Rationale and Objectives
Anterior/posterior commissure reference system (AC/PC reference system) and the fastigium/ventricular floor plane reference system (FFL/VFL reference system) are two reference systems used in the stereotactic localization of the invisible nuclei of the brainstem in magnetic resonance (MR) images. This study investigated the variation of the midsagittal brainstem in relation to the AC/PC and VFL/FFL reference systems with respect to age and gender.
Materials and Methods
High-resolution T1-weighted structural MR images were acquired from 64 adults (age range 21–60 years, 32 males and 32 females). The AC/PC and VFL/FFL reference systems were identified automatically. A set of landmarks of the midsagittal brainstem were defined and localized interactively.
Results
Results illustrated that there was significant difference between the variance of the anteroposterior coordinate of the landmarks in relation to the AC/PC reference system and that in relation to the FFL/VFL reference system ( P < .05), the former is larger than the latter. The positions of the landmarks in the females are more anterior than those in the males in relation to the AC/PC reference ( P < .05); the difference in relation to the FFL/VFL reference system was not found.
Conclusion
Either the FFL/VFL reference system or the AC/PC reference system has its own advantage in the stereotactic localization of the structure in the brainstem.
The brainstem comprises mesencephalon, pons, and medulla , which play crucial roles in regulating cardiac, respiratory, and central nervous system function and maintaining consciousness. However, because of the deep location and invisibility of some nuclei in the brainstem in common neuroimages, the brainstem has always been considered a dangerous stereotactic field. Indeed, the safe approach to most of the brainstem targets is still a major challenge even for the skilled neurosurgeons . Neurosurgeons always consult a reference system when locating the invisible nuclei.
Currently, there are two reference systems are used in the stereotactic field: the anterior/posterior commissure (AC/PC) reference system and the fastigium/ventricular floor plane (FFL/VFL) reference system. The AC/PC and FFL/VFL reference systems are derived from two stereotactic atlases: the Talairach and Afshar , respectively. Figure 1 shows the definitions of these two reference systems on the midsagittal plane (MSP): the AC/PC reference system based on AC and PC, and the FFL/VFL reference system based on the fastigial point (F) of the fourth ventricle and the VFL. Their spatial relationship was analyzed using x-ray images by Hitchcock et al . Niemann et al compared imaging findings of the brainstem to Afshar’s atlas, and found that the FFL in magnetic resonance (MR) images was often displaced in a more caudal location than that predicted by the atlas. These findings cast some doubt on the suitability of the FFL/VFL reference system as an appropriate landmark for stereotactic localization. Zrinzo et al reported that the anteroposterior coordinate of the caudal pole of pedunculopontine nucleus in the brainstem has a significantly greater variance in relation to the AC/PC reference system than to the VFL/FFL reference system ( F -test: P < .001). The study of the location in the brainstem is still undergoing. However, to the best of our knowledge, there is no quantitative morphometric analysis of the brainstem in relation to these two reference systems using MR images.
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Figure 1
Scheme of two reference systems defined on the MSP. AC, anterior commissure point; PC, posterior commissure point, origin of the AC/PC reference system; VFL, ventricular floor line, midsagittal tangent to the rhomboid fossa; F, fastigial point of the fourth ventricle; FFL, fastigial floor line, perpendicular to the VFL though the F; B, origin of the FFL/VFL reference system. MESJ, pontomesencephalic junction; MEDJ, pontomedullary junction; M1, inferior corner between the mesencephalon and the hypothalamus; M2, edge point on the line passing the center between MESJ and MEDJ and perpendicular to the VFL; M4, posterior corner between the medulla and spinal cord; M3, edge point on the line passing M4 and perpendicular to the centerline of the medulla; M5, midpoint between the superior and inferior colliculi.
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Materials and Methods
Data Overview
Subjects
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Image acquisition
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Method
Definition of the landmarks
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Localization of the landmarks
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Stage 1: Identification of the reference systems
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Stage 2: Extraction of the midsagittal brainstem
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Stage 3: Localization of the candidates of the landmark
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Stage 4: Selection of the best position of the landmark
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Statistical analysis
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Results
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Accuracy
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Table 1
Statistics of the Location Error of Each Landmark (Unit:mm)
M1 MESJ MEDJ M2 M3 M4 M5 Average 0.6 0.5 0.5 0.9 0.9 0.8 0.7 Maximum 1.6 1.3 1.5 2.2 2.3 1.9 1.7
M1, inferior corner between the mesencephalon and the hypothalamus; MESJ, pontomesencephalic junction; MEDJ, pontomedullary junction; M2, edge point on the line passing the center between MESJ and MEDJ and perpendicular to the VFL; M3, edge point on the line passing M4 and perpendicular to the centerline of the medulla; M4, posterior corner between the medulla and spinal cord; M5, midpoint between the superior and inferior colliculi.
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Intra- and Inter-observer Variation
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Normal Ranges
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Table 2
Statistics of the AP and SI Coordinate of each Landmark in Relation to the AC/PC Reference System (Unit:mm)
Landmarks Parameters Mean SD Maximum Minimum M1 AP −11.50 1.03 −9.03 −14.14 SI −6.18 0.9 −4.48 −8.16 MESJ AP −4.37 1.53 −1.70 −7.23 SI −14.31 1.45 −11.36 −17.53 MEDJ AP 1.18 3.14 9.16 −6.33 SI −39.13 2.81 −32.5 −43.98 M2 AP −10.09 2.60 −5.23 −16.64 SI −28.93 2.33 −23.39 −34.68 M3 AP 9.39 3.82 19.22 0.32 SI −53.35 3.62 −43.20 −60.69 M4 AP 19.56 3.49 28.85 10.22 SI −48.33 3.60 −38.61 −56.79 M5 AP 8.82 0.93 10.83 6.89 SI −4.88 0.97 −2.74 −7.35 B AP 12.19 2.39 17.71 6.59 SI −26.70 2.58 −21.50 −31.96
+, posterior or superior; −, anterior or inferior; AP, anteroposterior; SI, superoinferior; AC/PC, anterior/posterior commissure reference system. All other abbreviations as in Table 1 .
Table 3
Statistics of the AP and SI Coordinate of Each Landmark in Relation to the FFL/VFL Reference System (Unit:mm)
Landmarks Parameters Mean SD Maximum Minimum M1 AP −16.98 1.86 −13.08 −20.12 SI 26.29 3.39 33.30 19.90 MESJ AP −12.43 1.18 −9.55 −14.71 SI 16.49 2.27 21.52 11.78 MEDJ AP −13.97 1.30 −10.79 −16.65 SI −8.94 2.68 −2.95 −15.79 M2 AP −22.00 1.50 −18.14 −25.25 SI 3.99 2.51 9.08 −1.45 M3 AP −10.01 1.74 −5.27 −14.10 SI −24.88 3.13 −19.17 −33.85 M4 AP 1.15 1.25 5.76 −1.46 SI −22.85 2.78 −15.57 −29.04 M5 AP 2.85 1.18 5.84 0.05 SI 21.93 2.27 25.82 17.15
FFL/VFL, fastigium/ventricular floor plane reference system. All other abbreviations as in Tables 1 and 2 .
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Relationship between the Two Reference Systems
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Table 4
Statistics of the Angle between the Anterior/Posterior Commissure Line and the Ventricular Floor Plane (Unit:degree)
Minimum Maximum Mean Standard Deviation Angle 94.00° 119.67° 106.04° 4.63°
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Variations in the Two Reference Systems
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Table 5
Variance of the AP and SI Coordinates of Each Landmark in Relation to the AC/PC and FFL/VFL Reference System, Respectively (Unit:mm)
Variance (AP) Variance (SI) Landmarks AC/PC VFL/FFL_P_ value AC/PC VFL/FFL_P_ Value M1 1.0 1.9 .0 ∗∗ 0.9 3.4 .0 ∗∗ MESJ 1.5 1.1 .006 ∗ 1.4 2.7 .0 ∗∗ M2 2.6 1.5 .0 ∗∗ 2.3 2.5 .447 (>.05) MEDJ 3.1 1.3 .0 ∗∗ 2.8 2.7 .627 (>.05) M3 3.8 1.7 .0 ∗∗ 3.6 3.1 .346 (>.05) M4 3.5 1.2 .0 ∗∗ 3.6 2.8 .084 (>.05) M5 0.9 1.2 .185 (>.05) 1.0 2.3 .00 ∗∗
Abbreviations as in Tables 1 and 2 .
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Table 6
Pearson’s Linear Correlation Matrix (R-matrix) for the Age, the Angle between VFL and AC-PC line, and the Distance of each Landmark to PC and B
Abbreviations as in Tables 1 and 2 .
Dark shade cell-correlation is significant at the 0.01 level (two-tailed).
Light shade cell-correlation is significant at the 0.05 level (two-tailed).
Table 7
Significance Matrix (P-matrix)
Abbreviations as in Tables 1 and 2 .
Light shade cell-correlation is significant at the 0.05 level (two-tailed).
Dark shade cell-correlation is significant at the 0.01 level (two-tailed).
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Effect of Gender
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Table 8
Difference in the Mean of the AP and SI Coordinate of Each Landmark in Relation to the AC/PC Reference System between Males and Females (Unit:mm)
Mean (AP) Mean (SI) Landmarks Males Females_P_ Value Males Females_P_ Value M1 −11.3 −11.7 .107 −6.1 −6.3 .270 MESJ −3.7 −5.0 .0 ∗∗ −14.5 −14.1 .294 M2 −9.1 −11.0 .001 ∗ −29.4 −28.5 .134 MEDJ 2.5 −0.1 .003 ∗ −39.6 −38.7 .191 M3 10.9 7.9 .002 ∗ 10.9 7.9 .244 M4 21.0 18.1 .001 ∗ −48.9 −47.8 .245 M5 9.1 8.5 .008 ∗ −4.8 −4.8 .989 B 11.3 13.1 .002 ∗ −26.6 −26.8 .756
Abbreviations as in Tables 1 and 2 .
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Table 9
Difference in the Mean of the AP and SI Coordinate of Each Landmark in Relation to the FFL/VFL Reference System between Males and Females (Unit:mm)
Mean (AP) Mean (SI) Landmarks Males Females_P_ Value Males Females_P_ Value M1 −17.1 −16.9 .647 27.0 25.5 .084 MESJ −12.4 −12.5 .745 16.7 16.3 .508 M2 −22.0 −22.0 .86 4.1 3.9 .823 MEDJ −13.8 −14.1 .407 −9.2 −8.7 .528 M3 −10.1 −10.0 .814 −25.3 −24.5 .311 M4 1.1 1.2 .641 −23.4 −22.3 .094 M5 2.7 3.0 .468 22.2 21.7 .429
Abbreviations as in Tables 1 and 2 .
∗ P < .05.
∗∗ P < .001.
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Discussion
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Limitations
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Conclusion
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