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Regional and Segmental Characteristics of the Human Adult Spinal Cord A

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Regional and Segmental Characteristics of the Human Adult Spinal Cord A J. Anat. (1977), 123, 3, pp. 797-803 797 With 1 figure Printed in Great Britain Regional and segmental characteristics of the human adult spinal cord A. J. BARSON AND J. SANDS Departments ofPathology and Child Health, University of Manchester (Accepted 8 June 1976) INTRODUCTION Although the external and cross sectional features of the adult human spinal cord have been well documented, there have been relatively few quantitative studies of the variation along the cord in regard to weight, length, thickness and basic bio- chemical components. The average length of the adult cord is known with some precision from a survey of 234 cases by McCotter (1915), but there has been no comparable assessment of fresh cord weight. With regard to regional variations, Lasseck and Rasmussen (1938) assessed the volumes of cervical, thoracic, lumbar and sacral cords in six adult cadavers. More recently there has been interest in the anatomical variations between the individual cord segments. Segmental cord studies have been made in the adult cat (Thomas & Comb, 1962), monkey (Thomas & Combs, 1965) and dog (Fletcher and Kitchell, 1966). The only quantitative evaluations of the adult human spinal cord segments are those on the variation in the areas of the cord segments by Donaldson & Davis (1903) and in segmental volume by Malinska (1972). Quantitation of water, cholesterol and DNA-P has been performed on the spinal cord of the pig (Dickerson & Dobbing, 1967) and the guinea-pig (Dobbing & Sands, 1970), but not on a regional or segmental basis. These biochemical components have been quantitated in the human brain (Dobbing & Sands, 1973) and in the normal and dysraphic fetal spinal cord (Barson & Sands, 1975), but there is no com- parable information for the adult human spinal cord. The aim of the present study was to assess the adult human cord, regionally and segmentally, for weight, length, thickness, water, cholesterol and DNA-P composition. MATERIALS AND METHODS Ten spinal cords were obtained from five male and five female patients dying in the Manchester Royal Infirmary and ranging in age from 27 to 78 years (mean 59 years). All the cords were removed in a standardized way within 24 hours of death by one person (A.J.B.). The entire cord was exposed through a mid-line dorsal incision, excising all the spinal laminae and slitting the dura mater. The limits of the thoracic cord were defined by identifying Tl and T12 nerve roots in relation to the most cranial and caudal ribs and ensuring that twelve paired ribs were actually present. The cervical, lumbar and sacral regions of the cord were defined by counting the appropriate numbers of nerve roots away from the thoracic cord. The cord was excised from the point of origin of the most cranial dorsal rootlets of Cl to the junction of the conus medullaris with the ventriculus terminalis. The cervicothoracic, 798 A. J. BARSON AND J. SANDS Table 1. Weight, length and thickness of spinal cord regions Total Cervical Thoracic Lumbar Sacral Cord weight (g) Mean 28-2706 9-1684 13-8823 4-2419 0 9779 S.D. +3-4636 ±1-3806 i1-9796 ±0-6079 ±0-4185 Cord length (cm) Mean 43-08 9-42 24-23 5 87 3 59 S.D. ± 2-70 + 0-78 ± 2-09 0-67 +1 02 Cord thickness (weight/length x ICO) Mean 65-73 97-42 57-44 72-39 26-78 S.D. + 8-30 +12-57 + 7-92 + 7-43 ± 5-98 Table 2. DNA-P, cholesterol and water contents ofspinal cord regions Total Cervical Thoracic Lumbar Sacral DNA-P content (Amol DNA-P) Mean 31-2437 9-7688 14-9049 5-8921 1 2864 S.D. +5-5779 +1-4678 ± 3-9097 ±1-4543 +0 5399 Cholesterol concentration (mg cholesterol/g wet weight tissue) Mean 37-9985 37-6928 38-7262 32 5985 23-1159 S.D. +6-2153 +4-9808 + 6-6389 +4 8549 +3-7620 Water content (%) Mean 13-6596 72-8441 73-4171 75-2479 81-0520 S.D. + 2-8176 +2-6051 +3-3373 +2-3655 +1-9113 thoracolumbar and lumbosacral junctions were taken to be situated at the levels of origin of the most caudal dorsal rootlets on the cranial sides of the junctions. This arbitrary level was important for defining the thoracolumbar junction, where there are small but appreciable differences in the sites of origin of dorsal and ventral root- lets, and between the most caudal rootlets of T12 and the most cranial rootlets of LI. In each case the four regions of the cord were separated, measured for length, and weighed, immediately after removal from the cadaver. Average thickness was calculated by dividing weight by length. DNA-P was estimated by the method of Zamenhof, Bursztyn, Rick & Zamenhof (1964). Cholesterol content was assessed by the technique described by Leffler (1959). Water content was obtained by drying at 99 °C to a constant weight. RESULTS The quantitative analysis of the ten spinal cords was categorized into absolute regional values (Tables 1, 2 and 3) and mean segmental regional values (Tables 4 and 5). The values for the sacral region include the almost negligible contribution of the first coccygeal segment. Anatomically the bulk of the tissue in this region is encompassed by the first and second sacral segments. Quantitative study of human spinal cord 799 Table 3. Weight, DNA-P and length as a regional percentage Cervical Thoracic Lumbar Sacral Weight (%) 32-4 49-1 15.0 3-5 DNA-P (%) 31-3 47-7 18-9 4-1 Length (%) 21-9 56-2 13-6 8-3 Table 4. Average segmental weight, length and thickness in regions of the spinal cord Total (C1-L5) Cervical Thoracic Lumbar Sacral Weight per segment (g) Mean 1-0917 1-1460 1-1568 0-8483 0-1714 S.D. ±0 1389 +01725 ±0-1649 +0-1215 ±0-1422 Length per segment (cm) Mean 1-59 1-32 2 04 1-17 0-67 S.D. ±0-10 +0-12 +0 18 +0-13 +0-13 Thickness per segment (wt/length) Mean 9 09 12-18 4-79 14-48 4-46 S.D. ±1-07 +1-57 ±0-66 ±1-49 +1 00 Table 5. Average segmental DNA-P, cholesterol and water in regions of the spinal cord Total (C1-L5) Cervical Thoracic Lumbar Sacral DNA-P content per segment (jtmol DNA-P) Mean 1-2226 1-2210 1-2420 1-1783 0-2195 S.D. +0-2070 +0-1834 ±0-2814 ±0-2655 ±0 0817 Cholesterol content per segment (mg cholesterol) Mean 41-3693 42-9281 44-1450 28-0182 3-8269 S.D. ±10-1680 ±10-6156 ±12-5896 7-3895 + 1-8920 Water content per segment (g) Mean 0-8039 0-8328 0-8469 0 6456 0 1320 S.D. +0 0884 +0-1140 ±0-1081 +0-0904 +0-0569 Table 1 gives the physical characteristics of the adult cord and its regions by weight, length and thickness. Table 2 shows the biochemical composition of the whole cord and its regions in terms of DNA-P in ,umol, which may be used as an index of total cell numbers; cholesterol concentration in mg per g wet weight, which is an index of myelination; and water content in g per cent. Table 3 sets out the total regional values for weight, DNA-P and length as a percentage of the whole cord. Tables 4 and 5 record the same physical and biochemical parameters but on the basis of the mean segmental regional values. These were obtained bv dividing the absolute regional values as shown in Tables 1 and 2 by the number of cord segments appropriate for the particular region, that is by eight for the cervical region, twelve 800 A. J. BARSON AND J. SANDS +60 O Cervical +40 Q Thoracic ~+20 0 £0 DNA-P -2.0 Water Weight Length Cholesterol -40 Thickness Fig. 1. Physical and biochemical characteristics of the typical cervical, thoracic and lumbar cord segments shown as a percentage deviation from the mean segmental value for the whole cord between Cl and L5. for the thoracic, five for the lumbar and six for the sacrococcygeal. The mean segmental values for the cord between Cl and L5 is also shown (being equivalent to 25 segments). Figure 1 is a graphic comparison of the characteristics of the typical cervical, thor- acic and lumbar segments. The values are derived from those set out in Tables 4 and 5, and are represented as the percentage deviation from the mean segmental value for the combined cervical, thoracic and lumbar regions (Cl to L5). DISCUSSION Very little information exists in the literature with regard to the weight of the adult human spinal cord. Lassek & Rasmussen (1938) cite a study of thirty six spinal cords by Baistrocchi (1884) in which the average weight was found to be 27-2 g. More recently in the Russian literature Blinkov & Glezer (1968) quote Kononova (1955) as giving a range of 34-38 g. This difference is possibly due to weighing some cords after immersion in fixative. In the present study the fresh total cord weight was found to be 28x3 g with a standard deviation of ± 3 5 g and a range of 23x5- 35-8 g. Marshall (1892) states that the human cord is 2 06 % of the weight of the brain. This gives a figure of just below 30 g for the cord for commonly accepted fresh brain weights (i.e. about 1380 g). The last documented survey of adult spinal cord length is that by McCotter (1915). The average length of 199 male cords was found to be 44 79 cm, and 41 8 cm for 25 female cords.
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