Effect of spinal CSF dynamics on the subarachnoid diffusion of a substance applied close to the spinal cord

In order to better understand the effects and side effects of intraspinal administration of morphine we studied the rostral spread of a comparable substance within the cerebrospinal fluid (CSF). This study was performed in connection with nuclear medical diagnostics ruling out possible rhinorrhoea or disturbances of CSF-circulation in 14 patients: Following lumbar intrathecal injection of the tracer 111-Indium-DTPA, the radioactivity over the medulla oblongata was measured continuously for 2 1/2 hours with a single probe scintillation counter; thereafter the distribution of activity over the total spinal canal was determined; finally the spread of activity was registered with the gamma scintillation camera in the 3rd, 24th and 48th hour. The diffusion of the tracer was followed in a model of the subarachnoid space. A few minutes after injection, activity over the medulla oblongata could be detected; initially it increased markedly, later less so; at the end of the 2 1/2 h observation time, approximately 8% of the total activity had reached this level. The timing of activity increase and the peak activity over the medulla oblongata varied between the individuals. Up to 48 hours the activity continued to shift from the spinal canal to the endocranium. Diffusion played a secondary role. These results are further evidence that morphine is transported cephalad within the CSF rather quickly and may act on cervical spinal cord and brainstem.