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E.J. Wladis, N. Mirani, L.P. Frohman, P.D. Langer, R.E. Turbin; The Clinical and Radiographic Spectrum of Post–Operative Optic Nerve Sheath Fenestration Pseudomeningoceles . Invest. Ophthalmol. Vis. Sci. 2005;46(13):652.
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© ARVO (1962-2015); The Authors (2016-present)
To review features of optic nerve sheath pseudomeningoceles (PSM) in post–operative patients meeting the modified Dandy criteria for IIH
1 male, 2 females (14,34,56 years old, respectively) developed radiographic evidence of post ONSF PSM on MRI scans performed 6, 6 and 11 months after ONSF, respectively. Each patient underwent ONSF via superior–medial transcutaneous orbitotomy. The first patient required concurrent medial transconjunctival approach with medial rectus disinsertion. In the first patient, the 3.6 mm ovoid cyst was poorly defined, enhanced minimally, and found during a period of post–operative stability. In the second patient, a 2 x1 x 1.5 cm tubular non–enhancing cyst compressing and displacing the globe was found in evaluation of swelling and proptosis occurring after sleeping, and the physical findings of 1mm of proptosis and mild limitation of ipsilateral supraduction. In the last patient, a 10 x 10 x 8 mm nonenhancing spherical cyst compressing the optic nerve was found in evaluation for delayed post–operative visual loss. The cyst was excised, with improvement of visual function. Histopathology showed acellular thin collagenized cystic lining consistent with a PSM. On MRI, the cysts were of low intensity on T1–weighted images and bright on T2–weighted images, and had attenuated signal on FLAIR, consistent with CSF signal characteristics. Post–contrast images revealed minimal enhancement at the ONSF site in one case.
After ONSF, fluid–filled cysts may form at the fistula site. These PSM likely contain CSF based on MRI appearance. Although they are difficult to distinguish from a seroma, histopathology is consistent with a PSM. They may remain clinically silent and signify a functioning ONSF, or they may cause proptosis, periorbital swelling, motility disorder, or severe visual loss. Although the incidence is unknown, clinicians should be aware of the post–operative characteristics, and consider MRI or ultrasound imaging in evaluating post–ONSF visual loss.
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