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SKULL BASE TUMOR SURGERY

The term Skull Base Tumors refers to a group of tumors that have a tendency to grow along various regions of the bottom part of the Skull, mostly on the inside, but occasionally, also on the outside of the Skull. The Skull Base area separates the base of the Brain from the Skull.

Diseases of the Skull Base are rare, but potentially life threatening and, were considered inoperable because of their sensitive location, as well as the possible effects surgery could have on Brain function and complex senses, such as hearing, vision and balance.

Treatment for these lesions is different from other tumors, both in the surgical approach to their removal and the multi-disciplinary team of surgeons and physicians required to successfully manage these problems.

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 the Cranial Nerves (2, 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 Brain Stem and Cerebellum are located. 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. Skull Base Tumor Surgeons are often called upon to manage tumors that affect the Facial, Cochlear and Vestibular Cranial Nerves which are respectively responsible for facial expression, hearing, and balance. These 4 nerves are all located within a narrow passage traveling inside the dense Petrous Bone called the Internal Auditory Canal. Another vital structure in this region is the Jugular Vein.

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 Skull Base Tumor Surgeon's ability to remove and successfully manage 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. For example, 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 2 & 3 and 5 through 7 below) and Ossifying Fibromas.

Tumors that are unique to the Skull Base of the Middle Cranial Fossa are often benign. These tumors include Pituitary Adenomas, Craniopharyngiomas, Temporal Bone Tumors, Cholesteatomas, Enchondromas and Trigeminal Nerve tumors (such as Neurofibromas.)

Figure 1A (Left): MRI Scan (Coronal View). This is a partially cystic Left Trigeminal Neurofibroma (Arrow) that extends through the Skull Base.

Figure 1B (Right): MRI Scan (Gadolinium "Enhanced"-Transaxial View) The Trigeminal Neuroma tumor is mostly cystic with an "Enhancing" (Arrow) portion that is "solid".

Both benign and malignant tumors can affect the Skull Base of the Posterior Cranial Fossa. Of the benign tumors Acoustic Neuromas, Meningiomas, Epidermoids, Dermoids, Chondromas, and Chordomas are the more common while 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. 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 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 signs depend on the structure(s) impinged upon by the tumor. The Skull Base is a complex area, through which traverse the Cranial Nerves that carry signals to and from the Brain. It is these Cranial Nerves, as well as the Brainstem, that are at risk to involvement and damage by the Skull Base Tumor. Although Skull Base Tumors are "outside" of the Brain, they can affect many important functions such as taste, vision, hearing, swallowing, facial movement and hormonal balance. Because most tumors grow slowly, symptoms may be present for years before the correct diagnosis is made.

Tumor location determines the structures that are affected. Tumors in the Anterior Skull Base may cause dysfunction of the Olfactory or Optic Nerve, resulting in loss of smell and taste, or vision in one or both eyes. Tumors in the Middle portion of the Skull Base may cause eye muscle palsies and loss of sensation or painful sensations in the face. Symptoms from tumors in the Posterior Skull Base may include loss of hearing, imbalance, or difficulty swallowing.

Figure 2A: Coronal View CT Scan series showing a Tuberculum Sellae Meningioma Involving both Carotid Arteries (L>R) (Arrows).

Figure 2B: Sagittal View CT Scan series of this Skull Base Meningioma (Same patient as 2A and Operative Photos in Figures 3 A&B below).

Left: The Arrow indicates the Right Optic Nerve which has an intimate relationship to the Tumor.

Center: The Arrow indicates the Sphenoid Sinus.

Right: The Arrow indicates the Left Optic Nerve and its relationship to the Tumor.

Figure 3A (Left): Operative Photo-Same patient as Figures 2A & B - The tumor partially encircles both the Left Optic Nerve and the Carotid Artery. The nerve is compressed from below and is displaced superiorly.

Figure 3B (Right): The tumor has been completely removed. The Left Carotid Artery, Left Optic Nerve and Chiasm are well seen. The Right Optic Nerve is further to the right of the far right arrow.

DIAGNOSIS

The investigation of any Skull Base Tumor must include some form of Neuroimaging (CT and/or MRI scans). Once the presence of a tumor of this type is made, patients are generally referred to a center specializing in the care of these unique problems. Often times, additional specially designed CT and MRI scans are required by the treating team of physicians and surgeons. The following sophisticated investigational techniques are frequently required by a Skull Base Tumor Team. (See the list below under "TREATMENT")

CT Scan. Additional vital information regarding the Brain and Skull require that thin cuts, along with Sagittal and Coronal reconstructions, be obtained in order to determine the extent of the abnormalities of the bone of the skull and calcifications in the tumor. 3-D reconstruction of the skull and tumor provide exquisite details for the treatment team. CT Angiography can be used to provide some detail of the blood supply to the Brain and tumor.

MRI Scan. Studies done, with and without gadolinium (the "contrast agent"), are essential in order to evaluate the structure of the tumor and its relationship to vital Brain centers. Newer software programs allow for fine details of the Brain's anatomy to be highlighted and magnified, thus providing vital anatomical detail. In some instances, Magnetic Resonance Venography (MRV), as well as MR Angiography (MRA), may be useful to assess the patency of venous structures and arteries.

Cerebral Angiography is an important Neuroadiological procedure, particularly if the tumor encroaches on the Carotid or other major Intracranial Arteries or a major venous sinus. This can also help assess whether arteries and venous sinuses are patent and whether pre-operative embolization (obstruction) of the tumor's blood supply is feasible.

Neuroradiologists, specialists in Neuroimaging interpretation, are vital members of the treatment team at this point in the investigation of Skull Base Tumor patients. They use the various Neuroimaging techniques mentioned above to help the entire treatment team to understand the anatomical complexity of these tumors. Since these tumors frequently develop a robust blood supply, Interventional Neuroradiologists are available with techniques designed to reduce or eliminate the tumor's blood supply prior to initiating any definitive surgical therapy. This is a preparatory step for surgical intervention, which has helped reduce blood loss during operations.

Other tests

Other tests to assess hearing, balance, phonation and vision may require specialized technicians and physicians from other disciplines. This is one area of medicine where patients benefit from having a team of experts working together to solve these complex problems.

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:
  • Neurosurgeon
  • Craniofacial Plastic Surgeon
  • Neuro-ophthalmologist
  • Interventional Neuroradiology
  • Neuro-otologist
  • Otorhinolaryngologist
  • Plastic Surgeon (including free-flap reconstruction)
  • Endocrinologist
  • Neurophysiologist
  • Radiation Oncologist
  • Neuro-Oncologist
  • Ophthalmic Plastic Surgeon
  • Oral Maxillofacial Surgeon
  • Neurological Intensive Care Physician
Many factors should be considered in making a final decision about the appropriate form of treatment. No single approach is suitable for every patient. In dealing with these tumors, the Skull Base Tumor Team acquaints the patient with the benefits, risks and limitations of each of the available treatment alternatives; so that the patient and their family can make a well-informed decision about treatment that they choose.

Treatment Alternatives

For a discussion of Treatment Alternatives either alone or in combination with Skull Base Surgery please consult our SKULL BASE TUMOR section.

Surgery

Most Skull Base Tumors are approached surgically through a craniotomy, a procedure in which the Neurosurgeon makes a temporary opening in the skull as close as possible to the tumor site. 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. This permits exposure of the tumor with little or no retraction of the Brain.

In other cases, such as with many Acoustic Neuromas and Meningiomas, the tumor can be completely removed with acceptable risks. Among the considerable advances in modern Skull Base tumor surgery is the opportunity to PRESERVE HEARING FUNCTION as well as FACIAL NERVE FUNCTION in more patients with Acoustic Tumors.

In other 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.

Figure 4A (Left): MRI Scan (Transaxial View) A large Left Acoustic Neuroma (Arrow) with considerable pressure upon and distortion of the Brain Stem.

Figure 4B (Right): MRI Scan (Same Patient) Post-operative Minimally Invasive complete resection. (Note the reversal of the Brain Stem compression.) The 7th & 8th Cranial Nerves (whose function was preserved) can be seen entering the Internal Auditory Canal which has been opened at surgery.

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. 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.

Minimally Invasive Microendoscopic and Microneurosurgical Techniques

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. Neurosurgeons, together with the other Skull Base Tumor Team members, can then 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. 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.

Minimally Invasive approaches allow the Neurosurgeons to utilize a tiny endoscope with a camera on the end, which is inserted through the nostril, eyebrow, or other area of the face into the Skull Base. The camera provides surgeons with a panoramic view, and in some cases, allows them to remove the tumor completely. Endoscopic Brain Surgery is not appropriate for all cases of Skull Base Tumors although it can be particularly beneficial in treating certain types of benign tumors.

Figure 5A (Above): MRI Scan- Coronal View - of an ANTERIOR Skull Base Meningioma in a 70 year old lady.

Figure 5B (Left): MRI Scan-Transaxial View
Note: Same patient as Figures 5A, 6 & 7.

Figure 6A (Left): Dr. Lazar performing a Minimally Invasive Endoscopic Assisted Image Guided removal of the Anterior Skull Base Tumor using a "KEY-HOLE SURGERY" Craniotomy approach through an "eyebrow" incision.

Figure 6B (Right): Post-operative CT Scan demonstrates the small "Key-Hole" Craniotomy.

Figure 7: 1 Month post-operative photograph of the 70 year old lady represented in Figures 5 A&B and 6 A&B.

This patient was discharged from hospital on the 2nd post-operative day.

Note: The early post-operative scar at the right nasal bridge.

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 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 lesions.

The Neurosurgical Consultants' Skull Base Surgery Program particularly focuses on treatment for the following tumors:

For additional information or to have your Skull Base Tumor reviewed, please see (on this website) ARRANGING A CONSULTATION

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This page last edited on 2/17

All content ©2016 by Neurosurgical Consultants, P.A.
Author, Martin L. Lazar, MD, FACS
All Rights Reserved. See Usage Notices.