Endoscopic Orbital Decompression

Background and Historical Context

I. INDICATIONS

Primary Indication

Specific Operative Indications:

Clinical Signs Suggesting Urgency (CON):

• Dyschromatopsia (color vision loss)
• Relative afferent pupillary defect (RAPD)
• Decreased visual acuity
• These mandate urgent decompression before permanent visual loss ensues

II. PREOPERATIVE EVALUATION

Ophthalmologic Assessment

• Exophthalmometry - quantifies degree of proptosis (also used postoperatively to measure decompression)
• Extraocular movements and diplopia assessment - absence of diplopia preoperatively may invoke a "diplopia-sparing" technique
• Color vision testing (dyschromatopsia)
• RAPD assessment
• Visual acuity

Imaging

• CT orbits and sinuses WITHOUT contrast - evaluates bony orbital walls and sinonasal anatomy; also used for intraoperative image guidance
  • Important: IV contrast is strictly avoided in Graves orbitopathy - reported cases of severe and immediate exacerbation following iodine-rich contrast administration
• MRI - generally not necessary if diagnosis is clear

III. PROCEDURE (SURGICAL TECHNIQUE)

Anesthesia

• Performed under general anesthesia in most cases
• Local anesthesia with sedation is an option for patients with contraindications to GA, or if operating on the only-seeing eye (allows intraoperative monitoring of visual function)

Setup

• Patient in supine position (as for endoscopic sinus surgery)
• Eyes kept in the surgical field to check pupils and EOM motility throughout the case
• Scleral shields placed for corneal protection
• Topical vasoconstrictive agent applied
• Intranasal injections: 1% lidocaine with 1:100,000 epinephrine at axilla of middle turbinate and along the lateral nasal wall
• Stereotactic image navigation (CT-guided): widely used to identify anatomic structures, localize ethmoidal neurovascular bundles, and improve outcomes while decreasing operative times

Step 1: Exposure (Endoscopic Sinus Surgery Phase)

1. Uncinectomy - uncinate process removed
2. Maxillary antrostomy - large antrostomy contiguous with the natural os, extended posterior to the posterior maxillary wall and inferiorly to the superior edge of the inferior turbinate
   • Purpose: access to orbital floor AND prevention of postobstructive maxillary sinusitis from herniation of orbital fat
3. Total ethmoidectomy - exposing the ethmoid roof superiorly and lamina papyracea laterally
   • Thorough posterior ethmoidectomy = maximal decompression
   • Anterior-most and superior-most ethmoid air cells (frontal sinus outflow tract) are preserved to prevent postobstructive frontal sinusitis
4. Wide sphenoidotomy - performed if orbital apex decompression is needed (on the planum sphenoidale superiorly and orbital apex laterally)
5. Middle turbinate: generally preserved unless it precludes adequate decompression; if removed, it facilitates wider exposure
6. Mucosa overlying lamina papyracea is removed; maxillary sinus mucosa is temporarily reflected then redraped at completion to facilitate remucosalization

Step 2: Bony Decompression (Medial Wall - Lamina Papyracea)

1. An elevator or curette fractures the mid-portion of the lamina papyracea in a controlled fashion
2. Posterior bone fragments elevated and removed from underlying periorbita - from sphenoid face posteriorly to the frontal process of the maxilla anteriorly
3. Superiorly, lamina removed to the frontoethmoid suture (except near the frontal sinus outflow tract)
4. Care is taken to avoid premature violation of periorbita (which causes early fat herniation, compromising visualization)
5. The annulus of Zinn is encountered as a thickening of periorbita approximately 2 mm from the sphenoid rostrum - this marks the posterior limit of dissection

Step 3: Bony Decompression (Inferior Wall - Orbital Floor)

1. Visualized using an angled endoscope
2. Inferomedial strut preservation option: A high-speed curved drill with diamond burr thins the bone lateral to the inferomedial orbital strut and medial to the infraorbital nerve; further bone removed using ball-tipped probe + frontal sinus punch/through-cutting instruments
3. Without strut preservation: Periorbita elevated from orbital floor using ball-tipped probe, followed by controlled down-fracture using curette
4. Fracture line extends to the infraorbital canal - the lateral limit of endoscopic inferior wall decompression
5. Infraorbital nerve = lateral limit of inferior wall dissection
6. For compressive optic neuropathy: orbital apex decompression accomplished by removal of the orbital process of the palatine bone using a high-speed drill; if severe CON unresponsive to high-dose steroids, optic nerve decompression is considered

Step 4: Periorbita Opening (Soft Tissue Decompression)

1. A sickle knife penetrates the periorbita posteriorly first then carries the incision anteriorly
   • Posterior-to-anterior direction prevents fat prolapse from blocking visualization
2. Two parallel horizontal incisions can be made on the periorbita
3. Orbital sling technique (diplopia-sparing): a 10-mm strip of periorbita is preserved overlying the medial rectus muscle (coinciding with its upper and lower borders) to act as a sling, preventing prolapse into the ethmoid cavity
   • Not used when vision is threatened (CON) - complete periorbita removal is preferred in those cases
4. Additional sickle knife incisions release fibrous adhesions within orbital fat to facilitate herniation
5. Hemostasis confirmed
6. No nasal packing is placed - to avoid pressure along the orbital apex and optic nerve

Special Diplopia-Sparing Strategies (Summary)

IV. BALANCED ORBITAL DECOMPRESSION

• Lateral wall decompression performed via upper eyelid or lateral canthotomy incision, removing bone between lateral orbital rim and sphenoid trigone
• Medial decompression via endoscopic transnasal approach
• Decompresses equally medially and laterally - less likely to affect globe position
• If orbital fat is resected concurrently, degree of decompression equals three-wall (medial-inferior-lateral) decompression
• Postoperative new-onset diplopia: 0% to 15%
• Requires collaboration between rhinology and ophthalmology

V. OUTCOMES

• Average proptosis reduction with endoscopic medial + inferior wall decompression: 3.2 ± 1.1 mm (range 3.2 to 5.1 mm)
• Adding lateral wall decompression provides an additional 2.4 mm reduction (total 5.6 ± 1.7 mm)
• Balanced decompression (with preserved medial sling): 5.1 ± 1.1 mm reduction
• Strut preservation: mean reduction of 3.60 mm
• Significant improvements in SNOT-22 scores at 1 year - procedure does not negatively impair long-term sinonasal physiologic function

VI. COMPLICATIONS

A. Intraoperative Complications

B. Postoperative Complications

• Most common complication - reported in 30% to 64% depending on technique
• Even with endoscopic approach: 19% to 45% rate
• Mechanisms: direct muscular or neurovascular injury, significant orbital tissue prolapse, disruption of extraocular muscle axes, globe prolapse
• Management: diplopia-sparing techniques (strut, sling, balanced decompression) intraoperatively; corrective eye muscle surgery when permanent
• Surgical intervention for GO is typically reserved for optic nerve involvement or medical treatment failure given this risk

• Uncommon: less than 5% of patients
• Typically originates along the remnant middle turbinate
• Bedside nasal packing is specifically contraindicated - due to exposed orbital contents (packing pressure transmitted to orbit)
• Management: return to OR for endoscopic cauterization; in severe cases, sphenopalatine artery ligation
• Prevention: intraoperative cauterization of remnant middle turbinate edges

• Due to intraorbital dissection nature
• Even though orbit is decompressed, risk of permanent visual loss remains
• Additional decompression via lateral canthotomy with inferior cantholysis may be necessary

• From postoperative edema
• Prevention and management: intraoperative and postoperative corticosteroids with a taper

• Secondary to obstruction from herniated orbital fat into the sinonasal cavity
• Can be postobstructive maxillary sinusitis, frontal sinusitis, or sphenoid sinusitis
• Generally a late complication - may occur even decades after original decompression
• Prevention: prophylactic sinusotomy and judicious mucosal stripping; the anterior-superior orbit should NOT be decompressed (to protect frontal sinus outflow)

• Reported in 3% in large series (Garrity et al.) for transantral approach
• Minimized with endoscopic modification

• Sinusitis: 4%
• Lower eyelid entropion: 9% (infra-orbital nerve paresthesia may contribute)
• Frontal lobe hematoma: 0.2%
• Blindness from optic nerve injury or orbital hemorrhage: rare but reported

VII. POSTOPERATIVE CARE

• Similar to routine endoscopic sinus surgery
• Oral antibiotics
• Twice-daily nasal saline irrigations
• Endoscopic debridement in the office at 1 week postoperatively
• Intraoperative and postoperative corticosteroids with taper (to reduce edema and prevent compressive optic neuropathy)
• No nasal packing is placed

VIII. SEQUENCING OF SURGICAL REHABILITATION IN GRAVES ORBITOPATHY

1. Orbital decompression first (if proptosis is severe)
2. Extraocular muscle surgery - delayed at least 2 to 3 months after decompression (recession of globe is progressive for several months)
3. Eyelid surgery last - delayed at least 1 year after disease stabilization