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Three-Dimensional Reconstruction of the Optic Canal-Based on Multislice Helical CTA Comparison Analysis with Skull Dissection of 40 Postmortem Cases.

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THE ANATOMICAL RECORD 291:1662–1672 (2008)
Three-Dimensional Reconstruction of
the Optic Canal-Based on Multislice
Helical CT: A Comparison Analysis With
Skull Dissection of 40 Postmortem Cases
LI ZHIHAI,1 GAO QIXUE,2 TAO BAOHONG,1 LV JINGYAO,1 AND CAI ZHIYI1*
1
Department of Otolaryngology, Taizhou Municipal Hospital, Taizhou,
Zhejiang 318000, China
2
Department of Otolaryngology, Tongji Hospital, Tongji Medical College, Huazhong
University of Science and Technology, Hubei, Wuhan, China
ABSTRACT
Decompression operation of the optic canal via the nasal path under
endoscope is widely used, but it is both a challenging and controversial
method. Unsatisfactory results were largely associated with otolaryngologists’ limited understanding of the real anatomical situations of the optic
canal before operation. To provide otolaryngologists with the real situations and data preoperation, multislice helical CT was used to reconstruct
the images of the optic canal. Using multislice helical CT-aided threedimensional reconstructive methods in combination with direct anatomic
measurement, we dissected and analyzed the shape of the optic canal and
its anatomic relationship with the adjoining structures in 40 intact postmortem skull samples. The In-Space technique clearly showed the structure and the related region of the optic canal. The virtual endoscopy technique showed superbly the spatial appearance and topography of the
inner optic canal and also gave the inner structure of the optic canal optically. There was no statistic difference in three-dimensional reconstructive data with that obtained by anatomical measurements and thus can
be used to directly instruct the clinic operation. These results demonstrate that a combined In-Space technique with virtual endoscopy can
accurately define the subtle structure and the related region of the optical
canal. In conclusion, multislice helical CT-based three-dimensional reconstruction is of important value for clinical operations. Anat Rec,
291:1662–1672, 2008. Ó 2008 Wiley-Liss, Inc.
Key words: optic canal; virtual endoscopy; In Space
Decompression operation of the optic canal via the
nasal path under endoscope has been widely performed
in the recent years (Kountakis et al., 2000; Onofrey
et al., 2007; Pletcher and Metson, 2007); however, optimizing its effects remains a challenge (Chen et al., 2006;
Pletcher et al., 2006). Unsatisfactory results, besides the
choosing of an unsuitable indication, were largely associated with otolaryngologists’ limited understanding of the
real anatomical situation of the optic canal before operation. Multislice helical CT scanning and reconstructive
technique has proved to be a new and noninvasive technique in the detection of diseases. By choosing the different reconstructive technique, multislice helical CT could
clearly display the three-dimensional image of the norÓ 2008 WILEY-LISS, INC.
mal anatomic structures, the location, size, surface morphology, and extent of the lesion. To provide otolaryngologists with the real anatomical situation and data preoperation, we carried out a comparative study of the optic
canal as measured by multislice helical CT and anatomical methods.
*Correspondence to: Cai Zhiyi, Department of Otolaryngology,
Taizhou Municipal Hospital, Taizhou, Zhejiang 318000, China.
E-mail: caizy008@tom.com
Received 24 December 2007; Accepted 28 May 2008
DOI 10.1002/ar.20746
Published online 25 August 2008 in Wiley InterScience (www.
interscience.wiley.com).
Fig. 1. Reconstructed image by SSD. Normal lateral view. Arrowhead indicates the fossa orbitalis
endostoma of the optic canal.
Fig. 2. Reconstructed image by SSD. Rear-top view. Arrowhead indicates the cranium endostoma of
the optic canal.
Fig. 3.
canal.
Reconstructed image by SSD. Anterior view. Arrowhead indicates the endostoma of the optic
Fig. 4. Reconstructed image by SSD. Lateral view. Arrowhead indicates the fossa orbitali endostoma
of the optic canal.
Fig. 5. Reconstructed image by SSD. Normal lateral view. The inner wall structures were not shown
well. Arrowhead indicates the fossa orbitali endostoma of the optic canal.
Fig. 6. Reconstructed image by SSD. Anterior view. The inner wall structures were not shown well.
Arrowhead indicates the fossa orbitali endostoma of the optic canal.
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ZHIHAI ET AL.
Fig. 7. Reconstructed image (sectional area) of the optic canal by VE. Anterior view. Three dimensional
structures were shown clearly. Arrowhead indicates the fossa orbitali endostoma of the optic canal.
(3, superior wall of the optic canal; 4, parietal wall of the optic canal; 5, inferior wall of the optic canal;
6, inner wall of the optic canal).
MATERIALS AND METHODS
Specimens
Forty adult postmortem skulls, 24 men and 16 women,
were fixed in 10% formalin. All specimens were intact in
structure, without pathological findings such as tumors,
myxoma, or apparent inflammation.
Measurement Tools
A sliding caliper (size 0–125 mm and precision 0.02 mm)
was purchased from Shanghai Measurement and Tooting
Factory (Shanghai, China). Compasses were purchased
from Shanghai Pufa Pantography General Factory
(Shanghai, China).
THREE-DIMENSIONAL RECONSTRUCTION ON MULTISLICE HELICAL CT
1667
Fig. 8. Reconstructed image (sectional area) of the optic canal by VE. Normal lateral view. Four wall
structures were clearly displayed. Arrowhead indicates the fossa orbitali endostoma of the optic canal.
(3, superior wall of the optic canal; 4, parietal wall of the optic canal; 5, inferior wall of the optic canal;
6, inner wall of the optic canal).
Scanning Reconstruction
The postmortem skulls were scanned with a helical
CT (America General Electric Company); a 16-row helical CT with 120 kV of tube tension, 300 mA of current
flow, and interval coronal scanning thickness 1.0 mm,
distance 1.0 mm, window width 1,000, and window level
200. The scan line met the line linking the tuberculum
sellae and the infraorbital border at a right angle. The
scanning area started from the anterior nasal spine
through to the posterior clinoid process. Three-dimensional reconstruction was performed using surface
shaded display (SSD), In Space, and virtual endoscopy
(VE), with a thickness of 0.75 mm and a distance of
0.1 mm.
Anatomical Methods
After scanning, each skull specimen was first sawn
along the line linking the superior border of the arcus
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ZHIHAI ET AL.
Fig. 9. Reconstructed image (sectional area) of the optic canal by VE. The internal three dimensional
structures were shown clearly. Arrowhead indicates the fossa orbitali endostoma of the optic canal.
(1, supraorbital fissure; 2, sphenomaxillary fissure; 3, superior wall of the optic canal; 4, parietal wall of
the optic canal; 5, inferior wall of the optic canal; 6, inner wall of the optic canal).
superciliaris and the point 1 cm over the occipital tuberosity, and then sawn along the midline
Observation and Measurement
The imageological and real anatomical observations by
rhinological endoscope were performed over the inner
wall adjoining relationship of the optic canal and the
sphenoidal sinus. The thickness and length of the bulges
inside the optic canal were measured.
RESULTS
Reconstruction by SSD and In Space
The optic canal was observed from different angles via
SSD reconstruction; however, its inner wall and peripheral structures were unable to be visualized well
(Figs. 1–6). In contrast, the general spatial resolution of
In Space reconstruction was high, with clear visualization of the inner wall and peripheral structures of the
optic canal as required. Thus, the data measured were
accurate and reliable.
Reconstruction by VE
Statistical Analysis
All data were analyzed using SPSS11.5 software. Measurement data were expressed as mean 6 SD (X 6 S). A
t test was used for statistical analysis among group
data. P < 0.05 was considered statistically significant.
The reconstructed images by VE were in accordance
with the real anatomic form of the optic canal, with
global stereopsis, from which the inner wall structures
were clearly displayed (Figs. 7–10, and the internal
sclerotic succession could be dynamically monitored
THREE-DIMENSIONAL RECONSTRUCTION ON MULTISLICE HELICAL CT
1669
Fig. 10. Reconstructed image (sectional area) of the optic canal by VE. The internal three dimensional
structures were shown clearly. Arrowhead indicates the cranium endostoma of the optic canal. (3, superior wall of the optic canal; 4, parietal wall of the optic canal; 5, inferior wall of the optic canal; 6, inner
wall of the optic canal; 7, deossification in the inner wall of the optic canal).
(Figs. 10–12). In our studied cases, a congenital defect of
the inner wall of the optic canal was discovered with the
image reconstruction by VE (Fig. 11)
Combination of the Optic Canal Inner Wall
and the Sphenoidal Sinus
Based on the adjoining relationship between the optic
canal inner wall and the sphenoidal sinus, three types
were classified: (1) ethmoidal type: the whole optic canal
adjoined with posterior ethmoidal sinus; (2) ethmoidalsphenoidal type: the whole optic canal adjoined with
posterior ethmoidal and sphenoidal sinuses; and (3)
sphenoidal type: the whole optic canal adjoined with
sphenoidal sinus. The developmental types of sphenoidal
sinus were based on the criteria by Fan et al. (1997).
The reconstruction results by In Space were in exact
agreement with that observed by real autopsy. The combination of the optic canal inner wall and sphenoidal
sinus are summarized in Table 1.
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ZHIHAI ET AL.
Fig. 11. Reconstructed image (sectional area) of the optic canal by VE. Arrowhead indicates a congenital defect of the inner wall of the optic canal. (3, superior wall of the optic canal; 4, parietal wall of
the optic canal; 5, inferior wall of the optic canal; 6, inner wall of the optic canal).
The Combination of the Bulges Forms of the
Optic Canal and Their Adjoining Structures
Based on the classification criteria by Shi et al. (1997),
the bulge forms were classified into four types: canal
type: more than 50% of the circumference of the optic
canal intrudes into the sinuses; semicanal type: less
than 50% of the circumference of the optic canal
intrudes into the sinuses; impression type: optic canal
intrudes into the sinuses only a little; and no impression
type: optic canal does not intrude into the sinuses at all
and separate from the latter with a thick bone plate.
Reconstruction results by In Space were in exact agreement with that observed by real autopsy. The combination of the bulges forms of the optic canal and their
adjoining structures are summarized in Table 2.
Thickness and Length of Various Bulges Forms
of the Optic Canal Inner Wall
In-space technique is a reliable method for measuring
the spatial distance. In this study, we used the In-Space
1671
THREE-DIMENSIONAL RECONSTRUCTION ON MULTISLICE HELICAL CT
Fig. 12. Reconstructed image (sectional area) of the optic canal by VE, clearly showing the inner wall
structures and sclerotin succession. Arrowhead indicates the fossa orbitalis endostoma of the optic canal.
(1, supraorbital fissure; 2, sphenomaxillary fissure; 3, superior wall of the optic canal; 4, parietal wall of
the optic canal; 5, inferior wall of the optic canal; 6, inner wall of the optic canal).
TABLE 1. Anatomical relationship of the types of pneumatization of the sphenoid to syntopy
of the inner wall of optic canal (sides)
Ehmoid type
Ethmoid-sphenoid type
Sphenoid type
Conchaltype
Antero-sellar type
Semisellar
Pensellar type
Sellar-occipital
0
0
0
8
3
7
4
6
14
16
2
8
4
3
5
technique to reconstruct the optic canals and measured
the thickness and length of various bulge forms of the
optic canal inner wall. The measured data were compared with that measured by real autopsy. There were
no significant differences in these measured data
between the two methods, indicating that the reconstruction by In Space was in accord with that by anatomical measurement (Tables 3 and 4).
DISCUSSION
Application of In-Space Three-Dimensional
Reconstruction in the Study of the Optic Canal
In-space three-dimensional reconstruction is a powerful technique, which can simultaneously display onscreen images reconstructed by other three three-dimensional methods (Cheng et al., 2005). In this study, the
1672
ZHIHAI ET AL.
TABLE 2. Anatomical relationship of inner wall
bulges shape of the optic canal to syntopy of the
inner wall of optic canal (sides)
Canal type
Semicanal type
Impression type
No impression type
Ethmoid
type
Ethmoidsphenoid type
Sphenoid
type
1
6
17
8
0
2
9
3
1
6
17
10
TABLE 3. CT anatomic measurement of thickness
of various inner wall Bulges shape of the optic
canal (X 6 S; mm)
Anatomic
measurement
Canal type
Semicanal type
Impression type
No impression type
0.45
0.53
0.71
0.91
6
6
6
6
0.23
0.25
0.26
0.31
CT
measurement
0.43
0.51
0.70
0.89
6
6
6
6
0.23
0.27
0.30
0.31
optic canal model reconstructed by the In-Space technique accurately reflected the real measurement and
also the real spatial resolution and had the capability to
indicate the adjoining structures very well. In contrast,
the SSD technique had poor resolution when used for
image reconstruction. Thus, the In-Space technique can
provide otolaryngologists with detailed measured data
related to the operation of the optic canal and is of important value in the clinical setting.
Application of the VE Technique in the Study
of the Optic Canal
The VE technique is different from that using the real
endoscope, and the observed area can also be moved to
the outside canal (Cheng et al., 2005). In this study, VE
was used to observe the inner wall of the optic canal
and its adjoining structures with satisfactory results. In
particular, we found a congenital defect of the inner wall of
the optic canal, suggesting that the VE technique could be
used to judge bone fracture based on the sclerotin succession observed in the inner wall of the optic canal, thus
avoiding potential misdiagnosis owing to the irregular
inner wall. This would be of great practical clinical value.
Clinical Significance of the Inner Wall
of the Optic Canal and Its Adjoining Structures
in the Decompressive Operation
The relationship between the optic canal and its
adjoining ethmoidal/sphenoidal sinus is very complex
(Zhang et al., 2006). In this study, we demonstrated that
TABLE 4. CT anatomic measurement of length
of the inner wall of optic canal (X 6 S; mm)
Ethmoid type
Ethmoid-sphenoid type
Sphenoid type
Anatomic
measurement
CT
measurement
9.30 6 0.30
9.50 6 0.40
09.0 6 0.45
9.25 6 0.23
9.40 6 0.34
8.95 6 0.39
in the case where the whole optic canal adjoined with
the ethmoidal sinus, the bulges in the sinus become
apparent. In this situation, an operation would be less
problematic, as for the situation where the whole optic
canal adjoined with the sphenoidal sinus, and the latter
developed well. However, in the case where the whole
optic canal adjoined with the ethmoidal and sphenoidal
sinuses, and the former’s inner wall was thick, an operation would be considerably difficult. In this case, the
decompressive operation of optic canal needs to be performed safely with the aid of an endoscope and an electrodril. Prior to a decompressive operation of the optic
canal, it is necessary to perform an imageological examination to clarify possible variations of the ethmoidal and
sphenoidal sinuses and their association with the inner
wall of optic canal. In this study, we demonstrated that
the three-dimensional reconstruction with combined use
of In Space and VE techniques can provide otolaryngologists with precise information preoperation.
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dissection, dimensions, postmortem, helical, skull, cta, three, comparison, base, optics, analysis, case, canan, multislice, reconstruction
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