The method of the exophthalmos value predicted calculation when planning the orbital decompression procedure in patients with endocrine ophthalmopathy

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BACKGROUND

Endocrine ophthalmopathy (EOP) is an independent progressive autoimmune disease with a primary lesion of the adipose tissue of the orbit and oculomotor muscles and of the lacrimal gland with secondary involvement of the eye (i.e., optic neuropathy, corneal damage, and increased intraocular pressure) [1].

According to the classification of the Academician of the Russian Academy of Sciences (RAS) A.F. Brovkina, one of the manifestations of EOP is edematous exophthalmos, which has three course variants, namely, muscular, mixed, and lipogenic [2]. Currently, the most effective surgical treatment of the lipogenic and mixed forms of edematous exophthalmos is internal decompression of the orbit [3]. For this surgical procedure, excess pathologically damaged adipose tissues were removed from the external and internal surgical spaces of the orbit [4]. To date, various surgical options have been proposed and described [5, 6].

To determine the volume of the orbital tissue, various programs have been developed based on the examination results such as magnetic resonance imaging [7–11] and multispiral computed tomography (MSCT) [12–15]. However, all the proposed methods for calculating the soft tissue volume are not adapted to the calculations of predicting the postoperative protrusion of the eyeball, as they are quite time consuming and dependent on the operator [3].

The literature provides single publications describing the calculation methods used when planning internal orbital decompression in patients with EOP. Thus, in 2009, the Academician of RAS A.F. Brovkina et al. [16] proposed an equation for calculating the excess orbital tissue volume to be removed during decompression. However, they only used this equation for unilateral exophthalmos; as the calculation method is laborious, they recommended the use of a special computer program.

In 2021, Li et al. [17] proposed a new radiological method for evaluating the plastic effect of modified transconjunctival orbital fat decompression surgery in patients with inactive EOP. The authors measured the degree of eyeball protrusion according to the findings of spiral computed tomography 6 months before and after surgery on the Infiniti workstation. Based on the results obtained using the Philips IntelliSpace Portal, elliptical area and linear segment measurement tools, the standard elliptical cone volume equation was used to calculate the internal volume of the muscle cone. Changes in eyeball protrusion and the internal volume of the muscle cone before and after surgery were assessed [17]. Moreover, this technique is intended to assess the efficiency of the surgery and has not been evaluated in terms of prognosis.

Thus, the need to develop a method for predicting eyeball protrusion after internal decompression of the orbit, which can be used without additional equipment and software, is easy to learn, and does take a long calculation time, remains relevant. The technique should consider individual characteristics of the structure of the orbits and be used for calculations in the correction of bilateral exophthalmos.

This study aimed to develop and evaluate the efficiency of a new method for calculating the position of the eyeballs after orbital decompression.

MATERIALS AND METHODS

Sixty-six patients (128 orbits) with endocrine ophthalmopathy, including 54 women and 12 men aged 28–62 (mean age, 41 ± 8) years, were examined. A lipogenic EOP was identified in 45 patients and a mixed variant in 21 patients. In all patients, EOP was in remission. We used a different algorithm of actions to detect the myogenic form, so this group of patients was not included in the present study. Simultaneous (bilateral) internal decompression of the orbit was performed in 62 patients, and four patients underwent surgery of one orbit (unilateral). Preoperatively, a standard ophthalmological examination was performed to determine visual acuity, intraocular pressure, and status of the eyelids and periorbital region (Table 1).

 

Table 1. Clinical signs of patients depending on the course of endocrine oftalmopathy / Таблица 1. Клинические признаки у пациентов с эндокринной офтальмопатией в зависимости от варианта заболевания

Clinical signs	Mixed variant (42 orbits)	Lipogenic variant (84 orbits)
Visual acuity, average	0.81 ± 0.3	0.99 ± 0.04
Intraocular pressure, mm Hg	22 ± 1.0	21 ± 1.2
Degree of eye protrusion, mm	27.6 ± 2.0	23.6 ± 1.7
Lagophthalmos	8	–
Restrictions in eye movement	27	1
Conjunctival chemosis	3	–
Characteristics of the borders and the presence of edema of the optic nerve head	24	–

 

All patients underwent MSCT of the orbits using various devices Philips Brilliance 64, Somatom Sensation 40, and Aquilion ONE640 (Table 2).

 

Table 2. The parameters of the MDCT analysis of the orbit / Таблица 2. Параметры мультиспиральной компьютерной томографии исследования глазниц

Parameter	Apparatus type
	Somatom Sensation 40	Aquilion One 640	Philips Brilliance 64
Imaging mode	Spiral	Volumetric	Spiral
Slice thickness, mm	1	0.5	0.9
Gantry angle	0	0	0
Field of study, cm	20–30	16	20
Voltage, kV	100	100	120
Current, mA	60	60	100
Time of one revolution of the tube, s	0.37	up to 0.275	0.5
Study duration, s	4–5	1–2	3–4
Type of reconstruction	Bone, soft tissue	Bone, soft tissue	Bone, soft tissue

 

The MSCT study was conducted according to the following methods in the middle zone of the face. Before the study, the patient’s head was freed from all removable elements. With the patient in the supine position, the head was placed exactly in the standard headrest, and positioning was performed according to the laser marks in three mutually perpendicular projections. The patient’s eyes were open at the time of scanning, and the gaze was fixed centrally. To mark the study area, a topogram was obtained in a lateral projection, and the scanning area included the skull (from the upper border of the soft tissues of the cranial vault to the lower contour of the upper jaw teeth), with the jaws in habitual occlusion. Tomography was performed in the axial plane in the spiral or volumetric scanning modes (depending on the apparatus type) with a slice thickness of 0.5–1.0 mm, depending on the apparatus capabilities, using reconstruction in bone and soft tissue modes. Multiplanar reconstructions in the coronal and sagittal planes were added to the MSCT data obtained in the axial plane. Virtual three-dimensional (3D) models were constructed using the standard software of each tomograph.

Calculation method

Based on the data obtained as a result of the MSCT study, 3D reconstruction was performed in the bone mode in the axial plane. A mark was placed on the zygomaticoorbital suture (Fig. 1), through which the frontal plane was constructed (Fig. 2), and the entire array of data located behind this plane was eliminated from further analysis. Then, the orbital entry was contoured, and the entire data array located outside the resulting circle was also excluded from further calculations (Fig. 3). In the axial plane, a perpendicular line was drawn from the top of the cornea to the frontal plane. The resulting segment is the size of the exophthalmos (AB, before surgery). From the same point (from the corneal apex), a parallel segment AC was made, which was the estimated size of the exophthalmos after surgery (Fig. 4). Another frontal plane was drawn through point C, and the fragment of the image that included point A was removed. The volume of the resulting disk-shaped fragment was calculated (Fig. 5), and data obtained were entered into the table (Table 3).

 

Fig. 1. MSCT. 3D reconstruction in the bone mode. Placing a mark on the orbital seam of one of the orbits (arrow) / Рис. 1. Мультиспиральная компьютерная томограмма. Костный режим. 3D-реконструкция. Вид спереди. Метка на скулоорбитальном шве (стрелка)

 

Fig. 2. MSCT. 3D reconstruction in the bone mode. Alignment of the frontal plane and removal of the data array located behind this plane / Рис. 2. Мультиспиральная компьютерная томограмма. Костный режим. 3D-реконструкция. Вид сверху. Создание фронтальной плоскости

 

Fig. 3. MSCT. 3D reconstruction in soft tissue mode. Noted the zone of entry into the orbit along the bone edge, images outside the circle were excluded from the analysis / Рис. 3. Мультиспиральная компьютерная томограмма. Мягкотканный режим. 3D-реконструкция. Метка установлена на костном крае, изображения за окружностью исключены

 

Fig. 4. MSCT. 3D reconstruction in soft tissue mode. Measurement of the magnitude of the exophthalmos of the right orbit (AB segment) before surgery and the estimated exophthalmos (AС segment) after surgery / Рис. 4. Мультиспиральная компьютерная томограмма. Мягкотканный режим. 3D-реконструкция. Величина экзофтальма правой орбиты (отрезок АВ) до операции и планируемое положение после операции (отрезок АС)

 

Fig. 5. MSCT. 3D reconstruction in soft tissue mode. The amount of fatty tissue calculated using standard programs MSCT, which must be removed during surgery / Рис. 5. Мультиспиральная компьютерная томограмма. Мягкотканный режим. 3D-реконструкция. Необходимый к удалению объём жировой орбитальной клетчатки. Стандартная программа томографа

 

Table 3. Analysis of the results of preoperative and postoperative measurements of orbital structures / Таблица 3. Анализ результатов предоперационных и послеоперационных измерений структур орбит

Parameters	Values
Exophthalmos before surgery, mm	24.94 ± 2.5
Removable volume calculated using the method, mL	3.323 ± 0.9
Volume of adipose tissue removed during surgery, mL	3.319 ± 0.9
Postoperative exophthalmos assumed according to the method, mm	21.63 ± 2.2
Result of surgical treatment of eyeball protrusion after 6 months, mm	21.65 ± 2.2
Significance level	0.98

 

RESULTS AND DISCUSSION

From 2014 to 2020, we examined and analyzed 128 orbits in 66 patients with exophthalmos in EOP, who underwent surgical internal decompression of the orbit. Our findings revealed that preoperative exophthalmos varies from 18.6 to 33.0 mm (average 24.94 ± 2.5 mm).

Yatsenko et al. [12] presented a technique and based on which published calculations for the volumes of the bone orbit, adipose tissues, and other soft tissue structures. However, this method is time consuming and requires additional equipment, so the authors did not use this method for simultaneous bilateral decompression or an anophthalmic syndrome on the contralateral side [12]. When planning the volume for removal (mean value, 3.319 ± 0.9 ml), we consider the EOP variant, initial size of eyeball protrusion, and statistical data of patients who underwent surgery. The adipose tissue volume removed during surgery coincided completely with the volume planned for the MSCT study. The estimated postoperative position of the eyeball (mean value, 21.63 ± 2.2 mm), which we obtained during planning, was not significantly different from the actual measurement (mean value, 21.65 ± 2.2 mm) at the control MSCT study after 6 months. The significance level of the planned postoperative position of the eyeball relative to the horizontal plane in relation to the actual eye position was 0.98 (i.e., p > 0.05); thus, it can be argued that the study groups were not significantly different, and no significant differences were revealed. The average calculation error was 0.1 ± 0.1 mm. The surgical interventions led to a decrease in exophthalmos by 3.3 ± 0.9 mm. The correlation coefficient between the removed volumes of the adipose tissue and values by which the exophthalmos has changed was (ρ) 0.44; this means that these values are related (moderate constraint force).

CONCLUSIONS

The proposed method for calculating the estimated postoperative eyeball protrusion enables to preoperatively determine the amount of adipose tissue to be removed to achieve the desired outcomes without using time consuming calculations and additional software. This technique made it possible to calculate the planned amount of adipose tissue to be removed from each orbit for symmetrical eyeball position postoperatively based on the MSCT data. The technique will help reducing the risk of postoperative complications, such as diplopia.

ADDITIONAL INFORMATION

Author contributions. All authors confirm that their authorship complies with the international ICMJE criteria (all authors have made a significant contribution to the development of the concept, research and preparation of the article, and read and approved the final version before its publication). D.V. Davydov performed scientific editing and surgical interventions. D.A. Lezhnev contributed to scientific editing and prepared the illustrations. K.A. Konovalov wrote the text, formatted the references, and prepared the illustrations.

Conflict of interest. The authors declare no conflict of interest.

Funding. The study had no external funding

About the authors

Dmitrii V. Davydov

Peoples’ Friendship University of Russia; A.I. Evdokimov Moscow State University of Medicine and Dentistry

Email: d-davydov3@yandex.ru
ORCID iD: 0000-0001-5506-6021
SPIN-code: 1368-2453

Dr. Sci. (Med.), Professor, head of Department of Reconstructive and Plastic Surgery with an Ophthalmology Course

Russian Federation, 8, Miklukho-Maklaja street, Moscow,117198; Moscow

Dmitrii Anatolevich Lezhnev

A.I. Evdokimov Moscow State University of Medicine and Dentistry

Email: lezhnevd@mail.ru

Dr. Sci. (Med.), Professor, head of Department of Radiology

Russian Federation, Miklukho-Maklaja street, 8, Moscow, 117198

Konstantin A. Konovalov

1586 Military clinical hospital

Author for correspondence.
Email: kkonovalov82@mail.ru

Head of the ophthalmological Department

Russian Federation, Mashtakova street 4, Podolsk, Moscow region, 142110

References

Supplementary files