Endoscopic sinus surgery was first introduced in the 1980s and its potential to improve approaches to the peri-sinonasal structures including the orbit was quickly recognized. The endoscope provided a magnified, highly illuminated view as compared to a headlight or binocular microscope. Kennedy et al 3 was among the first to apply these new endoscopic techniques to peripheral orbital structures in their early description of the endoscopic orbital decompression. These techniques continued to proliferate as more complex pathologies of the sino-orbital interface were tackled such as sinonasal tumors with orbital extension and compressive optic neuropathy. 4 In recent years, endoscopic techniques have begun to breach the sino-orbital boundary by extending into the medial extra and intraconal spaces to access primary orbital neoplasms. Thus, current state-of-the-art methods of endoscopic orbital surgery have subtended an evolutionary arc from open to endoscopic-assisted techniques and finally to purely endoscopic techniques.
A wide range of space occupying lesions can present in the orbit. These occur at a rate of 3 to 5 tumors per year per 1 million people, and there are no clear differences in rate based on race or gender. 5 The most common lesions are vasculogenic, constituting approximately 17% of orbital masses. Among those, cavernous hemangiomas are the most common. Other common benign lesions include optic nerve glioma (4%) and pseudotumor (8%). 5 The most common malignant lesion is non-Hodgkin’s lymphoma (8%), followed by orbital metastases.
14.3 Diagnostic Workup
All patients presenting with an orbital tumor should be evaluated by a multidisciplinary team including an otolaryngologist and ophthalmologist. Neurosurgical consultation is not mandatory but should be considered if an adjunctive craniotomy approach may be required. All patients require a full ophthalmological examination including formal visual field testing. Patients should additionally undergo a high-resolution computed tomography (CT) scan to assess the bony structures as well as a magnetic resonance imaging (MRI) with contrast to assess the character of the lesion. Moreover, the contrast-enhanced MRI will help the surgeon assess whether the ophthalmic artery crosses above or below the optic nerve. Three-dimensional reconstruction can often help delineate the exact relationship between the lesion and the optic nerve; however, this is not mandatory ( ▶ Fig. 14.1). Angiography is not generally required; however, this may help differentiate primary orbital lesions from ophthalmic artery dolichoectasia in select cases.
Fig. 14.1 (a) T2-weighted coronal MRI (magnetic resonance imaging) demonstrating the classic appearance of a large extraconal cavernous hemangioma (CH) in the left orbital apex. (b) Three-dimensional reconstruction of the same patient demonstrating the relationship between the cavernous hemangioma (green), the medial rectus muscle (red), and the optic nerve (blue).
The decision as to whether an endoscopic approach is suitable for a specific tumor depends on the location, morphology, and anticipated histology. An endoscopic approach is suitable for orbital lesions inferior or medial to a plane between the nares and the long axis of the optic nerve. Lesions that extend lateral to the nerve but remain inferior to this plane are still candidates for an endoscopic approach as the tumor may be delivered without requiring nerve retraction.
14.4 Surgical Anatomy
The medial orbit is separated from the sinus contents by the lamina papyracea. The lamina is derived embryologically from the ethmoid bone and extends from the sphenoid bone posteriorly to the lacrimal bone anteriorly. Immediately lateral to the lamina is the periorbita, which surrounds the orbital structures and is penetrated superiorly by the ethmoid neurovascular pedicles. The orbital contents within the periorbita can be separated into extraconal and intraconal compartments. The medial extraconal space consists of the orbital fat and its lateral limit from an endonasal perspective is the medial rectus muscle. This region is relatively devoid of important neurovascular structures other than the ethmoidal neurovasculature, which cross from lateral to medial over the superior border of the medial rectus muscle and the medial ophthalmic vein. 6
The medial intraconal space is bounded by the medial and inferior rectus muscles and contains a complex and rich neurovascular arcade, which makes this region particularly challenging to address ( ▶ Fig. 14.2). The lateral boundary is the optic nerve, ophthalmic artery, nasociliary nerve, and the long ciliary artery and nerve. The superior boundary is the anterior and posterior ethmoid artery and nerve. The oculomotor nerve enters this space and branches almost immediately into superior and inferior rami. A branch of the inferior ramus inserts along the posterior third of the lateral aspect of the medial rectus muscle. Similarly, an inferomedial muscular trunk arborizes from the ophthalmic artery and sends multiple arterioles to supply the medial rectus muscle approximately 1 cm anterior to the sphenoid face. These vascular pedicles divide the medial intraconal compartment into three conceptual compartments of increasing technical difficulty. 6 Zones A and B lie anterior to the inferomedial muscular trunk and are differentiated by an imaginary line dividing the upper and lower halves of the medial rectus muscle belly. Lesions within the more superior zone B are therefore more challenging to address due to their proximity to the ethmoid vasculature and the necessity to work above the medial rectus. Zone C represents the potential space posterior to the takeoff of the inferomedial muscular trunk. This region is the most technically challenging to access due to the small space and proximity to the optic nerve 6( ▶ Fig. 14.3). While the ophthalmic artery usually crosses superior to the optic nerve, it may cross inferiorly in 16 to 33% of cases. 7 This variant brings the artery in even closer proximity to a zone C lesion and thus the course of the ophthalmic artery should generally be identified on preoperative imaging.
Fig. 14.2 Endoscopic approach to the medial intraconal space. (a) Endoscopic view of right orbit following complete opening of the sinuses (E, ethmoid roof; S, sphenoid sinus; M, maxillary sinus), resection of the middle turbinate (MT), and removal of the lamina papyracea to expose the periorbita (P). (b) Same view after removal of the periorbita to expose the medially positioned extraocular muscles (SO, superior oblique; MR, medial rectus; IR, inferior rectus). (c) Endoscopic view of the right medial intraconal neurovascular structures after removal of the intraconal fat and extraocular muscle retraction.
Fig. 14.3 (a) Intraoperative endoscopic view of the left intraconal space demonstrating several branches of the inferomedial muscular trunk of the ophthalmic artery (white arrows) inserting on the medial rectus muscle (MR; S, sphenoid sinus). These branches divide the medial intraconal space into three conceptual zones A, B, and C as illustrated. (b) Same intraoperative view as in (a). Here the oculomotor nerve (white arrow) may be seen coursing along the lateral aspect of the medial rectus muscle.
14.5 Surgical Technique
An endoscopic approach begins with wide exposure of the lamina by opening the adjacent maxillary, ethmoid, and sphenoid sinuses. For mid-orbit and posterior lesions the frontal outflow air cells may be preserved to protect the frontal recess from secondary obstruction. Adequate bony exposure including total removal of the lamina and drilling of the superior pterygoid process and optic canal is critical to enable adequate bimanual dissection. While wide exposure of the periorbita is desired, a hockey stick incision through the periorbita is carefully placed just anterior to the lesion in order to prevent unnecessary prolapse of extraconal fat into the endoscopic visual cavity. With lesions that extend inferolaterally, the orbital process of the palatine bone may be further drilled to allow for more lateral exposure and enhance the ability to dissect inferior to the lesion ( ▶ Fig. 14.4).
Fig. 14.4 (a) Wide bony exposure of the left lamina papyracea (LP) and optic canal (OC) with drilling of the orbital process of the palatine bone to provide improved access to the inferior aspect of the lesion. (b) Following removal of the lamina, a controlled vertical incision is made in the periorbita (PO) just anterior to the mass in order to minimize extraconal fat prolapse.