Positional Obstruction of Ventriculoperitoneal Shunt in a Patient With Idiopathic Intracranial Hypertension

A 32-year-old woman was seen in follow-up for history of long-standing severe idiopathic intracranial hypertension (IIH). Her condition was refractory to acetazolamide, eventually requiring cerebrospinal fluid (CSF) diversion procedure; thus, she had undergone ventriculoperitoneal (VP) shunt placement 9 years earlier.

Photo and Video Essay Section Editors: Melissa W. Ko, Dean M. Cestari, Peter Quiros, Kimberly M. Winges, MD MD MD MD Positional Obstruction of Ventriculoperitoneal Shunt in a Patient With Idiopathic Intracranial Hypertension Laura Donaldson, MD, PhD, Elie Côté, MD, Edward Margolin, MD A 32-year-old woman was seen in follow-up for history of long-standing severe idiopathic intracranial hypertension (IIH). Her condition was refractory to acetazolamide, eventually requiring cerebrospinal fluid (CSF) diversion procedure; thus, she had undergone ventriculoperitoneal (VP) shunt placement 9 years earlier. Shunt revision was required 1 year after initial placement, followed by complete shunt replace- ment 5 years later with a Strata II adjustable valve system. Her visual field loss stabilized, although she required ongoing medical treatment with oral acetazolamide and topiramate. Neuro-ophthalmic examination remained stable over the years demonstrating bilateral optic atrophy and visual field defects (Fig. 1A, B). She re-presented with the new onset of transient visual obscurations, nausea, and headaches, all present only FIG. 1. A. Baseline 24-2 automated visual fields and optical coherence tomography (OCT) of the optic nerves showing bilateral optic atrophy (B). With recurrence of headache, nausea, and transient visual obscurations, worsening in visual fields was present particularly in the left eye, (C) and there was new increase in the thickness of peripapillary RNFL on OCT (D). Department of Ophthalmology and Vision Sciences (LD, EC, EM), University of Toronto, Ontario, Canada; and Division of Neurology (EM), Department of Medicine, University of Toronto, Ontario, Canada. The authors report no conflicts of interest. Address correspondence to Edward Margolin, MD, Division of Neurology, Departmentt of Ophthalmology and Visual Sciences, Departmentt of Medicine, University of Toronto, 801 Eglinton Avenue West, Suite 301, Toronto ON M5N 1E3; E-mail: Edward. [e-mail] e588 when she was lying supine. Whenever she would get up to walk, her symptoms consistently quickly resolved. A nuclear medicine shunt series study was performed while supine and initially was interpreted as normal. On examination, the central visual acuity remained 20/ 20 and 20/30. Optic nerves were pale bilaterally but appeared slightly elevated. Automated visual fields (24-2 algorithm) showed worsening mean deviation, particularly in the left eye (Fig. 1C). Optical coherence tomography (OCT) demonstrated increased peripapillary retinal nerve Donaldson et al: J Neuro-Ophthalmol 2022; 42: e588-e590 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Photo and Video Essay fiber layer (pRNFL) thickness, indicating recurrence of papilledema, despite previously well-established bilateral optic atrophy (Fig. 1D). A shunt patency study was performed again in different positions (Fig. 2). Presence of only minute amount of injected radionuclide tracer in the distal shunt was observed while the patient was supine. After 5 minutes of sitting, however, early spillage was seen in the abdominal compartment, and after walking for 15 minutes, an extensive tracer activity was seen in the abdominal and peritoneal compartments. Exchange of shunt tubing was performed with no improvement in her symptoms; thus, she was then taken to the operating room for shunt revision. Interpretation of Findings Failure of VP shunts is common, estimated to occur in approximately one third of patients, with rates more than 50% reported in some series (1). Obstruction is the most common reason for failure and causes include blockage by tissue debris or choroid plexus, catheter tip migration, kinking of tubing, and thrombosis and distal obstruction due to peritoneal adhesions or loculations. Other mechanical reasons for shunt failure are interruption or disconnection and malpositioning. Migra- tion of the distal catheter is a particular problem in growing children or in adults with significant changes in body habitus. Nonmechanical shunt complications include infection and overdrainage or underdrainage (2). Body position also affects normal dynamics of CSF flow through a shunt: Shunt flow is regulated by a valve with a minimum opening pressure, and the pressure differential above this valve opening pressure determines the flow of CSF within the shunt. The pressure differential is equal to the sum of intracranial pressure (ICP) and hydrostatic pressure minus intra-abdominal pressure (3). Hydrostatic pressure is higher in the standing position; however, this is opposed by lower ICP (4) and increased intra-abdominal pressure in the sitting or standing position relative to supine position, which limits the flow increase when standing. Many valves also have a built-in antisiphoning mechanism to avoid rapid CSF drainage in this situation. In our patient, the proximal end of the shunt was found to be partially obstructed during the revision surgery, and the higher hydrostatic pressure, present only when she was upright, was required to overcome the obstruction, allowing the flow through the valve. FIG. 2. A. Ventriculoperitoneal shunt series demonstrating the patent shunt with the radionuclide tracer activity reaching the distal shunt in the supine position. Flow increased in the seated position and further increased after walking with extensive flow into the peritoneal cavity. Donaldson et al: J Neuro-Ophthalmol 2022; 42: e588-e590 e589 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Photo and Video Essay Management of patients with IIH with CSF-diverting shunts can be challenging, and the presence of shunt is associated with many visits to the emergency department (ED) and significant patient anxiety (5). Shunt malfunction can be difficult to diagnose because symptoms of failure are variable and may include headache, nausea and vomiting, behavior changes and altered mental status, and seizure (2). Requirement for ICP-lowering medication is common in the months before requiring shunt revision (1). A shunt series, or series of plain films of the skull, chest, and abdomen, has low yield in the diagnostic workup and only rarely leads to the revision of the shunt in the absence of other findings, unless an obvious disconnection in the hardware is seen (6). Nuclear medicine shunt patency studies, although much more invasive and resource intensive, are much more sensitive in detecting malfunction (7). Papilledema is the most important predictor of going on to revision in shunted adult patients with IIH presenting to an ED (8). In the acute care setting, evaluation of the optic nerve head by using funduscopy is difficult in the absence of pharmacologic dilation and is rarely performed in ED (9). Because of this, all patients with suspected shunt malfunction must be referred for neuro-ophthalmic examination on an urgent basis. All patients with IIH require regular follow-up with visual fields and funduscopy and OCT of the pRNFL. Patients with pre-existing optic atrophy can still exhibit swelling of the remaining retinal ganglion cell axons, and in these cases, OCT of the pRNFL should be used to make a quantitative comparison with their previous baseline (10). This case demonstrates that shunt flow obstruction can be positional and should be suspected in patients complaining of symptoms of raised ICP only in certain postures. In these patients, a dynamic nuclear medicine study should be performed in different body positions because positional shunt failure is otherwise difficult to diagnose. Knowledge of positional shunt failure can prevent persistent papilledema and worsening visual function in affected patients and allow for early shunt revision surgery. e590 STATEMENT OF AUTHORSHIP Category 1: a. Conception and design: L. Donaldson and E. Margolin; b. Acquisition of data: L. Donaldson and E. Margolin; c. Analysis and interpretation of data: L. Donaldson and E. Margolin. Category 2: a. Drafting the manuscript: L. Donaldson, E. Margolin, and E. Cote; b. Revising it for intellectual content: L. Donaldson, E. Margolin, and E. Cote. Category 3: a. Final approval of the completed manuscript: L. Donaldson, E. Margolin, and E. Cote. 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Rapid development of optic disc edema secondary to topical retinoid cream. Can J Neurol Sci. 2021 48;882–3. Donaldson et al: J Neuro-Ophthalmol 2022; 42: e588-e590 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited.