Magnetic resonance imaging of the spinal column
São Jose do Rio Preto, Brazil
* E-mail: dr.imbelloni{at}terra.com.br
Editor—Recently, the safe use of segmental spinal anaesthesia at T10 by using the combined spinal–epidural technique has been demonstrated.1 2 On the basis of these two papers, we evaluated the distance from the dura mater to the spinal cord by analysing the MRIs of 16 patients without spinal or medullary disease using the 1.5 T super-conducting system (Gyroscan Intera, Philips Medical Systems, Best, The Netherlands). Measurements were made through sagittal spin-echo at the second, fifth, and 10th thoracic segments. Using the means of variation, no difference was found between interspaces T2 [3.59 (0.79) mm] and T10 [3.30 (0.78) mm] (P=0.119). There was a significant difference between T5 and T2 (P=0.001) and T5 [4.32 (1.1) mm] and T10 (P=0.002). There was no evidence of correlation between the age and the measured distance between the dura mater and the spinal cord. There was evidence of correlation between the measurement at T2 and those at T5 (r=0.8; P<0.001) and T10 (r=0.6; P=0.015). The longest distance between the dura mater and the spinal cord was at the fifth thoracic segment (Fig. 1). The calculated entry angle for a needle at T5 was 60°.
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By our calculations, the distance from the entry point of the needle at an angle of 60° at T5 would double the distance to obtain cerebral spinal fluid when compared with a 90° angle at L3/L4 to 8.64 (2.2) mm. As the distance from the dura mater until the spinal cord at T5 is greater than at L1/L2, the 60° angle could increase the safety.
On the basis of these evaluations of T2, T5, and T10, we believe that the introduction of the needle in an acute angle (60°) may give greater safety for thoracic spinal anaesthesia.
References
1 van Zundert AAJ, Stultiens G, Jakimowicz JJ, van den Borne Beem, van der Ham WGJM, Wildsmith JAW. Segmental spinal anaesthesia for cholecystectomy in a patient with severe lung disease. Br J Anaesth (2006) 96:464–6.
2 van Zundert AAJ, Stultiens G, Jakimowicz JJ, et al. Laparoscopic cholecystecomy under segmental thoracic spinal anaesthesia: a feasibility study. Br J Anaesth (2007) 98:682–6.
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