Intraocular schwannoma

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Within medical ophthalmology, Intraocular schwannoma, also termed uveal schwannoma, is a type of schwannoma (homogeneous tumor) found in the eye. These tumors are almost always benign in nature and while malignant forms have been documented in other areas of the body, this has not been reported in the uveal region. Composed of Schwann cells, these masses are generally slow growing and can be found in the peripheral nerve tract, often around the head and neck. [1]

Contents

Signs and symptoms

There are several signs and symptoms of the eye that can indicate the growth of a tumor, which include:

Mechanism

Schwann cells are glial cells that were originally discovered by Theodore Schwann, a co-founder of the cell theory, during the nineteenth century. These cells are now known to be involved in maintaining the peripheral nervous system (PNS) and can be subdivided into two types, myelinated and non-myelinated. These cells wrap around the axons of the PNS, and due to the nature of their plasticity, they are able to perform a variety of essential functions. [3]

Function

The key function of Schwann cells is the myelination, or simply the insulation of axons. This fatty covering aids in the conduction of neuronal signals, allowing for efficient transmission. These cells also aid in the elimination of cellular debris, regeneration and upkeep of axons. Additionally, Schwann cells are actively involved in creating an inflammation reaction as a response to an injury of the PNS. Because injuries can lead to damaged axons, Schwann cells aid in fixing axonal damage and promoting new growth. Due to their healing properties, these cells can be used in spinal cord injuries to encourage regeneration of damaged axons. Finally, these multipurpose cells are key in the formation of protective outer barrier, or the perineurial sheath, that creates a vital separation for peripheral nerves. [3]

Associated conditions

There are also several diseases linked to Schwann cells that ought to be noted. To begin with, some demylelinating disorders include: multiple sclerosis, Charcot-Marie-Tooth disease (CMT), and Guillain–Barré syndrome. Although science has yet to offer up conclusive evidence that Schwann cell transplantation is an effective treatment for demylelinating disorders, it is possible that this could be applied in clinical practice in the future. There are also two inherited tumor disorders that have been connected with Schwann cells, neurofibromatosis type 1 and type 2. While both are genetic conditions associated with benign tumors, neurofibromatosis type I are neurofibromas and are therefore composed of a variety of cells and elements including Schwann cells and mast cells among others. In contrast, neurofibromatosis type II is characterized by schwannomas located on the eighth cranial nerve. This unfortunate placement leads to disruptions in balance, hearing and sometimes even vision. [3]

Description

While schwannomas in a general sense can be found in a variety of places where Schwann cells are located, intraocular schwannomas are a rare but serious condition that specifically targets the eye. These tumors are thought to come from Schwann cells of the ciliary nerves and have also been called "pseudomelanomas" and for good reason. [1] They are given this name due to the fact that they often resemble a common and dangerous eye tumor, a uveal malignant melanoma. This commonality can lead to misdiagnosis and the unnecessary enucleation of an eye as a result. Because of this confusion, schwannomas are most often diagnosed after removal. While it may be difficult if not impossible to make the distinction on the basis of routine examination and diagnostic measures, it is key to be aware of the possibility of intraocular schwannomas and look for any atypical features that may present themselves. [4]

Diagnosis

With the symptoms above in mind, practitioners would likely look for decreased vision and intraocular masses in making their diagnosis as these have been documented as the most common findings for intraocular schwannomas. Additionally, these tumors are most frequently found in the choroid, at 60%, as compared to the ciliary body (40%) and the iris (11%). Schwannomas generally present themselves as smooth, ovoid masses, lacking pigmentation. However, these tumors can also rarely be colored and lobulated. This overlap can lead to a uveal melanoma diagnosis, as these can be characteristics of both. [1]

Treatment

Intraocular schwannomas are treatable and there are several treatment options that may be considered, depending on the size and specific location of the tumor. For small tumors, caught early, observation can be initially used as long as good vision is maintained. However, it is important to note that in the study conducted by You et al. all of the patients whose tumors were initially observed needed further treatment and enucleation as their conditions declined. For tumors that are initially more aggressive, larger in size or suspected as cancerous, local resection and enucleation are also options. Radiation therapy, however, cannot be used in this instance as schwannomas are resistant to this treatment. [1]

Prognosis

The systemic and ocular prognosis for intraocular schwannoma is positive. While a patient may lose an eye, they are unlikely to encounter metastasized growth or life-threatening malignant change. Although follow-up data has shown the potential need for re-excision and side-effects, these issues are minor and the general outcome for patients is excellent. [1]

Epidemiology

A study by You et al. was only able to evaluate the 47 documented cases that have been made to date. According to this study, intraocular schwannomas are more prevalent in females as compared to males with a ratio of 3:1. Additionally, individuals are more likely to present with intraocular schwannomas at a younger age than with uveal melanomas, the most common intraocular tumor. According to the participants evaluated in this study, the average age of occurrence was 37 years old, however, it is important to note that the age range documented represented individuals 9–76 years old. [1]

Related Research Articles

Axon Long projection on a neuron that conducts signals to other neurons

An axon, or nerve fiber, is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action potentials away from the nerve cell body. The function of the axon is to transmit information to different neurons, muscles, and glands. In certain sensory neurons, such as those for touch and warmth, the axons are called afferent nerve fibers and the electrical impulse travels along these from the periphery to the cell body and from the cell body to the spinal cord along another branch of the same axon. Axon dysfunction has caused many inherited and acquired neurological disorders which can affect both the peripheral and central neurons. Nerve fibers are classed into three types – group A nerve fibers, group B nerve fibers, and group C nerve fibers. Groups A and B are myelinated, and group C are unmyelinated. These groups include both sensory fibers and motor fibers. Another classification groups only the sensory fibers as Type I, Type II, Type III, and Type IV.

Myelin Fatty substance that surrounds nerve cell axons to insulate them and increase transmission speed

Myelin is a lipid-rich material that surrounds nerve cell axons to insulate them and increase the rate at which electrical impulses are passed along the axon. The myelinated axon can be likened to an electrical wire with insulating material (myelin) around it. However, unlike the plastic covering on an electrical wire, myelin does not form a single long sheath over the entire length of the axon. Rather, myelin sheaths the nerve in segments: in general, each axon is encased with multiple long myelinated sections with short gaps in between called nodes of Ranvier.

Neurofibromatosis Medical condition

Neurofibromatosis (NF) is a group of three conditions in which tumors grow in the nervous system. The three types are neurofibromatosis type I (NF1), neurofibromatosis type II (NF2), and schwannomatosis. In NF1 symptoms include light brown spots on the skin, freckles in the armpit and groin, small bumps within nerves, and scoliosis. In NF2, there may be hearing loss, cataracts at a young age, balance problems, flesh colored skin flaps, and muscle wasting. In schwannomatosis there may be pain either in one location or in wide areas of the body. The tumors in NF are generally non-cancerous.

Optic nerve Cranial nerve II, for vision.

The optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual information from the retina to the brain. In humans, the optic nerve is derived from optic stalks during the seventh week of development and is composed of retinal ganglion cell axons and glial cells; it extends from the optic disc to the optic chiasma and continues as the optic tract to the lateral geniculate nucleus, pretectal nuclei, and superior colliculus.

Schwann cell Glial cell type

Schwann cells or neurolemmocytes are the principal glia of the peripheral nervous system (PNS). Glial cells function to support neurons and in the PNS, also include satellite cells, olfactory ensheathing cells, enteric glia and glia that reside at sensory nerve endings, such as the Pacinian corpuscle. The two types of Schwann cells are myelinating and nonmyelinating. Myelinating Schwann cells wrap around axons of motor and sensory neurons to form the myelin sheath. The Schwann cell promoter is present in the downstream region of the human dystrophin gene that gives shortened transcript that are again synthesized in a tissue-specific manner.

Nervous tissue Main component of the nervous system

Nervous tissue, also called neural tissue, is the main tissue component of the nervous system. The nervous system regulates and controls bodily functions and activity. It consists of two parts: the central nervous system (CNS) comprising the brain and spinal cord, and the peripheral nervous system (PNS) comprising the branching peripheral nerves. It is composed of neurons, also known as nerve cells, which receive and transmit impulses, and neuroglia, also known as glial cells or glia, which assist the propagation of the nerve impulse as well as provide nutrients to the neurons.

Node of Ranvier Aspect of anatomy

Nodes of Ranvier, also known as myelin-sheath gaps, occur along a myelinated axon where the axolemma is exposed to the extracellular space. Nodes of Ranvier are uninsulated and highly enriched in ion channels, allowing them to participate in the exchange of ions required to regenerate the action potential. Nerve conduction in myelinated axons is referred to as saltatory conduction due to the manner in which the action potential seems to "jump" from one node to the next along the axon. This results in faster conduction of the action potential.

Wallerian degeneration Biological process of axonal degeneration

Wallerian degeneration is an active process of degeneration that results when a nerve fiber is cut or crushed and the part of the axon distal to the injury degenerates. A related process of dying back or retrograde degeneration known as 'Wallerian-like degeneration' occurs in many neurodegenerative diseases, especially those where axonal transport is impaired such as ALS and Alzheimer's disease. Primary culture studies suggest that a failure to deliver sufficient quantities of the essential axonal protein NMNAT2 is a key initiating event.

Neurofibromatosis type II Type of neurofibromatosis disease

Neurofibromatosis type II is a genetic condition that may be inherited or may arise spontaneously, and causes benign tumors of the brain, spinal cord, and peripheral nerves. The types of tumors frequently associated with NF2 include vestibular schwannomas, meningiomas, and ependymomas. The main manifestation of the condition is the development of bilateral benign brain tumors in the nerve sheath of the cranial nerve VIII, which is the "auditory-vestibular nerve" that transmits sensory information from the inner ear to the brain. Besides, other benign brain and spinal tumors occur. Symptoms depend on the presence, localisation and growth of the tumor(s), in which multiple cranial nerves can be involved. Many people with this condition also experience vision problems. Neurofibromatosis type II is caused by mutations of the "Merlin" gene, which seems to influence the form and movement of cells. The principal treatments consist of neurosurgical removal of the tumors and surgical treatment of the eye lesions. Historically the underlying disorder has not had any therapy due to the cell function caused by the genetic mutation.

Ciliary ganglion Bundle of nerve parasympathetic ganglion

The ciliary ganglion is a bundle of nerve parasympathetic ganglion located just behind the eye in the posterior orbit. It is 1–2 mm in diameter and in humans contains approximately 2,500 neurons. The ganglion contains postganglionic parasympathetic neurons. These neurons supply the pupillary sphincter muscle, which constricts the pupil, and the ciliary muscle which contracts to make the lens more convex. Both of these muscles are involuntary since they are controlled by the parasympathetic division of the autonomic nervous system.

Neurofibroma Medical condition

A neurofibroma is a benign nerve-sheath tumor in the peripheral nervous system. In 90% of cases, they are found as stand-alone tumors, while the remainder are found in persons with neurofibromatosis type I (NF1), an autosomal-dominant genetically inherited disease. They can result in a range of symptoms from physical disfiguration and pain to cognitive disability.

Uveal melanoma Type of eye cancer

Uveal melanoma is a cancer (melanoma) of the eye involving the iris, ciliary body, or choroid. Tumors arise from the pigment cells (melanocytes) that reside within the uvea and give color to the eye. These melanocytes are distinct from the retinal pigment epithelium cells underlying the retina that do not form melanomas. When eye melanoma is spread to distant parts of the body, the five-year survival rate is about 15%.

Schwannomatosis Rare genetic disorder

Schwannomatosis is an extremely rare genetic disorder closely related to the more-common disorder neurofibromatosis (NF). Originally described in Japanese patients, it consists of multiple cutaneous schwannomas, central nervous system tumors, and other neurological complications, excluding hallmark signs of NF. The exact frequency of schwannomatosis cases is unknown, although some populations have noted frequencies as few as 1 case per 1.7 million people.

Schwannoma Medical condition

A schwannoma is a usually benign nerve sheath tumor composed of Schwann cells, which normally produce the insulating myelin sheath covering peripheral nerves.

Eye neoplasm Medical condition

Eye neoplasms can affect all parts of the eye, and can be a benign tumor or a malignant tumor (cancer). Eye cancers can be primary or metastatic cancer. The two most common cancers that spread to the eye from another organ are breast cancer and lung cancer. Other less common sites of origin include the prostate, kidney, thyroid, skin, colon and blood or bone marrow.

Ciliary body melanoma is a type of cancer arising from the coloured part (uvea) of the eye.

Nerve injury Medical condition

Nerve injury is an injury to nervous tissue. There is no single classification system that can describe all the many variations of nerve injuries. In 1941, Seddon introduced a classification of nerve injuries based on three main types of nerve fiber injury and whether there is continuity of the nerve. Usually, however, peripheral nerve injuries are classified in five stages, based on the extent of damage to both the nerve and the surrounding connective tissue, since supporting glial cells may be involved.

Malignant triton tumor (MTT) is a relatively rare, aggressive tumor made up of both malignant schwannoma cells and malignant rhabdomyoblasts. It is classified as a malignant peripheral nerve sheath tumor with rhabdomyosarcomatous differentiation.

Diktyoma Type of eye tumor

Diktyoma, or ciliary body medulloepithelioma, or teratoneuroma, is a rare tumor arising from primitive medullary epithelium in the ciliary body of the eye. Almost all diktyomas arise in the ciliary body, although, rarely, they may arise from the optic nerve head or retina.

Preferential motor reinnervation (PMR) refers to the tendency of a regenerating axon in the peripheral nervous system (PNS) to reinnervate a motor pathway as opposed to a somatosensory pathway. PMR affects how nerves regenerate and reinnervate within the PNS after surgical procedures or traumatic injuries. It is important to understand in order to further develop axonal regrowth surgical techniques. Further research of preferential motor reinnervation will lead to a better understanding of peripheral nervous system function in the human body regarding cell roles and abilities.

References

  1. 1 2 3 4 5 6 You, Jae Y., et al. "Intraocular Schwannoma." Survey of Ophthalmology (2012): Print.
  2. ↑ St. John, Tina. "Eye Tumor Symptoms". Livestrong. Retrieved Mar 30, 2011.
  3. 1 2 3 Bhatheja, Kanav; Field, Jeffrey (2006). "Schwann cells: Origins and role in axonal maintenance and regeneration". The International Journal of Biochemistry & Cell Biology. 38 (12): 1995–1999. doi:10.1016/j.biocel.2006.05.007. PMID   16807057.
  4. ↑ Turell, Mary E. et al "Uveal Schwannoma Surgery." Ophthalmology 116.1 (2009): 163. Print.
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