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Introduction
Idiopathic intracranial hypertension (IIH) or pseudotumor cerebri syndrome (PTC) is a clinical syndrome characterized by increased intracranial pressure (ICP) with no apparent cause and no hydrocephalus (Ball & Clarke, 2006). The exact reason is still unclear; headache and visual impairment are the most common symptoms, and blindness occurs in 10% of cases (Ball & Clarke, 2006). In overweight young adult women, the incidence in the United States is 15–19 cases per 100,000 people, and since IIH is associated with obesity, its incidence is likely to increase with increasing global obesity (NCD Risk Factor Collaboration, 2016). Diagnosis is based on clinical symptoms, absence of hydrocephalus, intracranial mass, structural or vascular lesion on imaging, elevated cerebrospinal fluid (CSF) pressure measured with a pressure gauge during lumbar puncture, and normal CSF composition. The purpose of this article is to review the current standard of management of patients with IIH and recent advances in the study of its pathogenesis.
Current Knowledge
It should be admitted that IIH can be over-diagnosed. The most common diagnostic error is an inaccurate fundus examination, which can be difficult (Burkett1 & Ailani, 2018). IIH can proceed without inflammation of the ocular disc; in these cases, the diagnosis depends on the interpretation of the MRI results. Criteria useful for diagnosing IIH are “empty” Turkish delusion, flattening of the posterior ball, stretching of the optic nerve sheath with or without optic nerve tortuosity, and transverse sinus stenosis. The accidental discovery of potential non-specific MRI features can lead to overdiagnosis of coronary artery disease, additional tests, including a lumbar puncture (Barmherzig & Szperka, 2019), and unnecessary treatment. The potential value of MRI has not yet been systematically explored. There are more and more literary sources suggesting the role of vitamin A, adipokines, sleep disorders, and stenosis of the venous sinus in the pathogenesis of IIH.
Headache with varying characteristics, often resembling migraines, is the most common symptom of IIH. People with IIH experience the most severe headache upon awakening; the nature of the pain is pulsating and is associated with photophobia or phonophobia (Mahajnah et al., 2020). Asymptomatic manifestations are not uncommon; temporary visual impairment (TVL) is observed in about 75% of patients with IIH (Sheldon et al., 2017). These are short (<1 min) episodes of monocular or binocular vision loss (partial or complete), often associated with a change in posture. The mechanism is unclear but may represent transient ischemia of the optic nerve. Pulsating tinnitus occurs in 60% of patients with IIH (NCD Risk Factor Collaboration, 2016). This relatively more specific symptom of increased ICP is usually not mentioned unless the patient is specifically interviewed.
Edema of the optic nerve head (ONH) is a secondary sign of ICP and an ophthalmological sign of IIH. It is necessary to distinguish the edema of the optic nerve head from pseudo papilledema due to druses of the optic disc and congenital anomalies of the optic disc. There are no features of the appearance of the optic nerve head to distinguish papilloma from other causes of disc edema. Signs suggestive of papilloma and optic neuropathy include bilateral vision, preservation of central vision, and the presence of accompanying symptoms such as headache, pulsating tinnitus, and VND. In rare cases, ONH can be asymmetric and very rarely absent. The division of the subarachnoid space, which prevents the bidirectional outflow of cerebrospinal fluid from the brain, may explain this phenomenon (Burkett1 & Ailani, 2018).
If left untreated, ONH can lead to vision loss. The nature and evolution of vision loss are predictable and similar to glaucoma. For reasons that are still unclear, the papillomacular bundle (the part of the ganglion cell layer that preserves central vision) persists until a very late stage, being affected only after the rest of the visual field is lost (Barmherzig & Szperka, 2019). Adequate visual field assessment, best performed with formal perimetry, is essential for the management of these patients. An increase in the physiological blind spot is the earliest and, in many cases, the only visual field defect in acute respiratory failure. The most common pathological field defect is the nasal rug or arcuate scotoma. Over time, arcuate defects can progress, resulting in a severe narrowing of the visual field (Burkett1 & Ailani, 2018). Ultimately, central vision begins to deteriorate; at this stage, the chances of recovery are slim.
It should be noted that many patients with IIH are able to maintain completely normal visual fields and function for long periods of time, despite severe acute respiratory failure. Thus, quantifying the visual field in patients with IIH is critical when making treatment decisions. Then, ischemic optic neuropathy can develop in patients with severely inflamed optic nerves, especially in patients with associated hypertension and a rapid decrease in blood pressure. These patients have acute vision loss and asymmetric visual acuity (Mahajnah et al., 2020). Severe ONH can cause macular edema. In these patients, central vision loss is due to macular edema, and the prognosis for maintaining vision is generally good. Moderately severe acute respiratory failure can cause folds in the retina or choroid, impairing vision; these cases also have a favorable prognosis (Sheldon et al., 2017). ONH itself is not a cause of vision loss, and there is no indication for aggressive surgical treatment.
The pathogenesis of IIH is unspecified, but any theory of IIH must take into account the following factors: obesity in women of childbearing age; absence of ventriculomegaly; relationship with systemic diseases such as cor pulmonale and polycystic ovary; relationship with systemic drugs. The concept of increasing pressure in the venous sinus of the venous sinus as a source of increased ICP during IIH was put forward in the 1990s with direct studies of venous manometry in patients with coronary artery disease and IIH studies (Karahalios et al., 1996). This theory is not fully supported by physiology as it does not take into account the influence of gravity in the upright position or the elasticity of the abdominal skin and soft tissues. This concept can also predict the virtual epidemic of IIH in the United States but cannot explain IIH in morbidly obese men.
Conservative therapy is the first step in specialized treatment. The indication for conservative treatment is the verification of the presence of benign intracranial hypertension syndrome. The most effective methods of conservative therapy are steroid therapy (glucocorticoids in a dosage of 16 mg per day in a descending scheme for two to three weeks) in combination with antibacterial (broad-spectrum antibiotic therapy with a duration of at least a week) and dehydration agents (diuretics) for the post-inflammatory genesis of PTC. In the group with symptoms of thrombosis of the main venous collectors and impaired venous outflow, vasoactive drugs are added to the above medicines, which affect the rheological properties of blood. In the case of sinus or vein thrombosis, anticoagulant therapy is usually not performed because the development of the IIH occurs in the late stages, with the formed thrombosis (Sheldon et al., 2017). Treatment should be carried out under the control of the fundus and visual function; serial lumbar puncture can only be recommended as a palliative measure. Periodic excretion of cerebrospinal fluid, although it improves the subjective condition of patients, in the long term (1 month or more), is ineffective.
In a situation of progression of the disease, despite the ongoing conservative treatment and an increase in visual impairment, indications for surgical treatment of the PTC should be made. The aim of the surgical treatment of patients with the syndrome of benign intracranial hypertension is to bypass the intrathecal space of the spinal cord to permanently reduce the cerebrospinal fluid pressure. The most common technique for surgical correction of IIH is the operation of lumboperitoneal bypass grafting. In isolated cases, if it is impossible for medical reasons to carry out lumboperitoneal shunting, it is possible to impose a ventriculoperitoneal anastomosis (Burkett1 & Ailani, 2018); however, it should be remembered that in the vast majority of patients with ICP, the ventricles are narrowed, have a slit-like shape, and the installation of a catheter into the cavity of the lateral ventricle presents significant technical difficulties. Decompression of the optic nerves in the area of bone canals and the operation of fenestration of the sheaths of the optic nerves are considered as another method of surgical treatment of PTC.
Conclusion
With the increasing incidence of obesity, the incidence of IIH has increased and will continue to grow. Despite all modern methods of IIH diagnosis, the pathogenesis and complete understanding of the disease mechanism remains unknown. Many patients are successfully treated conservatively, but the risk of visual impairment is a significant and validating factor. Further research is needed to understand the pathophysiology of IIH and clinical trials so that our understanding of IIH and its treatment can be optimized.
References
Ball, A, K., & Clarke, C. E. (2006). Idiopathic intracranial hypertension. Lancet Neurol., 5(5), 433–442.
Barmherzig, R., & Szperka, C. L. (2019). Pseudotumor cerebri syndrome in children. Current Pain and Headache Reports (2019), 23(58), 1–9.
Burkett1, J. G., & Ailani, J. (2018). An up to date review of pseudotumor cerebri syndrome. Current Neurology and Neuroscience Reports (2018), 18(33), 1–7.
Karahalios, D. G., Rekate, H. L., Khayata, M. H., & Apostolides, P. J. (1996). Elevated intracranial venous pressure as a universal mechanism in pseudotumor cerebri of varying etiologies. Neurology, 46(1), 198–202.
Mahajnah, M., Genizi, J., Andreus,R., Zahalka, H., & Zelnik. (2020). Pseudotumor cerebri syndrome: From childhood to adulthood risk factors and clinical presentation. Journal of Child Neurology, 35(5), 311–316.
NCD Risk Factor Collaboration. (2016). Trends in adult body-mass index in 200 countries from 1975 to 2014: a pooled analysis of 1698 population-based measurement studies with 19·2 million participants. The Lancet, 387(10026), 1377–1396.
Sheldon, C., A., Paley, G. L., Beres, S. J., McCormack, S. E., & Liu, G. T. (2017). Pediatric pseudotumor cerebri syndrome: Diagnosis, classification, and underlying pathophysiology. Seminars in Pediatric Neurology, 24, 110–115.
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