The parietal notch (Brammer's pointer): Accuracy of a surface landmark for temporal bone surgery.

ABSTRACT

Hypothesis: The parietal notch is a reliable surface landmark of the sigmoid sinus at the sinodural angle. Background: Currently no surface landmark approximates the anterior border of the sigmoid sinus. Additionally, the temporal line may not accurately identify the tegmen near the sinodural angle. This study examines the reliability of the parietal notch as a surface landmark of the sigmoid sinus at the sinodural angle. Methods: Forty-seven cadaveric temporal bones were used to identify the parietal notch by two observers. The parietal notch and sinodural angle were labeled with radiopaque markers, mounted on foam, and CT imaged in the axial plane. The horizontal and vertical distances between the labeled landmarks were measured using PACS software. Results: The parietal notch location was identified in 43/47 specimens. The notch was posterior to the sinodural angle in 90.6% and superior in 65% of the specimens. The average horizontal and vertical distance between the two landmarks was 6.1 mm (SD = 5.4) and 0.8 mm (SD = 8.7), respectively. In 60% of the specimens the parietal notch was within 6 mm of the sinodural angle in the horizontal dimension. Conclusions: The parietal notch is identified in most temporal bones. It also approximates the anterior boarder of the sigmoid sinus and level of the tegmen due to its proximity to the sinodural angle. The parietal notch helps to define the posterosuperior margins of a mastoid dissection and may assist surgeons during mastoid surgery.