Endoscopic Endonasal Transpterygoid Approaches to the Middle Cranial Fossa

History

• Mass effect or facial swelling

• Pain

• Trismus

• Double vision

• Dry eye

• Corneal ulcers

• Numbness

• Facial paralysis or weakness

• Medications:

  • Antiplatelet drugs

  • Herbal products

  • Vitamin E

  • Fish oil

• Prior surgery or radiation therapy

Physical Examination

• Thorough evaluation of cranial nerves (CN), specially CN 1–7;

• Ocular function

• Mouth opening

• Nasal endoscopy including nasopharynx

• Olfactory function

Imaging

• Computed tomography (CT)

• CT angiogram (CTA)

• Magnetic resonance imaging (MRI)

• Angiography

• An initial differential diagnosis is based on the appearance and site of origin of the lesion as demonstrated by MRI and/or CT. These imaging studies are considered complementary, as MRI is best in determining soft tissue relationships, whereas CT is best to show the bony architecture.

  • MRI demonstrates the interface between the tumor and the surrounding soft tissues, differentiating the tumor from secretions or inflammatory sinonasal disease, assessing the presence and extent of perineural spread, and the degree of involvement of the dural, brain, or orbit.

  • In addition, imaging studies allow the surgeon to estimate the extent of surgical exposure necessary. One may draw imaginary vertical lines in the coronal plane intersecting these foramina; thus, dividing the region into the sinonasal tract medially; the middle cranial and ITFe laterally; and the PPF in between. Imaginary horizontal lines, in the coronal plane, drawn through the lower level of foramen rotundum and the Vidian canal, approximate the locations of the middle cranial fossa, the lateral aspect of the petrous temporal bone (i.e., the petrous segment of the ICA), and the ITF. The spaces between the vertical lines are further divided by the horizontal line through the Vidian canal into two regions: the lateral sphenoid recess above this horizontal line, and the PPF below it (see Fig. 119.2 ). Matching a lesion height and width in relation to these landmarks helps the surgeon to estimate the surgical corridor required to expose any particular lesion ( Fig. 119.3A and B ).

    

• A full body positron emission tomography (PET) scan, or a fused PET/CT scan helps to identify the presence of regional or distant metastasis in patients presenting with a malignant tumor.

• Additionally, a high-resolution CTA appraises the course of the ICAs and their intracranial branches, evaluates the skull base bony anatomy, and may improve the accuracy of the intraoperative navigation.

• Using the intraoperative navigation software, MRI can be fused to the CT or CTA scan to plan the approach preoperatively.

• If there is involvement of the ICA, the patient must be assessed by one of the various balloon occlusion tests to determine the degree of collateral flow and to evaluate the tolerance to the loss of one ICA. Areas of hypoperfusion on imaging mandate an extracranial-to-intracranial artery bypass or stenting of the vessel.

  • Patients with benign lesions who can be operated on electively may benefit from ICA stenting as a protective measure. However, stenting requires antiplatelet therapy for 6 to 12 weeks; thus, ICA stenting is not a practical approach for patients with malignant tumors.

Indications

• Endoscopic endonasal transpterygoid approaches (EETPA) were first used to access pathologies in the lateral sphenoid sinus such as bony defects associated with CSF leaks and meningo/meningoencephaloceles.

• Multiple extensions and modifications of the EETPA followed, addressing select pathologies arising in the PPF, the petrous apex, the anterior aspect of Meckel’s cave, the cavernous sinus, the ITF, and the medial aspect of the middle cranial fossa.

  • Meningiomas, chordomas, chondrosarcomas, and trigeminal schwannomas, are tumors commonly affecting these regions.

  • Other less common pathologies that may be approached via a transpterygoid corridor include select sinonasal carcinomas, juvenile nasopharyngeal angiofibromas, aggressive pituitary macroadenomas, and metastatic neoplasms.

• One must consider the goals of surgery (cure vs. gross total resection vs. debulking or decompression), the relationship of the lesion to neurovascular structures (one must not cross a critical CN or vessel), expected sequelae, and the experience and expertise of the surgical team to decide whether to use an endoscopic endonasal technique or any other alternative approach.

  • Surgery for a benign tumor usually strives for a total resection; however, a partial resection may be preferred to avoid significant morbidity.

  • Even a malignant tumor involving critical structures may require compromising the resection and settling for just a gross total resection (as opposed to a wide resection) to be followed by adjuvant treatment.

• The use of multiple lesser approaches (concomitant or staged) may produce less morbidity than a massive resection with a single approach.

Contraindications

• Despite its perceived minimally invasive nature, an EETPA yields a resection equivalent to that of an open approach, albeit through a smaller access; thus, any uncontrolled comorbidity that would preclude an open approach also applies to the EETPA. Cardiopulmonary, infectious, or other systemic comorbidities should be taken into consideration.

• One must use the approach that will achieve the most complete and safest resection adjusted according to the histopathology and extent of the tumor, but not the other way around; thus, the resection should not be compromised because the surgical approach is inadequate.

• The presence of an active bacterial infection in the sinonasal tract is a contraindication for an intradural approach, as it can seed the bacteria in the subarachnoid space.

• Tumor histopathology and goals of surgery (i.e., wide resection, gross total resection, or decompression) geographical extent (within the realm of the approach limits), and the relationship to neurovascular structures (the lesion should not be attached or posterior to the ICA or functioning CN) are important considerations in choosing a surgical approach.

When a tumor encases the ICA, the risk of intraoperative vascular injury is significant. If a surgical resection is mandatory, one should consider alternatives including the sacrifice of the ICA, the use of a different approach, or a partial resection followed by adjunctive therapy.

Preoperative Preparation

• The patient’s symptoms and comorbidities, coupled with the histopathology and imaging characteristics of the lesion, are the most important determinants for establishing the goals of surgery and for estimating potential sequelae and risks.

• An informed consent should explain the risks involved, present clear goals, and set realistic expectations.

• Anticipate and plan for the social, financial, and psychological ramifications of the expected sequelae and potential complications of surgery.

• Skull base neoplasms frequently mandate a multimodal treatment. Evidence of perineural spread, aggressive bone, or dural invasion mandates adjuvant radiation therapy with or without chemotherapy. Occasionally, decompression of the orbit, the optic nerve, or the optic chiasm may warrant a palliative resection or debulking. Any remaining disease may have to be treated with adjuvant therapy. Therefore, it is important to discuss the clinical plan of management with radiation and medical oncologists in a multidisciplinary setting, such as a Tumor Board.

Anesthesia

• General

• Awake sedation

• Local