Major reviewAnomalous Orbital Structures Resulting in Unusual Strabismus
Section snippets
Historical review
Anomalous orbital structures that attach to the globe and cause restriction of motility have been reported as a rare cause of unusual strabismus during the last century. The earliest cases were discovered at autopsy, and no clinical information regarding motility abnormalities was included. Nussbaum first reported this anomaly in 1893 in a patient with an accessory muscle that arose from the lateral rectus muscle and divided into three heads. One of the heads rejoined the lateral rectus muscle,
Structures arising from the extraocular muscles themselves and inserting in abnormal locations
The first type of anomalous orbital structure is characterized by structures that originate from the rectus muscles and insert in abnormal locations. Apple reported a patient with a congenital abduction deficit who was found to have a 4-mm wide muscular band that inserted posterior to the normal medial rectus muscle insertion and extended posteriorly 1.5 cm, where it fused with the internal surface of the medial rectus muscle.1 He described a second patient with a similar accessory muscle band,
Histopathology of Anomalous Orbital Structures
Histopathologic findings have been reported in two patients with accessory extraocular muscles. In Fleischer's report published in 1907, the accessory structure was found to have fascicles of extraocular muscle.7 Histopathology of the distal portion of the structure in Lueder et al's patient revealed “a paucicellular strip of pale fibrous tissue with small fascicles of mature skeletal muscle at one end. Focally, atrophy and loss of individual muscle fibers were associated with encroachment of
Imaging of Anomalous Orbital Structures
Imaging studies have been reported in only a few patients with anomalous orbital structures. Mühlendyck et al reported CT results in two patients.14 The first patient, who had significant restriction of extraocular movements in all directions, had no abnormalities on her initial CT scan. Repeat studies with a higher resolution scanner later revealed a structure inserting near the supero-medial aspect of the optic nerve. The second patient, who had limited upgaze, had a structure that inserted
Clinical Findings Suggesting Possible Anomalous Orbital Structures
When evaluating patients with incomitant strabismus, one looks initially for motility abnormalities that are characteristic of a specific clinical entity (e.g., an elevation deficiency that is present only in adduction is typical of Brown syndrome). If the pattern of a restrictive strabismus is atypical, the differential diagnosis broadens to include orbital trauma, orbital masses (e.g., tumor), thyroid ophthalmopathy, and intrinsic extraocular muscle abnormalities. The presence of an accessory
Treatment
Not all anomalous orbital structures result in strabismus. Some of these structures appear to have been found in patients incidentally, either at autopsy24 or during surgery for a problem unrelated to the anomalous structure.2, 17 Therefore, it is important to correlate the motility findings with the location of the anomalous orbital structure. If the structure produces a clinical effect, it should be one of restriction, limiting motility in the direction away from the anomalous structure.
The
Conclusion
Anomalous orbital structures are a rare cause of strabismus. They should be considered in patients with atypical restrictive strabismus. Recognition of these structures may be difficult, given their rarity. The presence of specific unusual motility patterns and orbital imaging may assist in diagnosis. Release of the restrictive structures may improve motility in some patients.
Method of Literature Search
MEDLINE and Ovid were used to search the medical literature from 1966 to the present. Other sources included references in identified articles and textbooks. Key words used were extraocular muscles, anomalous, accessory, and retractor bulbi. Four German and one French article were translated.
Outline
I. Background
A. Historical review
B. Embryology of the extraocular muscles
II. Types of anomalous orbital structures
A. Structures arising from extraocular muscles and inserting in abnormal locations
B.
Acknowledgements
The author gratefully acknowledges the assistance of Joern Soltau, MD, and Alex Levin, MD, in translation of original articles. The author has no commercial or proprietary interest in any product or concept discussed in this article.
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Double-bellied inferior rectus muscles with aplasia of medial rectus muscles
2024, Journal of AAPOSTwo cases of Duane retraction syndrome with abnormal orbital structures
2024, Journal of AAPOSIsolated bifid medial rectus muscle in adult-onset divergence insufficiency esotropia
2021, Journal of AAPOSThe presence of anomalous extraocular bands in Duane retraction syndrome
2021, Journal of AAPOSAnomalous orbital structure mimicking fracture of orbital floor
2020, Journal of AAPOSCitation Excerpt :Surgical correction involves the severing of the structure from the globe, resulting in release of the tightness on forced duction test intraoperatively.5,7,10 Even if anomalous structures are identified, good results may not be possible because of extreme posterior location of the bands, inability to completely dissect and detach them, or reattachment to the globe postoperatively.3,5 Thus a guarded prognosis must be discussed with the patients.