Clinicopathological study of “snake-eye appearance” in compressive myelopathy of the cervical spinal cord

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Object. The goal of this study was to elucidate the pathophysiological features and clinical significance of the magnetic resonance imaging—documented small intramedullary high signal intensity known as “snake-eye appearance” (SEA) in cases of compressive myelopathy such as cervical spondylosis or ossification of the posterior longitudinal ligament.

Methods. One hundred forty-four patients with compression myelopathy who underwent surgery between 1998 and 2000 were selected. Intramedullary high signal intensity was found in 79 cases and was divided into two types, SEA and non-SEA (NSEA). The Japan Orthopaedic Association (JOA) scoring system was used for evaluation of pre- and postoperative neurological status. In nine cases of SEA autopsy was performed and specimens were histologically analyzed.

The improvement ratio determined by JOA score was 32.2 ± 15.1% in SEA, 47.1 ± 12.1% in NSEA, and 50 ± 18.3% (p < 0.01) in control cases in which high signal intesity was absent. There were significant differences among SEA, NSEA, and control groups. In a separate group of nine patients who died of unrelated causes, histological examination showed small cystic necrosis in the center of the central gray matter of the ventrolateral posterior column and significant neuronal loss in the flattened anterior horn.

Conclusions. Snake-eye appearance was found to be a product of cystic necrosis resulting from mechanical compression and venous infarction. Destruction of the gray matter accompanying significant neuronal loss in the anterior horn suggested that SEA is an unfavorable prognostic factor for the recovery of upper-extremity motor weakness.

Article Information

Address reprint requests to: Junichi Mizuno, M.D., Department of Neurological Surgery, Aichi Medical University, 21 Karamata Yazako Nagakute, Aichi-gun Aichi 480–1195 Japan. email: jmizuno@amugw.aichi-med-u.ac.jp.

© AANS, except where prohibited by US copyright law.

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Figures

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    Magnetic resonance images obtained in a 73-year-old man who presented with painful numbness and muscle atrophy in his upper limbs. Upper Left: Preoperative sagittal image revealing a linear high signal area from C3–4 to C-6 with cord compression. Upper Right: Axial image obtained at C-5 revealing an SEA in the central gray matter. Lower Left: Sagittal image obtained 1 month after surgery demonstrating cord atrophy with expanded high signal area at C3–4 and C5–6 despite resolution of cord compression. Lower Right: Axial image obtained at C-5 revealing persistent SEA.

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    Graphs. Upper: Correlation between IMHSI and weakness of upper-limb motor dysfunction in cases of one-level IMHSI, multilevel IMHSI, and control group patients (IMHSI(−)). There was a significant difference between multilevel IMHSI and other groups (p < 0.05). UL = upper-limb. Lower: Recovery rate between IMHSI (SEA and NSEA) and control group (IMHSI(−)). The recovery rate of SEA was significantly lower than those of other groups (p < 0.01).

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    Photomicrographs. Upper: Cystic necrosis was formed in the central gray matter near the ventrolateral posterior horn. The anterior column and right lateral column were well preserved, whereas the left lateral column was partially damaged. The anterior horn was flattened with right-sided predominance. Center and Lower: Higher-magnification image demonstrating localized cyst formation associated with a decrease of anterior horn cells. Klüver-Barrera, original magnification × 2.5 (upper) and × 20 (center and lower).

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    Upper: The spinal cord showed triangular deformity. Cystic necrosis was formed in the anterior horn as well as in the central gray matter of the posterior horn. The anterior horn was severely degenerated with marked neuronal loss. Klüver-Barrera, original magnifications × 2.5 (upper) and × 20 (center and lower).

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    Photomicrograph showing spongy degeneration of the pericystic area was observed. Small veins around cysts showed fibrous degeneration with narrowing of the lumen (arrows). H & E, original magnification × 40.

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