Classification<unk>  is classified into teratoid and nonteratoid types, based on heteroplastic tissue in the former. Each type may be sub-classified as benign or malignant based on histology. Based on histology, the tumor is classified as malignant if it contains poorly differentiated neuroblasts, nuclear pleomorphism, markedly abnormal mitotic activity, sarcomatous components, or invasion into the uvea, cornea, or sclera. Most<unk> s are malignant. Imaging findings Imaging studies such as ultrasonography (US), Computerized Tomography (CT) and Magnetic Resonance Imaging (MRI) may aid diagnosis. On ultrasound,<unk> s 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,<unk> s typically appear as dense, irregular masses in the ciliary body, which enhances with administration of intravenous contrast material. CT is excellent for demonstrating dystrophic calcifications in the teratoid type. On MRI,<unk> s typically appear 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 humour. 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 entire globe, similar to retinoblastoma. 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 cartilage on histology; the semi-translucent membrane covering the lens in some tumors corresponds to spreading neoplastic cells. Tumor cells form a characteristic<unk> tous 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<unk>  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<unk> s 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.
Diktyoma
Fibrillary astrocytoma
Pinealoma
Subependymal giant cell astrocytoma
Pituicytoma
Oligoastrocytoma
Spiradenoma
Pilocytic astrocytoma