Description, Causes and Risk Factors:
A rare, primitive, rapidly growing intracranial neoplasm thought to originate from the cells of the embryonic medullary canal and hence included with ependymoblastomas by some neuropathologists; ganglion cells and astrocyte maturation have also been reported. Tumors that occur in the ciliary body are referred to as embryonal medulloepitheliomas.
Intraocular medulloepitheliomas is a rare primary intraocular neoplasm derived from Neuroectoderm. This type of tumor characteristically arises from the non-pigmented epithelium of the ciliary body. On rare occasions, medulloepitheliomas also arises from the iris, retina, or optic disc. The tumors range from benign proliferation to malignant neoplasm with unequivocal invasive capacity but limited metastatic potential.
Medulloepithelioma is uncommon, but its precise incidence is unknown. Based on relative prevalence data from multiple clinical and pathological case series, however, its incidence can be estimated at approximately one thirtieth to one fiftieth that of retinoblastoma. This would correspond to a cumulative lifetime incidence of approximately 1 case per 450000-1000000 persons. Intraocular medulloepithelioma is usually a congenital or infantile tumor, but juvenile and even adult-onset cases have been reported. The average age of the affected individual at diagnosis is about 5 years in most series. Medulloepitheliomas affects all ethnic groups and both sexes equally. It does not appear to be transmitted genetically.
No known risk factors exist for this tumor. In exceptional cases, intraocular medulloepithelioma arises from the retina or optic discs. All reported cases of this type have occurred in children younger than 7 years. Because of this, such tumors have uniformly been misdiagnosed clinically as retinoblastoma.
A common complication of medulloepitheliomas of the ciliary body is development of neovascular glaucoma. In some cases, glaucoma of this type develops even when the tumor is limited in extent. In other cases, non-neovascular angle closure angle closure develops in response to the ciliary body tumors. Because the eye in such cases is extremely firm, it may ophthalmoscopy at examination under anesthesia to visualize the tumor. Also, the far peripheral location of the lesion may preclude the use of conventional contact B-scan to detect the tumor. In the face of unexplained neovascular glaucoma or angle closure and a posterior fundus of essentially normal appearance, the ophthalmologist should strongly consider the possibility of medulloepithelioma and evaluate the eye further by alternative methods of ocular imaging, computed tomography, magnetic resonance imaging, or ultrasound biomicroscopy or perform a paracentesis followed by re-examination of the peripheral fundus with scleral depression.
The usual presenting symptoms of medulloepithelioma are a red eye, change in color of the iris, visible mass in the iris, and visual impairment. Medulloepithelioma of the ciliary body typically appears as a tan-to-white lesion of the extreme peripheral fundus. Because of its peripheral location, the tumor may be detectable only by binocular indirect ophthalmoscopy with scleral depression during ophthalmic examination under anesthesia. A tumor of this type frequently appears intrinsically cystic or has prominent neuroepithelial cysts on its surface. In occasional patients, localized absence of the zonules and resultant abnormalities of lens curvature, lens subluxation.
An intraocular medulloepithelioma that involves the iris usually appears as a tan-to-pink mass that replaces the peripheral iris and fills the angle. Such tumors often have prominent intrinsic blood vessels.
The characteristics histopathological feature of intraocular medulloepitheliomas is a structural arrangement of cells that closely resembles that of neural medullary epithelium. The degree of cellular differentiation differs widely from case-to-case. Many well-differentiated medulloepitheliomas contain prominent rosettes and cystic spaces filled with hyaluronic acid. Medulloepitheliomas that contain heterotrophic elements such as hyaline cartilage, striated muscles, or brain are referred to as teratoid medulloepitheliomas. Those that do no contain such elements are termed non-teratoid medulloepitheliomas. About two thirds of intraocular medulloepitheliomas are categorized as malignant pathologically, largely on the basis of invasiveness and extraocular extension of the tumor, especially if associated with numerous mitotic figures and undifferentiated cells.
Although iridocyclectomy and episcleral plaque radiotherapy have both been employed in some cases of iridociliary or ciliary body medulloepitheliomas, such treatments have frequently failed to eradicate the tumor. In fact, local failure of such treatments appears to be almost rule in medulloepitheliomas judged to be malignant by histopathological criteria. Eyes that have an extremely large intraocular tumor at presentation, those that are blind and painful as a result of tumor-related complications, after primary attempted resection or plaque radiotherapy eventually require enucleation. Patients who have massive orbital extension may even require exenteration.
NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.
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