Magnetic resonance imaging of tissues compatible with supernumerary extraocular muscles.
OBJECTIVE
To determine by magnetic resonance imaging (MRI) the prevalence and anatomy of anomalous extraocular muscle (EOM) bands.


METHODS
Prospective, observational case series.


METHODS
High-resolution, multipositional, surface coil orbital MRI was performed using T1 or T2 fast spin echo weighting with target fixation control under a prospective protocol in normal adult subjects and a diverse group of strabismic patients between 1996 and 2009. Images demonstrating anomalous EOM bands were analyzed digitally to evaluate their sizes and paths, correlating findings with complete ophthalmic and motility examinations.


RESULTS
Among 118 orthotropic and 453 strabismic subjects, 1 (0.8%) orthotropic and 11 (2.4%) strabismic subjects exhibited unilateral or bilateral orbital bands having MRI signal characteristics identical to EOM. Most bands occurred without other EOM dysplasia and coursed in the retrobulbar space between rectus EOMs such as the medial rectus to lateral rectus, from superior to inferior rectus, or from 1 EOM to the globe. In 2 cases, horizontal bands from the medial rectus to lateral rectus muscles immediately posterior to the globe apparently limited supraduction by collision with the optic nerve. All bands were too deep to be approached via conventional strabismus surgical approaches.


CONCLUSIONS
Approximately 2% of humans exhibit on MRI deep orbital bands consistent with supernumerary EOMs. Although band anatomy is nonoculorotary, some bands may cause restrictive strabismus.
Khitri
Monica R
MR
Jules Stein Eye Institute and Department of Ophthalmology, University of California, Los Angeles, Los Angeles, California 90095-7002, USA.
Demer
Joseph L
JL
D000293:Adolescent; D000328:Adult; D002648:Child; D005124:Eye Abnormalities / Q000175:diagnosis*; D005260:Female; D006801:Humans; D007223:Infant; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009801:Oculomotor Muscles / Q000002:abnormalities*; D009915:Orbit / Q000473:pathology; D015995:Prevalence; D011446:Prospective Studies; D013285:Strabismus / Q000175:diagnosis*
Arch Ophthalmol. 1985 Apr;103(4):540-1
3985834
Ophthalmic Plast Reconstr Surg. 2001 Mar;17(2):120-2
11281584
Clin Anat. 1998;11(6):410-6
9800921
Am J Ophthalmol. 1980 Sep;90(3):416-8
7425058
J AAPOS. 2006 Apr;10(2):135-42
16678748
J AAPOS. 2007 Oct;11(5):491-4
17651998
Okajimas Folia Anat Jpn. 2002 Mar;78(6):235-43
12126054
J AAPOS. 2005 Oct;9(5):438-48
16213393
Invest Ophthalmol Vis Sci. 2010 Jul;51(7):3485-93
20164458
Thyroid. 2007 May;17(5):479-80
17542680
J AAPOS. 1998 Feb;2(1):17-25
10532362
Invest Ophthalmol Vis Sci. 2007 Jun;48(6):2576-88
17525187
Ophthalmology. 1997 Mar;104(3):415-8
9082265
Am J Ophthalmol. 1996 Apr;121(4):444-5
8604741
Clin Anat. 1998;11(4):271-7
9652543
Am J Ophthalmol. 2003 Aug;136(2):355-6
12888062
Invest Ophthalmol Vis Sci. 2005 Feb;46(2):530-9
15671279
Invest Ophthalmol Vis Sci. 1997 Jan;38(1):227-40
9008649