Tumors of the peripheral nerves of an extremity are predominantly benign. Nevertheless, such nerve tumors pose a challenge for the surgeon.
The nerve cells of the spinal cord form cylindrical nerve processes up to 2 meters long as a result of very high activity. Thousands of these are then located in certain groupings in the peripheral nerve of the arm or leg.
These nerve processes or nerve fibers conduct the electrically generated impulses that we need for functionality in the arm or leg.
There are two types of nerve fiber functions:
- Nerve fibers along which electrical excitation travels to the spinal cord and brain. They conduct sensitive functions such as sensation, pain and temperature.
- Nerve fibers whose electrical excitation runs from the spinal cord to the periphery, for example to a muscle. These fibers control motor functions.
The nervous system © SciePro | AdobeStock
Each of the thousands of nerve fibers is surrounded by a layer of cells, which in turn performs an insulating function. This is comparable to the rubber layer around a copper wire. The cells that form this fatty insulating layer are called "Schwann cells".
Unfortunately, they also become the majority of benign nerve tumors when they multiply abnormally. Such tumors are then called nerve sheath tumors. These include
- Schwannoma,
- neurinoma and
- the neurofibroma.
The reasons for their development are unknown. The growth of nerve sheath tumors is slow and they are only discovered years later when they produce symptoms. Individual patients with neurofibromatosis Recklinghausen tend to develop these nerve tumors in large numbers. This is caused by genetic changes.
The second most common type of nerve tumor, which can develop within a peripheral nerve, is more harmless. These so-called cysts are filled with a viscous, transparent substance. Histologically, they look like cysts on tendon sheaths, formerly known as "overbone".
Cysts can be located on the outside of a nerve, but can also form inside the nerve. Inside the nerve, they can even be present in multiple, elongated formations.
There is always a tiny connection between a neighboring joint and such cysts. This connection is oriented towards the nerve branch to the respective joint. This means that the cystic mass on or in the nerve is an external manifestation of the inside of the joint.
There are simple histological similarities between
- the mucous membrane of the inside of the joint,
- the mucosa of the tendon sheaths and
- the membrane of such extra- or intraneural cysts.
More is simply not known.
Very rare other nerve tumor manifestations originate from vessels within a nerve. These include
These nerve tumors are so rare that they are not mentioned here.
Each main nerve in the arm or leg has motor functions that affect a specific muscle group associated with the nerve. In addition, there are sensory functions in which very specific sections of the skin
- Sensation of touch,
- pain perception,
- temperature perception etc.
are assigned to specific skin areas.
The predominantly benign nerve tumors grow very slowly. The impairment of these functions then develops just as slowly.
This is the reason why it always takes many years before a nerve impairment is suspected. It takes even longer before a nerve tumor is actually discovered.
For the person affected, the focus for a long time tends to be on pain, which they only experience under certain circumstances. For example, when an external mechanical impact hits the arm or leg where a nerve tumor is growing.
The pain is comparable to the well-known phenomenon of the "musician's bone". This is a special pain that occurs when you bump yourself in the region of the elbow. It radiates into the little finger like an electric shock.
The origin and cause of this pain, which can be triggered by mechanical impairment, cannot be precisely determined.
Functional deficits of a motor or sensory nature only occur very late in nerve tumors.
A common symptom of nerve cancer is an "electric tug" like that of a musician's bone © shidlovski | AdobeStock
The diagnosis "nerve tumor" is initially far from the minds of many doctors when examining a patient. Without this suspicion, no targeted examinations can take place.
However, if there is a suspicion of nerve cancer, imaging procedures help to make a definitive diagnosis. These include ultrasound examinations(sonography) and magnetic resonance imaging(MRI).
Instrumental examinations, on the other hand, are less important for the diagnosis. These include measurements of nerve conduction velocity and the recording of electrical potentials from certain muscle groups that may be affected.
It is crucial to believe the patient's description of the pain. The pain that can be produced mechanically must be assigned to a responsible main nerve depending on its area of radiation. This can then be checked using imaging techniques.
Using MRI, doctors can get a comprehensive picture of suspicious areas © digitale-fotografien | AdobeStock
The surgical treatment of a nerve tumor poses a great challenge to the surgeon's ability to exercise care. The aim of the operation must be to completely preserve as many of the nerve fibers that are arranged in groups and have function. The removal of the nerve tumor should therefore damage as few nerve fibers as possible.
This can only be achieved using a surgical microscope. Micro instruments and microscopic magnification of the surgical field are standard in such procedures.
Each peripheral nerve is surrounded by an outer connective tissue sheath (epineurium). Inside, the nerve fibers are joined together by thinner connective tissue sheath structures (perineurium) to form individual smaller groups. Between the groups of fibers surrounded by thinner sheaths is loose connective tissue with small vessels.
Using microinstruments and the surgical microscope, it is possible to penetrate between these nerve fiber subgroups without destroying the continuity of the nerve fibers.
When operating on any nerve tumor, one must be aware of this possibility. In this way, it is possible to find the subgrouped nerve fibers that are regularly spread out in a fan shape over the entire nerve tumor, carefully detach them from the nerve tumor by microsurgery and thus preserve them anatomically and functionally.
Cross-section of a nerve with its fiber groups and the supplying blood vessels © crevis | AdobeStock
A schwannoma (neurinoma) originates only from the Schwann cells of a small group of nerve fibers. This is identified by microsurgery and completely severed above and below the nerve tumor. This ensures the total removal of the nerve tumor.
In the case of a neurofibroma (slight histological difference to neurinoma), the group of nerve fibers to be sacrificed is somewhat larger.
The procedure is different for neurofibromatosis. Neurofibromatosis is the genetically determined tendency to have very many neurofibromas in the body (Recklinghausen's disease).
Due to the multiplicity of many neurofibromas, which all originate from other nerve fiber groups, the decision can be made to leave the neurofibromas in place. This can prevent a total loss of function of the affected main nerve.
The decision-making processes here are very complicated and must be reserved for individual discussions between patient and doctor.
"Ganglia" and "pseudoganglia" are cysts filled with gelatinous fluid. The microsurgical standard is also used for these. Especially if the cysts are located inside the nerve, i.e. intraneurally.
Here, too, it is necessary to identify the subgrouped fibers located inside the nerve. The surgeon then carefully and gently separates the fiber groups from each other. The preparation can then be carried out in the direction of the cysts.
The viscous contents of the cysts are drained. However, the outer membranes of these cysts must not be completely removed. The cyst walls and nerve fiber sheath tissue are so intimately connected that the nerve fibers would also be removed.
Cysts that are only on the outside of the nerve are easier to remove.
Unfortunately, the pre-operative consultation includes the information that a cyst can form again even after a successful operation. This is particularly the case if there is a connection to the inside of a neighboring joint and the connecting duct cannot be identified and blocked.
It is not known that benign nerve tumor growth can be influenced by medication. Surgical removal of the nerve tumor is therefore not an alternative.
The situation is different with neurofibromatosis (Recklinghausen's disease), a definable genetic change. In this case, it is possible that a human genetically based treatment will be developed in a few decades.
Due to the complexity of the procedure, nerve damage can occur during surgery. The risk of this cannot be calculated in advance. A minor loss of function is possible, but also permanent functional damage.
The extent of the possible damage depends decisively
- the experience of the surgeon,
- the microsurgical instruments available and the care and
- the care and time required for the surgical procedure.
of the operation.
If the removal of the nerve tumor is successful
- in the case of intraneural cysts without nerve fiber sacrifice,
- in the case of schwannomas (neurinomas) with sacrifice of only a single group of fibers and
- in neurofibromas with sacrifice of at most a quarter of all fiber groups,
only a temporary functional impairment occurs.
This can almost completely disappear with physiotherapeutic follow-up treatment of any motor impairments.
Permanent nerve pain is very rare, but certain circumscribed sensory disturbances are fairly common.
Neurofibromatosis, however, presents a completely different situation. If it is discovered unexpectedly during the procedure, it may be necessary to abort the operation. Certain conditions are necessary to avoid a severe nerve function sacrifice, which are not always fulfilled.
A surgical microscope is used in all nerve cancer operations © AntonioDiaz | AdobeStock
If there were no or only very minor complications during the operation, no physiotherapeutic follow-up treatment is required. As a rule, the patient can retrain a small partial dysfunction on their own initiative. Sensory deficits, if they have occurred, are of course not treatable.
If an unintentionally severe and mainly motor dysfunction has occurred, physiotherapeutic follow-up treatment is required. Occupational therapy may also be necessary.
Experience has shown that nerve fibers preserved after nerve tumor surgery compensate (replace) the initial damage.
If the existence of multiple neurofibromas is discovered, genetic testing should be considered in order to determine the risk of inheritance.
Nerve tumors are so rare compared to nerve injuries that there are no relevant statistical findings.
There are only a few centers for the treatment of nerve tumors that have compiled scientific findings. These include, for example, the center in New Orleans under the direction of David Kline. It is known from here that neurinomas and neurofibromas in the extremities develop more frequently close to the trunk than further away in the periphery.
This finding only has consequences for the surgeon: the internal substructuring in the nerves is different close to the trunk than further peripherally. The microsurgeon must be able to take this into account.
Physiotherapy can help to eliminate temporary complications after an operation © suryafineart | AdobeStock
Nerve tumors are predominantly benign and grow very slowly.
In the case of neurinomas and neurofibromas, they grow solidly and from Schwann cells in the nerve sheath. In the case of cysts or pseudocysts, the encapsulated structures only increasingly fill with fluid.
Despite these positive statements, the surgical treatment of a nerve tumor is a challenge for the surgeon. It requires time and care and microsurgical instrumentation.
Under these conditions, the surgical removal of nerve tumors or cysts in the peripheral nerves is always indicated. Waiting would considerably worsen the chances.
The larger a nerve tumor has become, the less microsurgery can ensure the function of all nerve fibers within the affected nerve. There is therefore no argument that can be used to justify a repeated wait-and-see approach.
