Medulloepithelioma Diagnosed by Ultrasound and Vitreous Aspirate

Electron Microscopic Observations

JUAN ORELLANA, MD, ROBERTO A. MOURA, MD, RAMON L. FONT, MD, MILTON BONIUK, MD, DONNA MURPHY, BS

Abstract: Ultrasonography and cytologic examination of the vitreous aspirate established the correct pre-enucleation diagnosis of medulloepithelioma in the case of an 8-year-old boy. The use of a muscle hook allowed the examiner to elevate the eye and bring the ciliary body into adequate ultrasonographic view. Histopathologic examination of the enucleated eye showed a partially pigmented mass composed of elongated neuroepithelial tubules and cords arising from the ciliary body inferiorly. Several tubules displayed a central lumen with rosette­like structures. The tumor was classified as a benign, nonteratoid medulloe­pithelioma. Electron microscopically the lumens of the rosettes contained myriad, slender microvilli, and were bordered by numerous terminal bar complexes and areas displaying zonula adherens and zonula occludens type junctions. Additionally, invaginating gap junctions, which clearly established that the tumor originated from the ciliary epithelium, were identified. [Key words: Benign, Ciliary Epithelium, Diktyoma, Gap Junctions, Medulloepithelioma, Non-teratoid, Terminal Bar, Ultrasonography, Vitreous Aspirate.] Ophthalmology 90:1531-1539,1983

Medulloepithelioma (diktyoma) is a congenital, neu­roepithelial tumor of the ciliary body. These embryonal tumors of the nonpigmented ciliary epithelium have also been found to originate in the iris, 1 the optic nerve, and the retina.2- S In 1904, Verhoff described a case that he unfortunately called a "teratoneuroma," even though ter­atoid tissue was absent.6 Fuchs later described a lace or net-like tumor composed of neuroepithelial cells that he referred to as dikytoma,7 from the Greek diktyon, net. Grinker,8 Reese,9 and Duke-ElderlO have grouped both

congenital and acquired tumors of the ciliary epithelium under the classification of medullopithelioma. Zimmer­man reclassified these tumors based on their morphologic features and whether the tumor was congenital or ac­quired. 11 ,12 Zimmerman's classification was subsequently adopted by the World Health Organization.

From the McPherson Associates and The Department of Ophthalmology, Cullen Eye Institute, Baylor College of Medicine, Houston, Texas.

Supported in part by grant #500-G-10736 from the Retina Research Foundation, and in part by grant #500-G-1 0050 from the Lions Eye Bank, Houston, Texas.

Requests for reprints to Ramon L. Font, MD, Laboratory of Ophthalmic Pathology, Cullen Eye Institute, Baylor College of Medicine, Houston, TX 77030.

Medulloepitheliomas are unilateral congenital neo­plasms that display no evidence of genetic transmission.5

Clinical diagnosis of these tumors is based on the pre­senting clinical symptoms and a high index of suspicion. When confronted with a child in the first decade with poor visual acuity accompanied by the presence of a mass in the ciliary body, unilateral glaucoma, and/or cataract, the ophthalmologist should be alerted to the possibility of a medulloepithelioma.

In the case reported herein, the clinical history and ultrasonographic examination suggested this entity. The diagnosis was first established by cytologic examination and ultrastructural studies of the vitreous aspirate and

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Fig 1. Water immersion ultrasound depicting a cystic mass in the ciliary body. A muscle hook was placed in the inferior cul-de-sac to rotate the globe, and simultaneously with scleral depression, the mass was brought into ultrasonographic view.

subsequently confirmed by histopathologic examination of the enucleated eye.

CASE REPORT

The patient was an 8-year-old child, the full-term product of a normal pregnancy and spontaneous vaginal delivery. Devel­opmental progress was normal. At age 5 the child underwent a routine ophthalmic examination by an ophthalmologist who noted no abnormalities.

At the age of 8 a routine vision test performed at school disclosed poor visual acuity in the left eye. Examination by an ophthalmologist showed a cataract, and a possible anterior retinal elevation by ultrasonography. The patient's parents requested a retinal consultation for further evaluation.

During the examination the child, otherwise in good health, recalled being hit in the left eye during a basketball game ap­proximately 8 to 12 weeks earlier, but claimed to have expe­rienced no unusual pain at the time of the trauma. Recently he had become aware of a diminished visual acuity in the left eye, with which he could count fingers at 1 ft. His best-corrected visual acuity was 20/25 in the right eye. No improvement was achieved in either eye with a pinhole. Full ductions and versions were present. No proptosis was present. Slit-lamp biomicroscopy revealed a normal anterior segment in the right eye. Funduscopic examination of the posterior pole and periphery was unre­markable. In the left eye, there was a cataract with anterior and posterior cortical changes. Applanation tonometry showed an intraocular pressure of 15 mmHg, right eye and 9 mmHg, left eye. Funduscopic examination of the left eye was not possible because of the lens opacity.

The patient was admitted for an examination under general anesthesia in June 1982. Ultrasonography via waterbath dis­closed an attached retina. The periphery was then examined using a muscle hook to tilt the eye, and an acoustically non­homogenous ciliary body mass, located inferiorly and infer­onasally could be seen. Some regions of the mass were relatively solid, while other areas had a more cystic appearance. This cystic quality was apparent at the dome of the mass (Fig 1). Because of these findings the diagnosis of medulloepithelioma

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(diktyoma) was postulated. This clinical diagnosis was strongly suspected by fundus examination and direct visualization of the intraocular mass after removal of the cataract. Following lens extraction, it was decided to perform an anterior vitrectomy to obtain a vitreous sample for cytologic and/or histologic eval­uation. A small amount of vitreous mixed with blood from the tumor surface was submitted for microscopic examination. This material contained small fragments of the tumor (Figs 2, 3).

One month after surgery, a pigmented strand extended across the pupil and inserted onto the surface of the mass inferiorly (Fig 4).

Over the course ofthe next several months, the retina became detached completely and the visual acuity decreased to light perception. The intraocular pressure by applanation tonometry was 2 mmHg. The pupil was irregular with a large coloboma ofthe iris and a partially pigmented mass readily visible inferiorly (Fig 5). The ocular appearance was cosmetically poor, and since there was no guarantee than other areas of the tumor were benign, an enucleation was performed in March of 1983. The patient did well after surgery.

PATHOLOGIC FINDINGS

Pathologic examination revealed a specimen that con­sisted of an intact left eye measuring 20 X 21.5 X 20 mm with 4 mm of optic nerve attached. The pupil was irregular and peaked superiorly with a large colobomatous defect ofthe iris that extended from the 4- to 7-0'clock position. A pigment strand was observed through the pupillary space. The eye did not permit transillumination and was then opened in the vertical plane. Broad peripheral sy­nechias were present and the lens was absent. Inferiorly, the ciliary body showed a grayish-black mottled mass measuring 5 X 2 mm in maximal diameters (Fig 6). There was a total funnel-shaped retinal detachment. A 5 X 3 mm dark brown, cystic structure, which was attached to the outer retina, was located in the ciliary body inferiorly. The remainder of the globe was unremarkable.

Microscopically, there was early peripheral vascular­ization of the corneal stroma. A small focal rupture with coil-up of Descemet's membrane was present superiorly. The superior iris leaflet showed ectropion uveae with pos­terior synechias from fibrous vitreous strands extending from the ciliary body. Inferiorly, there was a coloboma of the iris with numerous pigment-laden macrophages. Arising in the ciliary body inferiorly was a partially pig­mented mass composed of elongated neuroepithelial tu­bules and cords, many of which were pigmented heavily. Other tubules were nonpigmented. The mass was confined to the surface of the ciliary body, involving both the pars plicata and the pars plana (Fig 7). The pigmented and nonpigmented neuroepithelial tubules were composed of uniform cells that exhibited round to oval nuclei and scanty cytoplasm (Figs 8, 9). Numerous melanin granules were present within the cytoplasm of the tumor cells. Some tubules displayed a central lumen with rosette-like structures (Figs 8, 9). Mitotic activity was minimal. The tumor mass was embedded in well-vascularized fibrous tissue. No areas of necrosis or hemorrhage were observed. Scattered foci of tumor were also seen adjacent to the

ORELLANA, et al • MEDULLOEPITHELIOMA

Fig 2. Top left. vitreous aspirate displaying a single neuroepithelial rosette (hematoxylin-eosin X 160). Fig 3. Top right. vitreous aspirate depicting a rosette containing mucopolysaccharide. The material was sensitive to hyaluronidase digestion (alcian blue X 160). Fig 4. Second row left. preoperative appearance showing a strand of pigment extending across the pupil from eleven to five o'clock and inserted on the surface of the mass, behind the pupillary border inferiorly. Fig S. Second row right. postoperation clinical appearance of the left eye (prior to enucleation) disclosing an irregular pupil with a coloboma of the iris and a partially pigmented mass, inferiorly. A pigmented strand crosses the pupil and is attached to the mass. Fig 6. Third row left. vertical section of the enucleated eye showing a total funnel-shaped retinal detachment. The ciliary body, inferiorly (on the right) is thickened by a mottled grayish-black mass. The pigmented strand, observed clinically, is readily visible extending obliquely onto the ciliary body mass (on the right). Fig 7. Third row right. the partially pigmented mass is attached to the inner surface of the ciliary body (hematoxylin-eosin X51). Fig 8. Bottom left. branching pigmented neuroepithelial tubules are embedded in a rich fibrovascular stroma (hematoxylin and eosin X 10). Fig 9. Bottom right. high power view of the tumor showing irregular neuroepithelial tubules, some of which are forming rosettes exhibiting a central lumen (hematoxylin-eosin X100).

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,/ bm

Fig 10. Vitreous aspirate showing a small lobule composed of tumor cells that exhibit irregular convoluted nuclei and contain melanin granules (M). Numerous interdigitating villous processes are observed between adjacent cells (asterisks). The cells display a polarized thin basal membrane (BM) with a plethora of slender microvilli (MV) on the apical surface (X7000).

totally detached retina and along the surface of the con­densed and fibrotic vitreous.

The retinal architecture was moderately well preserved with scattered collections of melanophages. A blood-filled macrocyst was attached to the outer surface of the de­tached retina. The photoreceptors were totally degener­ated. The choroid, sclera, and optic nerve were not re­markable.

Diagnosis was: (1) benign non teratoid medulloepithe­lioma of the ciliary body; (2) aphakia; (3) coloboma of iris; (4) broad anterior and posterior synechias; (5) total retinal detachment; (6) vitreous fibrosis; and (7) blood­filled macrocyst of the retina.

ELECTRON MICROSCOPY FINDINGS

Approximately 20 ml of vitreous aspirate was obtained with the Ocutome®. The material was filtered through several layers of gauze from which a few minute, dark­brown fragments of tissue were recovered and processed for light and electron microscopy. Sections from the par­affin blocks were cut at 6 JLm and stained with hema-

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toxylin-eosin and alcian blue at pH 2.5, before and after hyaluronidase digestion.

Microscopically, a neuroepithelial rosette with a central lumen was readily visible (Fig 2). Between the rosette and a flat single layer of cells a loose myxoid matrix was observed. This material contained a hyaluronidase-sen­sitive mucopolysaccharide (Fig 3). Additionally, several short ribbons of neuroepithelial cells containing scattered spheroidal melanin granules were noted. Electron mi­croscopy demonstrated small, neuroepithelial lobules composed of tumor cells with irregular, convoluted nuclei and myriad interdigitating villous processes. The cells displayed a thin, continuous basement membrane on the basilar surface and a plethora of slender microvilli on the apical surface (Fig 10). Numerous mature as well as late immature melanosomes of variable size and shape were noted. The results of the light and electron microscopic findings of the vitreous aspirate established the diagnosis of medulloepithelioma.

Portions of the ciliary body tumor from the enucleated eye were fixed in 2% gluteraldehyde, postfixed in 1 % os­mium tetroxide, and embedded in epon for electron mi­croscopy. Thick sections (1-2 JLm) stained with toluidine

ORELLANA, et al • MEDULLOEPITHELIOMA

Fig 11. Ciliary body tumor from the enucleated eye discloses a neuroepithelial lobule composed of tumor cells with irregular, pleomorphic nuclei that are arranged centrally. The pigment granules are concentrated mainly at the periphery of the tumor lobule. Three types of granules are identified: melanin (M), lipofuscin (L), and compound granules (C) (X5,400).

blue demonstrated small, branching, pigmented, and nonpigmented tubules composed of neuroepithelial cells. Thin sections were prepared from selected areas of the epon-embedded blocks and stained with uranyl acetate and lead citrate. Ultrastructural studies disclosed solid neuroepithelial lobules containing irregular nuclei that clustered centrally within the lobule (Fig II). The cyto­plasm showed numerous elongated to oval pigment gran­ules, of variable density and shape, that were arranged peripherally (Fig II). Three types of pigment were iden­tified: lipofuscin, melanin, and compound granules (Fig II). Several of the neuroepithelial tubules exhibited a small lumen (rosette). The lumen of the rosette was filled with numerous elongated microvilli (Fig 12, top and bot­tom). A polarized thin basement membrane ,-vas noted

on the basilar surface of the tubules (Fig 12, top). Dense terminal bar complexes were regularly seen at the inter­cellular borders near the lumen of the rosette (Fig 12, top and bottom). In some areas, the neuroepithelial struc­tures displayed a girdle-like configuration of dense, ter­minal bar complexes with scattered invaginating gap junctions (Fig 13). Several gap junction vesicles, which represent bulbous protrusion of one cell deeply indenting the surface of adjacent cells, were observed. Junctional complexes with zonula adherens and zonula occludens were also identified (Fig 13). The cytoplasm of the tumor cells displayed scattered mitochondria, short profiles of rough-surfaced endoplasmic reticulum, free polyribo­somes, Golgi lamellae, small vesicles, and a few lysosomes (Fig 13).

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ORELLANA, et al • MEDULLOEPITHELIOMA

Fig 12. Top. this micrograph depicts the edge of a rosette. Terminal bar complexes (arrows) are identified. Numerous microvilli (MY) protrude into the lumen of the rosette. A thin continuous basal membrane (8M) is present. The cells contain elongated to ovoid melanin granules (M) (X 12,000). Bottom. the lumen of a rosette contains abundant microvilli (MY). Many dense terminal bar complexes (arrows) are observed. Melanin granules (M) (X25,000).

(

DISCUSSION

Zimmerman classified tumors of the ciliary epithelium into congenital and acquired. Medulloepitheliomas and glioneuromas were grouped as congenital tumors while adenomas arid adenocarcinomas were grouped as ac­quired tumors of the adult ciliary epithelium.12 Medul-

loepitheliomas are embryonal masses arising from the primitive medullary epithelium. Broughton and Zim­merman noted a median age of 5 in their series of 56 cases. 13

These tumors are classified into teratoid and nonter­atoid types, and each further divided into benign or ma­lignant varieties. Teratoid medulloepitheliomas have one or more heterotopic tissues such as hyaline cartilage,

Fig 13. Girdle-like configuration of terminal bar complexes (arrows) with numerous interdigitating cell processes. Zonula adherens (ZA) and zonula occludens (ZO) are present. Other specialized intercellular junctions, ie, invaginating gap junctions (GJ) are observed. Several gap junction vesicles (asterisks), which on serial sections represent bulbous protrusions of one cell deeply indenting the surface of the adjacent cell, are noted. Arrowhead points to the narrow stalk that connects the cell protrusion encircled by the gap junction to the parent cell. Nucleus (N); Golgi lamellae (G); Lysosome (L Y) (X24,320).

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rhabdomyoblasts, undifferentiated mesenchymal cells, and neuroglial tissue. II ,12,14,15 Nonteratoid medulloepi­theliomas contain tissue that resembles the medullary epithelium but may also contain tissue derived from sec­ondary optic vesicle such as retinal pigment epithelium, ciliary epithelium, vitreous, and neuroglia. 12 Criteria for malignancy in these tumors include local invasion of other ocular structures and many poorly differentiated neu­roepithelial cells showing increased mitotic activity.

Medulloepitheliomas, for the most part, grow slowly and are locally invasive neoplasms. Anderson5 and Cogan and Kuwabaral6 considered this tumor to be potentially malignant; moreover Broughton and Zimmerman 13 noted four tumor deaths out of 33 cases in which follow-up examination was available. While Sirsat has proposed that these tumors do not metastasize,17 a more aggressive behavior has been noted in the tumors originating from the posterior pole which can grow into the orbit. 18, 19 Scleral invasion leading to perforation of the globe by aggressive medulloepitheliomas have also been documented.2o,21 Broughton and Zimmerman noted ten cases of extra­ocular extension. 13 It is significant, that these congenital tumors when seen in adults have shown a preponderance towards malignancy. Three of the four cases reported in adults have been malignant. 13,14,21,22 These cases may sug­gest that the tumor can be quiescent for years and then stimulated into an aggressive malignant phase. Some au­thors believe that the malignant potential is greater in the teratoid variant of medulloepithelioma.5,23-25

Medulloepitheliomas consist chiefly of multilayered sheets and cords of poorly differentiated neuroepithelial cells that resemble the embryonic retina and ciliary ep­ithelium. II ,12 These sheets of medullary epithelium can fold back upon themselves to form multilayered complex structures. Elongated tubules and cystic structures typi­cally demonstrated a hyaluronidase-sensitive mucopoly­saccharide resembling primitive vitreous. 13,26 If tumor buds escape from the main mass of cells, they can form a free-floating cyst in the aqueous, and such cysts may be the etiology of the cystic medulloepitheliomas that have been reported.27,28 Rosettes, larger than those seen in retinoblastomas, are usually present in medulloepi­theliomas.

In the case reported herein, neuroepithelial tubules were situated primarily on the surface of the ciliary body, in­volving both the pars plicata and pars plana. The large tubular structures detected may be responsible for the nonhomogeneous picture seen on waterbath ultrason­ography. The tubules also exhibited rosette-like structures. Tumor foci were observed adjacent to the detached retina on the vitreous face. These nests of cells may have been trapped and aspirated by the vitreous sampling. This vit­reous aspirate would seem to offer the ophthalmic pa­thologist a more adequate source of tumor cells than a fine needle biopsy.

Ultrastructural studies disclosed tumor cells forming rosettes with a plethora of microvilli at the luminal surface. Numerous terminal bar complexes with formation of zonula adherens and occludens were also present. These findings are similar to those observed by lakobiec et al27

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and Iwamoto et al.29 Additionally, we found scattered invaginating gap junctions which represent specialized cell junctions of the ciliary epithelium.30

Before surgery this tumor is infrequently diagnosed. A biopsy of free-floating cysts from the anterior chamber has led to the correct diagnosis in two cases.27,28 Thus, our diagnostic techniques should be expanded to diagnose correctly these tumors. Our method of scleral depression simultaneously with tilting of the globe during ultrason­ography allows the examiner access to the region of the ciliary body. A more elegant method has been described by Iijima and AsanagiY Using A- and B-mode real-time scanning with a contact scanner, these investigators were able to detect a detachment of the ciliary body and anterior choroid.

In summary, children presenting with a blind eye in the first decade of life should have an ultrasound per­formed with special attention to the ciliary body region. The diagnosis of medulloepithelioma can be confirmed by cytologic examination, including ultrastructural stud­ies, of the vitreous aspirate.

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