2.1 Patient population and data collection
From June 2022 to may 2023, 20 Chinese adult patients(10 male, 10 female, age, 55¡À13.4 years) were admitted to our study, and all patients complete a standard axial computed tomography scan of cranium in our hospital, in order to their data can be used on viewing system by us, for any slice, including the slice's location on topogram(scanogram) can be demonstrated, and any distance between two points can be measured easily on this viewing system when we needed. All CT images are scanning at a thickness of 6mm, and each patient's topogram(scanogram) is intact.
2.2 Location of the lateral projections of the mid-points of the AHLV and other structure on topogram(scanogram)
When we view routine a standard CT scanning of cranium on viewing system, in which any slice and any distance between two points can be measured easily when we needed, and each topogram(scanogram) is a standard X-ray lateral view of head. We always can find a slice on which the AHLV can be shown more distinctly from them. The mid-points of the AHLV are very easy confirmed on the slice that being selected above, then using simple measurement of the distance between the anterior external surface of frontal bone and the mid-point of AHLV, the lateral projection of the mid-point of the AHLV can easily located on the topogram(scanogram) (Fig. 1A). Using the same method, We also can locate the coronary suture on midline of head and the projections of bilateral external auditory meatus on the topogram(scanogram) too (Fig. 1B-E).
If we want to locate the lateral projections of the mid-point of the AHLV on the head. We can draw a linear (linear A) through bilateral mid-point of the AHLV on the slice that being selected, and the sites where the linear cross the scalp surface are the lateral projections of the mid-point of the AHLV (Fig. 2). The projections cannot be confirmed on scalp surface of head directly. But by the help of cranial bone structure nearby, we can locate it.
If we carefully look at the CT slice above, we always find that there are always apparent bone grooves of lateral surface just anterior (or posterior) to the projections slightly. We can find and mark this bone grooves after the slice being selected above is marked out on the surface of head, then we will gain a linear (linear B) through bilateral bone grooves (Fig. 2). The distance between linear A and linear B on scalp can be measured on the CT slice, and with the measurement above, we can locate the projections on the surface of head easily after the bone grooves are confirmed. Coronary suture of bilateral surface of head also lies nearby, but its location is difficult on CT image or on the surface of head.
So we can first mark out the slice on the scalp surface of patient's head with a mark pen, then we can locate and mark the bone grooves on the marked line. After that, according to distance measurement of CT, the projection of lateral view of the mid-points of the AHLV are located on the marked line of patient's scalp surface, then we can mark the contralateral point.
There is another method following our experience to locating the projection of lateral view of the mid-point of the AHLV. We can mark out the linear from the external auditory meatus to the mid-point of eyebrow arch on CT topogram(scanogram), the linear is parallel with the line of anterior floor of skull, and the distance between two lines often is 1cm or 1.5cm (Fig. 3). The Paine point often being used in neurosurgical operation lies 2.5cm above the line of anterior floor of skull [2], so the distance between the Paine points and the linear from the external auditory meatus to the mid-point of eyebrow arch often is 3.5cm to 4cm. Our data of this distance is male 3.7¡À0.3, female 3.5¡À0.3. The anterior-posterior locations of projections are also confirmed indirectly from the groove's locations as before.
2.3 Coronary plane of puncturing being confirmed
After the projections of lateral view of the mid-points of the AHLV being located, we mark the bilateral bur hole point, like the Kocher point. As said above, we often locate the Kocher point as 1-2cm anterior to the coronal suture at the midline and this method is easily done in practice. Then a curve line can be drawn through the four points, these makes up a coronary plane and the trajectories of catheter are all in it. As a part of the curve line, a linear is drawn between the projection and the Kocher point, but it's end often reach the cross-point that the coronary suture and the sagittal suture on median line (as Fig. 4A-B). So we can obtain a rough direction (red line, not green line) of the Kocher point to the mid-point of the AHLV on CT topogram(scanogram) (Fig. 5).
Two methods above can verify mutually, in order to finally locate the projections better.
Considering all possibilities of burr-hole point as the location of the Kocher's point described by different authors, some linear can be drawn on CT topogram(scanogram) as the possible puncturing trajectories. The trajectories orient to the cross-point of sidebums and zygomatic arch, but none of them orients to the external auditory meatus (Fig. 5).
If you bur hole on the point which lies 7-8cm superior and posterior to the nasion or 5-6cm anterior to the coronal suture at the midline, the trajectory just right orient to the external auditory meatus (Fig. 6A-B). The point often lies on the anterior hairline of head. This result also can be verified on patient's head.
2.4 The projection of AP view of the mid-point of the AHLV bilateral being located
We can also draw a linear (linear D) from projections of the mid-point of the AHLV to the patient's face the on CT topogram(scanogram), to obtain the next plane which is perpendicular to the coronary plane of puncturing. The cross-point between the plane which is perpendicular to the coronary plane of puncturing and the mid-line of the face can be located, and the point can be marked on the face easily (usually 2cm superior to the arcus superciliaris).
Because the cross-point often lies on forehead where the next plane is perpendicular to the midline of head on surface of scalp, so there is not a deviation like drawing a linear from the lateral projection to the Kocher point.
In our experiences, if the point of burr hole lies 1.5cm anterior to the coronal suture at the midline, the point between bilateral projection of AP view of the mid-point of the AHLV is usually located on 2cm superior and posterior to the nasion, just above the bone groove superior to the arcus superciliaris. Certainly, you yet can draw a line on scalp which is perpendicular to the coronary plane of puncture mentioned above, and the cross-point of the line and the midline of scalp on head can be marked too. The A-P projections of the mid-points of the AHLV lies on both side of the cross-point, and the distance lateral to the midline can be marked on forehead based on CT measurement.