When should I do dynamic CT myelography? Predicting fast spinal CSF leaks in patients with spontaneous intracranial hypotension

Abstract

Background and purpose: Some patients with SIH have fast CSF leaks requiring dynamic CTM for localization; however, patients generally undergo conventional CTM before a dynamic study. Our aim was to determine whether findings on head MR imaging, spine MR imaging, or opening pressure measurements can predict fast spinal CSF leaks.

Materials and methods: A retrospective review was performed on 151 consecutive patients referred for CTM to evaluate for spinal CSF leak. Head MR imaging was evaluated for diffuse dural enhancement and "brain sag," and spine MR imaging for presence of an extradural fluid collection. The opening pressure was recorded. The CTM was scored as no leak, slow leak localized on conventional CTM, or fast leak that required dynamic CTM.

Results: Fast CSF leaks were identified in 32 (21%), slow leaks in 36 (24%), and no leak in 83 (55%) of 151 patients on initial CTM. There was significant association between spinal extra-arachnoid fluid on MR imaging and the presence of a fast leak (sensitivity 85%, specificity 79%, P < .0001). There was not significant association between fast leak and findings on head MR imaging (P = .27) or opening pressure (P = .30).

Conclusions: If all patients with spinal extra-arachnoid CSF on MR imaging had been sent directly to dynamic CTM, repeat myelography would have been avoided in most patients with fast leaks (23 of 27; 85%). However, a minority of patients with slow or no leaks would have been converted from conventional to dynamic CTM (16 of 77; 21%). Spinal MR imaging is helpful in premyelographic evaluation of SIH.

Fig 1.

Classic findings of SIH on MR imaging of the brain with “brain sag” demonstrated on midline sagittal T1 image (A), including descent of the cerebellar tonsils below the foramen magnum, flattening of the ventral pons (white arrows), and inferior displacement of the optic chiasm (open arrow). Postgadolinium coronal T1 image (B) demonstrates diffuse dural enhancement (white arrows.)

Fig 2.

Fast CSF leak in a patient with extra-arachnoid fluid on spinal MR imaging, localized on dynamic CTM. Large extra-arachnoid fluid collection is seen on sagittal T2 images of the thoracic spine, predominantly posterior to the thecal sac (A), which involved the entire cervical and thoracic spine. Axial gradient images through the spine confirm extra-arachnoid fluid (B). Conventional CTM shows a collection of contrast outside of the thecal sac (C, D), which extends from C3 to L4 and the leak cannot be localized. Dynamic CTM shows extraarachnoid extravasation of contrast on the right at T6-T7 (E) and also at right T7-T8 (not shown), consistent with 2 sites of CSF leak.

Fig 3.

Fast CSF leak with spinal extra-arachnoid fluid collection requiring dynamic CTM for leak localization. Fluid collection ventral to the thecal sac is best seen on axial T2-weighted images (A). This collection is smaller than the collection seen in Fig 2 and involves only the lower cervical and upper thoracic spine. Conventional CTM (B) shows a ventral contrast collection from C3 through T9, but the site of leak cannot be specified. Dynamic CTM (C) shows extra-arachnoid contrast accumulating ventral to thecal sac at C6-C7, consistent with a ventral leak at this level.

Fig 4.

Imaging algorithm in persistent spontaneous intracranial hypotension unresponsive to conservative management and nontargeted therapy.