Telltale Signs of Idiopathic Intracranial Hypertension With Normal Opening Cerebrospinal Fluid Pressure

Abstract

Introduction

Idiopathic Intracranial Hypertension (IIH) with normal opening cerebrospinal fluid (CSF) pressure comprises a rare IIH variant.

Case Report

We report the case of a non-obese Caucasian woman, who presented with asymmetrical papilledema, typical IIH-findings on optic nerve sonography and brain magnetic resonance imaging (MRI), and was diagnosed with IIH despite normal opening CSF pressure. Following treatment with acetazolamide, a complete remission of her symptoms was achieved, accompanied by significant improvement of the fundoscopy findings.

Conclusion

Although normal opening CSF pressure in IIH patients is rare, clinicians should be aware of this IIH variant and promptly indicate IIH treatment in patients presenting with typical clinical symptoms and neuroimaging findings suggestive of IIH.

Introduction

Idiopathic intracranial hypertension (IIH) is an embroiled syndrome of raised intracranial pressure (ICP) with obscure etiology in the absence of space occupying lesions. Headache, pulse synchronous tinnitus, transient visual obscurations and progressive visual loss comprise typical IIH symptoms, while diplopia due to sixth cranial nerve paresis and papilledema are also encountered in IIH patients. IIH usually occurs in women of childbearing age and has been classically associated with obesity and rapid weight gain. Epidemiological evidence suggests an increasing incidence of IIH with increasing obesity prevalence, ranging between .14 to 1.48 per 100 000 population per year in countries with obesity prevalence of < 10% or > 20%, respectively. ¹ Besides female gender and obesity, endocrine disorders, including hypoparathyroidism and Addison’s disease, as well as nutritional disorders, such as hypervitaminosis A, have also been acknowledged as risk factors for IIH. ²

IIH has long been perceived as a disorder of raised ICP. There is growing awareness however, that instant measurements of opening cerebrospinal fluid (CSF) pressure via lumbar puncture may be misleading or reflect insufficiently the fluctuations of ICP, due to dynamic fluctuations of the CSF flow. IIH with normal opening CSF pressure has recently been acknowledged as a rare IIH variant. ³ Although current diagnostic criteria for IIH no longer mandate CSF opening pressure >25 cm H2O for IIH diagnosis, ⁴ the diagnosis of IIH with normal opening CSF pressure remains a diagnostic challenge, requiring high clinical suspicion to recognize and interpret correctly supporting ophthalmological, optic nerve sonography and neuroimaging findings.

Here, we present the case of a non-obese Caucasian woman diagnosed with IIH at a postmenopausal age, displaying asymmetrical papilledema, typical neuroimaging IIH findings and normal opening CSF pressure.

Case Description

A 62-year-old woman reported intermittent blurred vision in both eyes for the past 3 months. The patient deteriorated rapidly with permanent fixation and worsening blurred vision 3 weeks before presenting herself at the emergency room of our Department. There were no complaints of concomitant headache. Her medical history included arterial hypertension moderately regulated with antihypertensive treatment, hypothyroidism, and hyperlipidemia well-treated with L-thyroxine 100 μg o.d. and atorvastatin 10 mg o.d., respectively. Her body mass index was within normal limits and she denied having gained weight recently.

Physical and neurological examination findings were normal. Ophthalmological examination revealed: 1) best corrected visual acuity 0,7 decimal (20/28 or 6/8.7 with the Snellen chart) in the right eye and 0,8 decimal (20/25 or 6/7.5 with the Snellen chart) in the left eye, 2) no pain with ocular motility, 3) no proptosis, and 4) no afferent pupillary defect, 5) intraocular pressure with Goldmann applanation tonometer of 18mmHg at the right eye and 14mmHg at the left eye (normal values 10-21). On fundus examination, the left eye exhibited an excessively swollen optic disk (Figure 1, Panel A), but the right eye examination revealed an almost normal appearing optic nerve. Visual field examination using Goldmann perimetry revealed blind spot enlargement in the left eye, while the right eye did not have any defects.

Figure 1.

Fundus examination revealing a swollen left optic disc (Panel A, arrow). Transcranial Color-Coded Duplex (TCCD) B-Mode showing left optic nerve protrusion within the ocular bulb (Panel B, arrow). Brain MRI with axial T1 sequence showing subarachnoid space expansion around the optic nerves (Panel C, arrows), a finding that is suggestive of IIH. Sagittal T1 sequence on brain MRI showing empty sella turcica that is also supportive of IIH diagnosis (panel D, arrow). The presence of occipital emissary vein-an inconstant emissary vein that connects the torcular Herophili with the suboccipital veins of the external vertebral plexus (Panel E, arrow) and arachnoid granulations on right transverse sinus (Panel F, arrow) represent other neuroimaging findings consistent with IIH diagnosis.

Transcranial Color-Coded Duplex (TCCD) sonography showed a left optic nerve protrusion within the ocular bulb (Figure 1, Panel B) without a corresponding finding in the right optic nerve. Brain Magnetic Resonance Imaging (MRI) indicated the diagnosis of IIH. More specifically, a small intraocular protrusion of the head of the left optic nerve head was identified in the left ocular bulb. Mild posterior globe flattening appeared bilaterally. The optic nerves had normal thickness but there was an enlarged subarachnoid space around the optic nerves (7 mm in the right, 6 mm in the left; (Figure 1, Panel C). Tortuosity of the optic nerves with a slight helix at a transverse level was observed. An empty sella turcica (Figure 1, Panel D) was also detected. Neuroimaging signs of IIH including presence of occipital emissary vein (Figure 1, Panel E) ⁵ and arachnoid granulations in the transverse sinuses were also noted (Figure 1, Panel F). ⁶ Magnetic Resonance Venography excluded the presence of thrombosis or stenosis of cerebral venous sinuses or cerebral veins.

Lumbar puncture was performed and the opening cerebrospinal fluid (CSF) pressure was measured at 170 mm H₂O; CSF composition was normal. A total of 30cc of CSF was removed. Notably, the patient reported significant improvement of the reported eye symptoms following the lumbar puncture. In view of (a) the absence of alternative etiologies of increased intracranial pressure on brain imaging; (b) the exclusion of alternative causes of swollen optic nerve (i.e., anterior ischemic optic neuropathy or optic disk drusen) on ophthalmological exam; and (c) the normal opening CSF pressure on lumbar puncture, we reached the diagnosis of the IIH variant with normal CSF pressure with unilateral swollen optic disc. ⁷ Acetazolamide was subsequently prescribed at a dose of 1000 mg daily. The patient was reassessed at 30 days following treatment initiation and improvement of the swollen disk was documented. The patient also reported complete symptom resolution.

Discussion

There are scarce reported data on the presence of normal CSF pressure as a variant of IIH.^4,8-11 These previous reports and our case lend support to the assumption that the lumbar puncture opening pressure measurement indicates the CSF pressure at that specific timepoint. Thus, elevated opening CSF pressure should not be considered a “conditio sine qua non” (mandatory criterion) for the diagnosis of IIH. ⁴ The present case highlights that if a patient has symptoms or signs typical of IIH, normal opening CSF pressure should not refute IIH diagnosis. In fact, the present case also conveys another important message: that early recognition of this IIH variant may have major consequences in terms of visual outcome, as prompt treatment initiation is pivotal for the preservation of visual function. At one-month follow-up, under treatment with acetazolamide, our patient reported a complete remission of her visual symptoms and a significant improvement of her fundoscopy findings was noted.

An alternative explanation for normal opening CSF pressure in patients with this IIH variant is that pseudo-normal CSF pressure may correspond to early IIH stages. At early stages of IIH, CSF pressure may be marginally or intermittently raised and thus, IIH may remain undetected. The presence of very asymmetric papilledema in this case may be in line with the hypothesis of early IIH, as only very few studies have previously reported asymmetric papilledema in IIH patients. Nonetheless, anatomical reasons could also account for this noted asymmetry. For example, it has been postulated that asymmetric papilledema may occur due to differences in the size of bony optic canals regulating the CSF flow between the peri-optic subarachnoid spaces and the suprasellar cistern. Additionally, the difference in intraocular pressure may modulate the amount of swelling that occurs at each optic nerve head. ¹²

In view of the previous considerations, it is important to raise awareness that IIH with normal opening CSF pressure is rare, but may in fact remain underdiagnosed in clinical practice. Diagnosis of IIH with normal opening CSF pressure entails meticulous assessment of patient history , including assessment of IIH risk factors, clinical examination and ancillary tests, including lumbar puncture, ophthalmological, optic nerve sonography and neuroimaging studies. With respect to the latter, neurologists should be familiar with typical findings on optic nerve sonography and brain MRI to suspect early IIH in the absence of raised CSF pressure on lumbar puncture. Moreover, high clinical awareness is warranted to recognize IIH-suggestive signs that will enable prompt treatment initiation, with major implications for clinical prognosis and patient outcomes.

ORCID iDs

Aikaterini Foska https://orcid.org/0000-0002-5164-4952

Lina Palaiodimou https://orcid.org/0000-0001-7757-609X