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Neuroradiology Case of the Week

Case 56

Ravinder Sidhu MD, Jeevak Almast MD, Leena Ketonen MD, PhD,
and P-L Westesson MD, PhD, DDS

Clinical Presentation: A 60-year-old female presented with sudden onset of paraplegia. She had a past history of surgery for abdominal aortic aneurysm.

Radiological Findings: T2-weighted MR image of the thoracolumbar spine revealed a longitudinal hyperintense signal within the cord, which was extending from T5 to the level of conus medullaris. The cord was not widened (Fig. 1A). Axial T2-weighted image of the spine also showed increased signal within the cord, however, there was no swelling of the cord (Fig. 1B). Post-contrast sagittal MR image showed mild diffuse enhancement of the hyperintense signal within the cord in the thoracolumbar region (Fig. 1C).
   Contrast enhanced axial CT of the abdomen showed a large infrarenal abdominal aortic aneurysm with a thrombus and small residual lumen along with extensive arteriosclerotic changes of the aorta. No evidence of aortic dissection was seen (Fig. 2A). Left kidney was small and atrophic in size with negligible parenchymal enhancement along with few strands in perinephric region suggestive of non-functioning post-inflammatory atrophic kidney (Fig. 2B).

Diagnosis: Acute spinal cord ischemia syndrome

Discussion:  Acute spinal cord ischemia syndrome is an infrequent disease but can cause permanent disabling sequale. It mainly affects the area of the anterior spinal artery, described by Spiller in 1909 [1].
   Spontaneous anterior spinal cord infarction primarily affects individuals with severe arthrosclerotic disease or aortic dissection. Other etiologies include aortic aneurysm, syphilis, vasculitis, emboli from disk herniation, hypotension, hematological disorders, pregnancy, diabetes, trauma and aortic repair. Incidence of neurologic symptoms in patients with aortic aneurysm is described to be approximately 18.5% whereas in some cases, neurologic dysfunction herald’s aortic rupture or dissection. At present, the appearance of ischemic spinal cord syndrome after abdominal aortic surgery continues to be unpredictable. In spite of the preventive measures used during abdominal aortic surgery, it often affects the thoracolumbar region due to the distribution of spinal cord irrigation [2,3].
   The blood supply to the entire spinal cord depends primarily on three longitudinal arteries: a single anterior spinal artery and paired posterior spinal arteries. The anterior spinal artery is the major source of perfusion. Segmental radicular arteries contribute to the anterior spinal artery. The largest of the radicular arteries is the arteria radicularis magna also referred to as the great radicular artery of Adamkiewicz.The radicular artery of Adamkiewicz arises at approximately the T10-T12 area and supplies the lower thoracic and lumbar cord. However, despite this large artery, blood flow is seen to be lowest at the lower thoracic region. Since at this level, the anterior spinal artery has the poorest collateralization, making spinal cord perfusion more dependent and sensitive to blood flow of the arteria radicularis magna. Additional impairment of hypogastric blood flow with eventual interruption of the greater radicular artery has also been reported to be critical in the development of spinal cord ischemia. Therefore, this anterior arterial system, crucial for spinal cord supply, is vulnerable to hypoperfusion [4].
   The classical presentation of acute spinal cord ischemia syndrome is sudden onset of flaccid para or quadriparesis with or without burning pain. Dissociated sensory loss with preserved touch, vibration, and position sense is common.
   MR imaging is the mainstay of diagnosing acute spinal cord ischemia syndrome. In acute infarction, T1-weighted MR imaging may show enlarged cord. Central or intramedullary high signal is typically present on T2-weighted images. Enhancement following contrast may be initially absent but occurs a few days to few weeks following the onset. Follow up scans may show focal cord atrophy with myelomalacia and residual high signal intensity on T2-weighted MR images.
   MR diffusion imaging is an important adjunct to the diagnostic processes of spine, but physiological motion and magnetic susceptibility artifacts make it difficult to perform. Echoplanar imaging has limited application in the spine because of its low spatial resolution. Pulsed-gradient spin-echo diffusion imaging is sensitive to motion and requires approximately 15 minutes to image a single diffusion axis. Line-scan diffusion imaging is a conventional spin-echo based technique that is relatively insensitive to magnetic susceptibility effects and to bulk motion. Line-scan diffusion imaging provides robust diffusion imaging of the spinal cord, without the need for specialized hardware, cardiac gating, or respiratory compression [5].
   Richard et al. performed line-scan diffusion imaging of cervical and thoracic spinal cord in 18 children. They concluded that line-scan diffusion imaging can be performed in spinal cord maturation, detection/assessment of a variety of pathologic entities such as myelin loss, ischemia, trauma, tumors, and inflammatory processes [6].
   The differential diagnosis of acute spinal cord ischemia syndrome includes transverse myelitis, however it is usually associated with gradual onset symptom except in cases of acute myelitis, where it is of sudden onset.

References:

1. Silwa JA, Maclean IC. Ischemic myelopathy: a review of spinal vasculature and related clinical syndromes. Arch Phys Med Rehabil 1992; 73:365-372.
2. Sandson TA, Friedman JH. Spinal cord infarction. Report of 8 cases and review of literature. Medicine 1989; 68:282-29.
3. Friedman DP, Flanders AE: Enhancement of grey matter in anterior spinal infarction. AJNR Am J Neuroradiol 1992; 13:983-985.
4. Joo JB, Cummings AJ. Acute thoracoabdominal aortic dissection presenting as painless, transient paralysis of the lower extremities: a case report. J Emerg Med. 2000; 19:333-337.
5. Bammer R, Herneth AM, Maier SE, Butts K, Prokesch RW, Do HM, Atlas SW, Moseley ME. Line-scan diffusion imaging of the spine. ANJR Am J Neuroradiol 2003; 24:5-12.
6. Robertson RL, Maier SE, Mulkern RV, Vajapayam S, Robson CD, Barnes PD.Line- scan diffusion imaging of the spinal cord in children. AJNR Am J Neuroradiol 2000; 21:1344-1348.