Adhesive Arachnoiditis: Chronic Scar Phase (Class III)
By the time the process has reached the chronic phase there is prominent collagenous scar deposition. The nerve roots are adherent to each other and to the meninges. Surgically opening the dura often shows what appears to be an empty sac because the nerves are now actually part of the dural membrane. By the Class III stage the inflammatory cells seen document a chronic process. The nerves themselves have been progressively deprived of nourishment as the nutrient blood vessels have atrophied and the "percolating" nourishment derived from the cerebrospinal fluid has markedly decreased. It is, in fact, a tribute to the human nervous system that in the face of such adversity, in can, in the great majority of cases, continue to maintain "normal" function. The only way this can happen is if the adverse process occurs slowly enough to allow the system to adapt and acclimate. The acclimization is, however, fragile. Because function is maintained precariously any additional insult (i.e. trauma, surgery, myelography, etc.) can tip the balance and cause onset of clinical disability and incapacitation.
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By far the greatest number of cases of adhesive arachnoiditis which have occurred throughout the world during the 20th century resulted from oil myelography with either Pantopaque® or Myodil®. Because these substances are hyperbaric once they were placed in the subarachnoid space they would migrate to the distal portion, where they remained, producing progressive scarring.
The patterns of adhesive arachnoiditis scar are typically quite variable in their patterns. Sown above are drawings of variable scar patterns in three actual cases. These are patterns reflecting diffuse, multi-level involvement, characteristic of the introduction of a toxic foreign body substance into the sub-arachnoid space. The last illustrations to the right shows how residual droplets of foreign body substance (in this case Pantopaque®) are surrounded by encapsulating scar reflecting the body's defense against foreign body substances.
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The Anatomy of Adhesive Arachnoiditis