Accuracy of brain imaging in the diagnosis of idiopathic intracranial hypertension
Introduction
Idiopathic intracranial hypertension (IIH), also known as benign intracranial hypertension or pseudotumour cerebri, is characterized by increased cerebrospinal fluid (CSF) pressure in the absence of an identifiable structural cause.1, 2, 3 IIH typically occurs in young and overweight female patients who develop symptoms and signs of raised intracranial pressure, including headache, visual disturbances, pulsatile tinnitus, and papilloedema.1, 2, 3 Diagnosis is typically confirmed by a lumbar puncture, which demonstrates raised CSF pressure with normal composition.1, 2, 3 Neuro-imaging has been traditionally used to exclude other causes of increased intracranial pressure such as mass lesions, hydrocephalus, or venous sinus thrombosis.1, 2, 3
Certain signs on cross-sectional imaging have been reported to be associated with IIH,4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17 including flattening of the posterior aspect of the globes, protrusion of the intraocular portion of the optic nerve, vertical tortuosity of the optic nerve, distension of the optic nerve sheaths, enhancement of the optic nerve head, partial empty sella turcica, slit-like ventricles, tight subarachnoid spaces. However, these cross-sectional imaging findings are non-specific and can be seen in association with other conditions or causes of raised intracranial pressure.18, 19, 20 Venography is also necessary in the workup of patients with IIH in order to rule out venous sinus thrombosis, which can mimic IIH in clinical presentation.21 A high proportion of patients with IIH have been found to have bilateral severe transverse sinus stenosis using magnetic resonance venography (MRV).22, 23 Thus, the combination of findings from cross-sectional imaging, in addition to the presence of non-thrombotic transverse sinus stenosis on MRV, would be expected to be highly specific for IIH. However, few studies have examined the diagnostic utility of these individual magnetic resonance imaging (MRI) signs for IIH4, 6, 11, 22, 23 or combinations thereof,4 and only one group has examined their inter-rater reliability.4, 22 No published study has specifically evaluated the utility of combining the cross-sectional imaging signs with findings on MRV in the diagnosis of IIH.
The objectives of the current study were threefold: (a) to assess the sensitivity, specificity, and inter-observer reliability of individual MRI imaging (cross-sectional and venographic) signs associated with IIH; (b) to compare the sensitivity of time of flight (TOF) and contrast-enhanced (CE) MRV techniques in the detection of severe transverse sinus stenosis; (c) to determine whether the combination of cross-sectional MRI and MRV findings increases the diagnostic certainty for IIH.
Section snippets
Materials and methods
This study was approved by The Ottawa Hospital Research Institute Research Ethics Board without informed consent.
Patients and control subjects characteristics
Forty-three patients (39 female, four male) and control subjects (28 female, 15 male) were included in the analysis (Table 1). Although there was a statistically significant difference in the gender ratio between the IIH and control groups (p < 0.01), the two groups were well matched in age (IIH mean age 34.3 ± 11.9; range 17–63 years and controls mean age 37.2 ± 14.6; range 18–65 years). There was no significant difference in the proportion of MRIs performed at 1.5 T versus 3 T field strength
Discussion
Several conclusions can be drawn from this analysis of the accuracy of MRI and MRV in the diagnosis of IIH. First, a brain MRI and MRV that demonstrated: (1) no evidence of a mass lesion, hydrocephalus, or sinus thrombosis, and (2) either one of flattening of the posterior globe, partially empty sella combined transverse sinus stenosis score CSS <4, or any combination of these signs, significantly increased the diagnostic certainty for IIH. The probability of a diagnosis of IIH was increased
Limitations
There are several limitations inherent to the design of this study. The conclusions, consequently, require validation in a prospectively collected population of patients and age and sex-matched control subjects. The calculated sensitivities and specificities are highly dependent on the prevalence of the disorder in the population being tested (50% in the present study), in addition to the composition of the control group. The control group in the present study was retrospectively identified and
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