OLFACTORY GROOVE MENINGIOMAS

Introduction
Surgical treatment in meningiomas.
Histological aspects in meningiomas.
Supratentorial meningiomas in general.
Parasagittal meningiomas.
Falx meningiomas.
Convexital meningiomas
Olfactory groove meningiomas.
Tuberculum sellae meningiomas.
Sphenoid wing meningiomas.
Optic sheath meningiomas.
Middle fossa meningiomas.
Cavernous sinus meningiomas.
Intraventricular meningiomas.
Malignant meningiomas.
Peritorcular meningiomas.
Tentorial meningiomas.
Infratentorial meningiomas.
Meningiomas outside the nervous system.

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  Clinical Features

These tumors arise from the midline of the anterior fossa between the crista galli and the tuberculum sellae. They are usually bilateral but may be asymmetric and attain a large size before causing symptoms. The most common presenting symptom is a subtle change in mental function or headache alone or in combination with mental function change, but a disturbance in vision or a seizure disorder may also be the initial manifestation. Loss of the sense of smell was recorded as "possibly" the primary symptom in only 3 of 28 patients in Cushing's series, and he questioned the reliability of this finding.

MRI clearly defines the extent of the tumor, the edema in the surrounding brain, the relationship of the tumor to the optic nerves and anterior cerebral arteries, and any extension into the ethmoid sinus. Angiography is rarely needed.

Surgical Management

In planning the operation, it is important to remember that the blood supply comes into the tumor through the bone in the midline of the anterior fossa from branches of the ethmoidal, middle meningeal, and ophthalmic arteries; the posterior capsules may be attached to the optic nerves, chiasm, and anterior cerebral arteries. For patients with a large tumor, It is preferable to perform a bifrontal craniotomy. This approach is associated with the least amount of retraction on the frontal lobes, gives direct access to all sides of the tumor, and allows the surgeon to decompress the tumor while working along the base of the skull to interrupt the blood supply. For smaller tumors, a right subfrontal approach coming from laterally over the orbital roof, as for tuberculum sellae meningioma, may be used. Some uses a pterional approach. Others use either exposure and may resect part of the frontal lobe. The patient is placed carefully in the supine position with the head elevated and slightly extended. Using a coronal incision, the skin flap and underlying tissue, including pericranial tissue, are turned down together. Burr holes are placed just below the end of the anterior temporal line and on each side of the sagittal sinus at the level of the skin incision. The cut just above the supraorbital ridge is made from each side as far medially as possible. Usually this leaves a centimetre or less of bone in the midline. Because of the irregular bone projecting from the inner table of the skull in this area, it is often not possible to cut completely across the area, but the external table can be cut with a fine drill attachment and the bone can be broken at this point. The frontal sinuses are almost always entered. The mucosa is removed and the sinuses are packed with bacitracin-soaked Gelfoam. A flap of pericranial tissue from the back of the skin flap is turned down over the sinuses and sewn to the adjacent dura. The dural incision is made over each medial inferior frontal lobe just above the edge of the craniotomy opening. While the frontal lobes are retracted carefully, the superior sagittal sinus is divided between two silk sutures and the falx is cut. The frontal lobes are then retracted carefully laterally and slightly posteriorly. The tumor will come into view in the midline; at times it is found to have grown into the region of the crista galli and falx. The anterior capsule of the tumor is exposed, and then an extensive internal decompression is done. The base of the tumor in the midline is gradually divided, interrupting the blood supply that is coming in through numerous openings in the bone. These are occluded with coagulation and bone wax. The capsule can now be reflected into the area of the decompression without undue pressure on the frontal lobes. Great care is taken during the dissection of the posterior portion of the capsule. The surgeon reflects it anteriorly and is careful to look for the pericallosal branch of each anterior cerebral artery. The frontal polar branch will often be adherent to the tumor and may need to be divided. It is usually possible to follow the capsule back to the sphenoid wing and then, working medially, to identify the anterior clinoid processes and the optic nerves. At times it may be difficult to see the nerves because of the posterior and inferior compression and the thickened arachnoid. However, under magnification, the tumor can be reflected off the optic nerve(s). Once the bulk of the tumor is removed, the dural attachment is totally excised and any bone hyperostosis removed, with care taken to avoid entering the ethmoid sinus unless it is known that the tumor extends into the sinus. The region of the cribriform plate is covered with a graft of pericranial tissue and Gelfoam to prevent a cerebrospinal fluid (CSF) leak.

Results

Complete removal can be achieved in 90% of cases and 5% with a radical subtotal removal with a small fragment left on the internal carotid artery or other vitally important structures. In 90% of patients a good result can be achieved. Postoperative death due to various causes is around 5%.

The incidence of complications is low and do not interfere with eventual recovery. CSF leak through the ethmoid sinus that required transethmoidal repair can be in 5% of cases. A wound infection also 5%, A subdural hygroma requiring a subdural-peritoneal shunt in 5%. Disturbance in mental function and personality changes when present preoperatively or transiently in the postoperative period usually recover completely. Preoperative visual symptoms usually recover and headache is relieved. The recurrence rate also very low.

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