A novel theory for rapid localization of the transverse-sigmoid sinus junction and "keyhole" in the retrosigmoid keyhole approach: micro-anatomical study, technique nuances, and clinical application.

To determine a rapid and accurate method for locating the keypoint and "keyhole" in the suboccipital retrosigmoid keyhole approach. (1) Twelve adult skull specimens were selected to locate the anatomical landmarks on the external surface of the skull.The line between the infraorbital margin and superior margin of the external acoustic meatus was named the baseline. A coordinate system was established using the baseline and its perpendicular line through the top point of diagastric groove.The perpendicular distance (x), and the horizontal distance (y) between the central point of the "keyhole" and the top point of the digastric groove in that coordinate system were measured. The method was applied to fresh cadaveric specimens and 53 clinical cases to evaluate its application value. (1) x and y were 14.20 ± 2.63 mm and 6.54 ± 1.83 mm, respectively (left) and 14.95 ± 2.53 mm and 6.65 ± 1.61 mm, respectively (right). There was no significant difference between the left and right sides of the skull (P > 0.05). (2) The operative area was satisfactorily exposed in the fresh cadaveric specimens, and no venous sinus injury was observed. (3) In clinical practice, drilling did not cause injury to venous sinuses, the mean diameter of the bone windows was 2.0-2.5 cm, the mean craniotomy time was 26.01 ± 3.46 min, and the transverse and sigmoid sinuses of 47 patients were well-exposed. We propose a "one point, two lines, and two distances" for "keyhole" localization theory, that is we use the baseline between the infraorbital margin and superior margin of the external acoustic meatus and the perpendicular line to the baseline through the top point of the digastric groove to establish a coordinate system. And the drilling point was 14.0 mm above and 6.5 mm behind the top point of the digastric groove in the coordinate system.

Precise Localization in Craniotomy With a Retrosigmoid Keyhole Approach: Microsurgical Anatomy and Clinical Study.

Objective: We aimed to explore a method of precise localization within craniotomy based on skull anatomical landmarks via the suboccipital retrosigmoid approach. Method: Craniometric measurements were taken from 15 adult dry skulls and eight cadaver head specimens. In the anatomical study, the keypoint corresponded to the transverse-sigmoid sinus junction's corresponding point on the external surface of the temporal mastoid process, eight cadaveric heads underwent a simulated craniotomy using the suboccipital retrosigmoid approach. The center of the burr hole is precisely oriented 12 mm vertically above the top point of the mastoid groove based on the line between the infraorbital margin and the upper edge of the external auditory canal. Clinical application was verified in clinical surgery by evaluating the accuracy, safety, rapidity, and minimal invasiveness of the procedure in 29 patients. Result: No venous sinus injuries were observed. Within clinical application, 29 patients underwent craniotomy using the suboccipital retrosigmoid approach. The operative area was clearly exposed in all patients and the microsurgical anatomy of the intracranial region after the dura mater incision was satisfactory. No venous sinus ruptures were observed. The average craniectomy time was 27.02 ± 0.86 min. The diameter of the bone window was 1.7-2.9 cm. Conclusion: We conclude that the method can ensure safe, accurate, and rapid craniotomy with good vision while avoiding injury to the venous sinus.

Developing a Method to Precisely Locate the Keypoint During Craniotomy Using the Retrosigmoid Keyhole Approach: Surgical Anatomy and Technical Nuances.

Objective: To explore the precise location of the keypoint during craniotomy using the retrosigmoid keyhole approach. Methods: This study included 20 dry skulls and 10 wet cadaveric specimens. On the inner surface of dry skulls, the junction between the inferior margin of the transverse sinus (ITS) and the posterior margin of the sigmoid sinus (TSJ) was marked. The keypoint (D) was identified as the TSJ's corresponding point on the external surface of the temporal mastoid process (MP). The distance from the keypoint to the top point of the digastric groove, mastoidale, and asterion were noted (AD, BD, CD, respectively). A method to accurately locate the keypoint was developed based on these relationships. The developed method was used on the wet cadaveric specimens to evaluate its accuracy, safety, rapidity, and minimal invasion. Results: No significant difference was found between the AD, BD, and CD of the left and right sides. The drilling point was oriented on a straight line 12 mm above the top point of digastric groove, perpendicular to the Frankfort horizontal plane (FHP). In the cadaveric specimens, the operative area was clearly exposed. No venous sinus rupture occurred. The average craniotomy time was 28.74 ± 3.89 min. Conclusions: A potentially safe, accurate, and rapid craniotomy procedure was developed with the added advantage of preserving the visibility of the operating field and preventing venous sinus injury.