MR Diffusion Tensor Imaging and Fiber Tracking in Spinal Cord Arteriovenous Malformations: A Preliminary Study
A. Ozannea,
T. Kringsa,
D. Facona,
P. Fillardb,
J.L. Dumasc,
H. Alvareza,
D. Ducreuxa and
P. Lasjauniasa
a Service de Neuroradiologie Diagnostique et Thérapeutique, Hôpital de Bicêtre, Le Kremlin-Bicêtre, Paris, France
b Department of Computer Science, University of North Carolina, Chapel Hill, NC
c Department of Radiology, Hôpital Avicenne, Université Paris, Bobigny, France
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Fig 1. Venous congestion of the spinal cord and separated tracts (patient 1, DTI25d). This 57-year-old woman presented with a 2-year history of progressive paresthesia in the bilateral lower limbs, followed by further development of leg weakness and sphincter problems. The McCormick score was II. A pial arteriovenous fistula that was fed by the lateral spinal artery arising from the left posteroinferior cerebellar artery was found.
A, T2-weighted images showed enlargement of the spinal cord at the C6 level with hyperintensity reflecting local venous congestion (arrow).
B, There was a dilated vessel at the anterior surface of the cord, which corresponded with a vein draining the shunt caudally, as depicted on selective injection during angiography.
C, Posterior view of the FT25d showed separated fascicles at the level of C6 (arrow), with global enlargement of the beam of tracts. The remaining fibers were grouped together into fascicles. By counting the tracts at the level of the congestion (674) and below it (741; ratio: lesion level/caudal to lesion = 0.91), we were able to show that there was no evidence of focal interruption of the tracts.
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Fig 2. Cavity in the cord: thinning of the beam of tracts and separated tracts (patient 2, DTI6d). This 29-year-old woman presented to our service 3 months after she had experienced a sudden complete paraplegia. Subsequently, no clinical improvement was noted.
A–C, The T2-weighted (A and B) and T1-weighted (C) morphologic sequences showed a central cavity within the thoracic cord, an AVM nidus located at T5, and dilated perimedullary vessels mainly cranial but also caudal to the nidus. There was only a moderate enlargement of the cord, which may have been because of the mass effect of the venous pseudoaneurysm.
D, Anteroposterior view of the angiogram showed the venous drainage of the arteriovenous shunt. There was a venous false aneurysm at the level of the nidus that was partially thrombosed as depicted on MR imaging (hyperintensity on both T1 and T2) and surrounded by hemosiderin (hypointensity on T1 and T2), indicating a previous hemorrhage, responsible for her initial symptoms.
E, Posterior view of the FT6d caudal to the nidus (arrow) showed a global thinning but no interruption of the beam of tracts at the level of the cavity in comparison with the normal size of the white matter tracts at C7 (double arrows). The tracts were separated from the midline but still grouped into fascicles.
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Fig 3. Nidus and segmental interruption of tracts (patient 3, DTI25d). A 23-year-old man presented with bilateral upper limb paresthesia, predominantly on the right side with a sensory deficit. MR imaging showed edema of the cervical spinal cord around the cervical AVM nidus at C2-C3, without any sign of hemorrhage. Angiography revealed a nidus inside the right hemicord, posteriorly located, fed by the pial network arising from the right vertebral artery. First embolization was followed by a clinical improvement of the right upper limb and regression of the T2 hyperintensity on MR imaging. A second session of embolization was performed 1 year later.
A, The third (and last) angiogram performed 3 years 9 months after the onset of the symptoms was not followed by embolization.
B, MR imaging performed at that time with DTI showed T2-hyperintensity inside the inferior part of the nidus corresponding with the embolized part of the nidus.
C, FT25d showed segmental interruption of the tracts of the right posterior column (arrowhead) as could be verified by counting the tracts at the level of the lesion (681) and below it (1017; ratio: lesion level/caudal to lesion = 0.67). The remaining tracts of the lateral column and the midline were slightly shifted showing a mild mass effect on the midline.
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Fig 4. Nidus at the surface of the cord shifting the tracts (patient 5, DTI25d). A 14-year-old boy presented 4 months after he experienced a sudden paraplegia, which secondarily completely resolved (McCormick I).
A–C, MR imaging showed a nidus located close to the right surface of the thoracic cord, at the level of T8-T9. On these T2-weighted images, no hyperintensity of the cord was visualized.
D shows the anisotropy that, because of the small remaining volume of the cord at that level, cannot be determined.
E demonstrates displacement of the beam of fibers to the right without focal interruption (FT25d). Distal to the nidus, the fibers seem to be more separated compared with the proximal part, which may indicate an increased water content of the cord that is not yet visible on T2-weighted images as edema, which in fact suits the decreased FA values that were found in this area (Table 2).
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Fig 5. Increase of the tracts (FT6d) after embolization (patient 6, DTI6d). A 21-year-old woman with cervical spinal cord arteriovenous malformation first presented with a sudden tetraplegia when she was 12 years old. The neurologic status gradually improved (the McCormick score was grade I at the time of referral to our hospital). MR imaging, angiograms, fiber tracking before (A, C, and E) and after embolization (B, D, and F), and FA and ADC images (G and H) are shown.
At the level of the nidus (arrow), located within the cord, there was partial discontinuity of the tracts (E). Above and below the nidus, conventional T2-weighted images (A,B) showed a central cavity in the cord. Here, FT6d showed both a global thinning of the beam (double arrow in E) and separated tracts around the central cavity. When we compared the evolution after embolization, angiography demonstrated decrease of flow inside the nidus and the draining veins (D). T2-weighted images did not show any modification of the appearance of the perinidal cord. The FT6d showed (F) an increased number of tracts at the level (arrow) and just above (double arrow) the nidus, presumably due to a reduction of venous congestion with concomitant higher FA values and therefore better visualization of fiber tracts. Panels G and H demonstrate the FA values and the ADC map with the ROI placements (white areas) at 3 different levels.
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Fig 6. Hemorrhage in the spinal cord (patient 7, DTI6d). An 18-year-old male patient presented with a sudden paraplegia because of hemorrhage in a thoracic AVM. When he was admitted 3 months later, the neurologic status was the same (McCormick IV).
A, MR imaging showed a nodular heterogeneous signal intensity inside the thoracic cord at the T2 level, corresponding with the point of bleeding.
B, The cord hemorrhage was located in the vicinity of the nidus that harbored an associated arterial aneurysm in the anterior sulcus of the cord with concomitant mass effect on the anterior spinal artery (arrow). An associated T2 hypointensity corresponding with hemosiderin was located at the anterior part of the cord and spread cranially to the midbrain and caudally to T4 level.
C, FT6d showed an interruption of all of the tracts at the T2-level (arrow), presumably because of susceptibility artifacts related to hemosiderin.
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