Magnetic Resonance Imaging of Cerebrospinal Fluid Volume and the Influence of Body Habitus and Abdominal Pressure

Abstract

CSF volume is widely variable between individuals. The decreased CSF volume that results from increased abdominal pressure, such as with obesity or pregnancy, may produce more extensive neuraxial blockade through diminished dilution of anesthetic. The mechanism by which increased abdominal pressure decreases CSF volume is probably inward movement of soft tissue in the intervertebral foramen, which displaces CSF.

Thoracic Spinal Anesthesia

“…The modern means of image, associated to computed means have facilitated the evaluation of the CSF volume, through anteroposterior and height measures of the subarachnoid space based on bi-dimentional studies of MRI [21].…”

“…The total amount of CSF in the thoracic segment is less in comparison to the lumbar and cervical segment [21], and the toracic radiculae are thinner as compared to the lower or upper ones [36]. So, there is a lesser dilution of the anesthetic per segmento f the distance of the site of injection, and the rootles as easily blocked due to its small diameter, both factors of good block.…”

Trying to understand spinal anesthesia

“…Because the surgical indication was Cesarean delivery, they sought a high block, and it is not entirely surprising that the peak block height clustered tightly around T2 and T3, due to certain non-uniform features of the subarachnoid space. The amount of CSF at thoracic levels is diminished compared to lumbar and cervical levels, 3 and the thoracic nerve roots are very slight compared to segments above and below. 7 Thus, there is less anesthetic dilution per segmental unit of distance from the site of injection, and the roots are easily blocked due to their small size, both factors predicting efficient blockade of these segments.…”

“…La mesure directe du volume du LCR vertébral n'est devenue possible qu'avec l'invention de l'imagerie axiale, et les décou-vertes effectuées à l'aide de l'imagerie par résonance magnétique (IRM) confirment en effet qu'il y a notamment une distribution étendue de volumes de LCR lombaire, par exemple une gamme de 21 mL à 74 mL chez 25 patients typiques. 3 Il est facile de croire que des différences si extraordinaires doivent réguler la dilution anesthésique et ainsi l'étendue du bloc, 4 et que le volume du LCR d'un patient en particulier serait une mesure précieuse qu'il faudrait connaître avant la rachianesthésie. Bien que les techniques d'IRM récentes soient efficaces, 5 il ne s'agit pas encore d'une modalité utile à la pratique clinique.…”

“…Direct measurement of the vertebral CSF volume only became possible with the invention of axial imaging, and findings using magnetic resonance imaging (MRI) indeed confirm that there is a notably wide span of volumes of lumbar CSF, for instance a range of 21 mL to 74 mL in 25 typical subjects. 3 It is easy to believe that such extraordinary differences must regulate anesthetic dilution and therefore extent of blockade, 4 and that a particular patient's CSF volume would be very valuable to know prior to spinal anesthesia. Although newer MRI techniques are more efficient, 5 this is not yet a feasible approach for planning clinical care.…”