Many different tumor types originate from or extend into 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. At MD Anderson, physicians and specialists in the Skull Base Tumor Program treat patients with both cancerous and noncancerous tumors of the skull base.
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. The team of experts in the Skull Base Tumor Program at MD Anderson applies highly specialized knowledge and skills from across disciplines to treat patients with tumors in all of these locations.
Following is a list of the most common locations for skull base tumors.
The sinonasal tract consists of the nasal cavity (or the "nasal passage") and the paranasal sinuses, more commonly known as simply "sinuses." The nasal cavity and the paranasal sinuses form a major portion of the bone skeleton of the face and the anterior or front part of the base of the skull. Four pairs of sinuses are located around the nasal passage and include:
- Maxillary sinuses, which are located to the side of the nose, within the cheek bone;
- Ethmoid sinuses, which are located between the nose and the eye;
- Frontal sinuses, which are located in the forehead; and
- Sphenoid sinuses, which are located deep behind the nose.
Behind the nasal cavity and above the soft palate (the back portion of the roof of the mouth) lies the nasopharynx. This is the top portion of the pharynx, which is the passageway that runs from behind the nose and mouth down to the esophagus. The nasopharynx sits right under the middle portion of the skull base.
The orbit is the bony cavity that contains the eyeball. Tumors can start within the orbit (these are known as primary orbital tumors) or they can start in the sinuses and invade into the orbit. Tumors in the orbit present unique challenges, given the proximity to structures critical for visual function. Orbital tumors include vascular tumors of the orbit, primary lacrimal gland tumors and metastatic lesions to the orbit.
Deep within the head lies the floor of the cranial cavity, which contains the brain. The bone in the central portion of this cranial floor is known as the clivus. Access to this region is often obtained through the nasal cavity and sinuses, thus avoiding external scarring. Common tumors in this region are chordoma, chondrosarcoma and meningioma.
The front portion of the cranial floor is known as the anterior cranial fossa. The anterior cranial fossa supports the frontal lobes of the brain. It includes the olfactory grooves where the sense of smell is perceived. The middle part of the anterior cranial fossa forms the roof of the nasal cavity, whereas the outer parts of the anterior cranial fossa form the roofs of the orbits. Meningioma is a common tumor in this area.
This is the space that 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 the jugular vein. Tumors in this location can come from the ear, the salivary glands and the upper or lower jaw.
To the side of the throat or pharynx is the parapharyngeal space. It contains the lowest four cranial nerves, which are involved with speech, swallowing and shoulder movement. 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.
Two temporal bones form part of the side surfaces and the base of the skull. The temporal bone is the hardest bone in the body and has a very complex anatomy. It contains the ear canal (external ear) with the eardrum, and small bones (ossicles) in the middle ear. The temporal bones encase the facial nerve and the organs deep within the ear that control hearing and balance (the inner ear). Large air-filled spaces are present in part of the temporal bone. The carotid artery passes from the neck through the temporal bone, and blood from the brain drains through a space underneath the temporal bone.
The sella turcica is 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. The cavernous sinuses are on each side of the sella turcica. The sella turcica is most commonly accessed through the nasal cavity.
Below the brain and on either side of the pituitary gland and sella turcica lie the two cavernous sinuses. These sinuses contain blood and are part of the venous drainage of the brain. 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.
The middle portion of the cranial floor is known as the middle cranial fossa (includes the Greater Sphenoid Wing). The middle cranial fossa supports the temporal lobes of the brain and forms the outer walls of the orbits. The bone of the middle cranial fossa separates the ear from the brain.
The tip of the bony portion of the temporal bone is known as the petrous apex. The petrous apex is located close to several cranial nerves, including nerves designated as V through VIII. It is the bony boundary of the cerebellopontine angle.
The cerebellopontine angle is the area between the cerebellum (the portion of the brain that 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. Acoustic neuroma and meningioma are the most common tumors located at this site.
The jugular foramen is an opening in the skull base that contains several vital structures. It is located underneath the temporal bone. Blood drains from the brain down to the jugular vein in the neck by passing through the jugular foramen. The lower cranial nerves designated as IX, X and XI pass from the brain through the jugular foramen into the neck.
At the base of the skull lies this large, bony opening, through which the lowest portion of the brain joins and becomes continuous with the spinal cord. This region contains the complex joint system that attaches the skull to the spine.
The back portion of the cranial floor, known as the posterior cranial fossa, encases the cerebellum (the portion of the brain that controls coordination of movement) and the brainstem (made up of the midbrain, pons and medulla oblongata).
Twelve pairs of nerves are located in the head and neck. These nerves are known 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. Care is taken during surgery to preserve the function of these nerves whenever possible.
Tumors of the skull base are categorized based on 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 radiology tests – such as computed tomography (CT) and magnetic resonance imaging (MRI) – and histopathologic analysis of tissue obtained during biopsy. A biopsy 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 that is introduced through the nose and sinuses. Occasionally, an open surgical procedure is needed to obtain a biopsy.
Radiologists and pathologists who have special expertise in tumors of the head and brain work closely with the head and neck surgeons and the neurosurgeons to determine tumor type. This tumor type, together with the unique health profile and needs of each patient, helps the skull base team to specifically tailor treatment for each patient.
The most common types of skull base tumors include:
- Squamous Cell Carcinoma
- Non-Squamous Cell Carcinoma. Four major subtypes are as follows:
- Neuroendocrine Carcinoma
- Sinonasal Undifferentiated Carcinoma
- Salivary Gland Carcinoma. The most common subtype of salivary gland carcinoma is Adenoid Cystic Carcinoma.
- Sarcomas. The more common sarcomas are as follows:
- Ewing's Sarcoma
- Myeloma/Plasma Cell Tumors
- Pituitary Tumors
- Schwannoma. The major Schwannoma subtypes are as follows:
- Acoustic Neuroma (Vestibular Schwannoma)
- Trigeminal Schwannoma
- Jugular Foramen Schwannoma
- Other Schwannomas
- Paraganglioma. This type includes the following:
- Carotid Body Tumors
- Glomus Vagale
- Glomus Jugulare
- Glomus Tympanicum
- Epidermoid Cysts
- Dermoid Cysts
- Other Cysts
- Fibro-Osseous Lesions. These include the following:
- Fibrous Dysplasia
- Ossifying Fibroma