Tumors of the Ear & Cranial Base
All tumors are collections of cells that are growing faster or dividing faster than the normal cells around them. They are referred to as benign or malignant depending on a few characteristics. Their appearance under the microscope, their rate of growth and their ability to spread beyond their primary site of involvement are just a few of these characteristics. In general benign tumors grow slowly and do not spread. They can push on adjacent structures and remodel bony structures. On the other hand, malignant tumors grow at a faster rate, can spread to surrounding lymph nodes and involve distant organs.
What is an acoustic neuroma?
An acoustic neuroma is a benign tumor that can affect the balance and hearing nerves behind the inner ear. Tumors are classified as benign or malignant based upon their growth characteristics. Benign tumors generally grow slowly and do not spread throughout the body. When they grow, they usually invade or push adjacent structures aside. Unlike benign tumors, malignant tumors like breast cancer, colon cancer, lung cancer and prostate cancer generally grow faster and can spread to other regions of the body.
Important Points To Know About an Acoustic Neuroma:
1) An acoustic neuroma is a benign tumor.
An acoustic neuroma (sometimes termed a neurolemmoma or schwannoma) is a benign (non-cancerous) tissue growth that arises on the eighth cranial nerve leading from the brain to the inner ear. This nerve has two distinct parts, one part associated with transmitting sound and the other sending balance information to the brain from the inner ear. These pathways, along with the facial nerve, lie adjacent to each other as they pass through a bony canal called the internal auditory canal. This canal is approximately 2 cm (0.8 inches) long and it is here that acoustic neuromas originate from the sheath surrounding the eighth nerve. The facial nerve provides motion of the muscles of facial expression.
Acoustic neuromas usually grow slowly over a period of years. They expand
in size at their site of origin and when large can displace normal brain
tissue. The brain is not invaded by the tumor, but the tumor pushes the brain
as it enlarges. The slowly enlarging tumor protrudes from the internal
auditory canal into an area behind the temporal bone called the
cerebellopontine angle. The tumor now assumes a pear shape with the small end
in the internal auditory canal. Larger tumors can press on another nerve in
the area (the trigeminal nerve) which is the nerve of facial sensation. Vital
functions to sustain life can be threatened when large tumors cause severe
pressure on the brainstem and cerebellum part of the brain. Tumors are
typically described as small (less than 1.5 cm), medium (1.5 cm to 2.5 cm) or
large (more than 2.5 cm).
Are Acoustic Neuromas hereditary?
How often do Acoustic Neuromas occur?
Symptoms of Acoustic Neuroma
Since the balance portion of the eighth nerve is where the tumor arises,
unsteadiness and balance problems may occur during the growth of the neuroma.
The remainder of the balance system sometimes compensates for this loss, and
no imbalance will be noticed. Larger tumors can press on the trigeminal
nerve, causing facial numbness and tingling, constantly or intermittently.
Increase of intracranial pressure may be experienced with headaches, clumsy
gait and mental confusion. This is a life-threatening complication requiring
Identifying the tumor
An audiogram should be performed to effectively evaluate hearing in both ears. This test is important to begin the diagnosis of acoustic neuroma. Magnetic resonance imaging (MRI) is the diagnostic test that is preferred for identifying acoustic neuroma. Gadolinium, an enhancing material, is required to reveal the tumor. The image formed clearly defines an acoustic neuroma if it is present. Currently, this imaging study is the preferred test for identifying acoustic neuroma.
An auditory brainstem response test (ABR) may be done in some cases. This test provides information on the passage of an electric impulse along the circuit from the inner ear to the brainstem pathways. An acoustic neuroma can interfere with the passage of this electrical impulse through the hearing nerve at the site of tumor growth in the internal auditory canal. This implies the possible diagnosis of an acoustic neuroma when the test is positive.
When a MRI is not available or cannot be performed, a computerized
tomography scan (CT scan), with contrast, is suggested for patients in whom an
acoustic neuroma is suspected. The CT scan and audiogram can provide valuable
information to determine the presence of an acoustic neuroma. However, the
MRI is nearly 100% accurate in identifying the presence of an acoustic neuroma
and should be performed.
A paraganglioma is a tumor which can originate from cells called paraganglia found in the middle ear, . Other names commonly used for paraganglioma include chemodectoma, glomus tympanicum and glomus jugulare tumors.
Tumors are classified according to whether they are benign or malignant. Benign tumors in general grow slowly and do not spread throughout the body, whereas their malignant counterparts have a faster growth pattern and can spread to other organs in the body. In most instances, paragangliomas behave as benign tumors. In very rare circumstances, these tumors can behave like malignant lesions and spread to lymph nodes in the neck.
There are certain types of cells called paraganglia which are found within the middle ear on the surface of the inner ear and are also found on the surface of the jugular bulb. Other locations for paraganglia include the carotid bulb in the neck and the abdomen. The function of these paraganglia is believed to be the detection of oxygen and carbon dioxide levels in the blood. It is also thought that a mutation within the genetic makeup of a paraganglia cell causes uncontrolled growth which eventually leads to a tumor. The cause for the mutation remains unclear.
Paraganglioma usually develop a rich blood supply from surrounding blood vessels. These tumors produce substances which act on local blood vessels causing them to grow toward the tumor. In addition the tumors that originate from the jugular bulb, or glomus jugulare tumors, can grow to fill the entire bulb thereby effectively blocking blood flow to the heart from that side of the brain. Because of their incremental growth, blood flow from the brain is gradually diverted toward the opposite sigmoid sinus and jugular bulb. The oppposite venous system becomes larger to accomodate the increased blood flow.
Typically paragangliomas which have not previously been treated receive their blood supply from branches of the external carotid artery. The common carotid artery is a vessel which allows oxygenated blood to flow from the heart to the region of the head and neck.
On occasion paragangliomas can also produce and secrete proteins into the bloodstream that can lead to high blood pressure, fast heart rate, palpitations, sweating, and/or diarrhea. The breakdown products of these proteins can be detected prior to any treatment by collecting and checking the urine. Manipulation of the tumor during surgery may cause hypertension.
Paraganglioma or glomus tumors are named according to where they originate from. Glomus tympanicum tumors are small sized tumors originating in the middle ear. They generally do not involve the jugular bulb but can at times erode the bone over the jugular bulb. Symptoms of these tumors include pulsatile tinnitus or ringing in the ears that is heard with each heartbeat. Oftentimes this tinnitus can be heard by a stethoscope placed over the ear.
A conductive hearing loss occurs when the tumor impairs the normal vibration of the ossicles or bones behind the eardrum. A nerve-type or sensorineural hearing loss and/or dizziness can result only in unusual circumstances where the tumor has invaded the inner ear.
There are two options in terms of following or treating these lesions. If the symptoms are not too troubling, these lesions can be followed by periodic examinations to determine the growth rate. These tumors may not follow a linear growth pattern. A period of little growth can be followed by rapid growth and vice versa.
Another option involves surgery to remove the lesion. Depending on the size of the tumor, sometimes a day or two before surgery a procedure is done by a radiologist to place particles within the arterial blood vessels which supply blood to the tumor. This allows for less blood loss during the surgery. Then, under general anesthesia, incisions are made in the ear canal and sometimes behind the ear. The ear canal skin along with the eardrum is lifted. Occasionally some bone around the chorda tympani nerve needs to be removed to allow better visualization of the tumor. The chorda tympani nerve sends information regarding taste from the front two-thirds of the tongue back to the brain. This nerve may need to be mobilized in order to adequately visualize the tumor. Hence temporary taste disturbance may occur following surgery.
After tumor removal the eardrum is laid back down and packing is placed in the ear canal.
Glomus Jugulare tumors
These tumors arise from paraganglia in or around the jugular bulb and as they grow they occlude this venous structure. With additional growth, venous blood from the brain also gradually begins to shift toward the other sigmoid sinus and jugular bulb. Symptoms of these tumors include pulsatile tinnitus or ringing in the ears that is heard with each heartbeat. Oftentimes this tinnitus can be heard by a stethoscope placed over the ear. A conductive hearing loss occurs when the tumor impairs the normal vibration of the ossicles or bones behind the eardrum. A nerve-type or sensorineural hearing loss and/or dizziness can result only in unusual circumstances where the tumor has invaded the inner ear.
The nerves that control the swallowing mechanism and the vocal cord are located close to the jugular bulb. Occasionally these tumors can push or invade these nerves and create dysfunctional swallowing and hoarseness of the voice. Not infrequently because of the relative slow growth, the swallowing mechanism and vocal cord from the opposite side overcompensate so that the patient may not even notice a swallowing or vocal problem. It is not currently possible by imaging (X-rays) to determine whether the tumor has merely pushed the nerves aside or frankly invaded them. As these tumors grow they can also invade the facial nerve leading to a facial paralysis or the hypoglossal nerve leading to paralysis of half of the tongue. Additional growth can lead to tumor compression of the brain and/or brainstem.
These tumors are diagnosed by careful examination of the eardrum. The tip of the tumor can be seen through the translucent eardrum. The natural pulsations of the tumor can be suppressed by introducing positive air pressure in the ear canal. Usually the entire perimeter of the tumor can not be visualized. A CT scan and MRI scan are used to assess the extent of tumor involvement.
There are three options for management of these lesions. The first involves watching the tumor and using MRI scans to help determine the growth rate. These tumors may not follow a linear growth pattern. A period of little growth can be followed by rapid growth and vice versa.
Radiation therapy is another way to manage these lesions. Radiation is not known to cause actual killing of tumor cells but rather induces fibrous tissue proliferation around tumor cells in hopes of preventing further growth. There are a number of disadvantages to radiation therapy. First tumor growth can occur even after having radiation treatment. Surgery becomes more complicated if previous radiation has been used. Radiation causes the loss of the dissection plane between the tumor and surrounding nerves. Consequently, dissection within this plane may increase the chances of nerve injury. Healing from surgery is also impaired when previous radiation has been given. Radiation has also been known to change a benign glomus tumor into a malignant tumor. Radiation therapy may also cause other tumors to occur within the radiated site. For these reasons I recommend radiation therapy when a patient has an actively growing tumor and can not tolerate general anesthesia.
The third option is to have the tumor surgically removed. Usually all aspirin-containing products and non-steroidal antiinflammatory agents are stopped at least two weeks prior to surgery. Preparation is made for blood donation from a friend or relative who has a blood type which is compatible. The day prior to surgery, the patient undergoes angiography with embolization of the tumor. This is a procedure done by a radiologist to place particles within the arterial blood vessels which supply blood to the tumor. This allows for less blood loss during the surgery.
The surgical approach involves an incision behind the ear extending into the neck. The major blood vessels in the neck are identified and smaller arterial blood vessels feeding the tumor can also be tied off. A mastoidectomy is performed exposing the sigmoid sinus and facial nerve. When exposing the jugular bulb, the facial nerve is usually in the way. Consequently, the bone around the facial nerve must usually be removed and the nerve mobilized to allow better visualization of the tumor. When the nerve is mobilized, patients usually have weakness of the face immediately following surgery which recovers over the next several months. With smaller sized tumors, it may not be necessary to mobilize the facial nerve and have any facial nerve following surgery.
The internal jugular vein is tied off in the neck and the sigmoid sinus is packed off in the mastoid. This allows for tumor removal and wide opening of the jugular bulb. The tumor is then dissected from the nerves that control the vocal cord and swallowing mechanism. Occasionally, a spinal fluid leak can occur. This is usually controlled by placing fat from the abdomen into the area of leakage. Sometimes a spinal drain is placed in the back to allow drainage of spinal fluid over several days. This is an effort to keep the pressure in the spinal fluid space low to allow the area of the jugular bulb to heal and seal off.
Weakness of the vocal cord and swallowing mechanism can occur after surgery. This usually recovers in time. Temporary diet modification might be required. In the extreme case a tube may need to be placed in the stomach for a few months until the nerves recover.
Carotid Body Tumors
Carotid body tumors arise from paraganglia located within the covering of the carotid artery in the neck. The initial symptoms can be pain and a pulsating mass in the neck. A CT, MRI and angiography can define the extent of the mass. Management options, again like the other tumors discussed above, include either periodic clinical examination or radiation treatment or surgical excision. Surgery involves excision of the lesion after angiography and embolization. The tumor is then dissected away from the carotid artery.
Another reason for angiography is the detection of other smaller glomus tumors in the opposite ear or in the neck which would otherwise go undetected