SUMMARY:A novel transosseous approach for percutaneous access of the lumbar subarachnoid space is described in a patient with advanced ankylosing spondylitis (AS) and instrumented spinal fusion who presented for myelography. Use of a coaxial threaded bone biopsy system to provide transosseous access to the thecal sac, imaging findings, and outcome are discussed. This technique provided access to an otherwise inaccessible subarachnoid space and is an alternative approach in the setting of advanced AS or posterior spinal fusion.A nkylosing spondylitis (AS) is a seronegative spondyloarthropathy that can affect the sacroiliac joints, vertebral bodies, intervertebral disks, spinal facet joints, costovertebral joints, costotransverse joints, and the paravertebral soft tissues, including tendon and ligament attachments.1 In the setting of AS, access to the subarachnoid space for myelography can be difficult or impossible by using conventional lumbar puncture techniques due to spinal ankylosis, associated softissue abnormalities, and prior spinal fusions. 2 We describe a novel controlled transosseous approach to access the lumbar subarachnoid space safely in a patient with complete spinal fusion from AS and prior surgical fusion by using the Bonopty Bone Biopsy System (Radi Medical Systems, Uppsala Sweden).
Technical ReportA 44-year-old man with advanced AS and prior posterior spinal fusion from the occiput to the pelvis presented with progressive myelopathy (Fig. 1). CT and MR imaging were attempted but were limited due to metal artifacts from the extensive spinal fusion hardware. There were findings of upper and midthoracic spinal cord syringohydromyelia on MR imaging, but the presence/absence of subarachnoid adhesions, which could be causative, could not be determined (Fig 2). A total spine myelogram was requested via the C1-2 approach.Review of prior cervical imaging showed extensive ossification at the craniocervical junction and a diminutive dorsal CSF space at C1-2. The C1-2 approach was deemed unsafe. A decision was made to attempt myelography via a lumbar approach by using CT guidance. The preprocedural CT scan showed complete ankylosis across the facets joints and between the lamina in conjunction with prior surgical bone graft fusion material over the posterior elements, resulting in a confluent continuous osseous barrier. A classic interlaminar lumbar puncture with standard spinal needles was not possible due to the extent of ossification/fusion. A lumbar transforaminal approach was considered but dismissed due to anatomic considerations and patient positioning/comfort issues. It was decided to attempt access by drilling through the lamina and coaxially introducing a spinal needle into the thecal sac.The patient was placed prone on the CT table and made comfortable, which required significant bolstering due to his fixed spinal kyphosis. After initial scanning of the lumbar spine, a left paramedian approach at L2-3 was selected due to the relative thinness of the osseous fusion in that position. Through a sma...