How frequent is chronic lumbar arachnoiditis following intrathecal Myodil?

Chronic lumbar arachnoiditis has numerous causes, including the introduction of contrast media into the lumbar subarachnoid space. The oily contrast medium Myodil (iophendylate) is often cited but the true incidence of symptomatic lumbar arachnoiditis due solely to the presence of Myodil is unknown. A retrospective review of 98 patients in whom Myodil was introduced by ventriculography or cisternography, i.e. remote from the lumbar spine, revealed no cases of chronic lumbar arachnoiditis. All patients were monitored closely for periods ranging from 1 to 28 years. We conclude that, in these circumstances, it is rare for Myodil to produce symptomatic arachnoiditis.