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Endoscopic Endonasal Approach to Lateral Cavernous Sinus Lesions


Acknowledgements

We are indebted to Karam Asmaro, MD, and Nyall London, MD, PhD, for preparing the surgical video presented.

Introduction

The lateral cavernous sinus is bounded medially by the cavernous segment of the internal carotid artery (ICA), laterally by the lateral cavernous sinus dura and its intimately involved cranial nerves, superiorly by the distal dural ring of the ICA, and inferiorly by the maxillary strut and V2. This irregularly shaped space filled with critical structures has been cautiously approached via transcranial techniques for decades, most notably via the surgical contributions of Dolenc. As endoscopic endonasal approaches (EEAs) have been popularized, a “bottom-up” endoscopic trajectory via an endoscopic endonasal transpterygoid approach to this anatomical space has gained popularity in comparison to the now-classic anterolateral extradural transcranial approaches. In this chapter, we will review the anatomy of the lateral cavernous sinus, and the equipment and surgical technique to safely access it from an endoscopic endonasal approach, as well as the indications for this approach.

Anatomy

The cavernous sinus is a blood-filled dural venous sinus that lies within the middle cranial fossa between the sella medially and the anteromedial temporal lobe laterally. It transmits multiple cranial nerves as well as arteries of the anterior circulation. In relation to surgical anatomy, the lateral portion of the cavernous sinus is defined as that which lies between the ICA, to the boundary of the cavernous sinus laterally at the dura. In contrast, the medial cavernous sinus is that portion of the sinus between the sella in the midline and the ICA laterally. In traditional endonasal microscopic approaches to the sella, it is this medial cavernous sinus that is often entered to retrieve an invasive pituitary tumor, revealing only a glimpse of the lateral compartment beyond the ICA ( Fig. 13.1 ). However, the advent of endoscopy has led to a greater interest in accessing the lateral cavernous sinus from an endonasal standpoint, and therefore an intimate knowledge of the critical structures in this anatomic space is required. Superiorly, the lateral cavernous sinus is bounded by the upper cavernous ICA and its distal dural ring, and inferiorly by the maxillary strut , (the bone arising between V1 at the superior orbital fissure and V2 at foramen rotundum) and the V2 segment of the trigeminal nerve ( Fig. 13.2 ). Within these boundaries are the ICA and its associated sympathetic plexus, and cranial nerves III (oculomotor nerve), IV (trochlear nerve), V1 (ophthalmic trigeminal nerve), and VI (abducens nerve; Figs. 13.3 and 13.4 ). Importantly, the abducens nerve runs freely within the cavernous sinus ( Fig. 13.5 ) and is medial to cranial nerves III, IV, and V1, which run in the lateral dura leaflet. , The abducens is therefore more prone to injury in EEA to the lateral cavernous sinus, since it is the first cranial nerve encountered within the sinus when approached from an endonasal perspective and its displacement by a mass lesion is not always predictable. The other cranial nerves, however, are on the far (lateral) side of any mass lesion within the cavernous sinus when approached from an EEA, and this is an advantage over the transcranial route where the cranial nerves are superficial in the field to the pathology and must be worked around.

FIGURE 13.1, The lateral cavernous sinus as viewed through the more familiar medial compartment, using a standard endoscopic endonasal transsphenoidal transsellar approach with an angled endoscope. This provides a satisfactory view of the lateral cavernous sinus contents, but surgical manipulation is difficult unless the lesion addressed is soft and easily removed with an angled suction (such as a pituitary adenoma that has invaded the lateral compartment from the medial compartment). The working space is behind the cavernous internal carotid artery and requires angled instruments. For firm lesions such as meningiomas, the en-face view and surgical freedom afforded by the transpterygoid approach to the lateral compartment are superior. In this view, the bone of the clivus has also been removed, allowing visualization of most of the course of the abducens nerve. III , Oculomotor nerve; IV , trochlear nerve; V1 , ophthalmic division of trigeminal nerve; VI , abducens nerve; cICA , cavernous internal carotid artery; ellipse , distal dural ring of carotid artery; Pg , pituitary gland.

FIGURE 13.2, Left cavernous sinus cadaveric dissection viewed slightly medial-to-lateral from the midline sphenoid sinus after an endoscopic endonasal transpterygoid approach and total removal of surrounding bone. III , Oculomotor nerve; IV , trochlear nerve; V1 , ophthalmic division of trigeminal nerve; V2 , maxillary division of trigeminal nerve; VI , abducens nerve; cICA , cavernous internal carotid artery; SOF (ellipse) , superior orbital fissure. Dashed line , roof of cavernous sinus (distal dural ring of carotid artery).

FIGURE 13.3, Left cavernous sinus cadaveric dissection viewed en-face from the lateral sphenoid sinus after an endoscopic endonasal transpterygoid approach and total removal of surrounding bone. III , Oculomotor nerve; IV , trochlear nerve; V1 , ophthalmic division of trigeminal nerve; V2 , maxillary division of trigeminal nerve; VI , abducens nerve; cICA , cavernous internal carotid artery; SOF (ellipse) , superior orbital fissure. Dashed line , roof of cavernous sinus (distal dural ring of carotid artery).

FIGURE 13.4, Similar projection to Fig. 13.2 , after inferior mobilization of abducens nerve to better visualize the lateral cranial nerves within the lateral wall of the cavernous sinus. III , Oculomotor nerve; IV , trochlear nerve; V1 , ophthalmic division of trigeminal nerve; VI , abducens nerve; cICA , cavernous internal carotid artery; SOF (ellipse) , superior orbital fissure. Dashed line , roof of cavernous sinus (distal dural ring of carotid artery).

FIGURE 13.5, Cranial nerve VI (abducens) runs freely within the cavernous sinus, as demonstrated by the surgical ball-probe. Therefore, it is the most prone to iatrogenic injury in lateral cavernous sinus surgery from an endoscopic endonasal approach. III , Oculomotor nerve; IV , trochlear nerve; V1 , ophthalmic division of trigeminal nerve; V2 , maxillary division of trigeminal nerve; VI , abducens nerve; cICA , cavernous internal carotid artery; pICA , paraclival internal carotid artery; SOF (ellipse) , superior orbital fissure; T , temporal lobe.

Surgical Indications

The surgical indications for an endoscopic endonasal transpterygoid approach to the lateral cavernous sinus must be carefully examined for each patient, due to the potential for iatrogenic morbidity and the relatively benign nature of most diseases in this anatomic compartment. The most common surgical indication is an invasive pituitary macroadenoma that has invaded the lateral cavernous sinus from the medial compartment. Meningiomas of the cavernous sinus may also be treated via EEA. The fibrous nature of some meningiomas and other cavernous sinus pathologies may preclude a gross-total resection, with the goals of surgery being to decompress the cranial nerves and obtain tissue for pathology, and planned stereotactic or fractionated radiation thereafter, to minimize morbidity. Other benign and malignant lesions in this area include schwannomas, chondrosarcomas, chordomas, hemangiomas, metastases, and local spread of sinonasal malignancies such as squamous cell carcinoma. We do not believe there is a role at present for endoscopic endonasal management of vascular lesions within the cavernous sinus, such as ICA aneurysms; these are best left to either endovascular management or traditional open approaches. Benign lesions with significant intradural expansion into the middle or posterior fossa may require a staged approach, with a planned craniotomy 8 to 12 weeks following an initial EEA.

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