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SKULL BASE TUMORS
The Skull Base, upon which the Brain's undersurface rests, has three main regions. The Anterior (front) Cranial Fossa is the region located above the eyes and includes structures such as: the Olfactory Bulbs, the Nasal Cavity, and Cranial Nerves (1 & 2 and sections of 3, 4 & 6) that control vision, as well as movement of the eyeballs. The Middle Cranial Fossa is the region containing the dense, boney Petrous Ridge, and houses the Internal Carotid Artery, along with sections of the Cranial Nerves (5 & 7) that control chewing and facial sensation. The Middle Cranial Fossa also contains the Cavernous Sinus, an extremely difficult structure from which to remove tumors. The Posterior (back) Cranial Fossa is where the Internal Auditory Canal (IAC) and the Cranial Nerves (7 & 8) responsible for hearing, facial expression and balance are located; the Jugular Vein also passes through this region. Of the 24 highly specialized Cranial Nerves, which control many vital functions of our head and neck, 18 (Cranial Nerves 3, 4, 5, 6, 7, 8, 9, 10 & 12 — two on each side of the Skull) originate within this Posterior Cranial Fossa. For decades, tumors within the Skull Base's delicate and complicated bone anatomy were difficult for surgeons to access safely. Patients with Skull Base Tumors often had a poor prognosis. Advances in both technology and microsurgical techniques have dramatically increased the Neurosurgeons' ability to successfully manage a wide variety Skull Base Tumors. There are several ways to classify Skull Base Tumors. One common method is to arrange them by the region that they most often affect. Anterior Skull Base Tumors may be malignant or benign. The malignant tumors in this group include tumors arising in the Nasal Cavity and Paranasal Sinuses (such as Juvenile Angiofibroma, Esthesioneuroblastoma, Inverted Papilloma, Lymphomas and Nasopharyngeal Carcinoma). Other malignant tumors in this group include Orbital Gliomas and other orbital tumors, Rhabdomyosarcomas, and Osteogenic Sarcomas. The benign tumors that occur in the Anterior Skull Base include Meningiomas (see Figures 1 through 5 of this monograph) and Ossifying Fibromas. Middle Cranial Fossa Skull Base Tumors are often benign with some being unique to this region. These tumors include Pituitary Adenomas, Craniopharyngiomas, Temporal Bone Tumors, Cholesteatomas, and Enchondromas. Posterior Cranial Fossa Skull Base Tumors may be benign or malignant. Of the benign tumors Acoustic Neuromas, Meningiomas, Epidermoids, Dermoids, Chondromas, and Chordomas are the more common. Chondrosarcoma is the malignant tumor that occurs in this area. Another way to classify these tumors is by their area of origin. For example, Primary Tumors arise from the cells of the anatomical structures in the Skull Base location. Therefore, Primary Tumors arising from inside the Skull such as Meningiomas, Schwannomas, Chordomas, Glomus Jugulare and Pituitary Tumors, Ossifying Fibromas and Osteoid Osteomas are often Benign. Secondary and Metastatic Tumors are, by definition, malignant. They generally come from outside the Skull such as tumors arising in the Nasal Cavity and Paranasal Sinuses (Lymphomas, Juvenile Angiofibroma, Esthesioneuroblastoma, Inverted Papilloma, and Nasopharyngeal Carcinoma). Other malignant tumors in this group include Orbital Gliomas and other orbital tumors, Rhabdomyosarcomas, and Osteogenic Sarcomas. Nasopharyngeal Carcinoma is the most common Skull Base lesion, which along with tumors such as Squamous Cell Carcinoma or Adenoid Cystic Carcinoma and Esthesioneuroblastoma (also called Olfactory Neuroblastoma), may extend intracranially through the thin bone of the Cribriform Plate, which is a part of the Anterior Skull Base. SYMPTOMS The patient's symptoms and Neurological deficits depend on the structure(s) impinged upon by the tumor. The Skull Base is a complex area. Vital structures such as the Cranial Nerves (that carry signals to and from the Brain and Brain Stem) and the Carotid Arteries (part of the main blood supply to the Brain) traverse the different segments of the Skull Base. It is these Cranial Nerves, as well as the Brain Stem, that are at risk to involvement and damage by the Skull Base Tumor. Although Skull Base tumors are located "outside" of the Brain, they can affect many important functions such as taste, vision, hearing, swallowing, facial movement and hormonal balance. Most Skull Base Tumors grow relatively slowly. The symptoms associated with these lesions often develop slowly as well and may be present for years before the correct diagnosis is made.The location of the Skull Base Tumor determines the Neurological structures that are affected. Tumors in the Anterior Skull Base may cause Olfactory (smell) or Optic Nerve (vision) symptoms. There may be complete loss of smell (which also affects the sense of taste) or visual impairment o varying degrees of severity in one or both eyes. Tumors in the Middle portion of the Skull Base may affect the 3rd, 4th and/or 6th Cranial Nerves resulting in diplopia (double vision) as a result of eye muscle palsies. If the 5th Cranial Nerve (Trigeminal Nerve) is involved, there may be loss of sensation in the face or face pain. Symptoms from tumors in the Posterior Skull Base may include loss of hearing, imbalance, or difficulty swallowing.
DIAGNOSIS Neuroimaging Some form of Neuroimaging (CT and/or MRI scans) is fundamental to the correct diagnosis of any Skull Base Tumor. Once the presence of a Skull Base Tumor has been identified, patients are usually referred to a Neurological Center where there is a team of Skull Base Tumor specialists experienced in the care of these unique problems. Additional specially designed CT and MRI scans are frequently required by the specialists who make up this team of physicians and surgeons."Thin Cut" CT Scans along with Sagittal, Coronal and 3-Dimensional "reconstruction" views provide vital additional information regarding the Brain and Skull. CT Angiography is used in selected cases, where a more invasive study is not appropriate. CT Angiography provides some detail of the blood supply to the Brain and Tumor. MRI Scans done with and without gadolinium (the "contrast enhancing agent"), are essential studies to evaluate the anatomical details and Neuroimaging characteristics of the substance that constitutes the tumor as well as the tumor's relationship to vital Brain structures. Additional information about the extent of involvement by the tumor of vital venous structures and arteries may be obtained from MR Venography, as well as MR Angiography. Cerebral Angiography is another important Neuroadiological procedure that provides precise details about the arteries that supply blood to the tumor and Brian as well as the Brain's venous drainage patterns. Skull Base Tumors that involve these blood vessels must be thoroughly assessed in order to effectively plan the technical details required to manage this particular lesion. Skull Base Tumors frequently develop a considerable blood supply which may require special Interventional Neuroradiological techniques designed to reduce or eliminate the tumor's blood supply prior to initiating any definitive surgical therapy. Other tests The Skull Base Tumor Team includes specialized technicians and physicians from many disciplines. This includes experts to assess hearing, balance, speech and vision. These evaluations are conducted on as needed basis depending on the type of tumor, its location and size.TREATMENT The goal of therapeutic intervention is to maximize the functional outcome of the patient, while minimizing their morbidity. Only a team approach can accomplish this. The multi-disciplinary Skull Base Tumor Team, which includes specialists from Neurosurgery and many other disciplines, offers patients the best of care for these very difficult cases. The composition of a Skull Base Team varies depending upon the nature and location of the tumor. Among the specialists that may be involved in the diagnosis and treatment of patients with these lesions are the following:
Treatment Alternatives Skull Base Tumor treatments often incorporate some combination of surgical procedures, medical (Neuro-oncology) therapy and Radiation Therapy. A Pathological tissue diagnosis is almost always required before Neuro-oncologic Chemotherapy or Radiation Therapy is initiated. Chemotherapy is more often used as an adjunctive treatment (rather than a Primary form of treatment) for some Skull Base Tumors whereas Radiation Therapy (usually in the form of Stereotactic Radiosurgery) may be appropriate as a primary form of treatment of some Skull Base Tumors. More often, Radiation Therapy is, however, usually utilized ONLY AFTER an initial surgical procedure either for biopsy or more extensive removal.Many factors are considered in making a final decision about the appropriate form of treatment since no single approach is suitable for every patient. There are significant risks to in dealing with these tumors. It is the responsibility of the Skull Base Tumor Team to instruct the patient with the risks and limitations of each of the treatment alternatives as well as the indications for and experience with the particular treatment(s) being proposed. Surgery The basic concept of Skull Base Surgery is to approach the tumor from the undersurface of the Brain and tumor, or from the side, by removing specific parts of the bone of the Skull Base (a procedure known as a Craniotomy or Craniectomy). This permits exposure of the tumor with little or no retraction of the Brain.In order to fulfill the previously stated requirement to maximize the functional outcome for the patient, while minimizing the morbidity, the aggressiveness of the surgical approach must be adjusted according to the potential impact of the operation on the patient's quality of life. We recognize that many of these tumors are benign and often are slow growing. MANY OF THESE TUMORS CAN BE ENTIRELY REMOVED. Among these cases are many Acoustic Neuromas and Meningiomas which often lend themselves to complete removal with acceptable risks. Combined Therapy It is frequently in the best interests of the patient to attempt to remove only part of the tumor, without adding any major new neurological deficit to an already difficult neurological situation. In patients where the tumor is intertwined with important nerves and arteries, it is wise to consider removing only that part of the tumor, which can be removed without damaging the vital arteries and nerves. The remaining part of the tumor that is intricately involved with the arteries and nerves can, subsequently, be treated with Focused Beam Radiation therapy (a specialized form of radiation treatment called Radiosurgery.) In some cases this Radiation Therapy is preferable to surgery since some tumors cannot be approached, nor substantial amounts of the tumor removed, without causing a significant neurological deficit.ADVANCED TEHNOLOGY UTILIZED TO TREAT SKULL BASE TUMORS The treatment of Skull Base Tumors has changed dramatically in recent years. There are several highly advanced technologies that are now available to assist the Skull Base Tumor Team in the management of these cases.Computer-assisted tumor removal is a surgical method that uses information obtained from state-of-the-art computer 3-D imaging techniques, to form computer-generated models of the tumor. Using this tool allows Neurosurgeons, together with the other Skull Base Tumor Team members, to plan and simulate the surgical procedure prior to operating, with the goal of reaching the Brain tumor using the safest and least invasive method possible. Real Time Image Guidance uses advanced optical or magnetic technology to identify the precise location of a lesion within the Skull and guide the Neurosurgeon directly to that lesion along the path that was previously chosen as the most appropriate. It assists the Neurosurgeon in defining the location of vital structures that are directly adjacent to the operative region in order to avoid injury to these important parts. It is now possible to COMBINE Image Guidance and Minimally Invasive Technologies to assist in the management of these tumors as demonstrated in the case illustrations below. Among the other technological advances are the Minimally Invasive Microendoscopic and Microneurosurgical techniques, which incorporate smaller incisions and thus less injury to normal Brain tissue, less blood loss and less post-operative pain compared to more traditional surgery. These Minimally Invasive Microendoscopic approaches allow the Neurosurgeons to utilize a small endoscope, with a camera on the end, to reach lesions within the Skull through small openings in the Skull. The camera provides surgeons with a panoramic view, and in some cases, allows them to remove the tumor completely. In other cases this technology is a useful addition to the advanced optics of the modern Neurosurgical Operating Microscope. Endoscopic Brain Surgery is not appropriate for all cases of Skull Base Tumors. Case1. ANTERIOR SKULL BASE MENINGIOMA 
Case2. POSTERIOR CRANIAL FOSSA/PETROUS RIDGE CHONDROSARCOMA 
Radiation Therapy Stereotactic Radiosurgery is the modern and advanced method to deliver Radiation Therapy. This can be used as adjunctive therapy after surgical resection or, in some cases, be used to primarily treat a Skull Base Tumor.Advantage to Radiosurgery: The primary advantage of this form of management lies in AVOIDING Direct Surgical intervention. While there are significant limitations to Radiosurgery regarding the particular type of tumor as well as the size, configuration and location of the targeted tumor, there are circumstances where patients should consider this as an alternative to a direct surgical approach. In some unusual cases, it may be helpful in advance of a planned operation in an attempt to "shrink" the tumor. Disadvantage to Radiosurgery: The greatest disadvantage to Radiosurgery is that it can only hope to slow or stop the growth of the tumor. Unlike direct surgical methods, Radiosurgery DOES NOT REMOVE the tumor. In time (usually measured in quite a few years) the body's mechanisms may remove some or all tumor residue. Other disadvantages include:
NEUROSURGICAL CONSULTANTS' SKULL BASE SURGERY PROGRAM The Neurosurgeons involved with Neurosurgical Consultants' Cranial Base Surgery Program specialize in the treatment of complex tumors, pain syndromes, and congenital defects at the Base of the Skull.Our philosophy is to use Minimally Invasive Microsurgical and/or Microendoscopic techniques whenever possible. Dr. Lazar and his colleagues use Endoscopic and Minimally Invasive approaches to remove a variety of tumor types from various locations including Transsphenoidal Surgery for Pituitary Tumors, Glabellar approaches (through an eyebrow incision) for Anterior Skull Base Tumors (such as Meningiomas), Pterional Burr Hole access for the Endoscopic resection of Giant Arachnoid Cysts of the Middle/Anterior and Posterior Cranial Fossa as well as for different approaches for Clival and Petrous Ridge lesions. The Neurosurgical Consultants' Skull Base Surgery Program particularly focuses on treatment for the following tumors:
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All content ©2024 by Neurosurgical Consultants, P.A. Author, Martin L. Lazar, MD, FACS All Rights Reserved. See Usage Notices. |