Occult Spinal Dysraphism by R. Shane Tubbs & Rod J. Oskouian & Jeffrey P. Blount & W. Jerry Oakes

Author:R. Shane Tubbs & Rod J. Oskouian & Jeffrey P. Blount & W. Jerry Oakes
Language: eng
Format: epub
ISBN: 9783030109943
Publisher: Springer International Publishing

Biology

LMCs arise from disordered neurulation (see Chap. 2) leading to fatty-fibrous masses that occupy variable amounts of space within the spine and lumbar soft tissue [4, 5]. Several classification schemes have been proposed, but each fails to characterize the extreme variability of LMCs simply yet adequately [7, 17, 24, 25]. The fatty tissue is mature adipose tissue arranged in a loose connective stroma histologically indistinguishable from normal adipose tissue [26]. Detailed analysis of large series has demonstrated rare mesenchymal elements such as muscle, nerve, and keratin and occasionally other ectoderm-derived tissues [26, 27]. This has led some investigators to consider all LMCs as variant forms of benign teratomas , but this concept has not been widely accepted and has limited practical utility [28]. These findings are more likely to attest to the early stage in development at which the critical pathophysiological events occur.

LMCs injure neural tissues in two ways [4, 29]. The first is by direct invasion of fatty tissue into the conus medullaris with direct disruption or replacement of neurons [1, 3, 9, 30, 31]. This is incompletely understood but is currently thought to result from premature detachment of the neural tube from the cutaneous ectoderm during primary neurulation. Fatty-fibrous tissue then replaces normal neural tissue in a cleft anomaly of the caudal and dorsal cord that variably extends rostrally to connect with the central canal of the spinal cord. Fatty-fibrous tissue displaces the overlying meninges, extends into the region of focal spina bifida, and fills the mesenchymal subcutaneous spaces of the back [9, 24, 30, 31]. Spinal lipomas occur when the fatty-fibrous tissue is confined to the subdural space and the meninges are largely or entirely preserved [26]. However, many writers and surgeons do not consider these distinctions and often use the terms lipomyelomeningocele (LMC) and spinal lipoma interchangeably. The extent of clinical deficit resulting from fundamentally disordered anatomical development is controversial, but it appears to be a significant and underreported (in surgical series) component of the overall burden of disease in LMCs.

The second way in which LMCs adversely affect normal neurological function is via tethering the spinal cord (TSC) [30, 32–34]. The traditional concept of TSC is that the fatty-fibrous mass connects the caudal end of the spinal cord to the surrounding soft tissue, thereby fixing the cord and preventing its normal ascent in response to disproportionate physiological growth between musculoskeletal and neural spinal elements [34]. Fixation can also restrict the free movement that could dissipate the transmitted forces associated with normal activities of moving and stretching in daily living and perhaps even the force of pulsatile delivery of cardiac output to the nervous system [33]. The classic studies of Yamada showed oxidation was impaired in neural tissue subjected to longitudinal stress, though those studies have never been repeated or independently verified [34]. Clinically, progressive longitudinal stress and microtrauma give rise to pain and progressive impairment of the delicate reflexive arcs of the bladder and bowel and lower extremity motor function, which manifests as progressive incontinence and sensorimotor dysfunction of the lower extremities [34].

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