Radiographic Analysis of Extraocular Muscle Volumetric Changes in Thyroid-Related Orbitopathy Following Orbital Decompression

Impact of sphenoid trigone size and extraocular muscle thickness on the outcome of lateral wall orbital decompression for thyroid eye disease

BACKGROUND

To retrospectively review lateral wall orbital decompression for thyroid eye disease (TED) and to evaluate pre-operative CT scans to analyse the variation in proptosis reduction.

METHODS

Consecutive lateral wall orbital decompressions performed by a single surgeon were retrospectively reviewed. Pre-operative CT scan features and post-operative proptosis reduction were analysed. The sphenoid trigone cross-sectional areas were summed and multiplied by the slice thickness to yield bone volume. Cumulative extraocular muscle thickness was calculated by combining the maximum thickness of the four recti. "Trigone volume" and "cumulative muscle thickness" were correlated with proptosis reduction at 3 months post-surgery.

RESULTS

Out of 73 consecutive lateral wall orbital decompressions, 17 orbits had prior endonasal medial wall orbital decompression. In the remaining 56 orbits, the mean pre-operative and post-operative proptosis were 24.3 ± 1.6 mm and 20.9 ± 2.3 mm respectively. The proptosis reduction ranged from 1 to 7 mm (mean of 3.5 mm ± 1.3 (p < 0.001)). Mean sphenoid trigone volume was 895 ± 434.4 mm3. The mean cumulative muscle thickness was 20.4 ± 5 mm. The correlation coefficient between muscle thickness and proptosis reduction was - 0.3 and was statistically significant (p = 0.043). The correlation coefficient between sphenoidal trigone volume and proptosis reduction was 0.2 (p = 0.068). With a multivariate analysis, the coefficient of efficient of regression for muscle thickness was - 0.007 (p = 0.42) and the coefficient of regression for trigone volume was 0.0 (p = 0.046).

CONCLUSION

Proptosis reduction following lateral wall orbital decompression can be variable. Extraocular muscle thickness had a significant correlation with the outcome, with greater proptosis reduction in orbits with thin muscles. The sphenoidal trigone size had a weak correlation with decompression outcome.

Comparison of surgical effect in active and inactive Dysthyroid Optic Neuropathy after Endoscopic Transnasal Medial Orbital Decompression

PURPOSE

To evaluate and compare the changes in orbital soft tissue volume and visual function after endoscopic transnasal medial orbital decompression in patients with active and inactive dysthyroid optic neuropathy (DON).

METHODS

This prospective, cohort study recruited 112 patients (112 eyes) with DON who were divided into an active and inactive DON group (56 eyes each) by clinical activity scores. All patients underwent endoscopic transnasal medial orbital decompression. The pre- and post-operative orbital soft tissue volumes were measured with high-resolution computed tomography (CT) using Mimics software. Visual function, including best-corrected visual acuity (BCVA), visual field (VF), and visual evoked potential (VEP), was recorded before and after surgery.

RESULTS

Preoperatively, compared with the inactive DON group, the active DON group had greater extraocular muscle volume (EMV) and EMV/orbital volume (OV) ratio, but worse BCVA, VF, and exophthalmos. Postoperatively, although the EMV slightly increased, with the enlarged medial rectus muscle contributing dramatically, the EMV/OV ratio decreased in patients with DON. Besides, visual function including BCVA, VF, VEP and exophthalmos was also improved in both groups after surgery. There were no significant differences in postoperative OV; EMV; EMV/OV ratio; and the BCVA, VF, and VEP parameters between both groups (all P > 0.05).

CONCLUSION

Patients with DON who did not respond well to steroids, regardless of disease activity, may benefit from orbital decompression via the decrease in the proportion of EMV in OV, especially patients with active DON, who showed more improved visual function than patients with inactive DON.

Combined endonasal and orbital approach for annulus of Zinn area decompression in dysthyroid optic neuropathy

BACKGROUND

Dysthyroid optic neuropathy (DON) is a serious complication of thyroid-associated ophthalmopathy (TAO) that can cause permanent vision loss from orbital apex syndrome. Urgent management of high-dose corticosteroid pulse therapy is recommended, and salvage orbital apex decompression surgery may require in refractory patients ineffective with corticosteroid pulse therapy.

PURPOSE

To evaluate the short-term efficacy and safety of combined endoscopic endonasal and orbital approach decompression in the annulus of the Zinn (AZ) area in refractory dysthyroid optic neuropathy (DON).

METHODS

In this retrospective study, patients who underwent combined endoscopic endonasal and orbital approach decompression around the AZ area for the treatment of refractory DON from May 2021 to March 2022 were enrolled. A total of 15 orbital apex were decompressed across 9 patients. The demographic, imaging, and surgical data, as well as preoperative and postoperative best corrected visual acuity (BCVA), proptosis degree and Modified-Chinese-TAO-QOL scores, were collected and assessed. The t-test was used to identify differences between preoperative and postoperative parameters: visual acuity, proptosis and QOL scores.

RESULTS

The mean best corrected visual acuity (BCVA) improved from 0.79 ± 0.77 LogMAR preoperatively to 0.21 ± 0.27 LogMAR (P < 0.001) postoperatively. Additionally, proptosis decreased from 22.25 ± 2.01 mm to 18.42 ± 1.85 mm (P < 0.01), with an average decrease of 3.7 mm. The preoperative scores of the visual, psychological, and comprehensive components of QoL were 14.60 ± 9.08, 37.49 ± 6.26 and 26.75 ± 3.70, respectively, which significantly improved postoperatively to 54.18 ± 7.23, 68.78 ± 12.53 and 61.88 ± 9.37, respectively. The postoperative follow-up time ranged from 2 to 11 months, and the median follow-up time was 7 months. There was 1 case of transient postoperative sinusitis and 1 new case of transient diplopia, which was relieved after 3 months.

CONCLUSION

Combined endoscopic endonasal and orbital approach adequate decompression for AZ area significantly improves visual acuity and QOL in patients with DON.

Identification of optimal surgical plan for treatment of extraocular muscle damage in thyroid eye disease patients based on computational biomechanics

This study replicated the behavior of intraorbital tissue in patients with thyroid eye disease (TED) based on finite element analysis for general orbital decompression risk evaluation in thyroid eye disease patients. The orbit and intraorbital tissues of thyroid eye disease patients who underwent orbital decompression were modeled as finite element models. The stress was examined at specific locations of the removed orbital wall of a thyroid eye disease patient with undergone orbital decompression, and its variation was analyzed as a function of the shape and dimension (to be removed). As a result, in orbital decompression surgery which removes the orbital wall in a rectangular shape, the stress at the orbital wall decreased as the width and depth of the removed orbital wall increased. In addition, in the case of orbital decompression, it can be seen that the chamfered model compared to the non-chamfered model (a form of general orbital decompression) have the stress reduction rate from 11.08% to 97.88%. It is inferred that if orbital decompression surgery considering the chamfered model is performed on an actual thyroid eye disease patient, it is expected that the damage to the extraocular muscle caused by the removed orbital wall will be reduced.

Chromatic visual evoked potentials identify optic nerve dysfunction in patients with Graves' orbitopathy

PURPOSE

To explore visual dysfunction in Graves' orbitopathy (GO) objectively by analyzing chromatic visual evoked potentials (cVEP) and evaluate its diagnostic efficiency for dysthyroid optic neuropathy (DON).

METHODS

In this cross-sectional study, we analyzed pattern-reversal VEP (pVEP), red-green (R-G) and blue-yellow (B-Y) cVEP in 93 subjects (21 with DON, Group A, 30 with GO, Group B, and 42 healthy controls, Group C) at Wuhan Union Hospital, China.

RESULTS

Compared with Group C, the amplitudes of B-Y cVEP were significantly lower in Group B, whereas all amplitudes of cVEP, latencies and amplitudes of pVEP in Group A were significantly impaired. In addition, the pVEP latency at 60 arcmin (60'), pVEP amplitudes and R-G cVEP amplitudes were significantly different between Group A and B. Moreover, 60'cVEP R-G negative-positive (N-P) amplitude was correlated with crowding index (P = 0.001), the average thickness of ganglion cell layer and inner plexiform layer (P = 0.004). Furthermore, combination of 60'cVEP R-G amplitude and 60'pVEP P100 latency had better diagnostic efficiency than each single parameter, with optimal cut-off values of 14.20 μV and 110.65 ms, respectively.

CONCLUSION

GO may induce electrophysiological changes. The presence of B-Y cVEP anomalies in moderate to severe GO patients may be an early sign of preclinical DON. A decline in 60'cVEP R-G amplitude is associated with apical crowding and thinner inner intra-retinal layers. The combination of 60'cVEP R-G N-P amplitude and 60'pVEP latency can be a useful diagnostic index for DON.

Lateral Wall Implant as an Adjunct to Lateral Wall Orbital Decompression in Severe Thyroid Eye Disease

PURPOSE

To describe the use of a lateral wall implant as an adjunct in lateral orbital wall decompression in severe thyroid eye disease.

METHODS

This study is a retrospective review of 6 patients who underwent prior orbital decompression but had persistent proptosis. These patients underwent lateral wall decompression with adjunct lateral wall implant placement with a manually vaulted 0.6-mm polyethylene-coated titanium mesh implant. Data collection included: visual acuity, intraocular pressure, exophthalmometry, ocular motility, eyelid position, and complication rates.

RESULTS

Eight orbits in 6 patients underwent maximal lateral wall decompression and reconstruction using the polyethylene-coated titanium implant. Four males and 2 females were included with ages ranging from 25 to 73 years. Visual acuity improved an average of 2.4 lines (range 0-5 lines). Intraocular pressure improved an average of 7.5 mm Hg (2-13 mm Hg). There was reduction of proptosis by 3.4 mm on average (1-7 mm). Upper eyelid retraction improved on average by 1.8 mm (0-5 mm). Horizontal eye movements improved by 11% on average (-3.1% to +25%). Excellent cosmesis was achieved with no visible temple deformity, trismus, conjunctival scarring, orbital hemorrhage, or vision loss.

CONCLUSIONS

The amount of volume created in lateral wall decompression is limited by the amount of native bone present and the temporalis muscle. In severe or recalcitrant cases, the authors propose the placement of a lateral wall implant as an adjunct to laterally displace the temporalis muscle and create additional volume. This technique accomplishes further reduction of proptosis in patients who have undergone prior orbital decompression.

Extraocular muscle expansion after deep lateral orbital wall decompression: influence on proptosis reduction and its predictive factors

PURPOSE

To examine the relationship between extraocular muscle expansion and proptosis reduction (Δproptosis) in patients with thyroid eye disease who underwent deep lateral orbital wall decompression and to analyze the factors that contribute to extraocular muscle expansion.

METHODS

This retrospective, observational study included 133 sides from 77 patients with thyroid eye disease. The cross-sectional areas of the greater wing of the sphenoid bone (trigone), extraocular muscles, and superior ophthalmic vein were measured on computed tomographic images. Variables influencing Δproptosis were analyzed using multivariate linear regression analyses with stepwise variable selection. Predictive factors for the rate of postoperative increase in the cross-sectional extraocular muscle areas (Δextraocular muscle) were analyzed using the same statistical method.

RESULTS

The amount of orbital fat removed (P < 0.001) and rate of Δlateral rectus muscle (P < 0.001) were positively and negatively correlated with Δproptosis, respectively (r = 0.425; adjusted r² = 0.168; P < 0.001). The cross-sectional trigone area (P < 0.001) was positively correlated with the rate of Δlateral rectus muscle, whereas the preoperative cross-sectional lateral rectus muscle area (P < 0.001) and amount of orbital fat removed (P = 0.036) were negatively correlated with the rate of Δlateral rectus muscle (r = 0.551; adjusted r² = 0.288; P < 0.001).

CONCLUSION

Lateral rectus muscle expansion was negatively correlated with proptosis reduction and proved to be predictable before surgery. The results of this study will help predict proptosis reduction after deep lateral orbital wall decompression and to preoperatively plan additional orbital bony and fat decompression.

Orbital Decompression for Thyroid-Related Orbitopathy During the Quiescent Phase

PURPOSE

To describe historical and modern surgical approaches to orbital decompression in patients with thyroid-related orbitopathy in the quiescent phase.

METHODS

A literature review of published techniques using the National Institutes of Health PubMed database.

RESULTS

Historically, orbital decompression has been accomplished via transantral, transcranial, transnasal, and orbital approaches. Current techniques use predominately periocular incisions to achieve effective decompression and proptosis reduction. Based on exophthalmometry and desired proptosis reduction, the authors propose a graded surgical approach to decompression for thyroid orbitopathy beginning with fat reduction, followed by deep lateral orbit via a superior eyelid crease incision, then medial wall by retro-caruncular approach, then posterior medial orbital floor either via transconjunctival or swinging eyelid approach, and finally with lateral orbital rim removal by superior eyelid crease incision as needed. These approaches can result in a range of proptosis reduction of up to 10 mm.

CONCLUSIONS

A structured approach to orbital decompression results in predictable and effective outcomes in proptosis reduction.

Abducens nerve palsy after orbital decompression

INTRODUCTION

Double vision after decompression surgery for Thyroid Eye Disease (TED) is well described in the literature and the incidence ranges from 0 to 64%. The Mechanisms for new onset diplopia after orbital decompression are poorly understood. Common theories include: Fibrosis of muscles, displacement of the muscle cone, and reactivation of the TED.

AIM

We present two cases with Abducens nerve palsy after uncomplicated secondary orbital decompression surgery.

RESULTS

Two patients with inactive TED, who were followed for an average of 2 years prior to uneventful secondary decompression surgery, presented at the first postoperative visit with double vision and limitation of abduction in the recently operated eye. Magnetic resonance imaging(MRI) was done in both cases and revealed no abnormal bleeding or scaring.

DISCUSSION

Our two cases of Abducens palsy following reoperative orbital decompression may be due to ischemic neuropathy caused by postoperative hemorrhage or inflammation.

Double Vision After Minimally Invasive Orbital Decompression

INTRODUCTION

New onset Diplopia following orbital decompression in thyroid eye disease patients is estimated to occur in up to 30% to 40% of decompression patients, mostly related to deep lateral and medial wall decompressions.

METHODS

A retrospective chart review of all minimally invasive (fat and minimal bone orbital decompression performed at the UCLA Stein Eye Institute between 2005 and 2015. Inclusion criteria were thyroid eye disease patients older than 18 years undergoing fat only orbital decompression with no previous muscle surgery.

RESULTS

The chart review revealed only 5 patients with new onset diplopia after this surgery. The cases are discussed and a possible mechanism for the diplopia is proposed.

DISCUSSION

Double vision following minimally invasive orbital decompression is rare and the mechanisms are poorly understood.

The Effect of Systemic Steroids and Orbital Radiation for Active Graves Orbitopathy on Postdecompression Extraocular Muscle Volume

PURPOSE

To evaluate the effect of orbital radiation prior to surgery on the clinical course and extraocular muscle (EOM) radiologic volume changes after decompression in Graves orbitopathy (GO).

DESIGN

Retrospective, interventional case series.

METHODS

The medical records of patients treated with orbital decompression for GO and who underwent postoperative orbital computed tomography were reviewed. Only patients who underwent rehabilitative decompression in the inactive phase and who received systemic corticosteroids alone (ST group) or combined orbital radiation and systemic corticosteroids (SRT group) in the active inflammatory phase of the disease were selected. The main outcome measure was the comparison of preoperative and postoperative EOM volumes. Secondary outcome measures were changes in proptosis and diplopia after decompression.

RESULTS

Thirty-seven of 114 patients were selected for this study. There were no differences between the ST group (n = 22, 42 eyes) and SRT group (n = 15, 30 eyes) in terms of demographics or predecompression characteristics. After decompression surgery, the total EOM volume significantly increased by 15% in the ST group, but radiated EOMs in the SRT group did not expand, resulting in decreased induction of postoperative diplopia. The percentages of patients showing increased diplopia after decompression differed significantly between the groups (ST group, 40.9% vs SRT group, 13.3%, P = .04). However, there was no difference in exophthalmos reduction after decompression between the 2 groups.

CONCLUSIONS

Orbital radiation prior to orbital decompression can reduce both the postoperative increase in EOM volume and deterioration in diplopia.

Compressive Optic Neuropathy and Repeat Orbital Decompression: A Case Series

PURPOSE

To characterize the presenting characteristics, preoperative clinical activity score (CAS), surgical approach, and visual outcomes in patients with thyroid eye disease undergoing repeat orbital decompression for recurrent or recalcitrant compressive optic neuropathy (CON).

METHODS

The medical records of patients with recurrent or recalcitrant CON undergoing repeat orbital decompressions were retrospectively reviewed. The primary outcome measures included pre- and postoperative Humphrey visual field mean deviation, visual acuity (VA) measured in logarithm of the minimal angle of resolution, color vision measured by Ishihara plates, and presence of relative afferent pupillary defect. Details of the surgical procedure and each patient's CAS at presentation were also recorded.

RESULTS

Six patients, 9 orbits, with a mean preoperative CAS of 3.8 were included in this review. The mean time between initial decompression and presentation to our center for recurrent or persistent CON symptoms was 8.6 years (range, 1 to 15 years). At presentation, the average Humphrey visual field mean deviation was -16.5 (standard deviation: 8.8), improving to -3.8 (2.4) postoperatively with a mean of 9.3 months follow up (mean improvement of 75%). Preoperative VA was 0.34 (0.23) LogMAR, improving to 0.05 (0.10) LogMAR with a mean follow up of 10.4 months. Pre- to postoperative comparisons of clinical measures all showed statistically significant improvement (p < 0.05). Eight eyes presented with decreased VA (any VA < 20/20), 4 with decreased color vision (any color vision < 11), and 1 with a relative afferent pupillary defect, and all these patients demonstrated improvement following repeat orbital decompression.

CONCLUSIONS

In patients with thyroid eye disease, symptoms of recurrent CON occurred up to 15 years following initial orbital decompression underscoring the smoldering, progressive nature of the disease. Repeat decompression that focused on the orbital apex resulted in visual improvement in all 6 patients. Despite clinical evidence of CON, the mean CAS of these patients at presentation was only 3.8, highlighting the importance of close monitoring of patients with thyroid eye disease following decompression regardless of the external manifestations of disease activity.

Clinical factors affecting intraocular pressure change after orbital decompression surgery in thyroid-associated ophthalmopathy

OBJECTIVE

To report the physiological monitoring of intraocular pressure (IOP) during the postoperative periods after orbital decompression surgery and ascertain the correlation between the clinical factors and IOP changes.

METHODS

The medical records of 113 orbits from 60 patients who underwent orbital decompression surgery were reviewed retrospectively. IOP measurement during the postoperative periods was classified based on the postoperative day: week 1 (1-7 days), month 1 (8-41 days), month 2 (42-70 days), month 3 (71-97 days), month 4 (98-126 days), and final (after 127 days). The mean postoperative follow-up was 286.5 days for orbits with at least 6 months of follow-up. Univariate and multivariate linear regression analyses were performed to assess the correlation between the IOP reduction percentage and clinical factors.

RESULTS

The mean IOP increased from 16.9 to 18.6 mmHg (10.1%) at postoperative week 1 and decreased to 14.4 mmHg (14.5%) after 2 months. Minimal little changes were observed postoperatively in the IOP after 2 months. Preoperative IOP had a significant positive effect on the reduction percentage both at postoperative week 1 (β=2.51, P=0.001) and after 2 months (β=1.07, P=0.029), and the spherical equivalent showed a positive correlation with the reduction level at postoperative week 1 (β=1.71, P=0.021).

CONCLUSION

Surgical decompression caused a significant reduction in the IOP in thyroid-associated orbitopathy, and the amount of reduction was closely related to preoperative IOP; however, it may also cause a transient elevation in the IOP during the early postoperative phase in highly myopic eyes.

Normative measurements of extraocular musculature by multislice computed tomography

Objective To establish the normal measurements of diameter of extraocular muscles (EOMs) by multislice computed tomography (CT). Methods Orbits of 50 volunteers (25 male and 25 female) were scanned with a multislice CT scanner. For each subject, one axial image at the central level of the eyeball, one coronal image about 1 cm behind globe, and two oblique sagittal images respectively along the left and right optic nerve were used for measurements of the thickness and width of EOMs. The statistic significance of measurement value between male and female and between left and right eyes was evaluated. Results There were no significant differences in the thickness and width of superior muscle group, lateral rectus, medial rectus, lateral rectus, superior oblique, inferior oblique and the thickness of levator palpebrae superioris between the left and right eyes as well as between male and female groups (all P>0.05). The thickness of superior muscle group and inferior rectus had not significant difference (2.9±0.7 vs. 3.3±0.8 mm, P=0.162), while the thickness of medial rectus was significantly higher than that of lateral rectus (3.1±0.5 vs. 2.2±0.6 mm, P=0.000). Conclusions The CT measurement of extraocular musculature is simple and time-saving and can be applied in the clinical work. The normative data obtained may be useful in determining pathologic enlargement of the EOMs in both thyroid-associated orbitopathy patients and other various orbital conditions.

Predicting dysthyroid optic neuropathy using computed tomography volumetric analyses of orbital structures

OBJECTIVE

To evaluate the ability of orbital apex crowding volume measurements calculated with multidetector-computed tomography to detect dysthyroid optic neuropathy.

METHODS

Ninety-three patients with Graves' orbitopathy were studied prospectively. All of the patients underwent a complete neuro-ophthalmic examination and computed tomography scanning. Volumetric measurements were calculated from axial and coronal contiguous sections using a dedicated workstation. Orbital fat and muscle volume were estimated on the basis of their attenuation values (in Hounsfield units) using measurements from the anterior orbital rim to the optic foramen. Two indexes of orbital muscle crowding were calculated: i) the volumetric crowding index, which is the ratio between soft tissue (mainly extraocular muscles) and orbital fat volume and is based on axial scans of the entire orbit; and ii) the volumetric orbital apex crowding index, which is the ratio between the extraocular muscles and orbital fat volume and is based on coronal scans of the orbital apex. Two groups of orbits (with and without dysthyroid optic neuropathy) were compared.

RESULTS

One hundred and two orbits of 61 patients with Graves' orbitopathy met the inclusion criteria and were analyzed. Forty-one orbits were diagnosed with Graves' orbitopathy, and 61 orbits did not have optic neuropathy. The two groups of orbits differed significantly with regard to both of the volumetric indexes (p<0.001). Although both indexes had good discrimination ability, the volumetric orbital apex crowding index yielded the best results with 92% sensitivity, 86% specificity, 81%/94% positive/negative predictive value and 88% accuracy at a cutoff of 4.14.

CONCLUSION

This study found that the orbital volumetric crowding index was a more effective predictor of dysthyroid optic neuropathy than previously described computed tomography indexes were.