Endoscopic Transmaxillary Approach to The Pterygopalatine Fossa
Paolo Castelnuovo
INTRODUCTION
The pterygopalatine fossa (PPF) is a critical area located posterior to the posterior wall of the maxillary sinus and is bordered by the pterygoid plates posteriorly, palatine bone medially, and middle cranial fossa superiorly. The PPF 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. Given this fact, the PPF represents the main pathway for the spread of inflammatory or neoplastic disease from the head and neck to the skull base.
The management of lesions arising in or extending to the PPF presents anatomic and surgical problems related to the difficulty of access. A number of traditional external techniques (lateral and anterior approaches) have been performed for gaining direct access to the PPF, entailing nonnegligible morbidity such as facial edema and pain, injury to the infraorbital nerve (ION), oroantral fistula, and chronic maxillary sinusitis. Recently, the widespread use of endoscopic endonasal techniques has progressively led toward treating selected lesions involving this critical area through a minimally invasive approach, thereby potentially reducing these risks.
Tumors arising specifically in the PPF are uncommon, with the most frequent being tumors of nerve sheath origin while benign and malignant tumors of the sinonasal tract are the most common tumors extending into this area. Since a wide variety of tumors involve this region, a precise diagnosis is often difficult to make. For this reason, a detailed history, clinical examination, and imaging studies are essential in defining the nature and extent of these tumors.
HISTORY
Most patients with a tumor involving the PPF are asymptomatic in the initial stages so that a delay in diagnosis is the rule and not the exception. When the patient complains of some form of discomfort, it is usually related to sinonasal symptoms such as unilateral nasal obstruction, discharge, epistaxis and facial pain. The epidemiologic data could be remarkably helpful in these cases to achieve a diagnosis: young male patients are suspect of juvenile nasopharyngeal angiofibroma (JNA), older patients with an occupational history in the field of wood or leather manufacturing are consistent with the possibility of sinonasal malignancies such as adenocarcinoma. Moreover, unilateral facial numbness, localized primarily on the upper lip or hard palate, should be always evaluated for compression (benign tumor) or infiltration (malignant lesion) of the maxillary nerve (V2).
PHYSICAL EXAMINATION
A detailed inspection of the nasal fossae, eyes, oral cavity, and facial profile is mandatory in these patients. Nasal endoscopy is currently considered the best diagnostic step for the assessment of the sinonasal and skull
base pathologies. Endoscopic exploration of the nasal fossa, nasopharynx, and skull base allows detection of any tissue abnormality or lesions in these compartments. Traditional examination of the cranial nerves should be performed in the evaluation of skull base tumors, with particular attention focused on maxillary nerve function that could be compromised by diseases involving the PPF. Ocular motility and morphology has to be investigated as well, in order to exclude proptosis or ocular paresis related to spread of tumor through the inferior orbital fissure toward the eye. Evaluation by an ophthalmologist is necessary in such cases. Moreover, inspection of the oral cavity is important to exclude erosion or deformity of the hard palate as a result of spread of the disease inferiorly through the palatine foramina. In some instances, particularly in very large lesions involving surrounding structures such as the eye and maxilla, the mass may be visible with deformity of the facial profile. Finally, examination of the neck is required to establish the possibility of metastasis to the cervical lymph node, especially in case of malignant tumors of the skull base.
base pathologies. Endoscopic exploration of the nasal fossa, nasopharynx, and skull base allows detection of any tissue abnormality or lesions in these compartments. Traditional examination of the cranial nerves should be performed in the evaluation of skull base tumors, with particular attention focused on maxillary nerve function that could be compromised by diseases involving the PPF. Ocular motility and morphology has to be investigated as well, in order to exclude proptosis or ocular paresis related to spread of tumor through the inferior orbital fissure toward the eye. Evaluation by an ophthalmologist is necessary in such cases. Moreover, inspection of the oral cavity is important to exclude erosion or deformity of the hard palate as a result of spread of the disease inferiorly through the palatine foramina. In some instances, particularly in very large lesions involving surrounding structures such as the eye and maxilla, the mass may be visible with deformity of the facial profile. Finally, examination of the neck is required to establish the possibility of metastasis to the cervical lymph node, especially in case of malignant tumors of the skull base.
INDICATIONS
Surgery is indicated in every case of tumor involving the PPF. The endoscopic endonasal transantral approach can be used depending upon such factors as extension of the disease and the experience of the surgeon. The aim of surgery could be to sample the lesion for diagnostic tissue or to treat it with the intent of radical resection. When lymphoproliferative disorder, mesenchymal tumor (e.g., sarcoma), or poorly differentiated cancer are suspected, surgery is performed only for a biopsy, so as to obtain the precise diagnosis essential for proper orientation of medical treatments (different protocols of radiotherapy and chemotherapy). On the other hand, fibro-osseous lesions, JNA, schwannoma, inverted papilloma, cavernous hemangioma, and selected cases of malignancies (e.g., squamous cell carcinoma, adenocarcinoma, adenoid cystic carcinoma) are some examples of the tumors originating in or extending to the PPF that can be resected radically with curative intent.
CONTRAINDICATIONS
Contraindications for an exclusive endoscopic endonasal approach are related to the extension of the tumor to selected anatomical 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 tumor.
The critical areas not amenable to transnasal endoscopic resection include the parapharyngeal spaces with encasement of the internal carotid artery (ICA), the hard/soft palate, the cavernous sinus, and massive infiltration of tumor into the orbit.
Obviously, the most important contraindication when choosing a specific type of approach remains the surgeon’s inadequate experience in the endoscopic management of this anatomical region and overall in the handling of possible complications. Finally, comorbidities such as severe cardiovascular disease, markedly debilitated or demented patients, or patients with end-stage renal or pulmonary disease will probably not benefit by excision of these tumors.
PREOPERATIVE PLANNING
Endoscopic and radiologic examinations allow precise evaluation of the site, size, and extent of the lesions and in some cases can provide a preoperative diagnosis. Imaging provides information on anatomical details (e.g., septal spur, concha bullosa, sphenoidal rostrum pneumatization, superior turbinate pneumatization) that can influence the surgery. Moreover, the identification of radiologic landmarks such as the vidian nerve, V2 (with its terminal branch called ION), SPF, and the pneumatization of pterygoid plates could be useful in terms of ensuring an adequate surgical corridor and to reduce risks during surgery. Moreover, multiplanar scans are extremely helpful in delineating the integrity of the bone. The finding of bone remodeling or erosion requires careful assessment of complementary soft tissue details on MRI. A contrast-enhanced MRI scan in T1- and T2-weighted sequences is particularly important to reveal the behavior of the lesion as well as its consistency and thereby differentiate between benign and malignant tumors. Generally, both CT and MRI scans are required to properly study the PPF lesions. Complementary information provided by these two examinations must be integrated to investigate every case of enlargement or asymmetry of the pterygomaxillary fissure. Moreover, PET-CT scan or other radiologic systemic assessments are required for staging purposes in malignant lesions prone to distant metastasis.
Clearly, knowledge of the tumor’s biology is essential to developing an appropriate plan for an adequate surgical procedure. The great majority of pathologies can be diagnosed using only clinical and radiologic assessment, aligning the biopsy with the radical resection of the lesion during the same surgical procedure. In this perspective, the biopsy is obviously strongly contraindicated in case of highly vascular lesions such as JNA. On the contrary, in these latter cases, preoperative intra-arterial angiography with embolization of the
hypervascular component is recommended. Tissue biopsy could be useful, however, for the pretreatment evaluation in selected cases of unclear diagnosis, especially when a malignant tumor is suspected and histotype of the lesion is required.
hypervascular component is recommended. Tissue biopsy could be useful, however, for the pretreatment evaluation in selected cases of unclear diagnosis, especially when a malignant tumor is suspected and histotype of the lesion is required.
Prior to surgery, the patient should discontinue anticoagulant drugs and nonsteroidal anti-inflammatory drugs, in order to avoid excessive bleeding during surgery.
SURGICAL TECHNIQUE
All procedures are performed with the patient under general anesthesia, after decongestion of the nasal cavities. A perioperative prophylactic antibiotic regimen is administered intravenously. The step-by-step surgical procedure is tailored to the tumor extension and histology as follows:
1. Exposure of the sinonasal corridor. When tumors involving the PPF are of sinonasal origin, the bulky mass occupying the nasal cavity has to be removed according to an oriented piecemeal resection, to get more working space. In selected cases, posterior septectomy may be performed as well to allow the simultaneous work of two surgeons with four hands through the two nostrils.
