Kyu Yeon Hwang; Won Kyung Cho; Ji Sun Paik; Suk Woo Yang

doi:10.3341/jkos.2013.54.1.1

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Hwang, Cho, Paik, and Yang: Radiographic Analysis of Extraocular Muscle Volumetric Changes Following Orbital Decompression in Thyroid‐ Associated Orbitopathy: Comparison of Nunery Types 1 and 2

Original Article

J Korean Ophthalmol Soc 2013;54(1):1-6.

Published online: 25 September 2013

DOI: https://doi.org/10.3341/jkos.2013.54.1.1

Radiographic Analysis of Extraocular Muscle Volumetric Changes Following Orbital Decompression in Thyroid‐ Associated Orbitopathy: Comparison of Nunery Types 1 and 2

Kyu Yeon Hwang, MD, Won Kyung Cho, MD, Ji Sun Paik, MD, Suk Woo Yang, MD, PhD

Department of Ophthalmology and Visual Science, Seoul St. Mary's Hospital, The Catholic University of Korea College of Medicine, Seoul, Korea

Address reprint requests to Suk Woo Yang, MD, PhD Department of Ophthalmology, The Catholic University of Korea, Seoul St. Mary's Hospital #222 Banpo-daero, Seocho-gu, Seoul 137-701, Korea Tel: 82-2-2258-1200, Fax: 82-2-599-7405, E-mail: yswoph@catholic.ac.kr

Received 30 January 2012 Accepted 12 March 2012

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Purpose

To evaluate the radiographic volume change in extraocular muscles (EOM) following orbital wall decompression for Nunery type 1 and type 2 thyroid-associated orbitopathy (TAO).

Methods

Medical records of 31 orbits in 20 patients undergoing postoperative orbital CT after orbital decompression for TAO were retrospectively reviewed. The patients were divided according to Nunery classifications. A type 1 classification was assigned to patients who had no diplopia and essentially normal versions. A type 2 classification was assigned to patients with restrictive motility loss and diplopia within 20 degrees of the primary position. EOM volumes were determined by the summation of each EOM's cross-sectional areas in the coronal plane of the CT scans and multiplying the sum by the slice thickness. Main outcome measure was a comparison of EOM volume changes between types 1 and 2 TAO and a relationship between EOM volume and change in proptosis.

Results

In type 2 TAO, a significant increase in the volume of the medial rectus muscle, lateral rectus, and total EOM was detected postoperatively (p = 0.044, 0.022, 0.049), whereas no significant changes were found in the EOM's volume changes in type 1 TAO. The reduction of proptosis after orbital decompression in type 1 TAO was significantly greater than in type 2 TAO (p = 0.025). A significant positive association was observed between the preoperative EOM volumes and the reduction of proptosis following orbital wall decompression (r = 0.505).

Conclusions

The postoperative EOM volumes following orbital wall decompression was significantly increased in Nunery type 2 patients who had restrictive myopathy.

Keywords: Extraocular muscle (EOM), Nunery, Radiographic, Thyroid-associated orbitopathy (TAO)

References

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Figure 1.

(A) Orbital CT scan for a patient who had orbital decompression of both orbits. The medial rectus, inferior rectus, lateral rectus, and superior rectus group in the left side was outlined on coronal view. (B) Postoperative coronal CT of same patient documenting postoperative bilateral enlargement in cross-sectional area of medial rectus, inferior rectus, lateral rectus, and superior rectus.

Figure 2.

(A) The relationship between the changes in medial rectus muscle volume (postoperative-preoperative in ml) and the preoperative medial rectus muscle volume in ml. (B) Type 1 C. Type 2.

Figure 3.

(A) The relationship between the preoperative total extraocular muscle volume (in ml) and the changes in proptosis (postoperative-preoperative in mm). (B) The relationship between the changes in total extraocular muscle volume (postoperative-preoperative in ml) and the changes in proptosis (postoperative-preoperative in mm).

Table 1.

Demographic data of Nunery type 1 and type 2 patients

	Type 1^*	Type 2^†	p-value
Number	6	14
Orbits	11	20
Sex
Male	1	9
Female	5	5
Age (yrs)
Mean ± SD	32.17 ± 8.78	51.07 ± 10.88	<0.05
Range	23–43	31–65
Exophthalmos (mm)
Preoperative	20.1 ± 1.96	19.26 ± 1.69	0.364
Postoperative	15.98 ± 2.19	15.44 ± 1.85	0.251
Change (Post-Pre)	4.5 ± 0.9	3.5 ± 1.4	0.039

Values are presented as number or mean ± SD.

Table 2.

The preoperative and postoperative volume (ml) of the rectus muscles following orbital decompression

CT measure	Type 1 (n = 11)				Type 2 (n = 20)
CT measure	Pre-operative	Post-operative	Change^*	p-value	Pre-operative	Post-operative	Change^*	p-value
MR	0.63 ± 0.11	0.84 ± 0.4	0.21 ± 0.42	0.085	1.06 ± 0.52	1.32 ± 0.49	0.26 ± 0.32	0.022
LR	0.48 ± 0.32	0.55 ± 0.31	0.07 ± 0.17	0.225	0.71 ± 0.44	0.82 ± 0.43	0.11 ± 0.13	0.049
IR	0.71 ± 0.17	0.77 ± 0.27	0.06 ± 0.16	0.593	1.27 ± 0.44	1.30 ± 0.46	0.03 ± 0.21	0.866
SRG	0.53 ± 0.16	0.57 ± 0.22	0.04 ± 0.15	0.768	0.86 ± 0.43	0.88 ± 0.32	0.02 ± 0.20	0.851
Total EOM^†	2.35 ± 0.58	2.73 ± 1.04	0.38 ± 0.66	0.247	3.89 ± 1.51	4.32 ± 1.37	0.42 ± 0.61	0.044

Values are presented as mean ± SD.

EOM = extraocular muscle; IR = inferior rectus; LR = lateral rectus; MR = medial rectus; SRG = superior rectus group (superior rectus/levator complex).

^* Postoperative volume – preoperative volume

^† MR + IR + LR + SRG.

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