From the Department of Retinal Diseases (YO), the Department of Neuro-ophthalmology (GA), and the Department of Radiology (OG), Ulucanlar Eye Research Hospital, Ankara, Turkey.
The authors have no financial or proprietary interest in the materials presented herein.
Address correspondence to Yasemin Ozdamar, MD, Ulucanlar cad. No: 59 Altindag, 06100, Ankara, Turkey.
Pseudotumor cerebri (PTC) is a disorder characterized by increased intracranial pressure without clinical, laboratory or radiological evidence of an intracranial mass lesion, meningeal inflammation or venous outflow obstruction.1 The most important neurological manifestation is papilledema, which may lead to progressive optic atrophy and blindness. Although PTC is a self-limited disease, studies have shown it to be a chronic and recurrent condition. The only permanent morbidity in PTC is progressive and insidious vision loss that usually results from decompensation of papilledema with progressive optic atrophy.1–4
Presence and progression of visual loss determine the treatment modalities for pseudotumor cerebri as medical or surgical. Surgical approaches are considered in patients having progressive visual loss despite maximal medical therapy. Optic nerve sheath decompression (ONSD) is one of the effective surgical methods for the treatment of PTC.1–4 Several radiological studies have been performed to demonstrate the action of the ONSD and/or alterations of the retrobulbar optic nerve sheath in early and late periods after ONSD.5–11
In this report, a cyst-like structure of the distal optic nerve sheath at the operation site in the late surgical period after ONSD is demonstrated.
A 32-year-old woman presented with transient visual obscurations in the left eye and severe headache. Her visual acuity (VA) was 0.9 in the right eye and 0.7 in the left eye. Anterior segment findings and intraocular pressures were normal. Pupils were equal in size and reactive to light. Color vision (CV) was 10/10 in both eyes. Fundus examination showed blurred disc margins in both eyes and marked optic disc swelling in the left eye. Visual field (Humphrey 30–2 central) was normal in the right eye while the left visual field revealed an inferior arcuate defect. She had no clinically significant medical history. Laboratory and systemic evaluations were unremarkable. Neurological examination was found to be normal. Magnetic resonance imaging (MRI) of the brain and orbits were normal. Opening pressure on lumbar puncture (LP) was 230 cm H2O. Based on these findings, the diagnosis of PTC was made and medical treatment was given. Visual function deteriorated to a denser bi-arcuate scotoma and peripheral constriction in the left eye despite maximum medical treatment and ONSD was performed. One year after surgery, VA was 1.0 with full CV in both eyes. The superior half of the optic disc appeared atrophic in the left eye. The right fundus was normal.
One year later, she presented with recurring severe headaches. Repeated LPs had been performed in the neurosurgery department. Visual field was normal in the right eye; while in the left visual field, an inferior arcuate defect persisted. Optic disc was normal in the right eye, and pale in the left eye with 1.0 VA and 10/10 CV. Gadolinium-enhanced, fat suppressed orbital MRI demonstrated a cyst-like localized enlargement of the left distal optic nerve sheath close to the fenestration site (Fig. 1). Ultrasonographic examination was performed by an experienced radiologist. A 10 MHz linear probe was adjusted to give a suitable angle for displaying an oblique sagittal section of the left optic nerve at the distal portion. A localized cystic enlargement of the subarachnoid space to a width of 5.8 mm. adjacent to the left optic nerve sheath was demonstrated (Fig. 2).
Figure 1. Sagittal View of Orbital Magnetic Resonance Imaging (MRI).
Figure 2. Oblique Sagittal Ultrasonographic View of the Perioptic Cystic Space.
In optic nerve sheath decompression surgery, a fenestration is created on the optic nerve sheath, which forms a passage between the subarachnoid space and the orbital soft tissue for cerebrospinal fluid (CSF) egress and allows a local reduction of pressure around the optic nerve.2 Visual functions are stabilized or improved in the majority (68–100%) of patients after ONSD.3,4,6 The exact mechanism of ONSD is unclear; but two mechanisms have been proposed: scar formation of the surgical area preventing transmission of the high CSF pressure to the optic nerve head or the filtration of CSF through the operative site into the orbit.12,13 Occlusion of the nerve sheath gap and subarachnoid space by a proliferation of connective tissue has been observed in pathologic specimens.12,14 However, while Keltner et al. demonstrated fistulas in the dura compatible with CSF egress and maintenance of a normal subarachnoid space around the nerve in their histological study15, another study reported scar tissue and configuration of collagen deposition at the operation site, arguing that CSF filtration was allowed through the scar tissue.16 Several studies have been performed to detect the changes occurring in the retrobulber area of optic nerve and the operation site using radiological methods after ONSD. While authors could not demonstrate a fluid leakage, various reports described a cyst-like structure close to fenestration site and proposed that this indicated a filtration bleb allowing CSF egress.5–11
Untile recently, only one study was able to detect subarachnoid fluid in the orbit utilizing isotope scans, when early postoperative fluid collection was demonstrated adjacent to the decompression site with three-dimensional “constructive interference in steady state - CISS” MRI.9 In that study, the authors argued that this cystic structure indicated CSF filtration in the early postoperative period and was destined to disappear and the replaced by soft tissue formation in the late postoperative period.5 In our patient, we did not perform neuroimaging in the early postoperative period. Therefore we can not speculate about the first time appearance of this finding. Upon the second presentation of the patient it was noticed that the perioptic cystic space was present even after 2 years postoperatively without any deterioration of optic nerve function. Ultrasonographic findings were compatible with the MRI images, demonstrating a cyst-like enlargement contiguous with the fenestration site; a finding previously reported.5,6,8 Therefore, we presume that soft tissue replacement may not be absolutely necessary; instead, walls of the cystic space may fibrose and still allow minimal amounts of CSF filtration into the orbit while maintaining its integrity.
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- Yazici Z, Yazici B, Tuncel E. Findings of magnetic resonance imaging after optic nerve sheath decompression in patients with idiopathic intracranial hypertension. Am J Ophthalmol. 2007;144:429–435. doi:10.1016/j.ajo.2007.05.034 [CrossRef]
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- Spoor TC, McHenry JG, Shin DH. Long-term results using adjunctive mitomycin C in optic nerve sheath decompression for pseudotumor cerebri. Ophthalmology. 1995;102:2024–2028.
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