Dilated Vein of the Filum Terminale on MRI: A Marker for Deep Lumbar and Sacral Dural and Epidural Arteriovenous Fistulas

Abstract

Background and purpose: Conventional MR imaging can provide important clues regarding the location of a spinal vascular malformation. We hypothesized that a dilated vein of the filum terminale, identified as a curvilinear flow void on T2WI, could be an imaging marker for a lower lumbar (L3-L5) or sacral fistula.

Materials and methods: We retrospectively identified all spinal dural and spinal epidural arteriovenous fistulas from 2 large tertiary referral centers from 2005 to 2018. All patients had a lumbar spinal MR imaging and a conventional spinal angiography. Images were reviewed by 2 neuroradiologists who categorized the level of the arterial feeder to the fistula and the presence or absence of a dilated vein of the filum terminale on T2WI and T1 postcontrast images. We calculated the sensitivity, specificity, positive predictive value, and negative predictive value of the presence of a dilated filum terminale vein for a deep lumbar or sacral fistula.

Results: One hundred sixty-two patients were included. An enlarged filum terminale vein was identified in 39 patients. Sensitivity, specificity, positive predictive value, and negative predictive value of the presence of a dilated filum terminale vein for a deep lumbar or sacral fistula were 86%, 98.3%, 94.9%, and 95.1%, respectively.

Conclusions: The presence of a dilated vein of the filum terminale can accurately localize a spinal dural arteriovenous fistula/spinal epidural arteriovenous fistula to the lower lumbar or sacral spine in patients being evaluated for such lesions. This finding can be used to facilitate both noninvasive and conventional spinal angiography.

Fig 1.

A 63-year-old woman with a sacral dural arteriovenous fistula at S1. A, Sagittal T2-weighted MR imaging shows a dilated vein of the filum terminale (white arrow). B, Contrast-enhanced T1-weighted MR imaging again demonstrates the dilated vein of the filum terminale (white arrow). C, Rotational digital subtraction angiogram reformatted in the coronal plane following injection into the right internal iliac artery demonstrates a fistula at S1 (arrowhead), with a dilated vein of the filum terminale.

Fig 2.

A 75-year-old man with a sacral dural arteriovenous fistula at S1. A, Sagittal T2-weighted MR imaging shows a dilated vein of the filum terminale (white arrow). B and C, Contrast-enhanced MRIs demonstrate marked dilation of the vein of the filum terminale (white arrow). D, Conventional angiogram in the anteroposterior plane following injection into the right internal iliac artery demonstrates a fistula at S1 with a dilated vein of the filum terminale (black arrow).

Fig 3.

An 80-year-old man with a sacral dural arteriovenous fistula at S1. A, Sagittal T2-weighted MR imaging shows a dilated vein of the filum terminale (white arrows). B, Contrast-enhanced T1-weighted MR imaging again demonstrates the dilated vein of the filum terminale (white arrows). C, Conventional angiogram in the anteroposterior plane following injection into the right internal iliac artery demonstrates a fistula at S1 with a dilated vein of the filum terminale (black arrows).