ANATOMICAL VARIATION OF THE
POSTERIOR CLINOID PROCESS:
QUALITATIVE AND QUANTITATIVE
RADIOLOGICAL EVALUATION
Asem Salma MD, Nishanta B. Baidya, MD, Benjamin Wendt, BS, Francisco
Aguila, BS, Steffen Sammet, MD, Mario Ammirati MD, MBA
Department of Neurological Surgery
The Ohio State University Medical Center, Columbus, Ohio
Disclosures
• Nothing to disclose
Background
• Surgical management of interpeduncular fossa lesions such as basilar tip
aneurysms and retrochiasmatic craniopharyngiomas is challenging due to
the complex neuro-vascular relationships of this region. In addition, the
presence of the posterior clinoid process (PCP) complicates neurosurgical
approaches to this area.
• Awareness of the anatomical variations of the PCP and of its relationship
to other skull base landmarks could help in safe surgical access, both open
and endoscopic, of the retrosellar region.
Purpose
To investigate the anatomic variations of the posterior clinoid process from
the radiological perspective.
Materials & Methods
• We evaluated the radiological anatomy of the posterior
clinoid process region on thirty six, 3D reconstructed,
computerized tomography scans of the cadaveric heads
by using TeraRecon software (TeraRecon, Inc., San Mateo,
California, USA).
• The anatomical variation of the PCP was studied, and we
measured the distances between the lateralmost
extension of the PCP and different anatomical landmarks
in the skull base such as the posterior border of the crista
galli (CG), the middle point of basiocciput (BO) at the
level of the foramen magnum (FM), the superior orbital
fissure (SOF), the foramen rotundum (FR) and the
foramen ovale (FO). Figure 1 and figure 2.
Fig. 1. 3D reconstructed CT of the skull base anatomy. Base of the crista galli, CG; anterior clinoid
process, ACP; posterior clinoid process, PCP; foramen ovale, FO; middle point of basiocciput at
the level of the foramen magnum, BO. Fig. 2. Colored lines with labels showing how the
measurement from each PCP has been taken. A, distance between PCP and CG; B, distance
between PCP and ACP; C, distance between PCP and SOF; D, distance between PCP and FR, E,
distance between PCP and FO; F, distance between PCP and BO. (“r” for right, “l” for left). SOF,
superior orbital fissure; FR, foramen rotundum.
Results
Qualitative Analysis
• The study revealed a considerable variation in the gross anatomy of the
posterior clinoid process.
• Two specimens did not have the dorsum sella and hence the PCPs were absent
(Figure 3a).
Fig. 3a. The dorsum sella
(DS) and PCP are missing.
Fig. 3b. Normal anatomy.
• In one specimen the ACPs and PCPs were connected with each other on the
right side (Figure 4).
• In two specimens the ACPs and PCPs were connected with each other on both
sides (Figure 5 and figure 6).
Fig. 4. 3D reconstructed CT of the skull base. The arrow showing the
fused ACP and PCP on the right side. Fig. 5. 3D reconstructed CT of
the skull base, right superolateral view. The arrows show the fused
ACPs and PCPs on both sides. Fig. 6. The arrowheads point to
bilaterally fused ACPs and PCPs.
Quantitative Analysis
• In the remaining 31 specimens we were able to measure the distances between the
posterior clinoid process and the selected skull base structures discussed in the Material and
Methods section. These results are shown in Table 1 and table 2.
Anatomical Landmarks
Mean± SD
Maximum
Median
(All distances are in mm)
From the base of the CG to the PCP
Right
Left
45.14±4.0
46.24±4.5
58.16
57.49
45.21
46.34
36.14
35.40
From the PCP to the middle point
of the BO at the level of the FM
Right
Left
40.41±5.1
41.0±5.2
47.83
47.99
40.64
40.50
27.52
28.57
Table 1. The table shows the values for the measurements of the distance
between the PCP and the base of crista galli (CG) anteriorly, and the middle
point of the basiocciput (BO) at the level of the foramen magnum (FM)
posteriorly. SD, standard deviation.
Minimum
Anatomical Landmarks
Minimum
Mean±SD
Maximum
Median
(All distances are in mm)
Distance between the anterior and
posterior clinoid process
Right
Left
12.03±3.18
12.11±2.77
24.30
20.09
12.08
12.20
8.9
7.89
Distance between the lateralmost
extension of the right PCP and the right
SOF
FR
FO
21.40±4.46
19.10±4.37
22.02±3.41
30.22
28.28
29.76
21.39
18.92
22.06
11.86
14.06
16.06
21.75
20.72
22.36
15.93
13.43
16.84
Distance between the lateralmost
extension of the left PCP and the left
SOF
21.83±3.4
32.75
FR
20.73±3.7
28.13
FO
22.42±3.43
30.32
Table 2. The table shows the values of the measurements of different
anatomical structures in relation to the posterior clinoid processes (PCPs). SOF,
supraorbital fissure. FR, foramen rotundum. FO, foramen ovale.
Conclusions
• The unique location of the posterior clinoid process
at the center of the skull base can be used as a
landmark for pre-surgical planning in surgeries of the
clinoid region. Therefore, knowledge of many
variations of the posterior clinoid process is crucial
for the execution of surgical maneuvers involving the
posterior clinoid process.
• All the above information can be obtained
preoperatively using the 3D reconstructed CT image.