Since tumors of the skull base sit underneath the brain, it can be difficult during surgery to get to the tumor in order to remove it. Traditional techniques used to approach tumors of the brain itself can be used to approach skull base tumors, but these often require significant force to retract the patient’s brain out of the way. This may lead to unwanted injury to otherwise normal brain tissue.
The basic concept of skull base surgery is to approach the tumor from underneath or from the side by removing specific areas of skull base bone. Thus, the tumor can be exposed with little to no brain retraction. Skull base procedures, for example, may be designed to traverse the bone containing the ear (trans-temporal/trans-petrosal/retrosigmoid approaches), low on the temple beneath the brain (middle fossa approach), around the eye (trans-orbital/orbital-zygomatic/craniofacial approaches), through the nose or paranasal sinuses (trans-sphenoidal/trans-ethmoidal/trans-facial approaches), or from the neck (trans-cervical). Fundamentally, these are minimally-invasive techniques designed to maximize tumor removal while preserving neurological function to the greatest extent possible.
Where is the skull base?
The skull base is the bottom part of the skull. While the sides, front, back, and top of the skull are essentially smooth, thin walls of bone, the skull base is dramatically more complex. The skull base is complex because every nerve in the body that carries signals to and from the brain crosses the skull base. Additionally, the large vessels that carry blood to and from the brain run through the skull base.
Which Types of Diseases Are Treated With Skull Base Surgery?
A variety of benign tumors are treated with skull base surgery. These include acoustic neuroma, meningioma, schwannoma, glomus jugulare and vagale, epidermoid, pituitary tumors, and many others. Malignant tumors managed with skull base surgery include squamous cell carcinoma, esthesioneuroblastoma, chondrosarcoma, chordoma, and endolymphatic sac tumors. Occasionally, particularly in the pediatric population, a skull base biopsy may be required in order to diagnose other diseases such as leukemia, lymphoma, plasmacytoma, Langerhans’ dell histiocytosis, rhabdomyosarcoma, osteosarcoma, fibrosarcoma, hemangiopericytoma, malignant fibrous histiocytoma, or metastatic disease. Skull base surgical techniques are also sometimes employed to repair fractures of the skull base, to treat cerebral aneurysms, as well as to remove deep-seated infections of the skull base bone.
What type of symptoms do patients with skull base tumors have?
Tumors arising within the skull base are rare and usually cause few symptoms until they grow to a size where they begin to affect neurologic function. These symptoms may manifest as double vision, facial pain or twitching, hearing loss, loss of balance or dizziness, hoarseness, or tongue weakness. Occasionally, an asymptomatic tumor may be diagnosed when a middle ear mass is noted during routine examination of the ears.
How is a skull base tumor diagnosed?
An MRI of the brain and/or skull base with and without gadolinium contrast is extremely sensitive at diagnosing these rare tumors with little risk to the patient. A CT scan of the skull base or temporal bone may also be needed to evaluate the condition of the surrounding skull base bone. Occasionally, an MRA or MRV (magnetic resonance angiogram and magnetic resonance venogram) are useful to study how the blood vessels to the brain are affected by the tumor. For large or very vascular tumors, an angiogram with embolization may be performed prior to surgical resection in order to plug the arteries that feed the tumor. This reduces blood loss during surgery.
