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19 The Medical Student Notebook Bariatric Times • March 2017 Nevertheless, acetazolamide r emains an important part of medical management of IIH. Furthermore, loop diuretics have been considered a useful adjunctive therapy to acetazolamide and may h elp normalize CSF pressure and reduce papilledema. 64,65 Indomethacin has also been explored as a possible treatment for IIH and has been shown to help r educe CSF pressure and produce symptomatic relief. It is thought to exert these effects by causing cerebral vasoconstriction, thereby reducing cerebral blood flow. 66,67 W hile serial lumbar punctures are theoretically an effective treatment, CSF volume quickly recovers. Serial lumbar punctures are an impractical primary t reatment strategy due to adverse effects, including pain associated with the procedure as well as risk for complications like headache, CSF leak, or infection. Historically, l umbar punctures had a role in IIH treatment as a temporizing measure until more definitive treatment could be offered, but these are no longer recommended. 55,68,69 The main nonbariatric surgical interventions employed in the treatment of IIH are CSF shunting procedures and optic nerve sheath fenestration (ONSF). The primary indication for surgery is worsening vision despite maximal medical therapy, but surgery may also be indicated for resolution of other symptoms, such as intractable headaches. With regards to CSF shunting, available procedures include ventriculoperitoneal shunting (VPS) and lumboperitoneal shunting (LPS). The efficacy of shunting procedures in IIH treatment remains controversial. While most studies demonstrate headache relief shortly after shunting procedures, the effect on visual loss is far less clear as some studies report up to 95- percent remission or stabilization of visual disturbances while others report progressively worsening visual symptoms in up to one-third of patients after shunting procedures. 58,70–75 Furthermore, shunting procedures can have high rates of complications. The most common complication is the need for shunt revision and this can occur in up to 86 percent of patients, while some will require multiple revisions. 58,72–76 Shunt infection and CSF leak are other common complications. 77 In contrast to the somewhat more controversial data on efficacy of shunting procedures, several studies have demonstrated the benefit of ONSF in preserving visual function in patients with IIH-associated papilledema. 71 As noted above, papilledema and visual loss in IIH are caused by axoplasmic stasis within the neurons that compose the optic nerve. Fenestration of the optic nerve sheath decreases the pressure of the optic nerve within the optic nerve sheath, thereby relieving the mechanism underlying development of axoplasmic stasis and associated papilledema and visual loss. As evidence of this, in one of the largest available data sets, ONSF led to stabilization or improvement of visual fields and acuity in 88 percent and 94 percent of patients, respectively. 78 Thus, while ONSF can be effectively used to manage the visual loss associated IIH, it must also be noted that this procedure does not address the underlying intracranial hypertension and so it cannot be used to address other symptoms of IIH, such as headache. This is in contrast to CSF shunting procedures, which may address both headache and visual loss as discussed above. Weight loss is another essential component to the treatment of IIH and may be even more beneficial than medical or surgical management, especially among patients with severe obesity (BMI > 35kg/m 2 ). All patients with overweight and obesity diagnosed with IIH should be counseled regarding weight loss. 79 Strategies for promoting weight loss include lifestyle modifications, such as regular exercise and dietary modification as well as bariatric surgery. With regards to bariatric surgery, common surgical procedures include Roux-en-Y gastric bypass (RYGB), sleeve gastrectomy (SG), and laparoscopic adjustable gastric banding (LAGB). The expected loss of excess weight after two years from RYGB, SG, and LAGB are approximately 70 percent, 60 percent, and 50 percent respectively. 6 3, 80–83 Given the potential for bariatric surgery to produce significant and sustained weight loss, it is reasonable to consider the role of bariatric surgery in the treatment of IIH. It is important to note, however, that isolating the effects of weight loss in patients with IIH has proven difficult as most studies include patients simultaneously engaged in other treatment modalities. Nonetheless, several studies have sought to measure the efficacy of weight loss, with and without bariatric surgery, in resolution of IIH symptoms and preservation of vision. One recent systematic review compared eight studies comprised of a total of 277 patients who underwent weight loss programs without surgical intervention with seven studies comprised of a total of 65 IIH patients who underwent weight loss surgery, including LAGB, SG, and RYGB. 84 With regards to weight loss, patient in the nonsurgical groups had an average reduction in BMI of 4.2 kg/m 2 whereas patients undergoing bariatric surgery had an average reduction in BMI of 17.5 kg/m 2 . Patients undergoing surgery had 100-percent resolution of papilledema in all reported results. Additionally, surgery was associated with clinically significant decreases in CSF pressure. In two of the surgical studies analyzed, for example, average CSF pressure decreased by 185mm and 196mm H2O, respectively. For reference, the maximum opening pressure considered normal in the general population is approximately 200mm H2O, whereas a slightly higher maximal normal opening pressure of 250mm H2O may be more appropriate in patients with obesity. 85,86 These results are clearly indicative of decreased intracranial pressure in patients who undergo bariatric surgery. Furthermore, bariatric surgery was associated with resolution of headaches in 90.2 percent of patients. With regards to resolution of visual disturbances, only two out of the seven studies of patients undergoing bariatric surgery reported outcome data from visual field examination, making evaluation of the effect of bariatric surgery on preservation of vision incomplete. However, one study of eight patients who underwent RYGB with a decrease in Figure 1. Schematic diagram of the possible pathophysiological mechanisms in idiopathic intracranial hypertension (IIH). Cerebrospinal fluid (CSF) is produced mainly by the choroid plexus epithelial cells, with a small amount being secreted by ependymal cells that line the ventricular system. Classically, CSF was thought to drain predominantly through the subarachnoid space through arachnoid granulations into the superior sagittal sinus. Evidence also suggests CSF drains through the cribriform plate along cranial nerves into the nasal lymphatics (yellow). The most recent hypothesis proposes bulk flow of fluid along perivascular routes (glymphatic pathway) which is cleared from the brain into the subarachnoid CSF, bloodstream or cervical lymphatics. Supporting this concept is the recent discovery of lymphatic vessels (yellow) in the dura that drain into the deep cervical lymph nodes. From Mollan SP, Ali F, Hassan-Smith G, et al. Evolving evidence in adult idiopathic intracranial hypertension: pathophysiology and management. J Neurol Neurosurg Psychiatry. 2016;87(9):982–992.