Diktyoma
Encyclopedia
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
.
The name "diktyoma" comes from its characteristic findings on histology
.
based on histology
.
Based on histology, the tumor is classified as malignant if it contains poorly differentiated neuroblast
s, nuclear pleomorphism, markedly abnormal mitotic activity
, sarcomatous components
, or invasion into the uvea
, cornea
, or sclera
. Most diktyomas are malignant.
and pain, while the most common signs are leukocoria
and presence of a mass in the iris
or ciliary body. Other signs and symptoms include lens subluxation
, glaucoma
, cataract
, exophthalmos
, buphthalmos
, strabismus
, and ptosis
.
(US), Computerized Tomography (CT) and Magnetic Resonance Imaging
(MRI) may aid diagnosis
. On ultrasound, diktyomas typically appear as echogenic, irregularly shaped to ovoid masses. Ultrasound is excellent for demonstrating cystic collections of vitreous fluid in the tumor, and may show calcifications
in the teratoid type.
On CT, dityomas typically appear as dense, irregular masses in the ciliary body, which enhances with administration of intravenous contrast material. CT is excellent for demonstrating dystrophic calcification
s in the teratoid type.
On MRI, dityomas typically apppear slightly to moderately hyperdense to vitreous on T1-weighted images and hypodense on T2-weighted images, with marked homogeneous enhancement (except for prominent parts of cystic components, which, if present, may impart heterogeneity) after administration of intravenous contrast material. MRI is excellent for detection of tumors as small as 2 millimeters.
. The tumor may also contain chalky grayish white particles. The lens may be covered by a semi-translucent membrane in some case. Tumor may invade locally to involve the iris or anterior retina, or through the cornea or sclera. In advanced cases, tumor may fill the enture globe, similar to retinoblastoma
.
on histology; the semi-translucent membrane covering the lens in some tumors corresponds to spreading neoplastic cells.
Tumor cells form a characteristic diktyomatous pattern, with folded cords and sheets resembling a fisherman's net. In early development of the retina, the medullary epithelial cells acquire polarity, such that a basement membrane associated with the vitreous forms the internal limiting membrane on one side, while terminal bars form the outer limiting membrane on the other side. Proliferating tumor cells of diktyoma maintain the same polarity, arranged in cords and sheets folding back upon themselves. Depending on the direction of the folding, some folds surround fluid collection, while others do not. These fluid-filled spaces correspond to the grossly observed small cysts, which are mainly composed of vitreous humor.
About 30-50 percent of diktyomas contain heteroplastic elements, and thus belong to the teratoid subtype. These heteroplatic elements may include hyaline cartilage
, rhabdomyoblasts, and neuroglial tissue. Sarcomatous elements may be seen in malignant tumors. Foci of dystrophic calcifications may be present.
is no longer done due to risk of late complications and metastases. Small lesions can be treated with iodine-125 plaque brachytherapy. Distant metastases and mortality are rare. Mortality may occur in patients with extraocular extension to the brain. Lack of glial differentiation, as demonstrated by negative staining for glial fibrillary acidic protein
(GFAP), may confer a favourable prognosis.
is similar in male and female and among different races.
Medulloepithelioma
Medulloepithelioma is a rare, primitive, fast growing brain tumour thought to stem from cells of the embryonic medullary cavity. Tumours originating in the ciliary body of the eye are referred to as embryonal medulloepitheliomas, or diktyomas....
, or teratoneuroma, is a rare tumor arising from primitive medullary epithelium in the ciliary body
Ciliary body
The ciliary body is the circumferential tissue inside the eye composed of the ciliary muscle and ciliary processes. It is triangular in horizontal section and is coated by a double layer, the ciliary epithelium. This epithelium produces the aqueous humor. The inner layer is transparent and covers...
of the eye
Human eye
The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...
. Almost all diktyomas arise in the ciliary body, although, rarely, they may arise from the optic nerve
Optic nerve
The optic nerve, also called cranial nerve 2, transmits visual information from the retina to the brain. Derived from the embryonic retinal ganglion cell, a diverticulum located in the diencephalon, the optic nerve doesn't regenerate after transection.-Anatomy:The optic nerve is the second of...
head or retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
.
The name "diktyoma" comes from its characteristic findings on histology
Histology
Histology is the study of the microscopic anatomy of cells and tissues of plants and animals. It is performed by examining cells and tissues commonly by sectioning and staining; followed by examination under a light microscope or electron microscope...
.
Classification
Diktyoma is classified into teratoid and nonteratoid types, based on heteroplastic tissue in the former. Each type may be sub-classified as benign or malignantCancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
based on histology
Histology
Histology is the study of the microscopic anatomy of cells and tissues of plants and animals. It is performed by examining cells and tissues commonly by sectioning and staining; followed by examination under a light microscope or electron microscope...
.
Based on histology, the tumor is classified as malignant if it contains poorly differentiated neuroblast
Neuroblast
A neuroblast is a dividing cell that will develop into neurons or glia. The characterisation of neuroblasts and their development in Drosophila melanogaster was widely achieved by Chris Doe, Corey Goodman and Mike Bate. In humans, neuroblasts produced by stem cells in the adult subventricular zone...
s, nuclear pleomorphism, markedly abnormal mitotic activity
Mitosis
Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...
, sarcomatous components
Sarcoma
A sarcoma is a cancer that arises from transformed cells in one of a number of tissues that develop from embryonic mesoderm. Thus, sarcomas include tumors of bone, cartilage, fat, muscle, vascular, and hematopoietic tissues...
, or invasion into the uvea
Uvea
The uvea , also called the uveal layer, uveal coat, uveal tract, or vascular tunic, is the pigmented middle of the three concentric layers that make up an eye. The name is possibly a reference to its reddish-blue or almost black colour, wrinkled appearance and grape-like size and shape when...
, cornea
Cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...
, or sclera
Sclera
The sclera , also known as the white or white of the eye, is the opaque , fibrous, protective, outer layer of the eye containing collagen and elastic fiber. In the development of the embryo, the sclera is derived from the neural crest...
. Most diktyomas are malignant.
Signs and Symptoms
The most common symptoms of diktyoma are vision lossVision loss
Vision loss or visual loss is the absence of vision where it existed before, which can happen either acutely or chronically .-Ranges of vision loss:...
and pain, while the most common signs are leukocoria
Leukocoria
Leukocoria is an abnormal white reflection from the retina of the eye. Leukocoria resembles eyeshine, but leukocoria can occur in humans and other animals that lack eyeshine because their retina lacks a tapetum lucidum....
and presence of a mass in the iris
Iris (anatomy)
The iris is a thin, circular structure in the eye, responsible for controlling the diameter and size of the pupils and thus the amount of light reaching the retina. "Eye color" is the color of the iris, which can be green, blue, or brown. In some cases it can be hazel , grey, violet, or even pink...
or ciliary body. Other signs and symptoms include lens subluxation
Ectopia lentis
Ectopia lentis is a displacement or malposition of the eye's crystalline lens from its normal location. A partial dislocation of a lens is termed lens subluxation or subluxated lens; a complete dislocation of a lens is termed lens luxation or luxated lens.-Ectopia lentis in dogs and cats:Although...
, glaucoma
Glaucoma
Glaucoma is an eye disorder in which the optic nerve suffers damage, permanently damaging vision in the affected eye and progressing to complete blindness if untreated. It is often, but not always, associated with increased pressure of the fluid in the eye...
, cataract
Cataract
A cataract is a clouding that develops in the crystalline lens of the eye or in its envelope, varying in degree from slight to complete opacity and obstructing the passage of light...
, exophthalmos
Exophthalmos
Exophthalmos is a bulging of the eye anteriorly out of the orbit. Exophthalmos can be either bilateral or unilateral . Measurement of the degree of exophthalmos is performed using an exophthalmometer...
, buphthalmos
Buphthalmos
Buphthalmos is a medical term that describes enlargement of the eyeball and is most commonly seen in infants and young children. It is sometimes referred to as buphthalmia . It usually appears in the newborn period or the first 3 months of life...
, strabismus
Strabismus
Strabismus is a condition in which the eyes are not properly aligned with each other. It typically involves a lack of coordination between the extraocular muscles, which prevents bringing the gaze of each eye to the same point in space and preventing proper binocular vision, which may adversely...
, and ptosis
Ptosis (eyelid)
Ptosis is a drooping of the upper or lower eyelid. The drooping may be worse after being awake longer, when the individual's muscles are tired. This condition is sometimes called "lazy eye", but that term normally refers to amblyopia...
.
Imaging findings
Imaging studies such as ultrasonographyMedical ultrasonography
Diagnostic sonography is an ultrasound-based diagnostic imaging technique used for visualizing subcutaneous body structures including tendons, muscles, joints, vessels and internal organs for possible pathology or lesions...
(US), Computerized Tomography (CT) and Magnetic Resonance Imaging
Magnetic resonance imaging
Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...
(MRI) may aid diagnosis
Medical diagnosis
Medical diagnosis refers both to the process of attempting to determine or identify a possible disease or disorder , and to the opinion reached by this process...
. On ultrasound, diktyomas typically appear as echogenic, irregularly shaped to ovoid masses. Ultrasound is excellent for demonstrating cystic collections of vitreous fluid in the tumor, and may show calcifications
Dystrophic calcification
Dystrophic Calcification is the calcification occurring in degenerated or necrotic tissue, as in hyalinized scars, degenerated foci in leiomyomas, and caseous nodules. This occurs as a reaction to tissue damage, including as a consequence of medical device implantation.Dystrophic calcification can...
in the teratoid type.
On CT, dityomas typically appear as dense, irregular masses in the ciliary body, which enhances with administration of intravenous contrast material. CT is excellent for demonstrating dystrophic calcification
Dystrophic calcification
Dystrophic Calcification is the calcification occurring in degenerated or necrotic tissue, as in hyalinized scars, degenerated foci in leiomyomas, and caseous nodules. This occurs as a reaction to tissue damage, including as a consequence of medical device implantation.Dystrophic calcification can...
s in the teratoid type.
On MRI, dityomas typically apppear slightly to moderately hyperdense to vitreous on T1-weighted images and hypodense on T2-weighted images, with marked homogeneous enhancement (except for prominent parts of cystic components, which, if present, may impart heterogeneity) after administration of intravenous contrast material. MRI is excellent for detection of tumors as small as 2 millimeters.
Gross pathologic findings
Grossly, the tumor appears white, gray, or yellow, with irregular surface, often studded with small cysts. More small cysts may be found on cut sections. These cysts may break off the surface and float freely in aqueous or vitreous humourVitreous humour
The vitreous humour or vitreous humor is the clear gel that fills the space between the lens and the retina of the eyeball of humans and other vertebrates...
. The tumor may also contain chalky grayish white particles. The lens may be covered by a semi-translucent membrane in some case. Tumor may invade locally to involve the iris or anterior retina, or through the cornea or sclera. In advanced cases, tumor may fill the enture globe, similar to retinoblastoma
Retinoblastoma
Retinoblastoma is a rapidly developing cancer that develops in the cells of retina, the light-detecting tissue of the eye. In the developed world, Rb has one of the best cure rates of all childhood cancers , with more than nine out of every ten sufferers surviving into...
.
Histologic findings
Microscopically, the tumor cells recapitulate embryonic sensory retina or nonpigmented ciliary epithelium. The chalky grayish white particles within the tumor mass correspond to foci of cartilageCartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
on histology; the semi-translucent membrane covering the lens in some tumors corresponds to spreading neoplastic cells.
Tumor cells form a characteristic diktyomatous pattern, with folded cords and sheets resembling a fisherman's net. In early development of the retina, the medullary epithelial cells acquire polarity, such that a basement membrane associated with the vitreous forms the internal limiting membrane on one side, while terminal bars form the outer limiting membrane on the other side. Proliferating tumor cells of diktyoma maintain the same polarity, arranged in cords and sheets folding back upon themselves. Depending on the direction of the folding, some folds surround fluid collection, while others do not. These fluid-filled spaces correspond to the grossly observed small cysts, which are mainly composed of vitreous humor.
About 30-50 percent of diktyomas contain heteroplastic elements, and thus belong to the teratoid subtype. These heteroplatic elements may include hyaline cartilage
Hyaline cartilage
Hyaline cartilage consists of a slimy mass, pearly bluish in colour with firm consistency and considerable collagen. It contains no nerves or blood vessels, and its structure is relatively simple....
, rhabdomyoblasts, and neuroglial tissue. Sarcomatous elements may be seen in malignant tumors. Foci of dystrophic calcifications may be present.
Treatment and prognosis
Diktyoma is treated by either close observation, or enucleation of the eye. Surgical resectionSegmental resection
Segmental resection is a surgical procedure to remove part of an organ or gland. It may also be used to remove a tumor and normal tissue around it. In lung cancer surgery, segmental resection refers to removing a section of a lobe of the lung.- External links :* entry in the public domain NCI...
is no longer done due to risk of late complications and metastases. Small lesions can be treated with iodine-125 plaque brachytherapy. Distant metastases and mortality are rare. Mortality may occur in patients with extraocular extension to the brain. Lack of glial differentiation, as demonstrated by negative staining for glial fibrillary acidic protein
Glial fibrillary acidic protein
Glial fibrillary acidic protein is an intermediate filament protein that was thought to be specific for astrocytes in the central nervous system . Later, it was shown that GFAP is also expressed by other cell types in CNS, including ependymal cells...
(GFAP), may confer a favourable prognosis.
Epidemiology
Mean age at diagnosis is 5 years. While most cases occur in young children, adult cases have been reported. IncidenceIncidence (epidemiology)
Incidence is a measure of the risk of developing some new condition within a specified period of time. Although sometimes loosely expressed simply as the number of new cases during some time period, it is better expressed as a proportion or a rate with a denominator.Incidence proportion is the...
is similar in male and female and among different races.