Devoted to diagnostic and interventional spine imaging and therapeutics


Suboccipital Puncture of the Cisterna Magna under CT-Guidance with Intravenous Enhancement in order to Circumvent Anomalous Course of Posterior Inferior Cerebellar Artery (PICA) 2005

Interventional Spine

Stuart R Pomerantz, M.D.
Bradley Buchbinder , M.D., Non ASSR Member
Joshua A. Hirsch , M.D>, ASSR Member


A 46 year old male presented with 10 days of progressively severe four-extremity weakness. He was found on MRI to have diffuse non-enhancing T2-hyperintense expansion of the cervical spinal cord. The differential diagnosis included infiltrative neoplasm as well as inflammatory etiologies such as transverse myelitis, infection and demyelinating disease. The neuroradiology service was asked to perform cerebrospinal fluid (CSF) sampling at a level cephalad to the lesion as the expansion had resulted in complete spinal block placing the patient at risk of herniation with lumbar puncture. Unfortunately, the typically safe location for high CSF sampling in the posterior C1-2 subarachnoid space was also too narrowed by cord expansion to attempt needle entry.

Collection of CSF by suboccipital puncture of the Cisterna Magna is only rarely performed currently. Though the size of the cistern is typically larger than the posterior subarachnoid space at the C1-2 level, it is a less favored site due to the relatively higher risk of encountering anomalous vessels and risking hemorrhagic or ischemic complications. When the procedure is necessary, as in this case, it is typically performed under fluoroscopic guidance using standard osseous landmarks. However, close examination of the vascular flow-void pattern in this patient's sagittal T2-weighted MRI images revealed an extradural origin of the PICA from the right vertebral artery. As is typical for this uncommon variant, the right PICA coursed postero-medially and would be along the expcted midline needle trajectory utilized in the fluoroscopic approach to cisternal puncture.

Utilizing CT-guidance with concurrent intravenous contrast administration, the course of the anomalous PICA as well as the posterior aspect of the medulla were adequately visualized. A safe approach tailored to this patient's particular anatomy was planned and the procedure successfully performed without complication. Final diagnsis is still pending at this time.

As cisternal puncture under CT guidance has, to our knowledge, not been described previously, several interesting technical issues arose in procedure planning and merit further discussion. Anatomic features such as the known propensity in this region for marked tenting of the dura and the requirement for a large CSF sample weighed heavily on the optimal choice of spinal needle. There are opposing risks and benefits with employing a large or small gauge needle or one with an atraumatic "pencil-point" tip versus a cutting bevel. The vascular variants encountered in this region will be disccused as well as additional planning issues such as ideal rate of IV contrast injection, patient positioning, and trajectory planning.


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