Midline Anterior Skull Base Meningiomas

Indications and Preoperative Considerations

• Meningiomas represent 34% of all primary brain tumors, originate from the arachnoid cells in the brain and spine and are histologically non-cancerous lesions.

• Anterior midline meningiomas can be classified according to their location ( Figure 31.1 ) into three different groups:

  • Olfactory groove meningiomas

  • Planum sphenoidale meningiomas

  • Tuberculum sellae meningiomas.

  

• Olfactory groove meningiomas arise from the cribriform plate of the ethmoid bone and correspond to up to 22% of all skull base meningiomas. They may grow symmetrically around the crista galli or extend predominantly to one side.

• Planum sphenoidale and tuberculum sellae meningiomas arise from the roof of the sphenoid sinus and at the tuberculum sellae between the optic nerves.

• Olfactory nerves are displaced either laterally or are adhered and compressed within the tumor capsule. Planum sphenoidale meningiomas usually push optic nerves dorsally and caudally, while tuberculum sellae meningiomas lead to an upward bulging of the optic nerves and chiasm ( Figure 31.2 ).

  

• Branches from the ophthalmic artery, anterior ethmoidal arteries and small meningeal arteries provide most of the arterial supply for midline anterior skull base meningiomas.

• Symptoms include:

  • Personality changes, such as apathy and akinesia: secondary to compression of the basal frontal lobes.

  • Smelling disorders: up to 7.1% of these patients may present with anosmia and it is more frequent in olfactory groove meningiomas. Lack of smell is not a frequent clinical complaint, but might be diagnosed during neurological examination. The patient usually complains of change in taste.

  • The Foster–Kennedy syndrome, classically related to olfactory groove meningiomas, is an unusual clinical finding nowadays. It is defined as an association between unilateral optic atrophy because of direct compression of the optic nerve by the tumor, with contralateral papilledema due to the increased ICP, and anosmia.

  • Other symptoms may include headache, seizures and visual deficits.

• Preoperative imaging evaluation ( Figure 31.3 ) consists of:

  • CT scan for analysis of bone (hyperostosis) and relation of the lesion with the planum sphenoidale, tuberculum sellae, medial sphenoid wing and sellar floor.

  • MRI for evaluation of the size, location and relation of the lesion with the optic nerves and chiasm, as well as relation to the internal carotid arteries and its branches and basal frontal lobes.

  • CT angiography, magnetic resonance angiovenography (MRA/MRV) and conventional angiography are useful for preoperative evaluation of arterial feeders and surrounding draining veins.

  • Preoperative embolization, although controversial, may be helpful in cases of large lesions (>5 cm) in order to reduce the arterial tumor supply prior to surgery.

  

• Management of midline anterior fossa meningiomas includes clinical follow-up, surgery and radiosurgery/radiotherapy.

  • Surgery is indicated for patients with:

    • Significant enlargement of the lesion compared to previous scans

    • Development of neurologic symptoms

    • Presence of marked surrounding vasogenic edema.

  • Asymptomatic patients with small lesions and no edema may be clinically followed with routine MRI scans.

  • Radiosurgery/radiotherapy is considered for treatment of recurrent lesions and as adjuvant treatment for grades II and III meningiomas.

Surgical Procedure

Pterional, orbitozygomatic, bifrontal and supraorbital approaches are useful for the resection of midline anterior skull base meningiomas.