Central neuraxial block has a low incidence of major complications, many of which resolve within 6 months.1 During attempts to insert a spinal needle into the lumbar subarachnoid space, patients occasionally experience paresthesia, with a reported incidence of 13.6%.1 Neurologic complications, including spinal cord injury,2 may arise during administration of the epidural block because the needle or catheter may cause direct nerve trauma. Accidental dural puncture during needle insertion occurred in 0.4%–1.2% of instances in a series of 6496 thoracic epidural blocks, but none of the 48 patients developed subsequent neurologic sequelae.3–5
Recently, the anatomy of the thoracic spinal canal was investigated with MR imaging in 50 patients.6 The space between the dura mater and spinal cord in the thoracic region measured with MR imaging was 5.19 mm at T2, 7.75 mm at T5, and 5.88 mm at T10 (Fig 1). The angle of entry between T5 and T6 (almost 50°) elongated the distance from the tip of the needle to the posterior surface of the cord. MR imaging (Fig 1) confirms that the cord and the cauda equina are touching the dura mater posteriorly in the lumbar region and anteriorly in the thoracic region (the spinal cord). This position increases the distance to a point that permits the advancement of a needle without touching the cord, such as in the case of accidental perforation of the dura mater during the administration of spinal anesthesia. This can be an explanation for the low incidence of neurologic complications during accidental perforation of the dura mater in an attempt to perform a thoracic epidural block3–5 and the safety of segmental spinal anesthesia when using a thoracic approach.7,8
Fig 1.
MR imaging of the thoracic column.
References
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