Doppler Ultrasound for Identification of Sinuses in the Retrosigmoid Approach

Purpose: The transverse and the sigmoid sinus mark the lateral und superior borders for the retrosigmoid approach. Injury to these anatomic structures bears a potentially lethal risk. We have investigated the applicability of a micro-Doppler ultrasound probe to avoid injury to the sinuses.

Method: In a series of 25 patients undergoing a surgery for lesions in the cerebello-pontine angle we have applied both image guidance and a micro-Doppler ultrasound probe (16 MHz, Multi-Dop pro^®, Compumedics, Germany) during the surgical approach. The mean maximum error of the image guidance system (Kolibri^®, Brainlab, Germany) was calculated. Visual detectability of the sinuses under the operating microscope was also noted.

Results: There were no inadvertent incisions of the transverse or sigmoid sinuses when both localizing methods were combined. Image guidance was off-target by a mean of 2.64 mm (range 0–6 mm, SD 1.55 mm). The exact location of the transverse sinus was invisible in 7 cases, while the sigmoid sinus was visually undetectable in one case. Ultrasound Doppler indicated blood flow outside the visible borders of the sinuses in 5 cases.

Conclusion: Combined image-guidance and intra-operative micro-Doppler allow for precise location of the transverse and sigmoid sinus and avoidance of injures to these important structures in retrosigmoid approaches to the posterior cranial fossa. The method can be applied to all craniotomies that border on a venous sinus.