Imaging description

The main role of imaging in this condition historically focused on exclusion of other pathological lesions that resulted in elevated intracranial pressure (ICP). CT was often used as a screening study to exclude a mass lesion prior to the lumbar puncture. The advent and widespread use of MRI disclosed abnormalities that indicate or suggest idiopathic intracranial hypertension (IIH) itself.

A number of imaging features have been described in IIH, and they uniformly pertain to sequelae of elevated intracranial pressure and/or CSF volume. The “empty sella” sign may result from a downward herniation of an arachnocele through the diaphragma sella. The pituitary gland may be compressed or flattened against the sellar floor. Elevated ICP may be transmitted to the optic nerve sheath (ONS), resulting in prominence of ONS, flattening of the posterior globe, or even intraocular protrusion of the optic nerve head (Fig. 49.1). Other signs include optic nerve tortuosity and optic nerve enhancement due to venous congestion.

There is an increasing realization that patients with suspected IIH must also be imaged with MR venography (MRV), in addition to routine MRI. MRV helps to rule out sinovenous thrombosis as a secondary cause of IIH and commonly demonstrates sinovenous stenoses in patients with IIH (Figs. 49.2, 49.3). Farb et al. identified venous stenoses in as many as 90% of patients with IIH, with a reported sensitivity and specificity of 93% using a contrast-enhanced elliptic centric-ordered imaging (1). It should be noted that standard time-of-flight (TOF) techniques are frequently associated with artifactual loss of signal in the transverse and sigmoid sinuses, and are unreliable in the detection of sinovenous stenosis. Optimal evaluation for underlying sinovenous stenosis includes either contrast-enhanced MRV or CT venography (CTV).