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LETTER TO EDITOR
Year : 2013  |  Volume : 61  |  Issue : 1  |  Page : 97-99

The enigma of dorsal cord migration after cervical laminectomy: A radiological entity or something else?


Department of Neurosurgery, Nizam's Institute of Medical Sciences, Hyderabad, Andhra Pradesh, India

Date of Submission03-Jan-2013
Date of Decision07-Jan-2013
Date of Acceptance21-Jan-2013
Date of Web Publication4-Mar-2013

Correspondence Address:
Ashish Kumar
Department of Neurosurgery, Nizam's Institute of Medical Sciences, Hyderabad, Andhra Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0028-3886.108048

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How to cite this article:
Narayana S, Kumar A, Alugolu R. The enigma of dorsal cord migration after cervical laminectomy: A radiological entity or something else?. Neurol India 2013;61:97-9

How to cite this URL:
Narayana S, Kumar A, Alugolu R. The enigma of dorsal cord migration after cervical laminectomy: A radiological entity or something else?. Neurol India [serial online] 2013 [cited 2019 Sep 22];61:97-9. Available from: http://www.neurologyindia.com/text.asp?2013/61/1/97/108048


Sir,

A 45-year-old male patient, who had a history of trivial trauma 15 days before, presented with gradually progressive weakness in all the four limbs associated with heaviness and clumsiness since then. On examination, there was hypertonia in all the four limbs and the power in all muscle groups was grade 4/5. Deep tendon reflexes were brisk and the plantars were extensors bilaterally. Magnetic resonance imaging (MRI) of cervical spine showed thick ossified posterior longitudinal ligament (OPLL) from C2-C7 with severe canal stenosis and cord compression and absolute cut-off on myelogram [Figure 1]. Cerebrospinal fluid (CSF) column was not seen either ventrally or dorsally to the cord at these levels but was maintained at the level of C1 [Figure 2]. In view of the diffuse thick OPLL extending all the way from C2-C7 (more than three levels), a posterior approach was planned and C2-C7 laminectomy was done. During the immediate post-operative period, power in all the four limbs deteriorated, more so in the upper limbs. It was felt that this deterioration was probably secondary to central cord syndrome, a known complication of decompressive laminectomy in severe cervical canal stenosis. [1] Four days post-surgery, power in both his lower limbs also worsened. A repeat MRI and computed tomography (CT) was done which showed evidence of C2-C7 post laminectomy status with evidence of decompression of cord in the form of appearance of CSF column all around the cord [Figure 3]. But at the level of C1 arch, the CSF column seen before the first surgery was lost along with change in cord contour. In view of the MRI findings of a new radiological compression at C1 level due to dorsal cord shift and giving a benefit of doubt, a second surgery consisting of C1 posterior arch excision and lateral mass screw fixation of the sub-axial cervical spine was done (to prevent development of delayed kyphotic deformity). Unfortunately, the neurological status did not improve significantly in the immediate post-operative period, but there was a minimal recovery (>2 weeks after second surgery) in the form of increase in muscle power by one grade in all four limbs. But this improvement cannot be specifically attributed to C1 arch removal since this could be a natural recovery from the central cord syndrome developed after C2-C7 laminectomy (alleviating the need for second surgery). This actually made us review the literature regarding the phenomenon of dorsal cord migration after posterior decompression and its radiological sequelae which may incite a feeling of "pseudo compression" at upper and lower limits of laminectomy defect. Dorsal cord shift after a laminectomy or laminoplasty for cervical canal stenosis due to OPLL or degenerative disease is a well-known entity and is described as one of the major factors to calculate the amount of decompression achieved and also in predicting the post-op neurological recovery. Sodeyama et al.,[2] found that dorsal cord shift of >3 mm was associated with good clinical outcome. Even though in our patient the cord shift was >3 mm, the recovery was not as expected. We also came across this study done by Lee et al.,[3] where they tried to identify pre-operative imaging parameters, which are predictive of postoperative dorsal cord shift after laminectomy and arthrodesis. They opined that a relative stenosis at the adjacent level to the laminectomy may also influence maximal cord drift, with level cephalad to the laminectomy having higher predictive value than the caudal one. According to their results, to achieve a mean post-operative cord drift of 4mm with laminectomy, the Space Available for Cord to Cord Diameter ratio (S/C ratio) should be 2 mm or more. If it is <2 mm, advice is to include that level in the laminectomy. In our patient at the cephalad level, i.e., at C1 arch, the S/C ratio was <2 mm, but still C1 arch was not resected during the first surgery. Junwei Zhang et al.,[4] concluded that outcomes are better if C1 is included in laminectomy for high cervical compression, i.e., at C2-C4 levels. However, in contrast to these findings Fujimura et al.,[5] proved no correlation in terms of outcome between dorsal cord shift and OPLL, but found a significant positive correlation between outcome and post-operative increase in cord diameter. In our patient, the post-operative diameter increased on imaging, but still the improvement was not on expected lines. This could well have been due to the intra-operative insult to the cord (and, hence, the deterioration is understandable), but the point which remains in question is not the deterioration. It is rather the radiological misinterpretation due to dorsal cord shift, which prompted us for the second stage surgery. We could not find a similar case in the literature where similar dilemma existed in the neurosurgeon's mind even after two surgeries. Whether the delayed recovery was secondary to the C1 arch removal or it was the natural course of the already improving central cord syndrome, we could not establish definitely. This possible misinterpretation by us about the dorsal cord shift causing an apparent compression at the higher level leading to another surgery may lead future generations to probably wait and watch for some time before they jump on to the secondary intervention based on pure radiology.
Figure 1: (a) MRI Sagittal sections of C-Spine showing evidence of thick OPLL extending from C2-C7 causing canal stenosis and compressed cord (b) MR Myelogram showing lack of CSF flow from C2 to C7 suggestive of severe compression

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Figure 2: MRI T2W Sagittal sections showing lack of CSF column ventral and dorsal to the cord from C2-C7, but maintained at C1

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Figure 3: (a) CT Sagittal section showing C2-C7 laminectomy status with deformed cord contour at C1 level (b) MRI T2W Sagittal sections showing evidence of post-laminectomy status from C2-C7 with newly formed CSF columns anterior and posterior to the decompressed cord and loss of CSF column at C1 (arrow)

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  References Top

1.Levy WJ, Dohn DF, Hardy RW. Central cord syndrome as a delayed postoperative complication of decompressive laminectomy. Neurosurgery 1982;11:491-5.  Back to cited text no. 1
[PUBMED]    
2.Sodeyama T, Goto S, Mochizuki M, Takahashi J, Moriya H. Effect of decompression enlargement laminoplasty for posterior shifting of the spinal cord. Spine (Phila Pa 1976) 1999;24:1527-31.  Back to cited text no. 2
    
3.Lee JY, Sharan A, Baron EM, Lim MR, Grossman E, Albert TJ, et al. Quantitave prediction of spinal cord drift after cervical laminectomy and arthrodesis. Spine (Phila Pa 1976) 2006;31:1795-8.  Back to cited text no. 3
    
4.Zhang J, Hirabayashi S, Saiki K, Sakai H. Effectiveness of multiple-level decompression in laminoplasty and simultaneous C1 laminectomy for patients with cervical myelopathy. Eur Spine J 2006;15:1367-74.  Back to cited text no. 4
[PUBMED]    
5.Fujimura Y, Nishi Y, Nakamura M. Dorsal shift and expansion of the spinal cord after expansive open-door laminoplasty. J Spinal Disord 1997;10:282-7.  Back to cited text no. 5
[PUBMED]    


    Figures

  [Figure 1], [Figure 2], [Figure 3]



 

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