chemotherapy).

The diseases originating in or extending to the PPF that can be resected radically with curative intent are as follows:

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  Fibro-osseous lesion (e.g., fibrous dysplasia).

  
  
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  JA.

  
  
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  Schwannoma arising from vidian nerve (VN), infraorbital nerve (ION), greater and lesser palatine nerve.

  
  
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  Inverted papilloma.

  
  
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  Cavernous hemangioma.

  
  
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  Selected cases of sinonasal and skull base malignancies (e.g., squamous cell carcinoma, adenocarcinoma, adenoid cystic carcinoma).

  
  
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  Selected cases of nasopharyngeal cancers (e.g., undifferentiated carcinoma).

Contraindications for exclusive endoscopic endonasal approach are related to the extension of disease to selected anatomic compartments surrounding the PPF not resectable through the transnasal corridor and requiring external approaches or when the tumor extension involves vital structures precluding the radical resection of the lesion at all. The critical areas not amenable for transnasal endoscopic resection include the parapharyngeal spaces with encasement of the internal carotid artery (ICA), the hard/soft palate, the cavernous sinus, and the massive infiltration of the orbit.3

24.2 Surgical Steps

The step-by-step surgical procedure is tailored to the extension and histology of the lesion to be treated, as follow:

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  Exposure of the sinonasal corridor ( Fig. 24.1 ). The lower portions of the middle and superior turbinate are trimmed, preserving the olfactory mucosa. Anteroposterior ethmoidectomy, large maxillary antrostomy, and sphenoidotomy are performed ( Fig. 24.2 ).

  
  
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  Identification of the surgical anatomic landmarks. A subperiosteal dissection on the lateral nasal wall is performed, starting approximately 1 cm anteriorly to the tail of the middle turbinate. Just behind the crista ethmoidalis of the palatine bone, the sphenopalatine artery (SPA) is identified, cauterized, and cut to expose the sphenopalatine foramen (SPF) ( Fig. 24.3 ). The SPF and the prominence of the ION, visible along the roof of the maxillary sinus, served as consistent landmarks to understand the position of the major neural structures of the PPF ( Fig. 24.4 ). The sphenopalatine ganglion, together with the VN and maxillary nerve (V2), will be located superior to the horizontal plane passing through the SPF, while the greater and lesser palatine nerves will be located inferiorly; all the neural elements of the PPF will be found medially to the virtual sagittal plane passing through the ION. In this phase, it is important to recognize the vascular network of the basisphenoid, including the palatovaginal artery ( Fig. 24.5 ) and the SPA with its branches ( Fig. 24.6 ).4

  
  
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  Opening the surgical window to approach the PPF. The surgical approach should be tailored according to the location and extension of the lesion into the PPF. When the lesion is confined superiorly to the virtual horizontal plane passing through the SPF, a large maxillary antrostomy (preserving the integrity of the inferior turbinate) should be sufficient for removing the upper part of the posterior wall of the maxillary sinus (medial to the ION) ( Fig. 24.7 ). For such a conservative approach, only the orbital and sphenoidal processes of the palatine bone are drilled out, exposing therefore the foramen rotundum ( Fig. 24.8 ) and the palatosphenoidal canal ( Fig. 24.9 ). The SPA and the palatovaginal artery are cauterized and divided. During this surgical step, the periosteum behind the posterior wall of the maxillary sinus, surfacing the PPF, has to be carefully preserved. In this way, the VN (medially) and the V2 (superolaterally) can be identified easily by displacing the PPF content, enveloped in the “periosteal bag,” in an inferolateral direction ( Fig. 24.10 ). For lesions localized or extended inferiorly to the horizontal plane passing through the SPF, the surgical window has to be expanded inferiorly by drilling out also the vertical plate of the palatine bone as well and by removing the posterior half of the inferior turbinate together with the posterior portion of the medial maxillary wall ( Fig. 24.11 ). Also in this case, the posterior wall of the maxillary sinus can be removed as much as required using Kerrison rongeurs, in a medial-to-lateral direction, generally as far as the sagittal plane and passing through the ION ( Fig. 24.12 ). By removing the vertical process of the palatine bone, the descending palatine artery and the palatine nerve are visible inside to the palatine canal ( Fig. 24.13 ). When the VN and artery are divided, the PPF content enveloped in the periosteal layer is gently lateralized to expose the base of the pterygoids ( Fig. 24.14 ). Dissection within the PPF. Once the periosteal layer containing the PPF has been incised, the fibrofatty tissue surrounding the internal maxillary artery and its branches is exposed ( Fig. 24.15 ). A medium-sized vascular clip is positioned on the lateral aspect of the internal maxillary artery to avoid bleeding into the surgical field. Behind the vascular network, the neural structures are now exposed. Blunt dissection is performed to identify the neural network of the PPF, composed of the V2 with the ION, the pterygopalatine ganglion, and the greater and lesser palatine nerves ( Fig. 24.16 ). Whenever possible during the surgical dissection and if they appear to be macroscopically spared from disease, these nerves have to be preserved to minimize the morbidity of the surgical procedure for the patient.5 The descending palatine artery is identified, cauterized, and cut, if necessary. Continuing the dissection posteriorly, the two heads of the lateral pterygoid muscle (LPM) inserting on the lateral pterygoid plate come into view ( Fig. 24.17 ). If needed, the LPM can be detached from its medial insertion on the pterygoids to improve the dissection.6

  
  
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  Drilling out of the limiting bone. In selected cases, radical resection of the tumor is obtained only by drilling out the limiting bone. In this respect, what seems to be important for preventing recurrences of juvenile nasopharyngeal angiofibroma is drilling out the cancellous bone of the pterygoid roots and basisphenoid, particularly around the vidian canal, to remove any residual disease that may not be immediately evident. This technical note is relevant in case of malignancies as well, where the pterygoid roots and/or pterygoid plates are usually drilled out following the vidian canal, as far as the anterior genu of the ICA.3