Preoperative evaluation for risk of venous air embolism in the sitting position

The diploic venous system: surgical anatomy and neurosurgical implications

Object

There are few systematic investigations of the dissected surgical anatomy of the diploic venous system (DVS) in the neuroanatomical literature. The authors describe the DVS relative to different common neurosurgical approaches. Knowledge of this system can help avoid potential sources of unacceptable bleeding and may impact healing of the cranium.

Methods

Using a high-speed drill with a 2-mm bit, the authors removed the outer layer of the compact bone in the skull to expose the DVS in 12 formalin-fixed cadaver heads. Pterional, supraorbital, and modified orbitozygomatic craniotomies were performed to delineate the relationship of the DVS.

Results

The draining point of the frontal diploic vein (FDV) was located near the supraorbital notch. The draining point of the anterior temporal diploic vein (ATDV) was located in all pterional areas; the draining point of the posterior temporal diploic vein (PTDV) was located in all asterional areas. The PTDV was the dominant diploic vessel in all sides. The FDV and ATDV could be damaged during supraorbital, modified orbitozygomatic, and pterional craniotomies. The anterior DVS connected with the sphenoparietal and superior sagittal sinus (SSS). The posterior DVS connected with the transverse and sigmoid sinuses and was the dominant diploic vessel in all 24 sides. Of all the major diploic vessels, the location and pattern of distribution of the FDV were the most constant. The parietal bone contained the most diploic vessels. No diploic veins were found in the area delimited by the temporal squama.

Conclusions

The pterional, orbitozygomatic, and supraorbital approaches place the FDV and ATDV at risk. The major anterior diploic system connects the SSS with the sphenoparietal sinus. The posterior diploic system connects the SSS with the transverse and sigmoid sinuses.

Severe intraoperative air embolism during convexity meningioma surgery in the supine position. Case report

BACKGROUND

Acute venous air embolism (AE) is a well-known intraoperative complication of neurosurgical procedures, especially during surgical procedures performed in the sitting position, but it is a rare complication in the supine position. A case of a patient who developed an AE during a supratentorial craniotomy in the supine position is presented and the literature is reviewed.

CASE DESCRIPTION

A 45-year-old man had a large left frontal convexity meningioma. He was operated upon and, during craniotomy in the supine position, suffered a massive episode of air embolism with severe respiratory and hemodynamic changes. The AE episode occurred while we were cutting the bone for the craniotomy before turning the bone flap. Because the patient was bleeding profusely, the bone flap was quickly removed to achieve hemostasis. Aspiration of irrigant into the cut bone surfaces through several venous diploic channels in the bone edges was observed. The procedure was terminated when hemostasis was achieved. The meningioma was successfully removed in a second operation.

CONCLUSION

We think that our case should serve to warn the neurosurgical community about the risk of AE in supratentorial procedures in the supine or semisitting positions when preoperative radiological imaging studies show the presence of important venous channels in relation to the site of the tumor.