A brain tumour is a mass of abnormal cells in the brain that usually multiplies in an uncontrollable way.
A skull base tumour is an abnormal growth in the part of the brain that meets the base of the skull. These tumours either arise from the cranial base and the basal meninges or reach the area through an intracranial/extracranial origin.
Although most skull base tumours are benign (non cancerous) and they don’t spread to other parts of the body, still these can cause serious damage typically due to their deep location, close proximity to critical neurovascular structures, and extension beyond certain boundaries.
Common Types of Skull Base Tumours
The many types of skull base tumours and conditions are classified by the type of tumour and its location in the skull base.
Tumour location often dictates the presenting signs and symptoms. The skull base can be divided into the anterior, middle and posterior fossae. This distinction helps the surgeon to choose correct surgical approach for complete removal of tumour with minimal chance for neurological injury.
Anterior compartment of the skull base (anterior cranial fossa), this includes the eye sockets and sinuses. These can be classified as:
*Meningioma
*Olfactory Neuroblastoma
*Paranasal Sinus Cancer
Central compartment of the skull base (middle cranial fossa), this includes the pituitary gland. Tumours arising in this area are called sellar tumours, and these may be classified as:
* Pituitary adenomas
* Craniopharyngioma
* Rathke’s Cleft Cyst
Posterior compartment of the skull base (posterior cranial fossa), these can be classified as:
*Acoustic Neuroma
*Chondrosarcoma
*Chordoma
*Epidermoid tumour
*Meningioma
Among these the most common skull base tumours include:
* Pituitary adenomas: These belong to a class of non cancerous tumour types and develop on the pituitary gland behind the eyes. These tumours can change levels in hormone production or cause vision loss.
* Vestibular schwannomas: These develop on the nerve that connects the ear to the brain and are non cancerous tumours. These can cause hearing loss, ringing in the ear, loss of balance or facial numbness.
* Meningiomas: Again a common type of skull base tumour, non cancerous, and it grows from the layers of tissue that protect the brain and spinal cord. These tumours are commonly found in men than women, and they grow very large before they actually produce any symptoms.
* Osteoma: These tumours grow slowly and rarely expand internally to compress the brain. When symptoms manifest, they may include local pain, headache, or recurrent sinusitis
* Chondroma: Chondromas of the parasellar region or cerebellopontine angle often manifest as cranial nerve palsies. Other manifestations may include nasal obstruction, shortness of breath, and hoarseness.
* Hemangioma: These tumours receive blood supply from the scalp or meningeal vessels, and may produce headaches.
* Dermoid and epidermoid tumours of the skull: These tumours usually arise in the midline, in the diploe of the bone, where they expand both the inner and outer tables of the skull.
* Metastasis to the skull base: The cardinal sign of metastatic skull base invasion is cranial neuropathy, which is typically sudden in onset. Although skull base metastasis are often painless, they may produce symptoms such as localised cranial or facial pain at the site of tumour invasion.
* Direct extension of malignant tumours to the skull base: These tumours affect cranial nerve function, but, unlike metastasis, they often cause pain.
* Chondrosarcoma and chordoma: Chordomas and chondrosarcomas of the skull base may cause similar symptoms such as headaches and diplopia, etc.
Most skull base tumours grow inside the skull, but some tend to grow outside. Also, there could be tumours that may originate in the skull base or spread there from cancer elsewhere in the body (metastatic). However, symptoms depend on factors like: the size of the skull base tumour, how quickly it grows and part of the brain it affects. Sometimes people don’t experience any symptoms and the tumour may be discovered incidentally. Often, though, a patient may experience a headache, vision or hearing loss, memory problems, weakness or numbness.
Diagnosis for a skull base brain tumour begins with a neurological examination, followed by a CT scan or MRI scan of the brain. Specialised testing such as PET scanning or cerebral angiography may then be required. In some cases an image-guided biopsy may be necessary for diagnosis.
In the past, skull base tumour surgery was extremely difficult due to the complexity and risks involved. However, advances in technology these days have made it possible to safely treat skull base tumours.
In addition to surgery, some skull base tumours may be treated with medication, stereotactic radiation and chemotherapy. Sometimes, simple observation is the best treatment, especially if the tumour is growing very slowly.
Techniques used for treatment may include:
* Image-guided, minimally invasive endonasal endoscopic neurosurgery: There are no incisions with this sophisticated ENT technique. Instead, a thin, flexible endoscope is placed through the nose while a computer tracks the location of the endoscope and provides a more targeted view of the tumour. Instruments attached to the endoscope are then used to remove the tumour.
* Stereotactic (“knifeless”) radiosurgery: The use of advanced image-guided software to precisely locate a hard-to-reach skull base tumour allows a radiation oncologists to administer a small, highly targeted dose of radiation to slow the growth of the tumour, without affecting nearby healthy brain tissue.