Overview

 

Skull Base Tumor

Many different tumor types originate from or extend into the base of the skull, which is the sloped area behind the eyes and nasal cavities that forms the “floor,” or base of the skull. The spinal cord, multiple nerves and the major blood vessels of the brain and head and neck pass through holes (foramina) in the skull base.

Not all tumors in the skull base are malignant. But even benign tumors can cause symptoms or threaten the health and well-being of the patient.

Because of their location and proximity to other vital structures, skull base tumors present unique challenges for surgeons. Recent advances in diagnostic and surgical techniques have made the area more accessible to surgery, providing new treatments for these patients.

Tumor Types

Skull base tumors can be classified based on their specific location in the head (the tumor site) or based on the cell structure and identifying characteristics of the tumor (the tumor type). Tumors of the skull base can occur within various anatomic sites.

Following is a list of the most common locations for skull base tumors.

Anterior Cranial Fossa: - The front portion of the cranial floor, which forms the roof of the nasal cavity and the orbits, or eye sockets. It includes the area where the sense of smell is perceived. Meningioma is a common tumor in this area.

Cavernous Sinus: -These two sinuses are located below the brain on either side of the pituitary gland. Important nerves run through the cavernous sinus, as do the internal carotid arteries. Cranial nerves III, IV, V and VI are located in this region (see table of cranial nerves, below).

Cerebellopontine Angle: -The area between the cerebellum (which controls coordination of movement), the pons (part of the central nervous system's brainstem) and the temporal bone. This space contains several cranial nerves, including nerves designated as V through XII (see table of cranial nerves, below). Acoustic neuroma and meningioma are the most common tumors located at this site.

Clivus: -This bone forms the central portion of the cranial floor. Common tumors in this region are chordoma, chondrosarcoma and meningioma.

Cranial Nerves: - Twelve pairs of nerves are located in the head and neck. These nerves are known both by their anatomic names and by their Roman numeral designation. Tumors, usually benign neuromas, can arise from these nerves. Malignant tumors can involve these nerves and cause pain, numbness or paralysis.

Craniocervical Junction/Foramen Magnum: - A large, bony opening at the base of the skull, through which the brain joins the spinal cord. This region contains the complex joint system that attaches the skull to the spine.

Infratemporal Fossa: - This space lies behind the maxilla (the upper jaw) and below the side wall of the skull. It contains several nerves that give sensation to the face, the muscles used for chewing and several blood vessels, including the carotid artery and jugular vein. Tumors in this location can come from the ear, the salivary glands and the upper or lower jaw.

Jugular Foramen: - An opening in the skull base located underneath the temporal bone. Blood drains from the brain down to the jugular vein by passing through the jugular foramen. Lower cranial nerves IX, X and XI pass from the brain through the jugular foramen into the neck (see table of cranial nerves, below).

Middle Cranial Fossa (includes the Greater Sphenoid Wing): - The middle portion of the cranial floor, which supports the temporal lobes of the brain and forms the outer walls of the orbits. The middle cranial fossa bone separates the ear from the brain.

Nasopharynx: - The area behind the nasal cavity and above the soft palate (the back portion of the roof of the mouth), which sits right under the middle portion of the skull base. This is the top portion of the pharynx, the passageway that runs behind the nose and mouth down to the esophagus.

Orbit: -The bony cavity that contains the eyeball. Tumors can start within the orbit (primary orbital tumors) or they can start in the sinuses and invade into the orbit. Orbital tumors include vascular tumors of the orbit, primary lacrimal gland tumors and metastatic lesions to the orbit.

Parapharyngeal Space: - The area to the side of the throat or pharynx, which contains the lowest four cranial nerves involved with speech, swallowing and shoulder movement. (The cranial nerves and their function are defined in a table at the end of this section.) It also contains the major blood vessels of the neck, such as the carotid artery and the jugular vein. The skull base forms the roof of the parapharyngeal space. The most common tumors in the parapharyngeal space are salivary gland tumors, paragangliomas (or vascular tumors) and tumors of the lower cranial nerves.

Petrous Apex: - The tip of the temporal bone, which is located close to several cranial nerves, including V through VIII (see table of cranial nerves, below). It is the bony boundary of the cerebellopontine angle.

Posterior Cranial Fossa: - The back portion of the cranial floor, which encases the cerebellum (the area that controls coordination of movement) and the brainstem.

Sella Turcica: - A depression in the midline of the sphenoid bone, an irregular shaped bone at the cranial floor. It contains the pituitary gland. Pituitary tumors typically arise in the pituitary gland within the sella turcica.

Sinonasal Tract: - This area includes the nasal cavity and the paranasal sinuses, more commonly known as simply "sinuses." This tract forms a major portion of the bone structure of the face and the front part of the skull base. Four pairs of sinuses are located around the nasal passage.

Temporal Bone: - Two temporal bones form part of the side and the base of the skull. The temporal bones contain the ear canal (external ear), encase the facial nerve and organs deep within the inner ear that control hearing and balance. The carotid artery passes from the neck through the temporal bone, and blood from the brain drains through a space underneath the temporal bone.

Diagnosis

Skull base tumors are categorized by the unique characteristics and cell structure of each type. This tumor typing is determined during the patient's diagnostic workup.

The workup can include diagnostic imaging tests – such as computed tomography (CT) and magnetic resonance imaging (MRI) – and analysis of tissue obtained during biopsy. A sample of the tumor may be obtained with a fine needle under precise image guidance, using CT or MRI. In some patients, the best way to obtain a biopsy sample is through an endoscope inserted through the nose and sinuses. Occasionally, an open surgical procedure is needed to obtain a biopsy.

Symptoms

Skull base tumors produce few symptoms until they grow large enough, and symptoms vary greatly depending on the specific location and growth rate of each tumor type. Symptoms may include: -
Having one or more of the symptoms listed above does not necessarily mean you have as skull base tumor. However, it is important to discuss any symptoms with your doctor, since they may indicate other health problems.

Treatment

Treatment for tumors of the skull base may involve surgery, radiation therapy, chemotherapy or a combination of therapies. Some skull base tumors are well-suited to proton therapy, a highly targeted type of radiation. Surgery for skull base tumors may involve either open or minimally invasive techniques.

Open Surgery

Access to the skull base often involves an open surgical approach. Incisions are made in both the cranium and face, and a small portion of bone may be removed to provide access to the target area. Open surgery is recommended for some patients, depending in part on the type of tumor and its location. After the tumor is removed, plastic surgeons reconstruct the soft tissues and bone to provide the best possible function and appearance.

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