Superior Rectus Intramuscular Lipoma

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Lipomas are benign mesenchymal tumors derived from mature adipocytes. Most of lipomas are located subcutaneously, and deeper locations such as intramuscular, retroperitoneal, or gastrointestinal are encountered less frequently. Rarely, simple lipomas can be found within the extraocular muscles. A review of the literature identified only 3 previous reports of intramuscular lipoma, affecting the medial rectus, superior oblique, and superior rectus.1–3 The authors describe an indolent presentation of a further case of intramuscular lipoma involving the superior rectus muscle belly.
A 70-year-old man incidentally noticed the prominent appearance of his left eye on looking at photographs of himself 6 months ago. He had no visual symptoms, pain, or diplopia. His history included reduced left vision following Herpes zoster ophthalmicus in childhood, Type 2 diabetes mellitus, ischemic heart disease, systemic hypertension, stroke, and investigations for a renal mass.
On examination, his best corrected visual acuity was 6/5 OD and 6/12 OS, there was no relative afferent pupillary defect, but colour vision was mildly reduced in the left eye (14/17). The patient was found to have left-sided proptosis (4 mm), increased resistance to retropulsion, and restricted motility (down and lateral gaze), though he denied diplopia. He had about 2 mm upper and lower eyelid retraction and mild, chronic chemosis. Intraocular pressure was within normal limits OU, and funduscopy was unremarkable.
MRI of the orbits revealed an enlarged left superior rectus muscle with reduced internal enhancement. A fatty signal was present seemingly within the superior aspect of the midmuscle fascial bundle (Fig. 1).
There was concern that this could be an intramuscular malignancy or metastasis, so we proceeded with a biopsy. This was performed via a superior bulbar conjunctival approach with blunt dissection between the superior rectus and levator palpebrae superioris, and identified posterior thickening of the superior rectus muscle with diffuse fatty infiltrate.
Histopathological examination showed skeletal muscle fibers and mature adipose tissue within the muscle, features in keeping with an intramuscular lipoma (Fig. 2). There was no evidence of atypia or malignancy.
Two months postbiopsy, no significant change was found clinically. The patient remains under clinico-radiologic follow up. The posterior location and diffusely infiltrated nature of the lipoma means that attempted surgical resection would carry a high risk of superior rectus paresis, so this has not been attempted. He has had intermittent symptoms of corneal exposure so orbital decompression or eyelid-lowering surgery may be offered in future.
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