Imaging signs in idiopathic intracranial hypertension: Are these signs seen in secondary intracranial hypertension too?

Abstract

Background: The purpose of this study was to evaluate the difference in the occurrence of the various "traditional" imaging signs of intracranial hypertension (IIH) on magnetic resonance imaging (MRI) in patients with idiopathic (IIH) and secondary intracranial hypertension.

Materials and methods: In a retrospective analysis, the MRI findings of 21 patients with IIH and 60 patients with secondary intracranial hypertension (41 with tumors; 19 with intracranial venous hypertension) were evaluated for the presence or absence of various "traditional" imaging signs of IIH (perioptic nerve sheath distention, vertical buckling of optic nerve, globe flattening, optic nerve head protrusion and empty sella) using the Fisher's exact test. Odds ratios were also calculated. Statistical Package for the Social Sciences version 17.0 was used for statistical analysis. Subgroup analysis of the IIH versus tumors and IIH versus venous hypertension were performed.

Results: Optic nerve head protrusion and globe flattening were significantly associated with IIH. There was no statistically significant difference in the occurrence of rest of the findings. On subgroup analysis, globe flattening and optic nerve head protrusion occurred significantly more often in IIH than in tumors. However, there was no statistically significant difference in the occurrence of any of these findings in patients with IIH and venous hypertension.

Conclusions: IIH is a diagnosis of exclusion. While secondary causes of raised intracranial pressure (ICP) have obvious clinical findings on MRI, some conditions like cerebral venous thrombosis may have subtle signs and differentiating between primary and secondary causes may be difficult. In the absence of any evident cause of raised ICP, presence of optic nerve head protrusion or globe flattening can suggest the diagnosis of IIH.

Keywords: Intracranial hypertension; magnetic resonance imaging; signs.

Figure 1

Idiopathic intracranial hypertension - note the T2 weighted images showing the vertical buckling of the optic nerve (a), globe flattening and prominance of the optic nerve head (b, d), partially empty sella (c) and prominent perioptic nerve sheath (d, f)

Figure 2

Diffuse fibrillary astrocytoma involving the left frontal lobe with signs of secondary intracranial hypertension - T2 weighted images with prominent perioptic nerve sheath (a), absence of globe flattening (b), and normal appearance of the sella (c)

Figure 3

Venous sinus thrombosis involving the right transverse and sigmoid sinuses - no significant vertical buckling of optic nerves (a, b), protrusion of the optic nerve head (b), empty sella (c), prominent perioptic nerve sheath (a, b, d), and globe flattening (e). Magnetic resonance venogram shows non - filling of right transverse and sigmoid sinuses (f)