Orbital decompression has been performed for more than 100 years and is aimed at decompressing the orbital content by partially removing its bony boundaries. It has evolved from a transfrontal orbital roof approach to the classical external transantral approach. The endoscopic orbital decompression (EOD) was first described by Kennedy et al. in the early 1990s as a surgical treatment for thyroid eye disease (TED), and it used the transnasal corridor to decompress the medial and inferior orbital walls. Since then, indications for EOD have expanded and involve not only TED but also procedures for other orbital diseases including neoplastic, traumatic, vascular, inflammatory, and infectious ones.
Decompression of the optic nerve (ON) is indicated for reducing the pressure at its intracanalicular portion and was first performed through an external approach via craniotomy. Only 20 years ago, the endoscopic approach was described. Its indications involve decompression of acute and subacute optic neuropathy, secondary to trauma, TED, neoplastic causes, fibrous dysplasia, and others.
Although complications in orbital surgery can lead to serious consequences, they are uncommon when surgery is performed by experienced surgeons. The chances of complications and their severity rise considerably depending on the complexity of the disease and proposed orbital procedure. For instance, surgery for intraconal orbital tumors, especially those located lateral to the ON, are of greater risk.
Because endoscopic orbital surgery is a relatively new surgical modality, there is a lack of reports and discussion in the literature of surgical complications specifically related to endoscopic orbital surgery. In didactic terms, complications of endoscopic orbital surgery can be categorized according to the time when they occur (intraoperative vs. postoperative; immediate, early, or late), the anatomic structure that is injured (neural, vascular, muscular, or cerebral), or the region where they manifest (orbital, sinonasal, or intracranial). In this chapter, complications are divided into two categories: immediate/early and late. Immediate/early complications are those easily identifiable in the intraoperative or early postoperative period, consisting mainly of vascular, muscular and neural injuries, and cerebral spinal fluid (CSF) leaks. Late complications, for their turn, consist of mainly orbital and sinonasal complications, such as diplopia, enophtalmos, nasal obstruction, and chronic rhinosinusitis.
Vascular injuries occur especially when dealing with intraconal disease. Injury to orbital vessels can lead to catastrophic sequelae, including orbital hematomas and total blindness.
The ophthalmic artery (OA) provides the main blood irrigation to the orbit in most individuals. Fortunately, injury to this vessel is rare owing to its anatomic location, inferolateral to the ON. The ciliary arteries are branches of the OA that form a vascular network surrounding the ON, and their damage may cause important visual impairment. The central retinal artery is one of the first branches of the OA, and injury to this artery causes sudden blindness. Lesions to muscular branches are rare; however, they may occur when working in the posterior orbit. Arterial branches to the medial rectus muscle (MRM) are the most commonly injured.
The anterior and posterior ethmoidal arteries are also at risk of injury during dissection of the ethmoidal cells and the lamina papyracea (LP). The superior limit of bone removal in EOD is traditionally the ethmoidal foramens.
Epistaxis and orbital hematomas can manifest immediately or in the early postoperative period, secondary to inefficient hemostasis or injury to blood vessels, especially during removal of orbital fat ( Fig. 22.1 ). Injuries to minor vessels are usually easily controlled and managed but may cause periorbital hematomas ( Fig. 22.2 ).
Neural injuries are infrequent and usually of a lesser degree of morbidity compared with vascular lesions. An exception to this would be ON injuries. Although uncommon, this complication usually leads to total blindness.
Motor nerves may be iatrogenically damaged during surgery. The most commonly affected nerve are branches of the oculomotor nerve that innervate the MRM and the inferior rectus muscle. Because these nerves enter the muscles medially in the posterior orbit, lesions are rare, but when they occur, they can cause diplopia. The long ciliary nerves are also at risk of trauma during surgery. They are usually medial to the ON and have mostly sensory fibers to the sclera.
Muscular Injuries and Cerebrospinal Fluid Leaks
The most commonly injured muscle in the orbit is the MRM, either by direct surgical trauma or intense manipulation. Although usually temporary, diplopia may manifest for months.
CSF leaks are another possible complication, and endonasal approaches offer the advantage of facilitating their prompt identification and management. These are exceedingly rare and can be accounted for less than 0.7% of all complications.
Chronic rhinosinusitis, mucoceles, and nasal obstruction are some of the most frequent complications encountered after orbital surgery. They can be avoided not only by performing an accurate and meticulous surgery but also by doing frequent postoperative endoscopic evaluations and nasal debridements to prevent synechia and blockage of paranasal sinuses ostia. Hyposmia can also occur as a sinonasal complication secondary to orbital surgery.
Enophtalmos occurs when there is excessive decrease in orbital volume, either by exaggerated removal of orbital fat or as a result of orbital fat herniation.
Diplopia is usually transient and secondary to manipulation of the MRM. Persistent diplopia happens after important damage of extraocular muscles or displacement of the globe.
Finally, subcutaneous emphysema may also occur when the periorbita is incised; therefore patients should be advised to avoid blowing their nose in the first postoperative weeks.
In aiming to prevent complications, it is imperative to correctly select patients or, at least, to understand which patients will benefit more from EOD. In Graves orbitopathy, for example, surgical timing is critical, as EOD should not be performed during the acute orbital inflammation period as the inflammatory process might worsen after surgery. In most cases of TED, it is feasible and advised to stabilize the condition before EOD is considered. Furthermore, it has been suggested that the best results occur for patients with TED caused by orbital fat expansion (type 1) rather than muscular hypertrophy (type 2), which can be assessed through imaging studies. For type 1 patients, EOD with removal of orbital fat has been associated with better outcomes in terms of proptosis reduction.
Preoperative imaging should be thoroughly studied and understood before attempting EOD. Correct knowledge of the anatomy of the anterior and posterior ethmoidal arteries, as they cross the orbit and nasal cavity from lateral to medial, is fundamental to avoid vascular damage and prevent epistaxis or orbital hematoma. Computed tomography scans assist in the identification of such anatomy.
The anatomic location of the MRM and its relationship to other structures are important; injury to this muscle may lead to transient or even permanent diplopia. In a retrospective study analyzing the position of the MRM in relation to the LP, Suh et al. identified that the distance between these two structures is larger anteriorly and permits safer dissection of the orbital content. Posteriorly, the MRM lays only 1 to 2 mm lateral to the periorbita, posing a greater risk of injury.
When proceeding to ON decompression, it is mandatory to know the position of the OA in relation to the ON. In the majority of cases, the OA enters the optic canal inferomedially to the ON and runs laterally toward the orbit, entering it through the optic canal inferolaterally to the ON. Other anatomic variations of the OA should be expected as its localization in the orbit is highly variable. In 8% of patients the OA may enter the orbit through the superior orbital fissure. Therefore preoperative gadolinium-enhanced magnetic resonance imaging is mandatory before operating on the ON, superior orbital fissure, or orbital apex.
Similarly, imaging studies are fundamental in identifying highly vascularized orbital malformations, such as ophthalmic artery aneurysms and arteriovenous malformations. These constitute a contraindication to orbital and optic canal decompression and must be identified before surgery. Injury to these vascular malformations might lead to serious complications.
Intraoperative image guidance can improve identification and avoid injury of key structures. It has been shown to improve intraoperative time and enhance outcomes, as well as avoiding unexpected hemorrhages. However, surgeons should use image guidance systems only to confirm their prior anatomic knowledge and to increase surgical safety.
Before initiating endoscopic orbital surgery, it is important to have adequate instrumentation in the operation room. An endonasal kit should be sufficient for orbital decompression. For more delicate dissection, especially involving the ON or intraconal tumors, a skull base surgery kit might be necessary.
For hemostasis, a bipolar cautery must be readily available for careful cauterization and as a way to shrink extraconal fat to improve visualization when necessary. It should not be used intraconally, as there is risk of damage to critical neurovascular structures. Additionally, neuropathies soaked in saline solution are useful for hemostasis and can be helpful in removing blood from the surgical field as well as assisting in retraction of orbital fat. Irrigation with warm saline solution may also be used for hemostasis.
With the LP exposed, a Freer elevator is used to enter it anteriorly to avoid trauma to the MRM, and blunt dissection is carried out to separate the LP from the periorbita. The LP adjacent to the frontal recess is left intact, and manipulation of the frontal recess is usually avoided to prevent disruption of the frontal sinus drainage pathway. The periorbita is then incised in a posterior to anterior fashion to avoid the prolapse of orbital fat into the surgical field. This maneuver might be assisted by navigation systems to prevent MRM injury.
Drilling of the optic canal should be done carefully and with constant and abundant irrigation to avoid thermal injury to the ON and OA. Opening of the ON sheath may expose the patient to a CSF leak and OA injury and should be reserved for very specific indications. If there are any Onodi cells that must be dissected, this should be done with caution as the ON might be dehiscent. Having navigation available is helpful, especially in sphenoid sinuses that are not well pneumatized.
When sinus dissection is carefully performed, sinonasal complications are rare. In a retrospective review, Antisdel et al. reviewed 86 orbital decompressions, with an incidence of complications of only 3.5%; complications were one case of hemorrhage that required intervention, three cases that demanded revision surgery owing to obstructive sinusitis, and one case of nasal obstruction secondary to adhesions. No patients had CSF leakage or orbital hemorrhage and all patients who underwent revision surgery had good outcomes. The authors attribute these results to creating a maximal antrostomy, preserving an intact rim of 2 mm of the LP superiorly, and prophylactically cauterizing the middle turbinate stump after resection.
Special consideration has been made to reduce the risk of postoperative diplopia. Dissection of the medial and inferior orbital walls with preservation of the inferomedial orbital strut, which is the junction of the medial and inferior orbital walls that extend from the maxillary line anteriorly to the palatine bone posteriorly, has been shown to prevent diplopia. This technique seems to avoid inferomedial displacement of the globe, lowering the risk of diplopia after surgery. Preservation of the periorbital sling, a strip of periorbita covering the MRM, also seems to prevent diplopia. Borboridis et al., in a systematic review that evaluated EOD for TED, demonstrated that a balanced orbital wall decompression (medial and lateral walls) has been related to better surgical results with fewer complications.
Endoscopic orbital surgery has evolved greatly over the years. The turning point for these procedures was the evolution of endoscopic approaches. Since then sinonasal surgery has become less morbid and more efficient. Endoscopic orbital surgery is a feasible and increasingly performed procedure, with a low incidence of complications when carried out by a team of experienced surgeons.