Introduction

The surgical management of orbital lesions is technically demanding regardless of the approach used. Traditional external approaches have been used in the past to address medially located lesions, usually by means of extensive surgical work. Endoscopic transnasal approaches have been recently introduced for the management of such located lesions. The direct approach, short trajectory, and an enhanced visualization allowed by the endoscope represent the critical aspect of such techniques.

14.1 Indications

Endoscopic endonasal technique allows one to approach adequately the medial and inferomedial wall of the orbit ( Figs. 14.1 and 14.2 ).

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  Orbital and optic canal decompression.

  
  
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  Medial and inferomedial wall fractures repair.

  
  
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  Lesions of the medial extraconal spaces, mainly inferomedially located.

  
  
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  Extraconal medially located orbital apex lesions.

  
  
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  Selected lesions of the medial intraconal space, mainly inferomedially located (for radical removal or diagnostic purpose).

  
  
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  In combination with superior and inferior eyelid approach, it can be used to manage more complex lesions (multiportal surgery).

14.2 Surgical Steps

Probably, the coronal views of the preoperative computed tomography (CT) and/or magnetic resonance imaging (MRI) scans are the most important perspective to look for when dealing with intraorbital lesions. An anterior-to-posterior visualization allows identifying anatomic details, reducing the risk of disorientation ( Fig. 14.3 ). Furthermore, the position of the lesion with respect to the vertical line of the optic nerve (ON) is another critical element to be evaluated. In all intraorbital procedures, neuronavigation is advisable.

To expose the ethmoidal box, which will be finally completely removed, the middle turbinate has to be resected ( Fig. 14.4 ). Natural ostium of the maxillary sinus is exposed after a partial uncinectomy.

A standard sphenoethmoidectomy ( Fig. 14.5 ) and a medial maxillectomy are performed to expose the medial orbital wall (mainly given by the lamina papyracea). The choice to spare or not the nasolacrimal duct depends on the position of the lesion and the use of an anterior septal window. Usually, ethmoidal foramina can be seen at the level of the frontoethmoidal suture. The anterior ethmoidal artery (AEA) passes through the ethmoidal complex at the level of the roof or even 5 mm below this level to enter the anterior cranial fossa. The artery runs in a membrane mesentery (rare) or a thin bony lamella. The AEA presents nasal branches and an anterior meningeal branch. The posterior ethmoidal artery (PEA) usually runs within the skull base/ethmoidal roof. Usually two in numbers, sometimes ethmoidal arteries can be three or even more (in up to 45%, ethmoidal arteries may be multiple). In a variable percentage of cases, PEA is absent, even bilaterally (for more details, please check Chapter 7).

Once the lamina papyracea is removed, the medial and inferomedial aspects of the periorbita remain exposed ( Fig. 14.6 ). Usually, the shape of the medial rectus muscle (MRM) shape is evident in the posterior aspect of the orbit where there is less extraconal fat.

After removal of the periorbita, the extraconal fat is exposed ( Fig. 14.7 ). Posteriorly, the extraconal fat is less evident, so, sometimes, 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.

The removal of the extraconal fat exposes the “medial muscular wall” ( Fig. 14.8 ). It is given mainly by the medial and inferior rectus muscles and, to a lesser extent, by the superior oblique muscle. Between the medial and inferior rectus muscle, it is possible to identify intraconal fat and the access to intraconal space. The AEA passes between the MRM and the superior oblique muscle, while the PEA usually passes above the superior oblique muscle.

Based on the anatomic relationship between the sinonasal complex and the orbit, endoscopic transnasal procedures are thought to offer a good approach to the medial and inferomedial orbital spaces ( Fig. 14.9 ). To manage the medial (mostly inferomedial) intraconal spaces, the best corridor is located between the medial and inferior rectus muscles. Sometimes, to increase the size of this window, the medial aspect of the orbital floor can be removed, paying attention to the infraorbital nerve. This allows an increase mobility of the structures ( Fig. 14.9 ).

In the superior aspect, above the MRM, within the intraconal space the most distal part of the ophthalmic artery (OA) can be seen, with its terminal branches (usually the AEA and dorsal nasal arteries) ( Fig. 14.10 ). In close proximity to the OA, the nasociliary nerve (NCN) runs branching off the anterior ethmoidal nerve and the infratrochlear nerve. The origin of the anterior and posterior ethmoidal nerves from the NCN can be identified transnasally. At the level of the trochlea, the NCN becomes the infratrochlear nerve. Close to the NCN and the OA, in the anterior part of the orbit, the superior ophthalmic vein (SOV) runs usually lateral to them and on the medial side of the superior rectus muscle.

Usually, a connecting vein is seen in the anterior part of the operative window. Within the orbit, a complex reticular system of fibrous septa divides the fat into distinct lobules. These septa are well evident in the anterior orbit and bridges together with the extraocular muscles, thus “creating” an intraconal and extraconal space. Posteriorly, this division is less evident. The lateral limit of dissection is given by the ON ( Fig. 14.11 ). In the upper part, above an axial plane passing through the ON, the OA, the NCN, and the SOV can be seen. SOV is usually close to the OA ( Fig. 14.11 ). SOV is the largest and most important vein of the orbit. In the retrobulbar fat, the SOV is embedded in and supported by a highly organized connective tissue. It usually originates from the fusion between the continuation of the supraorbital vein and the angular vein. On the medial aspect of the MRM, it is possible to identify the branch of the oculomotor nerve and the muscular arterial branches usually coming from the OA. As a general rule, the muscular branches are nearly all situated in the intraconal side of the muscles, principally at their posterior part.

Once the medial intraconal fat is removed, the intraorbital portion of the ON, with its tortuous course, becomes evident ( Fig. 14.12 ). Anteriorly, the ON is closely associated with a vascular network, mainly given by the ciliary arteries (branches of the OA). Close to these vessels, long ciliary nerves are usually well identifiable (they are branches of the NCNs that arose in the posterior part of the nerve). In the posterior aspect of the orbit, posterior ciliary arteries (PCAs) can be seen. They arose independently from the proximal part of the OA: the superior PCA is always located superior to the ON. The PCAs run forward and divide into numerous small, short ciliary arteries that are usually highly convoluted especially near the globe. The medial PCA and the central retinal artery (CRA) are usually the first branches of the OA. From an endoscopic transnasal perspective, it is usually possible to identify the CRA, which usually enters the ON from its inferior surface. Sometimes, it can also reach the nerve from its medial aspect. It should be noted that CRA is one of the smallest branches of the OA and its position is unpredictable preoperatively ( Fig. 14.12 ).

In the orbital apex region, by splitting the annulus of Zinn between the medial and inferior rectus muscles, the inferior division of the oculomotor nerve with its braches becomes evident. Between them, the proximal part of the orbital OA can be seen ( Fig. 14.13 ).