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Show Endoscopic Orbital Roof Fenestration as an Alternative Treatment Option for Idiopathic Intracranial Hypertension: A Cadaveric Anatomical Study Asem Salma, MD, Martin Lubow, MD, Ashley Scheffer, BS, Mario Ammirati, MD, MBA Background: We investigated a new minimally invasive surgical technique for the treatment of idiopathic in-tracranial hypertension in a cadaveric model. This tech-nique aims at establishing a communication between the intraorbital and intracranial compartments by creating a bone, dural, and periorbital window in the anterior cra-nial fossa. This procedure is predicated on intraorbital absorptive capability that has been demonstrated in animals and discussed in humans. Methods: Three fresh cadaver heads were fixed in a head holder so as to mimic the hyperextended supine position. The procedure was conducted bilaterally in each speci-men. Our technique is as follows: 1) An incision is made in the eyebrow medial to the supraorbital notch; 2) using an endoscope and a periosteal elevator, the intraorbital surface of the orbital roof is separated from the periorbita in an anteroposterior direction for a length of 1.5-2.5 cm; 3) a 1 cm2 of the exposed orbital roof is removed, and the dura and arachnoid are opened; and 4) slits are made in the exposed periorbita. Results: We were able to create a communication between the intracranial and the intraorbital compart-ments in all specimens. Conclusion: Our technique is new and does not require any foreign body implantation. Its applicability in humans needs to be evaluated in a clinical context. Journal of Neuro-Ophthalmology 2011;31:25-28 doi: 10.1097/WNO.0b013e3181e8a04e 2011 by North American Neuro-Ophthalmology Society Idiopathic intracranial hypertension (IIH), also known as pseudotumor cerebri or benign intracranial hypertension, is a syndrome of unknown etiology (1). The primary features of this condition are chronically elevated in-tracranial pressure (ICP) with negative neuroimaging studies (1-3). The most devastating neurologic complication of IIH is chronic atrophic papilledema that can lead to blindness (1-6). When medical management is ineffective, IIH is treated surgically with peritoneal diversion of cerebro-spinal fluid (CSF), either from the spinal subarachnoid space or from the ventricles (1-3). Optic nerve sheath fenestration (ONSF) is another surgical treatment option (1,2,7-9). CSF diversion procedures require multiple surgical interventions and often fail (1,2). The current surgical treatment options for patients with IIH have low rates of long-termsuccess and pose a significant risk of complications. In a cadaver model, we describe the anatomical basis of a CSF diversion technique that omits implanted hardware and takes advantage of natural anatomical pathways to help facilitate CSF drainage. This technique aims at establishing a communication between the intraorbital and intracranial compartments by creating a bone, dural, and periorbital window in the an-terior cranial fossa. This allows a direct path for CSF to reach the orbital fat where it may be absorbed into the venous circulation. This procedure is predicated on intra-orbital absorptive capabilities that have been demonstrated in animals (10-13) and discussed in humans (14). METHODS Three fresh cadaver heads whose vascular system had been injected with colored silicone material were used in this study. The specimens were held in a hyperextended position using a Spetzler head holder fixation device (V.Mueller, McGaw Park, IL).We used the hyperextended position to allow the gravity to retract the frontal lobe away from the floor of the anterior fossa. After an incision was made in the eyebrow, just medial to the supraorbital notch, the orbital cavity was entered and the intraorbital surface of the orbital roof medial to the supraorbital nerve was exposed using a periosteal elevator Dardinger Microneurosurgical Skull Base Laboratory, Department of Neurological Surgery, The Ohio State University Medical Center, Columbus, Ohio. The authors report no conflict of interest or financial support. Address correspondence to Asem Salma, MD, Department of Neurological Surgery, The Ohio State University Medical Center, 032 Hamilton Hall, 1645 Neil Avenue, Columbus, OH 43210; E-mail: asem.salma@osumc.edu Salma et al: J Neuro-Ophthalmol 2011; 31: 25-28 25 Original Contribution Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. and, in sequence, 2 rigid endoscopes 4 mm 0 angle and 4 mm 30 angle (Aesculap, Tuttlingen, Germany). This dissection was continued in an anteroposterior direction, just lateral to the medial wall of the orbital cavity, for a length of approximately 1.5-2.5 cm depending on the posterior extension of the frontal sinus. Computer-aided surgery (Stryker Instruments, Kala-mazoo, MI) was then used to make certain that the exposed orbital roof was beyond any ethmoidal air cells or frontal sinus extension (Fig. 1). The exposed bone was fenestrated using a curette and high-speed drill creating a 0.5 cm2 opening (Fig. 2). FIG. 1. Computer-aided surgery. The precise location of the surgical instruments (A), indicated by the blue line (arrow), is seen in the axial (B), coronal (C), and sagittal (D) projections. FIG. 2. Stepwise endoscopic views showing the fenestration of the orbital roof (A, B) and the overlying dura (C, D). Original Contribution 26 Salma et al: J Neuro-Ophthalmol 2011; 31: 25-28 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. The dura was then exposed with a dura hook and incised. Arachnoid was entered using a blunt micro hook, and multiple small 3-4 mm fenestrations were made in the adjacent periorbita with microscissors (Fig. 3). This pro-cedure was performed in both orbits of each specimen. RESULTS We were able to successfully create a window in the roof of the orbit in all of our specimens (Fig. 4). We were able to create this window without using a high-speed drill in 4 of the 6 orbits. DISCUSSION IIH primarily affects obese women of 20-44 years with an estimated prevalence of 13 per 100,000 (1,15). It ismuch less common in the pediatric and male populations (1,16-19). Goals of therapy include relieving headache and preventing visual failure (1-3,6,20,21). The first line of treatment is medical, consisting of weight loss, carbonic anhydrase inhibitors and furosemide (1,20,22). It has been reported that 40% of patients fail medical therapy within a 10-year period (1). Patients who fail medical therapy are treated with CSF diversion procedures and/or ONSF (1,19,23,24). CSF diversion procedures for IIH have failure rates from 48% to 55%, resulting in multiple operations in most cases (25,26). In one series, 56% of patients with IIH required shunt revision and over a 31-month period with the average number of revisions per patient being 2.4 (27). With progressive visual loss, ONSF has become a pop-ular surgical option. Using this technique, improvement of visual acuity and visual fields has been reported in 50% and 72% of patients, respectively (28). Yet, visual acuity and visual fields may worsen after the procedure in up to 11% of patients, and postprocedural blindness has been reported in 1.5%-2.6% of patients (22,28,29). Reoperation has been reported within 3-5 years in as many as 32% of patients who had an initial favorable response (30). More recently, the need for reoperation after ONSF has been estimated at 6% (28), with perioptic nerve fibrosis being a likely cause for failure of the initial procedure. Clearly, there is a need for improved surgical alternatives for patients with IIH. An increasing number of physiological and morpho-logical studies indicate that CSF drains via nonarachnoidal pathways in several mammalian species (4,8,10-13). In animal models, the orbital route is one such nonarachnoidal pathway (4,8,10,11,13). A connection between the sub-arachnoid space of the orbital optic nerve and orbital contents through a putative lymphatic system has been proposed to explain the observation of the transitory intraorbital presence of radioactive material following injections into the ventricular system or cisterna magna (4,8,10,11,13). Additional evidence supporting the exis-tence of an orbital lymphatic system in an animal model has recently emerged (31) including the report by Beden et al (32) demonstrating that the intraorbital space has the ca-pability of quickly clearing large molecules into the systemic circulation that cannot pass through blood vessel walls. Our proposed technique would rely on the CSF absorptive capacity of the orbit. Although not yet proven in FIG. 3. Multiple fenestrations are created in the exposed periorbita using microscissors. FIG. 4. Following removal of the orbital contents, the location of the bone window between the orbit and an-terior cranial fossa is visible. Original Contribution Salma et al: J Neuro-Ophthalmol 2011; 31: 25-28 27 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. humans, this mechanism has been postulated to explain the relief of headache following ONSF (1,2,14,29). With our surgical procedure, CSF drainage should be facilitated by the pressure gradient between the elevated ICP (.20 cm of H2O) in patients with IIH compared to lower intraorbital pressure (4.1-8.2 cm of H2O) (33). Our study has a number of limitations. First, it was performed in cadavers. Second, the rationale for this procedure in humans is currently speculative. Additional evaluation of our surgical technique in the animal model is essential to further test and validate this procedure. REFERENCES 1. Binder DK, Horton JC, Lawton MT, McDermott MW. Idiopathic intracranial hypertension. Neurosurgery. 2004; 54:538-551. 2. Brazis PW. Clinical review: the surgical treatment of idiopathic pseudotumour cerebri (idiopathic intracranial hypertension). Cephalalgia. 2008;28:1374-1376. 3. Wall M. Idiopathic intracranial hypertension (pseudotumor cerebri). Curr Neurol Neurosci Rep. 2008;8:87-93. 4. Ludemann W, Berens von Rautenfeld D, Samii M, Brinker T. 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Original Contribution 28 Salma et al: J Neuro-Ophthalmol 2011; 31: 25-28 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. |
