What are the other Names for this Condition? (Also known as/Synonyms)

• Cranial Nerve 4 Schwannoma
• Cranial Nerve IV Schwannoma
• Fourth Cranial Nerve Schwannoma

What is Trochlear Nerve Schwannoma? (Definition/Background Information)

• Schwannomas are mostly benign tumors that arise from the Schwann cells around the nerves; these tumors are nerve sheath tumors. Schwannomas involving the central nervous system (CNS) are classified as grade I tumors of the cranial and paraspinal nerves, according to the World Health Organization (WHO)
• WHO grade I brain tumors are the most benign of the brain tumors that are slow-growing and are not known to infiltrate into surrounding tissues. They offer a very high chance for surgery to be curative, and thus, have the best prognosis amongst all brain tumors; long-term survivals are usually noted
• A majority of schwannomas involve the cranial nerves, particularly cranial nerve VIII (causing vestibular schwannomas). Cranial nerves are 12 pairs of sensory and/or motor nerves having specific functions that connect parts of the head and neck region to the brain. Ten of these pairs originate from the brainstem; two pairs originate from the cerebrum
• Trochlear Nerve Schwannomas are very rare form of schwannomas that involve the cranial nerve IV (CN IV), or the trochlear nerve, which is responsible for controlling a single eye muscle, called the superior oblique muscle (obliquus oculi superior). It is an extraocular muscle that controls the inward, outward, and rotational eye movements
• Based on the location of the tumor, Trochlear Nerve Schwannomas are classified into the following three types. This is an important consideration with respect to the surgical approach to treat the tumor
  • Cisternal type: A vast majority of tumors belong to this type (over 90%)
  • Cisternocavernous type
  • Cavernous type
• Currently, no causative factors have been identified for Trochlear Nerve Schwannoma, although certain genetic, environmental, and occupational factors have been implicated in schwannoma development. Extremely rarely, the risk factors for the tumor may include the presence of neurofibromatosis type 2, which is a genetic disorder
• Trochlear Nerve Schwannomas may cause bulging of the eye (most common symptom), body weakness on one side (hemiparesis), lack of coordination, and rarely, trochlear nerve palsy. In some cases, the involvement of multiple cranial nerves is noted. Some individuals may also experience headaches and facial paralysis. In rare cases, schwannomas are known to undergo malignant transformations
• In some rare cases, the healthcare provider may undertake a ‘wait and watch’ approach for small-sized and slow-growing tumors. In many cases, a complete excision by surgery or treatment using Gamma Knife radiosurgery can be curative. The prognosis of Trochlear Nerve Schwannoma is typically excellent with appropriate management and follow-up care

Who gets Trochlear Nerve Schwannoma? (Age and Sex Distribution)

• Trochlear Nerve Schwannomas are extremely rare tumors that are observed in both children and adults. Currently, only about 35 cases have been reported worldwide
• Both males and females are affected
• There is no known geographical bias and racial/ethnic preference observed

What are the Risk Factors for Trochlear Nerve Schwannoma? (Predisposing Factors)

Based on the few available reports, a vast majority of Trochlear Nerve Schwannomas are sporadic in nature and no well-established predisposing factors are observed.

• The presence of neurofibromatosis type 2 (NF2) is noted highly infrequently in Trochlear Nerve Schwannoma. NF2 is a genetic condition characterized by the formation of non-cancerous tumors affecting the nervous system
• In general, for schwannomas the risk factors may include:
  • A family history of the tumor
  • Frequent exposure to ionizing and non-ionizing radiation

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Trochlear Nerve Schwannoma? (Etiology)

The exact cause and mechanism of Trochlear Nerve Schwannoma formation is unknown; in most cases, they are believed to be the result of sporadic mutations. This implies that they do not have a preceding family history of the condition. It is researched that certain genetic, environmental, and occupational factors may contribute towards the development of cranial nerve schwannomas.

Overall, the following factors have been identified as playing a role in schwannoma development:

• Abnormalities in chromosome 22
• Multiple schwannomas are known to occur in a background of genetic disorders, such as NF2 and Gorlin-Koutlas syndrome, or a positive family history
• The tumor is believed to be caused by the overproduction of Schwann cells that wrap around the nerve

In general, it is known that tumors form when normal, healthy cells begin transforming into abnormal cells - these cancer cells grow and divide uncontrollably (and lose their ability to die), resulting in the formation of a mass or a tumor.

What are the Signs and Symptoms of Trochlear Nerve Schwannoma?

The signs and symptoms of Trochlear Nerve Schwannoma may differ from one individual to another. It may be mild or severe, depending on several factors. The onset and speed of progression of the tumor can vary. In many individuals, tumors that grow slowly and remain asymptomatic, are only diagnosed during certain radiological imaging studies of the head and neck region, which are performed for unrelated health conditions.

It is reported that the signs and symptoms of Trochlear Nerve Schwannoma are similar to those observed in trigeminal nerve schwannomas. Also, the tumor is observed to involve other adjacent cranial nerves. Depending on the nerve involved, a set of associated signs and symptoms may be noted.

In general, the signs and symptoms include:

• The tumors are mostly slow-growing and solitary; they may appear as a cystic mass with some solid portion
• Usually a single eye is involved; however, rarely both eyes can be affected
• Injury to the trochlear nerve by the tumor can occasionally result in trochlear nerve palsy affecting normal eye movement. A damage to the trochlear nerve can result in the following issues:
  • Double vision (diplopia)
  • Repetitive uncontrolled eye movements (nystagmus)
  • Improper eye alignment or coordination (strabismus)
  • Headaches
  • Eye pain
  • If the optic nerve is affected, it can result in partial to complete vision loss
• Unilateral paresis or one-sided body weakness is commonly observed
• Cerebellar symptoms that may be noted include dysmetria (lack of movement coordination) and ataxia or gait disturbances
• Convulsions and memory impairment are not generally noted
• Facial drop and altered touch sensation on the face (facial paresthesia) may be observed, if the tumor compresses on the facial nerve
• Multiple schwannomas are known to occur in a background of neurofibromatosis type 2 disorder

Large tumors can cause significant signs and symptoms. Also, associated symptoms of the underlying condition, if any, may be noted.

How is Trochlear Nerve Schwannoma Diagnosed?

Trochlear Nerve Schwannomas may remain undiagnosed if they are asymptomatic and slow-growing. The slow development of symptoms may contribute to a delayed detection and diagnosis of these tumors. The tumors are detected when there is a sudden worsening of symptoms prompting the healthcare provider to perform radiological studies of the brain.

A diagnosis of Trochlear Nerve Schwannoma may involve the following tests and examinations:

• Complete physical examination with thorough evaluation of the individual’s medical history (including family history of NF2 or schwannoma)
• Assessment of the presenting signs and symptoms
• Tests and procedures related to the eye (ocular system):
  • Eye examination by an eye specialist (ophthalmologists or retinal experts)
  • Fundoscopic (ophthalmoscopic) examination by an eye specialist, who examines the back part of the eye (or the fundus)
  • Visual acuity test using a special and standardized test chart (Snellen chart)
  • Slit-lamp examination: Examination of the eye structure using a special instrument called a slit-lamp. In this procedure, the pupils are dilated, and the internal eye structure is examined
  • Visual evoked potential (VEP) test: It is a test to explore the cause for vision change, particularly when the optic nerve is affected using a visual stimulus; the responses are captured by a set of electrodes placed on the head. The electrical conductivity of the nerve is studied and analyzed for abnormalities
  • Tonometry: Measurement of intraocular pressure or eye fluid pressure, especially to detect conditions such as glaucoma
  • Fundus fluorescein angiography (FFA): In this technique, the eye blood vessels are examined using a fluorescein dye
  • Fundus autofluorescence (FAF): It is a non-invasive diagnostic technique to examine the fundus of the eye without using a fluorescent dye by a specialized fundus camera 
  • Indocyanine green (ICG) angiography: It is used to examine the blood vessels of the choroid using a dye, called indocyanine green, particularly to study the choroid
  • B-scan ultrasonography: Special ultrasound scan of the eye through a non-invasive diagnostic tool, to assess health of eye structures
  • Electroretinogram (ERG): It is a technique to measure electrical activities in the retinal cells
  • Optical coherence tomography (OCT) of eye: It is an ocular imaging technique to visualize the eye structure
• Cranial nerve examination: Usually, cranial nerves III, IV, and VI are examined together
• Neurological, motor skills, and cognitive assessment:
  • Checking intellectual ability, memory, mental health and function, language skills, judgment and reasoning, coordination and balance, reflexes, and sensory perceptions (space, sight, hearing, touch, etc.)
  • The healthcare provider/neurologist may use the Karnofsky Performance Scale in order to assess the neurological functioning of the individual’s central nervous system (CNS)
• Electroencephalography (EEG)
• Imaging studies that may be performed include:
  • X-ray of head and neck and/or vertebral column
  • Computerized tomography (CT) scan of the head and neck region; CT with contrast
  • Magnetic resonance imaging (MRI) scan of the central nervous system; MRI with contrast agents such as gadolinium
  • Cerebral angiographic studies or MR angiography: An angiogram involves injecting dye into the bloodstream, which makes the blood vessels to appear visually on X-rays
  • Positron emission tomography (PET scan): A PET scan is a nuclear medicine imaging technique that uses three-dimensional images to show how tissue and organs are functioning. It may be performed to detect any malignancy, and if there is a metastasis (spread) of the tumor to other regions
• Cerebrospinal fluid analysis, where a spinal tap or lumbar puncture procedure may be performed: This diagnostic test is used to remove a sample of cerebrospinal fluid (CSF) from the spaces in and around the brain and spinal cord. The sample is removed from the lower spinal cord using a thin needle, and it is then checked for the presence of cancer cells
• Magnetic resonance spectroscopy: This radiological technique is used to study the chemical profile of the tumor. It is often performed with and compared to corresponding MRI scan images of the affected region

Tissue biopsy: A biopsy of the affected region (brain) is performed and sent to a laboratory for a pathological examination. A pathologist examines the biopsy sample under a microscope. After putting together clinical findings, special studies on tissues (if needed) and with microscope findings, the pathologist arrives at a definitive diagnosis. Examination of the biopsy sample under a microscope by a pathologist is considered to be gold standard in arriving at a conclusive diagnosis.

There are two ways to perform a biopsy:

• First, a biopsy can be performed as part of a surgical procedure to remove the brain tumor
• Second, a stereotactic needle biopsy can be performed when the tumor is deep within the brain or located in a sensitive area. In this procedure, the surgeon drills a small hole (called a burr hole) into the skull. A thin needle, guided by CT or MRI scanning, is then inserted through the hole to help in the removal of tissue

A differential diagnosis to eliminate other conditions or tumor types may be considered, before arriving at a definitive diagnosis. These include:

• Ependymoma
• Epidermoid cyst
• Trigeminal schwannoma
• Other intrinsic brain tumors

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Trochlear Nerve Schwannoma?

The complications from Trochlear Nerve Schwannoma could include:

• Permanent damage to the trochlear nerve or other involved cranial nerves
• Permanent damage to the optic nerve causing irreversible loss of vision
• Severe facial paralysis
• Emotional and mental stress for both the patient and the caretakers, due to the diagnosis and during treatment of a brain tumor
• Large undetected tumors can severely affect brain function and be disabling or even life-threatening
• Very rarely, schwannomas can become malignant (malignant transformation of schwannoma)
• Complications due to an underlying genetic disorder, if any present, may be observed

Complications may arise from surgery, radiation therapy, chemotherapy, or any other treatment measures.

Surgery:

• Damage to the muscles, vital nerves, and blood vessels, during surgery to remove the tumor; injury to unaffected brain tissue during surgery
• Post-surgical infection at the wound site is a potential complication
• Sometimes, removing the tumor can worsen the signs and symptoms in some individuals
• Temporarily, post-operative trochlear nerve palsy is observed that resolves over time
• Infrequently, recurrence of the tumor after surgery, if the tumor is incompletely removed

Chemotherapy side effects depend on the type of chemotherapy medication used and may include:

• Nausea and vomiting
• Hair loss
• Mouth sores
• Loss of appetite
• Diarrhea
• Fatigue
• Increased risk for infections
• Easy bruising

Radiation therapy can cause short-term side effects. It depends on the type used and may include:

• Nausea and vomiting
• Hair loss
• Dryness of mouth; loss of taste
• Headaches
• Fatigue
• Skin color changes; usually darkening of skin on the face and neck may be noted
• Speech and hearing difficulties
• Memory issues
• Seizures
• Long-term side effects (seen after 6 months or beyond) may include loss of memory, impaired brain function, and appearance of symptoms that mimic stroke

How is Trochlear Nerve Schwannoma Treated?

In general, the treatment modality for a benign brain tumor is chosen depending on the size, location, and stage of the tumor, tumor growth rate, age and health status of the individual. Tumors that are small and slow-growing usually may be observed and no treatment necessitated, based on the healthcare provider’s specific case-by-case assessment. Often, a multidisciplinary team of specialists including ophthalmologists, otolaryngologists, neurologists, surgeons, radiation therapy experts, and other healthcare professionals may be involved in managing the condition.

The treatment measures for benign Trochlear Nerve Schwannoma may include:

• Wait and watch approach by the healthcare provider may be rarely considered for small tumors that are not associated with any underlying genetic disorders such as neurofibromatosis
• Symptomatic treatment may involve the use of antiseizure medications, painkillers, steroids (to reduce inflammation), and administration of anti-depressants

Surgical excision and tumor removal may be recommended for treating Trochlear Nerve Schwannoma. A very important criterion for surgery is a possibility of injury to the trochlear nerve, based on where the tumor is located. Permanent post-operative injury and compromised cranial nerve function is reported in a majority of cases. Large-sized tumors that impinge on or involve other cranial nerves are usually surgically resected. The surgical treatment options may include the following:

• Microsurgery: The surgery is performed using microsurgical techniques, which can help minimize damage to the accompanying nerve. Since the tumor mostly affects the covering around the nerves, it can be completely removed without affecting the nerve in most cases. The following techniques may be employed:
  • Subtotal removal; when the tumor is incompletely removed
  • Near total removal; when most of the tumor is removed and there is very little tumor remnants
  • Total tumor removal; when the tumor is removed completely
• Craniotomy: It is a surgical procedure wherein a tiny hole is created in the cranium to remove the tumor
• Post-operative care is important: One must maintain minimum activity levels, until the surgical wound heals

Surgical procedures to remove brain tumors carry risks, including infection, possible damage to healthy brain tissue, swelling, or possible fluid build-up in the brain.

In case of malignancy, additional treatment options, such as chemotherapy and/or radiation therapy, may be considered.

• Chemotherapy may be used to destroy the tumor cells:
  • It is not reportedly a very useful method to treat the condition
  • The response of the tumor to chemotherapy is an important consideration while using this treatment modality
  • Whether to use chemotherapy as a treatment modality is determined by healthcare provider on case-by-case basis
• Radiation therapy may be useful in individuals who are not candidates for surgery. Such cases include:
  • Individuals with overall poor health status
  • The presence of bilateral schwannomas
  • Individuals with minimal symptoms
• Stereotactic radiosurgery is a relatively new treatment method that can be helpful in some individuals. It is a radiation therapy technique and not an invasive surgical procedure. It can be administered using a Gamma Knife (Gamma Knife radiosurgery). This method is known to be beneficial in many cases and is preferred nowadays
• External beam radiation therapy using a linear accelerator is helpful in preserving neurological function, especially when tumors are smaller
• Treatment of the underlying neurofibromatosis type 2 or any other genetic condition, if present

Clinical trials: In advanced stages of tumor progression, there may be some newer treatment options, currently on clinical trials, which can be considered for some patients depending on their respective risk factors.

Regular observation and periodic checkups to monitor the condition is recommended following treatment. In order to avoid a relapse, or be prepared for a recurrence, the entire diagnosis, treatment process, drugs administered, healthcare recommendations post-treatment, etc. should be well-documented and follow-up measures initiated accordingly.

How can Trochlear Nerve Schwannoma be Prevented?

Presently, there are no specific methods or guidelines to prevent the formation of Trochlear Nerve Schwannoma. However, if it is associated with a genetic disorder, the following points may be considered:

• Genetic counseling and testing: If there is a family history of the condition, then genetic counseling will help assess risks, before planning for a child
• Regular health check-ups might help those individuals with a history of the condition in the immediate family, in order to help diagnose the tumor early

In general, the factors that may help reduce the incidence of schwannomas and other brain tumor include:

• Reducing exposure to ionizing radiation
• Avoiding cigarette smoke inhalation
• Weight loss, in case one is obese or overweight; maintaining a good BMI
• Availing early treatment for infections
• Using safety gear including wearing helmets when playing sports or while riding two-wheelers
• Wearing seatbelts while driving automobiles to minimize the risk for head/body injury

Regular medical screening at periodic intervals with blood tests, scans, and physical examinations are mandatory. Often several years of active vigilance are crucial and necessary.

What is the Prognosis of Trochlear Nerve Schwannoma? (Outcomes/Resolutions)

The prognosis of Trochlear Nerve Schwannoma (benign tumor) is excellent, particularly if the tumor can be removed without damaging the underlying nerve.

• Asymptomatic tumors may require no treatment; unless they cause discomfort, affect the quality of life, or affect functioning of the underlying nerve. In such cases, a close monitoring of the schwannoma is a treatment option
• Bilateral tumors and the presence of neurofibromatosis type 2 can adversely influence outcomes
• If benign schwannomas transform to malignant tumors (in very rare occasions), then the prognosis may depend upon a variety of factors such as the stage of the tumor, overall health of the individual, and response to therapy

In general, the prognosis of benign brain tumors may vary considerably from one individual to another and is dependent on a set of factors, which include:

• Tumor histology or grade of the tumor: The lower the grade, the better is the prognosis. Benign schwannomas are grade I tumors
• Age of the individual: Older individuals generally have poorer prognosis than younger individuals
• Overall health of the individual: Individuals with overall excellent health have better prognosis compared with those with poor health
• The size of the tumor: Individuals with small-sized tumors fare better than those with large-sized tumors
• Location of the tumor is an important prognostic factor: Tumors at certain sites involving the central nervous system are more difficult to surgically excise and remove
• Tumors that are slow-growing have better prognosis than rapidly-growing tumors
• Presence of certain genetic abnormalities may result in a rapid progression of tumor growth and development
• Sporadic tumors have generally better prognosis than syndromic tumors; tumors in a background of genetic disorders/syndromes may have additional complications
• The ease of accessibility and surgical resectability of the tumor (meaning, if the primary tumor can be removed completely). This is an important prognostic factor
• Extent of residual tumor in the body following a surgical resection: A complete surgical excision with entire tumor removal presents the best outcome. In some cases, large portions of the tumor may be removed; or, only a small portion for tissue biopsy
• Individuals with bulky disease may have a poorer prognosis
• Involvement of other vital organs may complicate the condition
• Whether the tumor is occurring for the first time or is a recurrent tumor. Recurring tumors have worse prognosis compared to tumors that do not recur 
• Response to treatment and absence of post-operative complications: Tumors that respond to treatment have better prognosis compared to tumors that do not respond to treatment
• Functional neurologic status based on neurological evaluation of the patient: A higher score on the Karnofsky Performance Scale may indicate a more favorable outcome

An early diagnosis and prompt treatment of the tumor generally yields better outcomes than a late diagnosis and delayed treatment.

Additional and Relevant Useful Information for Trochlear Nerve Schwannoma:

Please visit our Cancer & Benign Tumor Health Center for more physician-approved health information:

http://www.dovemed.com/diseases-conditions/cancer/