The clivus is a sloped, centrally located bone at the base of the skull that supports the brainstem and other neurological structures. Tumors developing here are rare, but their location creates complex challenges for diagnosis and treatment. The clivus is situated in close proximity to the brainstem, numerous cranial nerves, and major blood vessels. Any growth in this region is serious and requires specialized care due to the delicate surrounding neurovascular structures.
Defining the Clivus and Primary Tumor Types
The clivus is formed by the fusion of the basilar part of the occipital bone and the body of the sphenoid bone, joining at the spheno-occipital synchondrosis. This anatomical position places the clivus at the central skull base, extending from the dorsum sellae down to the foramen magnum. This deep location makes surgical access challenging and means tumors often cause symptoms by compressing adjacent structures.
The vast majority of primary tumors arising from the clivus are chordomas or chondrosarcomas. Chordomas are slow-growing tumors originating from remnants of the notochord. Although often considered benign, chordomas are locally aggressive, causing damage by invading nearby tissues, and have a high tendency to recur after treatment.
Chondrosarcomas are rarer and arise from cartilage cells, typically centered near the petro-occipital fissure. While malignant, these tumors are generally slow-growing and less aggressive than chordomas regarding recurrence. Chordomas usually arise directly in the midline of the clivus, while chondrosarcomas are often centered slightly to the side.
Recognizing the Neurological Symptoms
Symptoms result from the tumor mass pressing on or damaging the cranial nerves and brainstem. Since the abducens nerve runs along the clivus, a common early sign is diplopia, or double vision, caused by nerve compression. This symptom is often noticed first because the abducens nerve is highly susceptible to being trapped by the growing tumor.
As the tumor expands, it affects other cranial nerves, leading to facial numbness, persistent pain, or muscle weakness. Patients may also experience difficulty swallowing (dysphagia) and problems with speech due to nerve involvement controlling the throat and tongue. Severe headaches are frequent, sometimes caused by the tumor blocking cerebrospinal fluid flow, leading to hydrocephalus.
Compression of the brainstem can manifest as coordination problems, dizziness, or difficulty walking. Hearing loss and changes in vision can also occur depending on the tumor’s direction and extent. These varied neurological symptoms usually prompt medical evaluation, though the slow-growing nature of the tumors means symptoms develop gradually.
How Clival Tumors Are Diagnosed
Diagnosis begins with a thorough neurological examination to assess functions like eye movement, balance, coordination, and sensation. Advanced imaging studies are then required to visualize the tumor’s size and location. Magnetic Resonance Imaging (MRI) is the preferred method, providing detailed soft tissue images crucial for determining the tumor’s relationship to the brainstem and cranial nerves.
A Computed Tomography (CT) scan is a complementary tool, offering superior detail regarding the bony structures of the skull base. The CT scan assesses bone destruction and identifies internal calcifications, which can help differentiate tumor types; for instance, chondrosarcomas often show more calcification than chordomas.
Definitive classification requires a tissue sample obtained through a biopsy. Due to the tumor’s deep location, this procedure is often performed using stereotactic or image-guided techniques to safely access the mass. Analyzing the biopsied tissue confirms the tumor type, which fundamentally guides the subsequent treatment plan.
Comprehensive Treatment Modalities
Management of clival tumors requires a multidisciplinary team due to the complexity of the disease and its location. The primary goal of surgery is maximal safe resection—removing as much tumor as possible without causing new neurological deficits. Complete removal is often impossible due to the tumor’s proximity to the brainstem and major arteries, necessitating complex skull base approaches, sometimes using minimally invasive endoscopic techniques.
Following surgery, radiation therapy is nearly always recommended to treat residual tumor cells and improve long-term control. Specialized forms of radiation are employed because standard techniques damage surrounding brain tissue. Particle therapy, particularly proton beam therapy, is recommended because it delivers a high dose precisely to the tumor while minimizing the dose reaching sensitive structures like the brainstem and optic nerves.
Stereotactic radiosurgery is an alternative or supplemental technique, delivering a very high dose of radiation in one to five sessions (hypofractionation). A total radiation dose of at least 74 GyE (Gray Equivalents) is generally required for effective tumor control. Chemotherapy and other systemic therapies have a limited role, primarily reserved for palliative care or clinical trials.