What is the average length of the spinal cord

To combine the cross-sectional measurements and SDs of the human spinal cord from all studies into single estimates, we calculated weighted averages. Figure 5 shows the raw weighted averages and SDs along the spinal cord.

To construct continuous population estimates and achieve further smoothing, a generalized additive model was fit to the weighted averages and weighted SDs. The smoothed continuous population estimates of human spinal cord transverse and anteroposterior diameters are shown in Figure 3 cervical spinal cord with original data from the studies , Figure 4 whole spinal cord with original data from the studies , and Figure 5 whole spinal cord with weighted averages and SDs.

The transverse diameter of the spinal cord showed the expected shape with a marked cervical intumescence and a smaller lumbar intumescence. The anteroposterior diameter decreased throughout the spinal cord.

Figure 3. A,B : figure illustrates measurements of the human cervical spinal cord transverse [panel A ] and anteroposterior diameter [panel B ] from different published studies. The size of the dots represents the number of subjects included in each study.

Figure 4. A,B : figure illustrates measurements of the human spinal cord transverse [panel A ] and anteroposterior diameter [panel B ] from different published studies. Figure 5. A,B : figure illustrates the weighted averages of the human spinal cord transverse [panel A ] and anteroposterior diameter [panel B ] from different published studies.

The full black line shows the continuous population estimate from the general additive model, and the gray ribbon shows two standard deviations SDs from the population estimate based on the SDs of the studies. To facilitate comparison between our continuous population estimates and other studies, we extracted exact values for each spinal cord neuronal segment as well as vertebral bony segment.

Results for each spinal cord neuronal segment are presented in Table 5 and for vertebral bony segment in Table 6. Table 5. Estimated spinal cord diameters—spinal cord neuronal segment reference.

Table 6. Estimated spinal cord diameters—vertebral column bony segment reference. As seen in Figure 6 A, the number of measurements in the cervical spinal cord is much greater than in the thoracic, lumbar, and sacral parts, with around 10 times the sample sizes.

The proportion of in vivo methods is also greater in the cervical spinal cord Figures 6 B,C. Figure 6. A—C : figure demonstrates the total number of individual measurements contributed from each study at different points along the craniocaudal axis [panel A ] and the proportional contribution of studies [panel B ] and methods [panel C ] used to measure the diameters of the human spinal cord.

We estimated normal human spinal cord transverse and anteroposterior diameter from previously published data. To compare and combine these different studies, we created and analyzed a conversion method to place measurements correctly along a standardized craniocaudal axis. We created weighted averages of measurements and combined them with a generalized additive model to create a final continuous population estimate of transverse and anteroposterior diameter, as well as the associated SDs along the craniocaudal axis of the entire human spinal cord.

We included a variety of studies from different eras of research using different methodologies. We deemed this necessary because of the small number of studies available overall and the incomplete coverage of the spinal cord in these studies. The reliability of the estimated segmental spinal cord diameters presented is based on the quality of the reported data in the studies included.

These reported data were based on either radiology or postmortem examination of the healthy human spinal cord. When implementing a radiological approach for segmental measurements, the delimitation of the cord is vital in order to achieve accurate measurements Lamont et al.

Single reference points imply error consistency throughout the spinal cord but are likely to reduce the quality of the estimate and aggravate the comparison between previously published data. Sherman et al. Techniques such as computed myelography allow sectioning down to 13 mm thickness, which is significantly thicker than what is achievable through postmortem studies However, both Thijssen et al.

Other elements which might influence the quality of radiological measurement are: window settings, concentration of contrast media like computed tomographic myelography 20 , 25 , and window level and pulse sequence for MRI 20 , Finally, cranial parts of the cervical spinal cord are especially difficult to measure using the radiological approach, as overlap with the base of the skull, incisor teeth, and maxilla greatly obstructs vision Despite the potential for differences in quality between studies, we did not weigh the different studies based on their perceived quality.

Delimitation of the segments is vital when calculating the length of spinal cord neuronal segments. Donaldson and Davis measured the distance between the uppermost fila of successive nerves in four subjects on the dorsal and ventral aspect of the cord However, Ko et al. We have included three studies from the same research group reporting data on vertebral length 7 — 9.

When estimating the height of the vertebral body, the points of measurement are important. Panjabi et al. The authors reported that this resulted in an average underestimation of the height of each vertebral body by approximately 2 mm, when comparing to previously reported data 7 , 27 , The same research group 8 found that the posterior thoracic vertebral body height was consistently one to 2 mm less than that reported by Berry et al. The same applied for lumbar vertebral body posterior height 27 , 29 , Since we used relative vertebral size rather absolute measurements, a systematic error in measurement is of minor importance.

Therefore, we calculated approximate percentages for these vertebrae by using previously published relative positions of segments in the cervical spinal cord 10 , termination of the spinal cord between lumbar vertebral bony segments L1 and L2 11 , and the assumption that the upper end of the C1 vertebrae is aligned with the upper end of the C1 neuronal segment.

Therefore, the relative proportions of segments C1 and C2 in our model should be interpreted with care. Because we defined a vertebral bony segment as the vertebra and half of both the adjacent intervertebral disks, our model assumes that intervertebral disks increase in thickness along the craniocaudal axis by same proportion as the vertebrae. This is not an unreasonable assumption, but one that was not backed with any data. Despite the complexity and shortcomings of our model, with scarce data and reliance on a number of assumptions, the strategy to create a normalized craniocaudal axis for comparison of cross-sectional measurements of the human spinal cord was successful.

Success was indicated by the increase in adjusted R -squared from The relative positioning of segments along the spinal cord relies heavily on the studies by Cadotte et al.

The weighted averages were calculated by combining four adjacent measurements. This step was necessary to normalize the number of measurements along the spinal cord before fitting the generalized additive model to decrease problems where sample sizes changed suddenly along the spinal cord.

The number four was reached empirically by the authors and can therefore be questioned. We argue that it combined measurements to a reasonable degree without losing frequency response in the signal. In the measurements of anteroposterior diameter, the small number of measurements resulted in periodical oscillations of the weighted averages in the cervical spinal cord Figure 5 B.

This was ameliorated in the next step by fitting the generalized additive model. The weighted SDs were calculated by squaring the known SDs to become variances and computing the weighted average variances. Taking the square root of the weighted average variances yielded the weighted SDs. This approach assumes that samples were drawn from the same population, which is probably not entirely true but represented the only practical way of estimating aggregated SDs known to us without the original data.

The continuous population estimates of the transverse and anteroposterior diameter resulting from the combination of the included studies Figures 3 — 5 were consistent with the expected shape of the spinal cord e. The population SDs enclosed almost all data points when plotted as two SDs, giving further confidence that these data were combined with some accuracy. The choice of parameters for the generalized additive model was reached empirically just like the weighted average.

When choosing parameters that accurately described the data, we chose the lowest possible order polynomial that would follow the perceived shape of the spinal cord with some accuracy.

This was only evaluated visually and represents a weakness of the approach. It is reasonable to discuss the impact of morphometrics defining body size, such as gender, height and body weight. Kameyama et al. However, some contradictory results were presented by Kameyama et al.

They found that the cross-sectional area for C7 was significantly smaller in females when compared to males, hypothesizing that the difference in size of the spinal cord between sexes may be partly explained by the variation in height. However, they could not find any correlation between spinal cord size and body weight.

Individual variation in cord size was substantial between individuals with equal height and resulted in significant positive correlation to cross-sectional area, transverse diameter, and sagittal diameter However, Kameyama et al. The authors report that age had a slight negative correlation to cross-sectional area and sagittal diameter at C7, but not for transverse diameter at the same level.

They hypothesize that age-related degenerative changes may explain the flattening of the cervical spinal cord with age, confirming previously published data 16 , 19 , We observed that many of the included studies tended to include more males than females, which could have affected our analysis.

In summary, some contradictions seem to exist between the impact of body type characteristics on spinal cord size, but most previous studies have been underpowered to detect all but very strong correlations. Because our present study lacks the raw data, further investigation of predictors for spinal cord size was not possible. An interesting expansion of this study would be to gather all raw data and analyze predictors of size in a larger sample.

Continuous population estimates of the transverse and anteroposterior diameters of the spinal cord could be useful in diagnosing and monitoring patients with neurodegenerative and neuroinflammatory diseases. It is known, for example, that patients suffering from multiple sclerosis have a reduced cross-sectional area compared to healthy matched controls 1 , but these studies have low power.

Without population estimates, it can be difficult to determine whether a specific patient should be considered to have a pathologically small or large spinal cord. In the future, the model of spinal cord neuronal segment relation to vertebral bony segment could be used to achieve a better understanding of visible localized pathology on MRI in the spinal cord in situations where identification of spinal cord neuronal segments is challenging.

This would require a validating study in patients in whom a well-defined pathology of the spinal cord is present and can be correlated to a segmental symptom such as the motor or sensory level of a patient with a spinal cord injury.

Such a study is currently being planned in our research group. Multiple experimental studies for treatment of acute and chronic human spinal cord injuries are in different phases of development 2. In all studies where a premade device, instrumentation, or otherwise physical object needs to be applied to the spinal cord, the population estimates are of importance because they represent the variation in physical dimensions that will be encountered in patients.

During the design of the biodegradable device used in the study, knowing population estimates of the human spinal cord was a necessity, and, therefore, we believe that this work can be useful for other groups in similar projects. We conclude that segmental transverse and anteroposterior diameters of the healthy human spinal cord from different published sources can be combined on a normalized craniocaudal axis and yield meaningful population estimates with reasonable sample sizes.

Vertebrae Example of a vertebra The spinal cord is located in the vertebral foramen and is made up of 31 segments: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal. A pair of spinal nerves leaves each segment of the spinal cord. Receptors in the skin send information to the spinal cord through the spinal nerves.

The cell bodies for these nerve fibers are located in the dorsal root ganglion. The nerve fibers enter the spinal cord through the dorsal root. Some fibers make synapses with other neurons in the dorsal horn, while others continue up to the brain. Many cell bodies in the ventral horn of the spinal cord send axons through the ventral root to muscles to control movement. In the figures below, note the differences in the shape and size of the spinal cord at different levels.

The dark gray color in each segment represents "gray matter. Nerve cell bodies are located in the gray matter. Surrounding the gray matter is white matter lighter color shading - this is where the axons of the spinal cord are located. Compare the relative amount of gray and white matter at each level of the spinal cord. In the cervical segment, there is a relatively large amount of white matter. In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Objective: To obtain quantitative anatomical data on each spinal cord segment in human, and determine the presence of correlations between the measures. Methods: A total of 15 embalmed Korean adult human cadavers 13 males, two females; mean age The length of each cord segment was defined as the root attachment length plus the upper inter-root length.

After performing a total vertebrectomy, a transverse cut was made at the approximate proximal and distal point of each segment from segment C3 to S5. Sagittal and transverse diameters at the proximal end of each segment, and cross-sectional area, height, and volume of the segment were measured.

Results: The transverse diameter was largest at segment C5, and decreased progressively to segment T8. However, the sagittal diameter of each segment did not change distinctly with the segment.

The cervical and lumbar enlargements were determined by the transverse diameters of the segments. Segment C5 had the largest cross-sectional area, at Segment T6 was the longest, averaging The longest segment in the cervical spinal cord was segment C5, at The volume was largest at segment C5, with a value of Conclusions: We found characteristic quantitative differences in the values of the parameters measured in the thoracic spinal cord compared to those measured in the cervical and lumbar or lumbosacral spinal cords.

These measurements of spinal cord segments appear to provide valuable and practical standard quantitative features and may provide basic data for understanding the morphometric characteristics relevant to pathophysiologic conditions of the spinal cord.

Quantitative measures of the neuroanatomy of the spinal cord provide the basis for understanding and interpreting clinical implications, such as the relationship between vertebral injury level and segment level, the morphological characteristics of the severity of spinal cord injury, and the possible correlation between the number of injured spinal cord segments and duration of spinal shock or neurological recovery.

In addition, the dimensions of the spinal cord are important in cordotomy and other spinal operations. Spinal cord segments have been studied in the adult cat, 10 monkey, 11 and dog. Although the external and cross-sectional features of the adult human spinal cord have been well documented, there have been few quantitative studies on the variations and correlations along the human spinal cord in regard to the sagittal diameter, transverse diameter, cross-sectional area, length, and volume of each spinal cord segment.

The aim of this study was to obtain basic morphometric data of the human spinal cord, regionally and segmentally, from quantitative measurements. The authors measured the sagittal and transverse diameters, cross-sectional area, segment length, and volume of the human cadaveric spinal cord, and also investigated correlations among the measurements in order to determine quantitative characteristics of each spinal cord segment.

A total of 15 embalmed adult human cadavers 13 Korean males, two Korean females; mean age The cadavers were placed in a prone position on a flat table with hips extended. The superficial and deep muscles of the back were identified and removed, with resultant exposure of the entire length of the vertebral column. The neural arches were removed. The cut pedicles of the vertebrae and the dorsal root ganglia of the spinal nerves were exposed.

The dural and arachnoid membranes were opened by incision along the mid-dorsal line, exposing the spinal cord and the root filaments of the spinal nerves.

The relation between the neural segments of the spinal cord and the vertebrae was readily determined. The cervical, thoracic, lumbar, and sacral regions of the cord were defined by counting the appropriate number of nerve roots. The length of each segment was defined as the root attachment length plus the upper inter-root length.

A transverse cut was made at the approximate proximal and distal point of each segment from segment C3 to S5. A transverse cut was made at the approximate lower point of attachment of the ventral and dorsal roots of each just-proximal spinal cord segment. The following measurements were made: sagittal and transverse diameters, cross-sectional area, distance between the lowermost filament of the just-proximal segment and lowermost filament within each root height or length of each segment , and volume of each segment.

The sagittal and transverse diameters and cross-sectional area were measured at the proximal end of each defined segment. The absolute volume of each segment in cubic millimeters was calculated by multiplying the length in millimeters by the cross-sectional area in square millimeters. The results obtained from the 15 human cadavers studied were then averaged.

The correlations among the quantitative measurements of the spinal cord segments were evaluated using the Pearson coefficient in the 15 human cadavers. Significance was set at a probability level of 0. The statistical package used was SPSS, version The transverse diameter was largest in segment C5, and decreased progressively to segment T8. It increased from segment C3 to the main peak at segment C5 and then decreased markedly toward the upper thoracic segments.

It remained almost constant throughout the middle and lower thoracic levels, but began to increase again from segment T12, forming a secondary peak at segment L4 Figure 1a. In contrast, the sagittal diameter of each segment did not change distinctly with segment. With this characteristic difference between the variations in the transverse and sagittal diameters, the cervical and lumbar enlargements were determined by the lateral diameters of the segments Figure 2.

The sagittal diameter measurements exhibited a gradual decrease from segment C3 to the upper thoracic spinal cord levels, remaining almost constant throughout the thoracic spinal cord levels. The sagittal diameter began to increase again at segment T12, peaking at segment L3, and then decreasing markedly below segment S2 Figure 1b.

Transverse diameter a , sagittal diameter b , cross-sectional area c , segment length d , and volume e of each spinal cord segment. Vertical lines indicate ranges. Mean sagittal diameter a and mean transverse diameter b of each spinal cord segment. The variations in diameter were more prominent in the transverse direction than in the sagittal direction. Segment C5 exhibited the largest cross-sectional area, at The cross-sectional area of the spinal cord increased caudally with each successive level, reaching a peak at segment C5.

The area then decreased markedly at segment T1—T2, but changed very little throughout the thoracic region, with a minimum at segment T7—T8. The size increased again at segment T12, with the second peak at segment L4, and subsequently decreased markedly below segment S1 Figure 1c.

The longest segment in the cervical spinal cord was C5, at The volume was largest at segment C5, where the volume was