Twelve lateral tentorial meningiomas situated in the region of the asterion have been operated upon over the past 18 years at Walter Reed General Hospital. These tumors invaded the transverse sinus at its junction into the sigmoid sinus. Tho superior petrosal sinus which enters the transverse sinus in this area had to be ligated separately only in two instances. However, most of these tumors did extend from the middle into the posterior fossa and required a combined temporal-suboecipital craniectomy.

The main blood supply to the asterion meningioma comes from the middle meningeal artery and the occipital artery. The richness of this blood supply demonstrated angiographically will help decide if ligation of the external carotid artery should be done prior to removal of the tumor.

There are two ways to position the patient for surgery, either prone or sitting. However, both have their advantages and disadvantages.

The prone position is often fraught with more bleeding and may not be as comfortable to the surgeon.

In the sitting position, controlled hyperventilation should not be used because of the risk of air embolism. The patient should be in a pressure suit as a precaution against sudden drop in blood pressure. The skin incision starts in front of the ear, sweeps around and comes down between the mastoid process and the external occipital protuberance.

Two separate burr holes are made over the temporal and over the posterior fossa.

These burr holes are enlarged by the rongeur.

The incision in the dura should be carried parallel above and below the dural sinus. This further exposure will facilitate access to and ligation of the transverse sigmoid sinus.

Bilateral angiography is required. These studies are important not only to reveal the blood supply to the tumor and to see the extent of the tumor by the blush in the venous phase, but also to study the patency and/or presence of the dural sinuses. If the opposite transverse sigmoid sinus is patent, and the superior sagittal and straight sinuses each draining bilaterally the involved sinus can be clamped and then ligated.

The cerebrum and cerebellum are freed from the tumor using wet cotton strips (which are not shown for the sake, of clarity. The dura attached to the tumor is used for traction in delivery and exposure of the tentorium around the tumor.

The dura is closed using a free graft of pericranium or synthetic dura sub-stitute.

Methylmethaerylate cranioplasty may be used to cover the skull defect ¹⁾