Based on the anatomic relationship between sinonasal complex and orbit, endoscopic transnasal procedures could be a smart solution for approaching the medial orbital region. These techniques should be considered a valid option for optic nerve or orbital wall decompression in cases of Graves ophthalmopathy and post-traumatic optic neuropathy as well as for addressing extraconal or intraconal lesions placed medially to the optic nerve course. This article describes the anatomic principles, indications, technical nuances, and limitations of the endoscopic endonasal approaches for the management of selected orbital pathologic abnormalities.
Key points
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Endoscopic endonasal techniques are able to reach the medial orbital structures as well as the orbital apex region without skin incision and brain retraction.
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The endoscopic endonasal management of orbital pathologic conditions may include the complete removal of the lesion or only a tissue sampling for diagnostic purposes.
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The lateral limit of the transnasal approach is represented by the course of the optic nerve that must not be crossed.
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Endonasal approaches can be used in combination with superior/inferior eyelid approaches to manage complex lesions involving the orbit, the superior/inferior orbital fissure, and the anterior/middle skull base (multiportal surgery).
Introduction
External approaches to the orbit are well established, including transconjunctival, transcranial, or lateral orbitotomies, depending on the localization of the lesion. Among these, orbitozygomatic craniotomy is generally used for lesions that extend intracranially and into the orbit and is used for exposure of the optic nerve and canal.
The transnasal endoscopic route, initially developed for treating inflammatory sinuses disease, has emerged in the last decades as a minimally invasive corridor to approach adjacent anatomic areas such as ventral skull base, orbit, and orbital apex regions. What is paramount for the application of endoscopic transnasal approaches to the orbit is the close anatomic relationship between the paranasal sinuses and the orbital content, summarized in the concept of sino-orbito-cranial interface. In this respect, endoscopic visualization from the transnasal route has provided surgeons the possibility of reaching the medial orbital structures as well as the orbital apex region without skin incision, major bony work, or brain retraction.
Given these facts, endoscopic endonasal orbital and optic nerve decompressions have become accepted treatments for thyroid eye disease and traumatic optic neuropathy that is unresponsive to steroids. The endoscopic endonasal technique is widely used as well for ophthalmologic procedures such as drainage of subperiosteal abscesses and dacryocystorhinostomy. Recently, some studies concerning the endoscopic endonasal biopsy, debulking, or even radical resection of tumors involving the orbit also have been reported, expanding the indications for such endonasal approaches. Herein are described the anatomic principles, indications, technical nuances, and limitations of the endoscopic endonasal approaches for the management of selected orbital pathologic conditions.
Introduction
External approaches to the orbit are well established, including transconjunctival, transcranial, or lateral orbitotomies, depending on the localization of the lesion. Among these, orbitozygomatic craniotomy is generally used for lesions that extend intracranially and into the orbit and is used for exposure of the optic nerve and canal.
The transnasal endoscopic route, initially developed for treating inflammatory sinuses disease, has emerged in the last decades as a minimally invasive corridor to approach adjacent anatomic areas such as ventral skull base, orbit, and orbital apex regions. What is paramount for the application of endoscopic transnasal approaches to the orbit is the close anatomic relationship between the paranasal sinuses and the orbital content, summarized in the concept of sino-orbito-cranial interface. In this respect, endoscopic visualization from the transnasal route has provided surgeons the possibility of reaching the medial orbital structures as well as the orbital apex region without skin incision, major bony work, or brain retraction.
Given these facts, endoscopic endonasal orbital and optic nerve decompressions have become accepted treatments for thyroid eye disease and traumatic optic neuropathy that is unresponsive to steroids. The endoscopic endonasal technique is widely used as well for ophthalmologic procedures such as drainage of subperiosteal abscesses and dacryocystorhinostomy. Recently, some studies concerning the endoscopic endonasal biopsy, debulking, or even radical resection of tumors involving the orbit also have been reported, expanding the indications for such endonasal approaches. Herein are described the anatomic principles, indications, technical nuances, and limitations of the endoscopic endonasal approaches for the management of selected orbital pathologic conditions.
Indications and contraindications
Endoscopic endonasal technique allows reaching adequately the medial compartments ( Fig. 1 ). The lateral limit of the transnasal approach is represented by the course of the optic nerve that must not be crossed. Thus, tumors that are localized to the superior and lateral compartments of the orbit are contraindicated for a pure endoscopic endonasal approach. When dealing with orbital lesions, the intents of surgery can be not only the radical removal but also the partial removal (to decompress the orbit), the drainage of the mass (in the case of cyst, abscess, or hematoma), or the tissue sampling for diagnostic purposes. The current indications and contraindications for this minimally invasive approach are detailed in Table 1 .
| Indications | Contraindications |
|---|---|
| Orbital and optic canal decompression (Graves disease, posttraumatic optic neuropathy) | Orbital high-flow vascular malformations (OA aneurysms, arteriovenous malformations) |
| Medial orbital wall fractures repair | Lateral and superolateral orbital wall fractures repair |
| Sinonasal benign tumors invading the orbit (medial compartment). In these cases, the surgical corridor to pass through is represented by the tumor itself. | Sinonasal malignancies extending to the orbit (relative contraindication) |
| Lesions of the medial extraconal orbital spaces (mainly inferomedially located) | Lateral and superolateral extraconal and intraconal lesions |
| Extraconal medially located orbital apex lesions | Intraconal orbital apex lesions (posteriorly, the annulus of Zinn is difficult to open) |
| Selected lesions of the medial intraconal space (mainly inferomedially located) |
Surgical technique
Preoperative Planning
Nasal endoscopy is useful to explore the sinonasal spaces in close relation with the orbit that will be approached transnasally. Ophthalmologic evaluation (including visual acuity, pupillary reactions, visual fields, ocular motility, and color discrimination) and cranial nerves function examination are important as well to assess the preoperative conditions.
Radiological studies with computed tomographic (CT) scan and contrast-enhanced MRI are mandatory for the evaluation of the sino-orbito-cranial interface. Probably the coronal views are the most important perspective to analyze when dealing with intraorbital lesions. Radiological examinations allow the precise evaluation of the site, size, and extent of the lesions and in some cases can provide preoperative diagnosis. Imaging scans give information on anatomic details (Onodi cell pneumatization, anterior and posterior ethmoidal arteries position, supraorbital cell pneumatization, position of the lesion in respect to extraocular muscles, and optic nerve course) that can influence the surgical procedure. Based on patients’ features, evolution of the disease, and its radiological appearance, surgery has to be planned with diagnostic or curative intent.
Preparation and Patient Positioning
The transnasal approaches to the orbital spaces require adequate instrumentation for a correct procedure. The surgical set should include several dissectors of different sizes, and delicate scissors of different angles (like for cranial base surgery). Delicate bipolar forceps with straight and angled tips can be very useful. Moreover, in all intraorbital procedures, an intraoperative navigation system is strongly advisable.
Patients are placed in the anti-Trendelenburg position and under general anesthesia. A perioperative prophylactic antibiotic regimen is followed, including third-generation cephalosporin. Some minutes before surgery, the nasal cavities are packed with cottonoids soaked in 2% oxymetazoline, 1% oxybuprocaine, and adrenaline (1/100.000) solution to reduce bleeding and improve transnasal operative spaces.
Step-by-Step Surgical Procedure
Different pathologic conditions affecting the orbit and optic nerve can be treated transnasally, requiring a different combination of the following surgical steps, as described.
Transnasal corridor setup and lamina papyracea exposure
To gain adequate operative space, the middle turbinate has to be partially or completely resected, paying attention to preserve the olfactory mucosa. Natural ostium of the maxillary sinus is opened after a partial uncinectomy, to expose the inferomedial angle of the orbit. A standard spheno-ethmoidectomy and a large medial antrostomy are performed to expose the medial orbital wall (mainly given by the lamina papyracea). The choice to use an anterior septal window depends on the position of the orbital lesion. Once the lamina papyracea is exposed, the sphenoidotomy is enlarged laterally to expose the bony bulging of optic nerve and internal carotid artery. When present, Onodi cell represents a key marker for the optic canal and must be opened with caution.
Optic canal opening (if needed)
The optic canal is opened by a gentle drilling out, under continuous irrigation, from proximal (orbital apex) to distal, obtaining a bony pellicle that is finally removed with a spatula. The orbital apex identification is crucial for starting the procedure to localize the optic nerve course even in the case of low pneumatized (conchal) sphenoid sinus. When a clockwise 180° of freedom of the optic nerve is obtained, the nerve becomes pulsatile. Finally, the dural layer covering the nerve is incised superomedially to reduce the risk of damaging the ophthalmic artery (OA) situated inferomedially.
Lamina papyracea removal and periorbit exposure
Lamina papyracea is gently drilled out and finally removed with a spatula. Entry through the lamina papyracea should occur below the level of the ethmoidal foramina to avoid damage to the ethmoid arteries and to reduce the risk of retrobulbar hemorrhage and vision loss. Once the lamina papyracea is removed, the medial aspect of the periorbit is exposed. Generally, the superomedial angle of the orbit is preserved to keep the patency of the frontal recess ( Fig. 2 ).
Extraconal fat exposure
After removal of the periorbit, the extraconal fat is exposed. Posteriorly, the extraconal fat is less evident; therefore, sometimes, medial rectus muscle (MRM) can be found immediately below the periorbit. At the level of the orbital apex, the annulus of Zinn is rapidly exposed below the periorbit and not infrequently an extraconal venous channel is evident connecting the orbital system with the cavernous sinus.
Extraconal fat removal and medial muscular wall exposure
By removing the extraconal fat, the “medial muscular wall” comes into view. It is given mainly by the MRM and inferior rectus muscles (IRMs) and, to a lesser part, by the superior oblique muscle (SOM). Between the medial and IRM, it is possible to identify intraconal fat ( Fig. 3 ). The anterior ethmoidal artery (AEA) passes between the MRM and the SOM, while the posterior ethmoidal artery usually passes above the SOM.
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