The complications associated with 92 dorsal column stimulator implants are reported. They were of two types, technical and functional. In all there were 58 significant complications. Most technical complications were correctable but complications difficult to correct occurred in 26 patients. Late failure in stimulation was observed in 32 implants that had given excellent pain control for periods ranging from months to years. Improvements in the results of this procedure may be achieved by future technical developments and by clarification of physiological mechanisms.
The entry zone of trigeminal sensory root fibers displays a "glial dome" covered by a basal lamina. This zone constitutes the "fibrous cone" of gross descriptions of the root and demarcates a sharp transition from peripheral to central nervous system. The dome consists of closely interwoven astrocyte processes, and a p pears to be identical to the subpial astrocyte meshwork elsewhere in the central nervous system. In the peripheral portion of the root, axons are surrounded by Schwann cells; those associated with myelin sheaths display distinctive laminar inclusions and pinocytotic vesicles lacking in Schwann cells which surround unmyelinated axons. In the peripheral region, separate and distinct endoneurial and perineurial layers of collagen could not always be identified. In the central part of the root, Schwann cells, fibroblasts, and collagen are absent and from the point of transition, the axons are principally surrounded by astrocytes. Oligodendrocytes are relatively rare in the transitional zone. The axonal transition from central to peripheral, occurs at nodes of Ranvier where the basal lamina of the dome is continuous with the basal lamina of the Schwann cell of the last peripheral internode. Sqme "islands" of glial tissue are interspersed in the root and ganglion but it was not established if these are completely discontinuous with the central "glial dome." No ganglion cells have been found in such "islands," nor in the glial dome.The sensory root of the trigeminal nerve displays a grossly visible "fibrous cone" (Dandy, '32; Jannetta and Rand, '66) which demarcates the transition between peripheral and central nervous tissue and delimits an abrupt change in axonal environment. This "fibrous cone" is a periphereral extension of the central nervous system extending for a variable distance into cranial and spinal nerve roots (Tarlov, '37) and is known to contain neuroglial elements (Tarlov, '37; Horstmann, '56; Foncin, '61; Maxwell, '67). The present report constitutes a description of the distinctive cytologic features at the transitional zone of entrance of trigeminal nerve fibers into the central nervous system, where mesodermal and neural crest derivatives characteristic of peripheral nerve are continuous with components of the central nervous system. METHODSMaterial for the present study was derived from animals employed in a study of ANAT. REC., 164: 113-126.the degenerative events following trigeminal rhizotomy in Macaque monkeys (Pineda, Maxwell and Kruger, '67; Abbott and Jannetta, '68; Abbott and Maxwell, submitted for publication). Normal trigeminal roots and ganglia were removed for microscopic study following fixation of experimental and control animals, and the present observations are based upon study of unoperated roots in five experimental and control monkeys and have been confirmed in two normal cats.The fixative employed was either 2% glutaraldehyde and 2% formaldehyde (Pease, '64) or 0.5% glutaraldehyde and 4% formaldehyde, in both cases prepared in 0.1 M sodium cacodylate (dim...
Neurons and satellite cells in the trigeminal ganglion of cats and monkeys fixed by aldehyde perfusion were examined in the electron microscope. The fixative employed and its tonicity appear to be critical factors in accounting for some of the differences noted in earlier descriptions. With satisfactory preservation, only one variety of neuron is seen on the basis of cytoplasmic and nuclear features, although there is a substantial size range. Interdigitating processes of neurons into the satellite cell capsule probably accounts for the axon terminals and intracapsular nerve nets reported in early metallic impregnation studies. Axonal glomeruli are encased in satellite cells and become myelinated by Schwann cells as the axon leaves the region of the neuron soma.Satellite cells reveal layers of attenuated processes forming unusual membrane complexes around the axons. The external surfaces of the satellite cells are completely invested with a prominent basal lamin? which is continuous with that surrounding the Schwann cell at the first "internode.
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