Cranial Base (Skull Base) Program

The skull base is one of the most complex regions of the human body. Vital blood vessels and major cranial nerves pass through the base of the skull, making it a delicate area demanding precise skills for successful surgical interventions. Many disorders, including brain tumors, pituitary tumors, congenital craniofacial deformities, microvascular nerve compression syndromes (trigeminal neuralgia and hemifacial spasm), cranial extensions of head and neck cancers, acoustic neuromas, meningiomas and chordomas, however, require surgical intervention in the skull base region. The dedicated cranial base surgical team composed of neurotologists and neurosurgeons, using the latest imaging technology, have extensive experience in this area and are dedicated to treating these potentially devastating disorders.

Meningiomas

Meningiomas are tumors that originate from the meninges, which are membrane-like structures that surround the brain and spinal cord. Typically, they are benign and occur as solitary masses, but instances of malignancy and multiple concurrent lesions have been reported. About 15 to 20% of all primary brain tumors are meningiomas and commonly occur in the fourth through the sixth decade of life, mostly affecting women. Despite various theories, the origin and cause of the tumors is unknown.

Symptoms

Since the meninges surround the entire brain and spinal cord, meningiomas can occur anywhere in the central nervous system. Signs and symptoms depend on the size and location of the tumor. Symptoms usually develop as a result of compression of surrounding neurovascular structures. Intracranial meningiomas may manifest as headache, stroke, seizure, loss of vision or personality change. Meningiomas of the spinal cord may present with pain or weakness at the level of cord involvement. Due to their slow growth characteristics development and progress of symptoms can be subtle and extend over a period of years.

Diagnosis

Diagnosis begins with a thorough documentation of the patient's medical history, including a detailed description of the onset and duration of the symptoms and a complete physical examination focused on neurologic findings. Lab results do not play a major role in diagnosis, but radiologic studies are instrumental in defining the extent of a lesion. Although CT scans may be helpful as an initial diagnostic tool, magnetic resonance imaging (MRI) scans provide the best anatomical pictures of meningiomas and their relationship to surrounding structures.

Treatment

Treatment options vary, ranging from conservative expectant therapy to aggressive surgical resection. Therapy must be tailored to the needs of the individual patient. Elderly patients or those with multiple diseases who are at greater risk for surgical procedures may benefit from observation with periodic MRI studies, radiation therapy or radiosurgery.

Indications for surgical resection depend on clinical progress and the size and location of the tumor. In critical patients with worsening symptoms, resection of the mass is a priority. Advances in diagnostic tools, neuroanesthesia, surgical instrumentation and innovative surgical techniques have enabled surgeons to offer resection to a greater number of patients with less associated surgical risk.

The goal of surgery is complete tumor removal. The technique employed depends on the location of the tumor. When the tumor cannot be completely resected at the time of surgery, adjuvant radiotherapy or radiosurgery may play a role in subsequent management of the patient.

Tumors once thought to be "unresectable" are now regularly and safely removed at the Maxine Dunitz Neurosurgical Institute. Meningiomas located at the base of the skull are very difficult to access. Our use of highly specialized surgical techniques, sophisticated intraoperative monitoring equipment and minimally invasive surgical instruments allows us to expose hard-to-reach areas in their entirety without disturbing surrounding critical neurovascular structures.

Patient outcomes depend on the nature of the tumor and the therapeutic plan that is followed. It is difficult to summarize all treatment results, but the range of treatment options that are currently available provides a suitable approach to most every individual case.

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Cerebral Aneurysm

A cerebral aneurysm is an abnormally dilated segment of a blood vessel surrounding the brain. In some cases, the entire blood vessel widens and expands to resemble a balloon-like structure.

Cerebral aneurysms occur in three to five percent of the general population, are more common in patients older than 30 and are almost twice as common in women than men. The exact cause of many cerebral aneurysms is not completely clear. In general, aneurysms are thought to arise from weakened areas in the wall of a blood vessel. Some aneurysms may occur as a congenital defect in the lining of the blood vessels, resulting in continued enlargement of the aneurysm over time. There appears to be a familial component to the development of aneurysms, as they are much more common in first-degree relatives, especially siblings. On rare occasions, multiple occurrences are reported in the same patient. Aneurysms frequently have a thin wall and are particularly prone to rupture or bleeding.

Several factors can induce weakening of the blood vessel wall, including infection, trauma, brain tumor and arteriovenous malformation (abnormal blood vessel development). Factors that have been shown to increase the risk of aneurysm rupture include smoking, excessive alcohol consumption and arteriosclerosis.

Risk of Aneurysm Rupture

Nearly 1/4 of all cerebrovascular deaths are due to ruptured aneurysms. The annual incidence of cerebral aneurysm rupture is approximately 7/100,000 persons. The peak incidence of aneurysm rupture occurs around age 50 to 60, although rare cases may occur in children and patients over 75. The risk of aneurysm rupture is approximately 0.05 to 2% per year, depending on the size and characteristics of the aneurysm.

Symptoms

Occasionally an enlarging aneurysm can cause symptoms (such as visual changes, seizures and facial pain) through the compression of surrounding neurologic structures. Unfortunately, symptoms frequently do not appear until the aneurysm has ruptured or bled. The rupture of a cerebral aneurysm is usually sudden and occurs without warning. Symptoms of a ruptured aneurysm may include loss of consciousness, severe headache with nausea or vomiting, stiff neck, difficulty moving any part of the body, numbness or decreased sensation in any part of the body, blurred vision, drooping eyelids, seizure and/or a change in mental status (such as a person becoming extremely lethargic).

Once an aneurysm ruptures, blood accumulates between the brain and the subarachnoid space (a thin wall surrounding the brain), resulting in a subarachnoid hemorrhage (SAH). As blood collects in this space, it compresses and damages the surrounding brain tissue. The tissue injury causes the surrounding blood vessels to be susceptible to vasospasm (an abnormal constriction of the blood vessels of the brain, which can result in additional tissue damage through diminished blood flow to the brain). The combined effect of bleeding and vasospasm can result in serious neurologic impairment or even death.

Treatment

Ruptured cerebral aneurysms require urgent medical attention. The goal is to control the immediate symptoms and prevent further bleeding. Upon arrival at the hospital, a patient's vital organ systems, such as respiration and circulation, are stabilized. Following this a thorough neurologic exam is performed to assess mental status and determine specific deficits. In the past, examination of fluid from the spinal cavity provided evidence of bleeding in the subarachnoid space. Today, three-dimensional X-rays (CT scans) or MRIs of the brain are the standard tests used to diagnose cerebral aneurysms. These scans often visualize bleeding (SAH) but may fail to pinpoint the exact site of the aneurysm. Video X-rays of blood vessels using injected dye (cerebral angiography) provide more detailed images of the blood vessels in the brain, often visualizing the exact location of the aneurysm.

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Arteriovenous Malformations (AVM)

Arteriovenous malformations (AVM) involve an abnormal connection between one of the brain's arteries and veins. Although most AVMs are congenital, the exact cause of their formation is unknown. Approximately 0.14% of the U.S. population is affected with AVMs, and the incidence is equal in men and women.

AVMs are troublesome for many reasons. First, AVMs allow blood from the heart to bypass the brain's capillaries, which normally deliver oxygen and nutrients to the brain tissues. This may result in neurologic deficits.

The detoured blood also causes increased pressure on the fragile wall of AVM. The AVM may become swollen due to the effects of this pressure. The ballooned AVM can press down on adjacent brain tissue, inducing seizures or causing compressive damage to surrounding brain tissue.

A much more serious complication is the risk of an AVM hemorrhage (bleeding). This can be a life-threatening emergency, damaging surrounding brain tissues and in severe cases may even result in death. It has frequently been observed that small AVMs tend to bleed more frequently than larger ones. Once an AVM has bled, the re-bleed rate is 4% per year. Fortunately, hemorrhage from an AVM is rarely fatal (<10%), which is in contrast to the high mortality rate of ruptured aneurysms (>90%). However, neurologic deficits can still result from the compression and destruction of the surrounding brain tissue.

Symptoms

The presentation of AVMs varies from person to person. Unless the AVM enlarges or bleeds, it frequently causes no symptoms. AVMs may present with new onset seizures. Seizures resulting from AVMs often occur after age 20. The symptoms of AVM hemorrhage include sudden and severe headache, vomiting, vision change, abnormal weakness, decreased sensation or a change in mental status. The headache that often heralds hemorrhage from an AVM is similar to a classic migraine.

Complications and Treatments

Upon presentation, work-up includes a complete neurologic examination to detect any deficits. Additionally, CT or MRI scans of the brain are used to diagnose AVMs. Video X-rays of blood vessels using injected dye (angiography) can provide even more detailed images of abnormal vessels in the brain.

The final goal of the treatment is to remove or cut off the blood supply to the AVM. This will prevent further growth of the AVM and eliminate the risk of rupture. Current treatment options of AVM are surgery to clip off the AVM, embolization, radiosurgery or a combination of these therapies.

The location and size of the AVM, as well as the patient's overall health and desire to undergo surgery, must be considered in the ultimate decision as to which treatment is recommended. The technical challenges of surgically excising AVMs located in the critical or deep portion of the brain make it crucial that the surgeon performing the operation is highly skilled and well versed in the appropriate approach to the AVM. The neurosurgeons at the Maxine Dunitz Neurosurgical Institute have extensive experience in surgically excising AVMs.

Embolization of AVMs involves placing a long, thin flexible tube into a blood vessel in the leg. This tube is advanced through the blood vessel to reach the AVM, and a glue-like material is then injected into the abnormal vessel, cutting off the blood flow to the AVM. Occasionally, embolization is used in combination with surgery to allow for an easier and less hazardous operation.

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Acoustic Neuroma

An acoustic neuroma is a benign tumor of the eighth cranial nerve - the vestibulo-cochlear nerve - in the posterior fossa. It manifests itself with sensorineural hearing loss, dizziness and tinnitus. At the Cranial Base Program, a team of neurotologists and neurosurgeons from Cedars-Sinai's Maxine Dunitz Neurosurgical Institute and the House Ear Clinic in Los Angeles, provide state-of-the-art microsurgical treatment. When indicated, the most advanced treatments using stereotactic radiosurgery, including fractionated radiosurgery, are also available.

For more on acoustic neuromas, please see Acoustic Neuromas.

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Chordomas

Chordomas are tumors of notochordal origin that may affect the axial skeleton anywhere from the coccyx to the base of the skull, in either the midline or paramedian position. The cranial and caudal extremes of the spine are most often affected.

Symptoms

Chordomas of the skull base are particularly debilitating due to the aggressive involvement of local structures. Symptoms vary, but may include headaches, double vision or gait disturbance.

Diagnosis and Treatment

Imaging studies contribute to making the diagnosis of clival chordoma in a large number of cases, but not all.

There is no single surgical method for therapy or resection of these tumors. There are single-stage procedures that differ in the extent of the dissection and the area of optimum exposure. Surgical goals involve as complete a removal of the tumor as possible. The role of adjuvant radiotherapy thereafter is still subject to debate.

Continued development of skull base microsurgery combined with other minimally invasive endoscopic approaches may allow more complete resection. These innovative approaches developed and used by the neurosurgeons of the Maxine Dunitz Neurosurgical Institute involving craniofacial manipulation may be associated with greater disease-free survival.

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Cranial Extensions of Head and Neck Cancers

Cranial extensions of head and neck cancers include squamous cell and basal cell tumors that can originate in the sinuses, salivary glands or orbits (the area behind each eye). Since these tumors do not differentiate between where the skull base starts and where the brain ends, in many cases they infiltrate the skull base.

Treatment

Patients frequently require a combined exposure whereby a head and neck surgeon resects the tumor below the skull base and a skull base surgeon resects the portion that has gone through the skull base and into the brain. The multidisciplinary team at the Maxine Dunitz Neurosurgical Institute may also include neuroradiologists and radiation and medical oncologists, and head and neck surgeons.

One of the challenges is to resect the tumor without any disfiguring scars. This can be done by hiding all the scars either above the hairline, in the conjunctiva (inside the eyelid) or in the mouth.

For an appointment, a second opinion or more information, please call 1-800-CEDARS-1 (1-800-233-2771) or e-mail us.

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