Skull base tumors
Skull base tumors, also known as cranial base tumors, can often be asymptomatic (without symptoms) until they compromise neighboring structures, so they are often found at advanced stages. The symptoms that are produced are often dictated by the size and location of the tumor in the skull base and by the nearby structures. There are also some tumors that are identified incidentally on CT scan or MRI as a result of a generalized complaint of headache.
The anatomic site of the tumor's origin and growth is the most important factor in predicting symptoms. For example, squamous cell cancers of the nasal cavity present themselves differently from temporal bone lesions, primarily because of location rather than how the tissue appears under a microscope.
The anterior (front) skull base and involved paranasal (next to the nose) sinuses are closely related to the orbit (eye socket) and to the cribriform plate (a very thin plate of bone at the top of the nose where fibers of the olfactory nerve, nerve for smell, exit the brain).
If the tumor is predominately in the nasal cavity, initial symptoms may include:
- Nasal congestion
- Epistaxis (bloody nose)
- Anosmia (inability to smell)
- One-sided otitis media (fluid in the middle ear behind the ear drum)
Tumors from the front skull base can cause visual disturbances such as:
- Diplopia (double vision)
- Proptosis (bulging of the eyeball)
- Epiphora (drooping of the lower lid with eye drying)
- Vision loss
The close vicinity of the cribriform plate causes the changes to taste and smell. Neurologic findings become apparent when tumors erode into the ptyregomaxillary space (a space where the internal muscles closing the jaw attach to the skull base), epidural space (space between the skull and the outer tough covering of the brain, dura) or brain tissue itself.
The effects of the erosion of surrounding structures include:
- Cranial neuropathies (disease or non-function of the twelve large, paired nerves exiting the base of the brain)
- Frontal lobe symptoms such as alterations in personality.
Middle cranial base lesions can cause pituitary and hypothalamic (the part of the brain that signals the release of hormones to control the other endocrine glands throughout the body) abnormalities such as failure of the pituitary gland to function and excessive thirst due to lack of a hormone that helps the body retain water.
Alternatively, they can affect the optic chiasm, which is the structure where the optic nerves cross at the front of the base of the brain. Patients can experience facial pain, dysesthesia (disturbance of sensation) and nerve palsy (weakness). Tumors of the lateral (side), middle cranial base can affect the trigeminal nerve, lateral orbit, and infratemporal (below the temporal bone) fossa though both facial deformity and mouth and throat masses.
Tumors of the temporal bone and cerebellopontine angle (angle between the brainstem and the cerebellum), the two small lobes below and behind the big brain lobes (cerebrum) that smooth muscular movements and coordination can cause symptoms such as:
- Imbalance (vertigo)
- Pulsatile tinnitus (ringing in the ears in time with the pulse)
- Asymmetric hearing loss (one ear with greater hearing loss than the other)
- Otorrhea (draining ear)
- Vague headache
- Facial twitching or numbness
The hearing loss involved can either be conductive (due to disturbance of the small bones conducting sound from the ear drum to the inner ear) or high or low frequency sensorineural (when the inner ear nerve produces nerve impulses the brain interprets as sound), depending on the location and type of the tumor. If the top of the intracranial part of the temporal bone is involved, then the VIth cranial nerve can become involved and double vision can occur.
Tumors at the back of the skull base near the lower brainstem or jugular foramen will cause deficits of the lower cranial nerves controlling sensation in the back of the throat, voice box, neck muscles and tongue movement.