The term parasagittal meningioma applies to those tumors involving the sagittal sinus and the adjacent convexity dura and falx. Only the lateral wall of the sinus may be involved. or the tumor may grow to partially or completely occlude the sinus. Involvement of the overlying bone may occur with or without hyperostosis. In considering both the symptoms and the surgical aspects of these tumors. it is useful to divide them. according to the area from which they arise. into anterior. middle. and posterior thirds of the sagittal sinus and falx. The anterior third of the sinus extends from the crista Galli to the coronal suture. the middle third from the coronal to the lambdoid sutures. and the posterior third from the lambdoid suture to the torcular. Those tumors arising from the middle third of the sagittal sinus and falx are the most common and present with focal motor or sensory seizures or gradual loss of neurological function. usually beginning in the lower extremity. Meningiomas arising from the anterior third tend to have a more insidious onset and often become large before a diagnosis is made. There may be a gradual change in personality. progressive dementia. and/or apathy. Seizures can occur but are infrequent and nonfocal. Headache is common. A tumor arising from the posterior third often presents with headache or other symptoms and signs of increased intracranial pressure. There may be visual symptoms, often with some type of field defect. MRI outlines the tumor and may indicate the status of the sagittal sinus. Angiography is usually needed to assess the status of the sinus and the relationship of cortical veins. In some patients MRA may give the information needed. In parasagittal tumors this information is vital, particularly in middle- and posterior-third lesions, in deciding what to do about the sinus at operation.
Positioning of the patient is determined by tumor location. The patient is positioned so that the scalp over the center of the tumor is the highest point. For meningiomas located anterior to the coronal suture, the patient is placed supine with the head slightly elevated. A coronal incision is used. For tumors at the coronal suture and in the middle third of the sagittal sinus, the patient is placed in a supine position with the head well elevated. The scalp over the center of the tumor should be the highest point. A U-shaped incision is used, extending 2 cm across the midline, with the anterior limb at the hairline and the posterior limb well behind the tumor. For some tumors at the coronal suture, the skin flap may be turned forward rather than laterally. ]n posterior-third lesions, the patient is placed in the lateral position and the head is elevated and turned to the opposite side so that the center of the tumor is uppermost. A U-shaped incision turned inferiorly is usually used.
The skin and underlying tissue. including the pericranial tissue, are carefully elevated as one unit. A free bone flap that crosses the midline for I to 2 cm is used. Burr holes are placed across the base on the side of the bone flap and on each side of the sagittal sinus. If there is bone involvement, more burr holes may be placed near the tumor, and occasionally an area of bone is left attached to the tumor while a bone flap is turned around it. As the bone is elevated, bleeding from meningeal vessels is controlled with coagulation and that from the sagittal sinus with Gelfoam or Surgicele.
The dura is opened, usually starting anterior to the turn or. which in parasagittal lesions can most often be seen or palpated through the dura. The surgeon then curves the incision laterally and posteriorly around the tumor in a circumferential fashion, staying at least 1 cm from any involved dura. Great care is used. especially with middle third tumors, to avoid injury to the cortical veins. The dura is left attached to the tumor.
If the sinus is going to be removed. the dura is then opened on the opposite side and the sinus ligated anterior and posterior to the tumor. In some patients. the falx is now divided inferior to the tumor; in other patients this step is performed after dissection of the tumor. In anterior-third meningiomas the sagittal sinus should be excised even if it is still open. If the sinus is open in middle- or posterior-third tumors, it cannot safely be removed because of the cortical venous infarction that will probably occur in the motorsensory cortex; a subtotal removal may be indicated. In many patients the tumor involves only the edge or lateral wall of the sinus, and this can be removed. When the sinus is not going to be resected, the dura is cut parallel to the sinus initially. leaving a small plaque of tumor attached to it. The surgeon then comes back after the tumor mass has been removed, to deal with the involved sinus.
An internal decompression of the tumor is done. The capsule of the tumor is gradually reflected into the area of the decompression. Arachnoid and pial attachments are progressively divided in a circumferential fashion and the brain is separated. The surgeon places traction on the tumor and avoids as much as possible retraction of the surrounding brain tissue. In large tumors the surgeon must be aware of the anterior cerebral artery branches. which may be adherent to the deep surface of the tumor.
After the tumor that is compressing the brain has been removed, attention is turned again to the sinus area. Beginning at one end, the lateral edge of the sinus is opened and the tumor and walls of the sinus excised. After cutting 2 to 3 mm, the two leaves of the sinus are held with a forceps and the edge closed with a running suture. This step is repeated until the attachment has been divided completely and the tumor removed. The use of various types of grafts to replace or repair a portion of the sagittal sinus has been reported. The area of brain that was compressed by tumor is lined with Surgicele. Using a graft of pericranial tissue from the back of the scalp flap, the dural defect is closed.
In most patients a gross total resection can be accomplished by opening the sinus and resecting it but there was often not more than 1 or 2 mm of margin between the tumor and the edge of the resection. The majority of the patients has a good result; around 8% has a fair result because of significant preoperative deficits that did not fully recover. Some patients had temporary weakness in one or both contralateral extremities. No patient has permanent worsening caused by the operation. Two patients had pulmonary emboli.
About 6% of patients have had recurrence of the tumor, respectively. Despite gross total removal was done with a full recovery. In most patients, follow-up scans have not shown any recurrence over a period of 1 to 30 years.
In 30% of patients there is extensive involvement of the sagittal sinus. All patients with tumors in the anterior third has complete removal with a good recovery and there is practically no tumor recurrence. 40% of patients has tumors in the middle third. They often has more deficits preoperatively and frequently had a temporary increase in hemiparesis or sensory loss postoperatively. In 70% of these patients there is significant postoperative worsening that improve in weeks or months but in 10% of these patients a moderate paralysis persisted. 45% of patients has a good result and 45% a fair result. 20% of the patients with fair results has the same or better than before the operation but still has residual preoperative disability and two had new postoperative disabilities. In 55% of patients it is possible to do a total removal because the sinus was occluded by the tumor. In the other 40% tumor left in the wall of the open sinus. Follow-up scans from 1 to 4 years have shown no change in 75% of this group. In 25% of patients, gradual regrowth of tumor is noted on scan but it is not symptomatic until 7 years after operation, when seizures recurred. Angiography shows the sinus to be occluded and a total removal can be done.