The retrosigmoid sinus approach uses the posterior condylar catheter as an anatomical marker of craniotomy

Christos Koutsarnakis of the Department of Neurosurgery at Evangelismos Hospital, University of Athens, Greece, and others evaluated the significance of the posterior condylar catheter as an anatomical marker of this surgical approach, and the results were published in the December 2021 issue of World Neurosurgery
.

—Excerpted from the article chapter

【Ref: Koutsarnakis C, et al.
World Neurosurg.
2021 Dec 1; 158:174-179.
doi: 10.
1016/j.
wneu.
2021.
11.
118.
[Epub ahead of print] 】

Research background

The retrosigmoid sinus approach is ideal for the treatment of lesions in and around the pontine cerebellar angle (CPA region
).

This approach has undergone several modifications in terms of skin incision, soft tissue separation, and bone window size, and has been determined to extend the upper lateral boundary of the bone window to the sigmoid sinus, while its lower limit lacks precise anatomical landmarks
of extension.

The posterior condylar emissary vein (PCEV) has a constant spatial position with the hypoglossal neural tube, occipital condyle, mastoid, lateral part of the foramen magnum, and jugular bulb, which can be an ideal reference marker
for posterolateral skull base approach.

Christos Koutsarnakis of the Department of Neurosurgery at Evangelismos Hospital, University of Athens, Greece, and others evaluated the significance of the posterior condylar catheter as an anatomical marker of this surgical approach, and the results were published in the December 2021 issue of World Neurosurgery
.

Research methods

Research results

The results of the study showed that PCEV was present consistently on both sides of the corpse head specimen, with 87.
5% of patients visible on the left side of CT and 82.
5% on the right
.

Average distance between PCEV and vertebral artery in the part near the posterior condyle: cadaver specimens measured 8.
4-8.
6 mm, CT scan 9.
2-9.
3 mm
.

This distance is safe and effective during separation of standard retrosigmoid sinus approaches and provides easy access to the foramen magnum (Figures 1, 2, 3).

Figure 1.
Autopsy
of corpses.

A.
Standard posterior sigmoid sinus approach on the right
.

The superficial muscular layer of the neck is incised and separated along the superior neck line, revealing star spots (white stellate).


The deep muscles are located in the lower part
of the incision.

Note that the posterior abdomen of the digastric muscle is attached to the digastric groove, which serves as the lateral boundary
of muscle separation.

B.
Separation of the deep muscles, showing the contents of the PCEV and the suboccipital triangle, dotted lines delineating the extent of the open skull window, using PCEV as an anatomical marker, the open skull window can extend near the
foramen magnum.

The inset shows the spatial relationship
between PCEV and VA near the foramen magnum.

C.
The upper and lateral boundaries of the posterior sigmoid sinus open skull window are the transverse and sigmoid sinuses, respectively, while the lower limit extends near the foramen magnum, approximately the location of
PCEV.

Di.
The posterior condyle is indicated
by a white arrow.

Dii.
Osseous attachment
of the neck and suboccipital muscles.

diii.
Outline the extent of
the posterior sigmoid sinus opening skull window with a dotted line.

FM: foramen magnum; DG: digastric groove; MEV: mastoid catheter; OC: occipital condyle; PCC: posterior condylar canal; PCEV: posterior condylar catheter; RCPM: posterior rectus maximus cephalicis; RCPm: posterior rectus cephalicus; SO: Superior oblique muscle
.

Figure 3.
A.
Preoperative MRI (median sagittal plane)
of epidermoid tumor in the left CPA area of a 43-year-old patient.

The tail of the tumor may be seen extending to the foramen magnum
.

B.
Intraoperative photograph
of the patient undergoing a left posterior sigmoid sinus craniotomy.

After routine isolation of soft tissues, PCEV
can be seen.

The parallel dotted lines are the upper and lower lines, and the asterisk is the star point
.

The lateral boundary shows the digastric groove and the medial mastoid venous foramen
.

The illustration shows a view under the microscope that emphasizes the extent of the
open skull window.

C.
Left autopsy, similar to the patient's surgical soft tissue anatomy
.

The first step shows the relative position of the PCEV in the suboccipital triangle (outlined by the white dotted line).


In the second step, the muscle of the suboccipital triangle is removed, revealing the vertebral artery
covered by soft tissue.

The inset shows the posterior view of the dry skull, all bony anatomical landmarks
of the retrosigmoid sinus approach.

DG: digastric groove; EOP: extraoccipital carina; INL: lower line; IO: inferior oblique muscle; MEV: mastoid catheter; MEVF: mastoid venous foramen; OC: occipital condyle; PCC: posterior condylar canal; PCEV: posterior condylar catheter; RCPM: posterior rectus maximus cephalicis; RCPm: posterior rectus cephalicus; SO: superior oblique muscle; SNL: upper neckline; VA: Vertebral artery
.

Conclusion of the study

Finally, the authors point out that the posterior condylar catheter vein (PCEV) is a simple, intuitive, safe, and effective intraoperative anatomical marker; Neurosurgeons can extend soft tissue separation and bony exposure into the foramen magnum, which increases visibility and operability
of the CPA region.