National Neuroscience Institute
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Skull Base

Meningioma
Pituitary Tumours
Acoustic Shwannoma
National Neuroscience Institute
Contributed by Dept of Neurosurgery

Meningioma

This is a tumor arising from cells originating from the membrane covering the brain surface called meninges. Meningiomas account for 15% of intracranial tumors. They commonly occur in the fourth through sixth decades of life. Meningiomas are more common in females; they are rare in children (only 1.5% of all meningiomas occur in childhood). Ninety percent of meningiomas are intracranial. The meninges surround the brain completely hence such tumors can occur at many various locations around the brain and compress on brain structures producing the associated symptoms. The clinical symptoms and signs of meningiomas are related to those of an intracranial mass lesion or seizure. The tumor has a predilection for certain regions and produces symptoms and signs specific to the tumor's location. The clinical course of a meningioma characteristically spans a period of years. The tumors which are located along the midline of the brain or along the base of the brain are often associated with important blood vessels and nerves, hence making surgery more difficult and challenging. In such cases the risk of postoperative neurological deficits will be increased.

They are usually benign tumors which do not infiltrate into surrounding brain substance hence most tumors do not require further treatment after complete surgical removal. If here are areas of tumor which cannot be removed because of close proximity to important blood vessels or nerves, then post-operative radiotherapy or radiosurgery may need to be performed. In a small proportion of them, the cells are more aggressive and can turn into a malignant form of tumor or have the propensity to recur with a higher percentage even after complete removal. Patients with these more aggressive tumors will need to be treated with radiotherapy after surgery.

The following are the various types of meningioma based on the location where they occur:

Convexity Meningioma

More than 70% on convexity meningiomas are in the frontal region. If located in this region they may remain asumptomatic while growing to a large size. Epilepsy and focal neurologic signs are common. These meningiomas have the best potential for total removal.

Parasagittal Meningioma

These meningiomas arise in association with the superior sagittal sinus and are located in the midline. They often cause focal epilepsy and later paralysis, especially of the lower extremities.

Falcine Meningiomas

Tumors arising from the falx are located in the midline and often extend to both sides of the brain. These tumors are difficult to remove totally and often recur after surgery.

Olfactory Groove

Olfactory groove meningiomas arise from the cribriform plate. They grow bilaterally and become large without causing significant neurologic deficits or evidence of increased intracranial pressure. Loss of smell can often be the only symptom. Changes in mental status are seldom striking until the tumor has reached a large size. Once the tumor becomes large it impinges on the optic nerves and chiasm resulting in visual loss.

Tuberculum Sellae Meningioma

These meningiomas arise from the planum sphenoidale, tuberculum sellae or the diaphragm sellae. They cause early and characteristic visual failure. Typically, loss of visual acuity and field is progressive and asymmetric, although it can be sudden.

Sphenoid Ridge Meningioma

Meningiomas of the sphenoid ridge are traditionally divided into three types: outer, middle, and medial. The outer sphenoid ridge meningiomas are usually accompanied by epilepsy, focal weakness, and trouble with language function when present on the left side. The tumors of the inner sphenoid ridge usually compress the optic nerve and present with early unilateral visual loss. They also may involve the cavernous sinus to cause double vision and numbness of the face.

Posterior Fossa Meningioma

These constitute about 10% of all meningiomas. The neurologic findings in these tumors can be a combination of posterior fossa and supratentorial symptoms. These can be headache, language disturbance, visual changes, nausea/vomiting, and balance difficulties. These tumors can also cause extensive cranial nerve findings, including facial weakness, hearing loss, swallowing difficulty, and facial numbness. Some of these symptoms may mimic the usual symptoms seen with acoustic neuromas. Finally, some of these tumors may cause weakness and spasticity.

Pituitary Tumours

These neoplasms account for approximately 15% of primary brain tumors and are the third or fourth most frequently encountered intracranial tumor after gliomas, meningiomas and schwannomas. The pituitary gland is a small oval-shaped endocrine gland located at the base of the brain just behind the nose and below the optic nerve (the nerve which leads to the eye). It is about the size of a pea and is very important because it secretes several chemical messages known as hormones. Hormones produced by the pituitary gland helps to regulate and control the secretion of hormones from other endocrine glands which are responsible for the body's growth, metabolism and maturation.

Most of these tumors appear to remain small and do not cause the patient significant harm or symptoms. However some progress to cause major hormonal and neurological problems. Problems encountered are usually due to the following:

  1. Those caused by pressure on normal pituitary tissue so that it cannot deliver its normal production of hormones, e.g., general weakness and fatigue, apathy, pale complexion, loss of menstruation before menopause and loss of sexual function.
  2. Those caused by pressure on structures around the pituitary, e.g., headaches, loss of vision.
  3. Those caused by excessive hormone production:

Prolactin Hormone: loss of menstruation (menopause) and inappropriate milk production by the breasts (galactorrhoea) and infertility in women; impotence and infertility in men.

Growth Hormone: gigantism in children, and in adults who have reached their full height, condition is called acromegaly where the hands, feet and lower jaw becomes enlarged. Excessive growth hormone can aggravate diabetes mellitus, high blood pressure and heart disease.

Excessive Adreno-corticotrophic hormone (ACTH): this stimulates the adrenal gland to make and secrete glucocorticoids. Excessive amounts of glucocorticoid hormones cause build-up of fat in the face (moon-face), neck, trunk and prominent stretch-marks appear. The arms and legs remain thin. The skin is hairy, thin and easily bruised. Excessive amounts of sugar in the blood (diabetes mellitus) and high blood pressure may occur.

Tumours that are less than 1 cm in diameter are called microadenomas; those that are over 1 cm in size are called macroadenomas. The best way to determine if an adenoma is present in the pituitary gland is to perform an MRI of the pituitary without and with gadolinium (a contrast agent).

Treatment

There are three kinds of treatments available. The recommended treatment will depend on the type of tumour, its size and extent, and your age and overall health.

Surgery that is performed is the trans-sphenoidal approach where the tumour is removed through the nasal passage via an incision in the mouth or nose. Currently, minimally invasive endoscopic (key hole) trans-sphenoidal surgery can be performed via a small incision at the back of the nose and this procedure is done together with the ear,nose throat surgeons. This procedure is however only suitable in specific cases depending on the tumor size and features on the MRI scan. Another type of surgery is the craniotomy where a portion of bone in the skull is removed to gain access to the tumour, this is usually performed as second line surgery or if the tumor is very large. The bone is replaced following tumour removal.Large tumours that extend outside the pituitary fossa may require the addition of radiation therapy.

The commonest form of radiation therapy is standard external-beam radiation therapy where high energy X-rays are aimed at the tumour over 5-6 weeks to cause it to shrink. Radiosurgery (Gamma Knife treatment) using multiple radiation beams directed at the tumour has also been used to deliver a large single dose of radiation to stop it from growing.

Following surgery, one has to be followed-up by an endocrinologist for monitoring of the hormonal profile. Hormone deficiencies that may develop after treatment may require life long replacement medical therapy.

Regular follow-up with laboratory tests of hormone levels and X-ray studies such as MRI Scan are necessary to diagnose and treat recurrences. If recurrence is diagnosed, re-operation may be necessary. Large recurrence may require radiation therapy and or drug therapy as well.

Acoustic Shwannoma

An acoustic schwannoma (also called vestibular schwannoma, acoustic neuroma or neurinoma) is a non-cancerous growth that arises from the eighth cranial nerve.

The eighth cranial nerve has two divisions, the cochlear division is associated with transmitting hearing and the vestibular division is associated with sending balance information from the inner ear to the brain.These two parts pass through a bony canal called the internal auditory canal to reach the brain. The seventh cranial nerve (also called the Facial Nerve as it controls facial movements) and important blood vessels also pass through this canal. It is here that acoustic schwannomas usually begin to grow from the tissue surrounding the vestibular division of the eighth cranial nerve.

The cause is not known, except for a small percentage of individuals in whom both sides of the eighth cranial nerve are involved. In these instances there is often a hereditary factor.

Acoustic schwannomas are slow growing tumours, and usually enlarge by 1mm to 3mm per year, while some may grow by more than 5mm per year. In some patients, the growth can remain inert for several years, and in a small proportion of patients its growth can even regress with time.

The symptoms of this tumor include one-sided deafness, often accompanied by noise in the affected ear (tinnitus). The deafness may be gradual or sudden. Unsteadiness and balance problems may occur early in the growth of the tumour, and worsen as the balance function is destroyed on the affected side. Pressure by large tumours on other cranial nerves causes facial numbness, weakness of the facial muscles or swallowing problems. Unsteady gait may be caused by pressure on the cerebellum. Very large tumours can also cause headaches.

An MRI scan of the brain will be able to confirm the diagnosis and further tests will include a hearing test for baseline assessment.

The only cure for the patient with acoustic schwannoma is complete removal of the tumour by using microsurgery techniques. The surgery is performed by the neurosurgeon and sometimes, in conjunction with an ear, nose and throat (ENT) surgeon. Post-operatively, the patient will usually spend one to several days in the intensive care unit for close monitoring and treatment.

Possible complications from surgery are similar for all brain surgeries. These include infection, bleeding, death, coma, stroke and seizures. Other complications specific to acoustic neuroma surgery includes total hearing loss in the affected ear, tinnitus, facial weakness or paralysis due to surgical manipulation and post-operative swelling. Other problems include facial numbness and difficulties in speech and swallowing if the tumor is very large which makes surgeyr more complicated.

An alternative treatment to surgery for smaller tumors is the use of Gamma knife radiosurgery. The Gamma knife uses highly focused Gamma Ray beams produced by 201 independent Cobalt 60 sources to produce its biological effects on tissues inside the intact skull. The treatment is done in a single sitting and despite its name, no cutting is involved. It has been used to treat acoustic schwannomas. The tumour is not removed, but is prevented from growing further. The results of microsurgery in the best hands are still superior to the current results obtained with the Gamma Knife. However when a comparison is made to average available results of microsurgery for acoustic neuromas, Gamma Knife Radiosurgery emerges as a viable alternative for the management of these lesions. It is definitely indicated in patients with residual tumors following microsurgery and in cases where age or illness preclude open surgery.


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