Nerve Sheath Tumor

What is Nerve Sheath Tumor?

Peripheral nerve network is extended throughout the body and tumor progression can occur any place of this whole nervous system, which is covered with a myelin sheath. The tumor progression often causes pain and disability due to hampering of the normal functioning of nervous tissue. The nerve sheath tumor usually develops at the late stage of life, early onset is very rare.The nature of nerve sheath tumor can be benign or malignant¹.

Benign

The usual nerve sheath tumor is benign and non-cancerous in nature. Approximately 85% to 90% clinical case of the nerve sheath tumor are benign. Histological analysis showed that the benign nerve sheath tumor is mostly schwannomas or neurofibromatosis types. Other included lesions are ganglion cysts, hemangiomas and desmoids in nature. Genetic disorder leads to the formation of neurofibromatosis or schwannomatosis. Compared to neurofibromatosis, schwannomas are less common.

The different types of benign nerve sheath tumors are probably originated from Schwann cells, which are adjoined with the nerve axon¹.

Malignant

Generation of malignant nerve sheath tumors is less common but more aggressive than the benign nerve sheath tumors. This cancerous tumor growth directly or indirectly associated with neurofibromatosis type 1. The incidence rate reported that 8 to 10 % of patients having neurofibromatosis type 1 can develop malignant nerve sheath tumors in their life span, whereas 50% of malignant nerve sheath tumors patients have neurofibromatosis type 1.

The appearance of the lesions of the malignant peripheral nerve sheath tumors is white, firm nodules. The development of the malignant peripheral nerve sheath tumors leads to potential damage. The malignancy is not spread through the lymphatic system. The management of malignant nerve sheath tumors requires a multidisciplinary team of experts and early detection is a very essential for better treatment prognosis ^{1, 2}.

Causes

The exact cause of nerve sheath tumor is yet not discovered. It is expected that previous history of injury initiates the tumor development. In normal condition, Schwann cells are assisting to the restoration of damaged tissues and cells during injury.

But if the injury is extremely harmful and injury extends to Schwann cells then this may cause the initiate of the tumor, as Nerve Sheath Tumor originates from Schwann cells. Even tumorogenesis can take place during the process of repair. But this etiology has no scientific background¹.

The identified two types of nerve tumors progressed, which are not -cancerous are schwannomas and neurofibromas. Both type I and II schwannomatosis and neurofibromatosis may responsible for the formation of schwannomas and neurofibromas respectively. Some beliefs that inherited conditions influences the growth of the tumor on the nerve sheath.

The rare incidence of progression of Neurofibromatosis type 1 is one of the primary cause of development of multiple neurofibromas and also malignant nerve sheath tumors on the peripheral nervous tissues. This correlation is obtained as sporadic malignant tumors associated with neurofibromatosis type 1 and both the gender equally affected with this condition^3,4.

Symptoms

Symptoms can vary depending on the underlying cause, even some reported that Nerve Sheath Tumor is asymptomatic in their cases. Possible symptoms are as follows:

• Thoracic limb lameness can be progressed, which is as similar as musculoskeletal lameness.
• A flagrant axillary heap can form in some cases
• The mass is palpable means it can feel by touching
• Severe, impenetrable, persistent pain,
• Numbness,
• Burning sensation,
• Pricking of “pins and needles” sensation
• The affected nerve and associated muscles become weak
• Muscle degeneration
• Vertigo
• Difficulty in body balance
• Restricted movement due to partial defeat on one extremity
• Ataxia
• Absence of reflexes (hyporeflexia)
• Horner’s syndrome that can be defined as the associated symptoms occurs due to damage of sympathetic nervous system
• Suppression of spinal cord causes paresis
• Ptosis or drooping of the eyelid with one side of the face become affected due to schwannoma in the neck^5,6.

Diagnosis

The diagnosis process is quite similar to another tumor. For initial examination different imaging tools like MRI, CT scan or PET scan can be conducted to confirming the existence of a tumor. If any of these tests confirming the existence of Nerve Sheath Tumor, then a biopsy is required for diagnosing the nature of the tumor. In biopsy test, a small section of the tumor is scratched out and that tissue is microscopically analyzed.

Treatment

Primary option for management and treatment option for both the type of progressive tumors (nonmalignant and malignant) is surgery. The goal of the surgery is to complete removal of the tumor, including outer margin. This helps to restrict the spreading of the metastatic tumor to adjoined or distant organs. In case of malignant tumor to restrict the spreading of cancerous cell growth to distant organ surgical intervention is conducted for amputation of the entire limb or adjacent nerve removal.

In the case of a malignant tumor, radiation, chemotherapy, adjuvant therapies are also available. Oncologists prepare treatment depending upon the patient condition and also after discussion with the patient and their relatives.

Radiation therapy can be applied for both pre and post operative therapy, though the intention of application is differing in both the cases.

Chemotherapy mainly applied when the tumor size is too small that cannot be removed by surgical incision or available localized treatment options unable to provide benefits. Chemotherapy has several side effects which may interfere treatment process ^7,8.

Survival rate

The survival rate depends on upon the type of nerve sheath tumors formed. In the case of benign nerve sheath tumors, if the growth is stagnant then requirement of management based on routine observation of the size of the tumor. In cases of malignant nerve sheath tumors, the outcome is brutal, specifically if the cancerous growth spread to other tissues.

The nature of malignant nerve sheath tumors usually highly metastasis and spread overall body tissues and that is cause rapid fatal incidence. The life span is lesser in the case of a stalk of tumor typically associated with neurofibromatosis type 1⁷.

References

1. Nerve Sheath Tumors; National Canine Cancer Foundation; Retrieved from: http://wearethecure.org/learn-more-about-canince-cancer/canine-cancer-library/nerve-sheath-tumors/
2. Nerve Tumor; Neurology and Neurosurgery, Johns Hopkins; Medicine; Retrieved from: http://www.hopkinsmedicine.org/neurology_neurosurgery/centers_clinics/peripheral_nerve_surgery/conditions/nerve_tumors.html
3. Michael E Sughrue, Jon Levine, Nicholas M Barbaro; Pain as a symptom of peripheral nerve sheath tumors: clinical significance and future therapeutic directions; J Brachial Plex Peripher Nerve Inj. 2008; 3: 6.Published online 2008 Feb 29. doi:  10.1186/1749-7221-3-6
4. Valeyrie-Allanore L, Ismaili N, Bastuji-Garin S, Zeller J, Wechsler J, Revuz J, Wolkenstein P. Symptoms associated with malignancy of peripheral nerve sheath tumours: a retrospective study of 69 patients with neurofibromatosis 1. The British journal of dermatology. 2005;3(1):79–82. doi: 10.1111/j.1365-2133.2005.06558.x.
5. Nerve Tumors; The Center for Peripheral Nerve Surgery; Columbia University Medical Center; http://www.columbianeurosurgery.org/problems-and-treatments/nerve-tumors/
6. Nerve Sheath Tumors; Center for Nerve Injury & Paralysis; http://nerve.wustl.edu/nd_tumors.php
7. Peripheral Nerve Sheath Tumor; Florida Hospital; https://www.floridahospital.com/peripheral-nerve-sheath-tumor/screening-and-tests-peripheral-nerve-sheath-tumor
8. David S. Geller, Mark Gebhardt, Malignant Peripheral Nerve Sheath Tumors (MPNST); http://sarcomahelp.org/mpnst.html

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