J Neurosurg 74:278-282, 1991
An epithelialcyst in the cerebellopontine angle Case report SUET YI LEUNG, M.B.,B.S.(HK), THOMAS H. K. NG, M.R.C.PATH., F.R.C.P.A., C. F. FUNG, F.R.C.S.(EDIN), F.R.C.S.(GLAS), AND V. W. FAN, F.R.C.S.(EDIN)
Department of Pathology and Division of Surgical Neurology, Department of Surgery, University of Hong Kong, Hong Kong I A case of a benign epithelial cyst in the posterior cranial fossa is described. It had the unique histological feature of a double-layered cuboidal epithelial lining. Detailed immunohistochemical and electron microscopic ,
studies supported an endodermal origin. The differential diagnosis and the histogenesis of epithelial cysts in the central nervous system are discussed. KEY WORDS •
epithelial cyst • neurenteric cyst • cerebellopontine angle
epithelium-lined cyst in the posterior cranial fossa is a very rare occurrence. There is considerable controversy over the nature and origin of these cysts, whether they are endodermal or neuroepithelial in origin. 2,3.10.12.20 Other authors, however, have reported rare cases of neurenteric cysts lined by mucus-producing cells.".•' 4 °''' Most of these neurenteric cysts were diagnosed by simple histochemical examination only. Immunohistochemical staining and electron microscopic examination, which can yield important information regarding the histogenesis of these cysts, have rarely been performed."' We describe an epithelial cyst in the left cerebellopontine angle with detailed histological, immunohistochemical, and electron microscopic studies. We have not found a cyst with similar histological features in the literature. We believe this is a histological variant of neurenteric cyst with an endodermal origin.
A
N
Case Report
This 28-year-old man presented in May, 1989, with a 2-year history of progressive blurring of vision associated with nocturnal headache and vomiting. The headache had become more severe during the 3 months preceding admission. Examination. The corneal reflex was impaired on the left side, otherwise neurological examination was unremarkable. There was no nystagmus or hearing loss. Plain skull x-ray films were normal. Computerized to278
mography showed a well-demarcated low-density cyst in the left cerebellopontine angle, the attenuation value of which was just above that of cerebrospinal fluid; there was no enhancement with administration of contrast material (Fig. 1). The cyst was compressing the brain stem and was not contiguous with the fourth ventricle.
Operation. On May 30, 1989, a left suboccipital craniectomy was performed with the patient in the left lateral position. A large cyst with a whitish wall was found in the subarachnoid space between the cerebellum and petrous bone (Fig. 2). The contents of the cyst were slightly milky. The cyst wall was excised under the operating microscope. There was only minimal adhesion between the cyst wall and the surrounding structures. Postoperative Course. The postoperative course was uneventful and the patient was discharged 2 weeks after surgery. Computerized tomography was repeated 3 months postoperatively, showing no evidence of cyst recurrence.
Pathological Examination. The gross specimen consisted of a fragment of pale brownish membranous tissue with irregular folding, measuring 2 x 1 cm when opened and 1 to 2 mm in thickness. The cyst lining was composed of a double layer of cuboidal cells abutting on a continuous basement membrane (Fig. 3 left). Outside the basement membrane lay J. Neurosurg. / Volume 74 / February, 1991
Epithelial cyst in the cerebellopontine angle
FIG. 1. Contrast-enhanced computerized tomography scan
showing a low-density cyst in the left cerebellopontine angle.
collagenous fibrous tissue. The epithelium was irregularly folded with papillary formations (Fig. 3 right). The cells were cytologically benign with eosinophilic cytoplasm and microvilli in the luminal border. Occasional mucin globules were noted in the epithelial cells as evidenced by positive staining with alcian blue, periodic acid-Schiff, and carcinoembryonic antigen. Immunohistochemical studies using the peroxidase technique on paraffin sections demonstrated strong positive staining for cytokeratin (Mak 6 and Cam 5.2) in the luminal layer of cells while the outer layer was negative (Fig. 3 right). Both layers of cells failed to stain for S-100 protein, neurofilament, or glial fibrillary acidic protein.
FIG. 2. Operative photograph showing a cyst with a whitish semitranslucent wall between the cerebellum and the petrous bone.
Electron microscopic examination revealed a double layer of epithelial cells separated from the collagenous matrix by a double-layered basal lamina (Fig. 4 left). The cells in the lumina' border showed round nuclei with marginated chromatin. Abundant short microvilli were present which were coated by fine reticular electron-dense material (Fig. 4 right). Rootlets were not noted in the microvilli. There were no cilia. Tight junctions were present in the luminal border. There was extensive interdigitation between adjacent epithe-
FIG. 3. Left: Photomicrograph demonstrating the double-layered cuboidal cells resting on a continuous well-formed basement membrane, outside which is collagenous fibrous tissue. Gordon and Sweet silver reticulin, x 125. Right: Photomicrograph showing that only the luminal layer of cells is positive for cytokeratin. The cyst wall is irregularly folded with papillary formations. Cam. 5.2, x 63.
J. Neurosu►g. Volume 74 / February, 1991
279
S. Y. Leung, et al.
FIG. 4_ Lek Electron micrograph showing a double layer of cells resting on the basal lamina. There are tight junctions and extensive interdigitation with well-developed desmosomes. Microvilli are noted in the
luminal border. The cytoplasm contains abundant dilated endoplasmic reticulum. x 6000. Right: Higher magnification showing the microvilli coated by fine reticular electron-dense material. x 40,000.
lial cells with well-formed desmosomes. The cytoplasm contained lipid droplets and dilated smooth endoplasmic reticulum filled with secretory materials (Fig. 4 left). The outer layer of cells was smaller and lay directly on the basal lamina. There were prominent bundles of tonofilament in the cytoplasm. They also formed extensive interdigitation with adjacent cells. Numerous pinocytotic vescicles were noted adjacent to the basal lamina (Fig. 5). Discussion
Posterior Fossa Cysts Various kinds of cyst can occur in the posterior cranial fossa. In origin, they can be epithelial, such as endodermal (neurenteric) or neuroepithelial (ependymal and choroidal epithelial) cysts; mesenchymal, such as arachnoid cysts; or mixed, such as teratomatous cysts. In the present case, the histological appearance of a double-layered cuboidal epithelium with luminal microvilli and positive staining for cytokeratin and negativity for vimentin speak against a diagnosis of arachnoid cyst. The absence of a mixture of various types of epithelial and mesenchymal elements makes the diagnosis of teratomatous cyst unlikely. Thus, the picture is that of an epithelial cyst of the posterior cranial fossa. An epithelial cyst of the posterior fossa is very rare. There is considerable controversy over the source and origin of such cysts. A thorough survey of the literature reveals 16 such cysts reported in the posterior cranial fossa, with 10 considered to be neuroepithelial in origin 23,10-12,18,20.21 and six to be neurenteric cysts. 1 • 5-6 . 14 . 22,23 Most of these cases were diagnosed on histological examination alone. Immunohistochemical and electron microscopic studies, which can yield important 280
information regarding the histogenetic origin of these cysts, were performed in only six cases; there were three endodermal cysts"' and three neuroepithelial cysts.' la
Neuretueric vs. Neuroepithelial Cysts The present case has a unique feature of doublelayered cuboidal epithelium. It would be impossible to determine whether the cyst was neurenteric, ependymal, or choroidal in origin without the aid of immunohistochemical and electron microscopic studies. The structure of a double-layered cuboidal epithelium resting on a continuous well-formed basement membrane is not a feature of ependymal cysts. Both cilia and
FIG. 5. Electron micrograph showing the basal cells with bundles of tonofilaments (arrow). Many pinocytotic vescicles are noted adjacent to the double-layered basal lamina. x 25,000.
J. Neurosurg. / Volume 74 / February, 1991
Epithelial cyst in the cerebellopontine angle blepharoplasts, which are to be expected if the lesion is
of ependymal origin, were characteristically absent. The positive staining of the luminal cells with cytokeratin also argues against ependymal origin. The lack of staining with S-100 protein, glial fibrillary acidic protein, or neurofilaments would exclude a neuroepithelial cyst. Electron microscopic examination is a useful tool in the diagnosis of cysts. The presence of fine reticular material coating the microvilli is a feature of endodermal cells and such coating has not been described in cells of the central nervous system. • Although epithelial cells of the choroid plexus possess microvilli, they are well developed and club-shaped with terminal expansions,' unlike the finger-like projections in our case. The tightly packed abundant tonofilaments in the basal layer of cells are not seen in neuroepithelium. Moreover, the presence of well-developed desmosomes is not typical in ependymal or choroidal cells.' Thus, the overall features in this case are in favor of a neurenteric cyst.
Basal Cells in Epithelial Cysts The presence of basal cells is also supportive of an endodermal origin. Electron microscopic examinations performed by different authors have demonstrated basal cells in some cases.• Unlike the findings in our cases, these basal cells do not form a continuous layer. Ghatak, et al.,' considered these basal cells identical to the basal cells characteristically seen in various surface and visceral epithelia including the upper respiratory tract' and the gastrointestinal tract. These cells are considered to be the stem cells capable of differentiation in the different directions. The epithelial lining of ducts in the gastrointestinal tract (such as the parotid duct or the pancreatic duct) commonly have double-layered cuboidal epithelium. In summary, the cyst in our case is most likely derived from the endoderm with differentiation toward stratified cuboidal ductal epithelium.
Jlistogenesis of Epithelial Cysts Ultrastructural examinations have shed light on the histogenesis of epithelial cysts of the central nervous system. Based on their electron microscopic features, Hirano, et al., 7.9 and Matsushima, et al.,' proposed that colloid cysts of the third ventricle,' neurenteric cysts of the spinal cord," 5 Rathke's cleft cyst, and pretectal and posterior cranial fossa cysts" all have a common origin from endoderm. These cysts are characterized by columnar ciliated and nonciliated epithelial lining. The ciliated cells are not present in every case but, if present, show the 9+2 structure with no granular coating material. Nonciliated cells with microvilli are present in every case, with characteristic surface granular coating indicative of an endodermal origin. They possess features of secretory function including Golgi apparatus, dilated endoplasmic reticulum distended with electron-dense reticular material,' or secreJ. Neurosurg.
I Volume 74 / February, 1991
tory globules. They have regular nuclei with marginated chromatin and prominent interdigitation of the adjacent cell border with well-developed desmosomes. Tight junctions are present in some cases. Basal cells are occasionally present' but never form a continuous layer as in our case. Because these cysts arise in the midline, Hirano, et al., and Matsushima, et al., have called them "midline developmental cysts." However, since Nishioka, et described a similar cyst in the left pretectal region and our case arose from the left cerebellopontine angle, endodermal-derived cysts may not be limited to the midline. Unlike neurenteric cysts of the spinal cord, the embryogenetic mechanism of these endodermal-derived cysts in the intracranial region is still obscure.
References 1. Afshar F, Scholtz CL: Enterogenous cyst of the fourth ventricle. Case report. J Neurosurg 54:836-838, 1981 2. Andrews BT, Halks-Miller M, Berger MS, et al: Neuroepithelial cysts of the posterior fossa: pathogenesis and report of two cases. Neurosurgery 15:91-95, 1984 3. Fukushima T, Hirakawa T, Tanaka A, et al: Choroidal epithelial cyst of the prepontine region: case report and ultrastructural study. Neurosurgery 22;128-133,1988 4. Ghatak NR, Kasoff 1, Alexander E Jr: Further observation on the fine structure of a colloid cyst of the third ventricle. Acta Neuropathol 31:101-107, 1977 5. Giombini S, Lodrini S, Migliavacca F: Intracranial enterogenous cyst. Surg Neurol 16:271-273,1981 6. Hirai 0, Kawamura J, Fukumitsu T: Prepontine epithelial-lined cyst. Case report. J Neurosurg 55:312-317, 1981 7. Hirano A, Ghatak NR: The fine structure of colloid cysts of the third ventricle. J Neuropathol Exp Neurol 33: 333-341,1974 8. Hirano A, Ghatak NR, Wisoff HS, et al: An epithelial cyst of the spinal cord. An electron microscopic study. Acta Neuropathol 18:214-223, 1971 9. Hirano A, Matsui T, Zimmerman HM: [The fine structure of epithelial cyst in the central nervous system.] Neurol Surg 3:639-646,1975 (Jpn) 10. Ho KL, Chason JL: A glioependymal cyst of the cerebellopontine angle. Immunohistochemical and ultrastructural studies. Acta Neuropathol 74:382-388, 1987 11. Hoenig EM, Ghatak NR, Hirano A, et al: Multiloculated cystic tumor of the choroid plexus of the fourth ventricle. Case report. J Neurosurg 27:574-579, 1967 12. Inoue T, Kuromatsu C, Iwata Y, et al: Symptomatic choroidal epithelial cyst in the fourth ventricle. Surg Neurol 24:57-62, 1985 13. Koto A, Horoupian DS, Shulman K: Choroidal epithelial cyst. Case report. J Neurosurg 47:955-960, 1977 14. Lach B, Russell N, Atack D, et al: Intraparenchymal epithelial (enterogenous) cyst of the medulla oblongata. Can J Neurol Sci 16:206-210, 1989 15. Matsushima T, Fukui M, Egami H: Epithelial cells in a so-called intraspinal neurenteric cyst: a light and electron microscopic study. Surg Neurol 24:656-660, 1985 16. Nishioka T, Kondo A, Kusaka H, et al: Epithelium-lined cyst of the pretectal region: case report and electron microscopic study. Surg Neurol 31:448-453, 1989 17. Odland GF, Reed TH: Epidermis, in Zetickson AS (ed):
281
S. Y. Leung, et al. Ultrastructure of Normal and Abnormal Skin. Philadelphia: Lea & Febiger, 1967 18. Parkinson D. Childe AE: Colloid cyst of the fourth ventricle. Report of a case of two colloid cysts of the fourth ventricle. J Neurosurg 9:404-409, 1952 19. Rhodin JAG: Histology. New York: Oxford University Press, 1974 20. Schelper RL, Kagan-Hallet KS, Huntington HW: Brainstem subarachnoid respiratory epithelial cysts. Report of two cases and review of the literature. Hum Pathol 17: 417-422, 1986 21, Schwartz AM, Jensen ME, Saks DA, et al: Epithelial cyst in the cerebellopontine angle with xanthogranulomatous changes simulating cholesterol granuloma. Surg Neurol 31:454-458, 1989
282
22. Walls TJ, Purohit DP, Aji WS, et al: Multiple intracranial cysts. J Neurol Neurosurg Psychiatry 49:438-441, 1986 23. Zalatnai A: Neurenteric cyst of medulla oblongata — a curiosity. Neuropediatrics 18:40-41, 1987
Manuscript received February 15, 1990. Accepted in final form August 6, 1990. Address reprint requests to: Suet Y. Leung, M.B.,B.S., Department of Pathology, Queen Mary Hospital, University of Hong Kong, Hong Kong.
J. Neurosurg. / Volume 74 / February, 1991
An epithelialcyst in the cerebellopontine angle Case report SUET YI LEUNG, M.B.,B.S.(HK), THOMAS H. K. NG, M.R.C.PATH., F.R.C.P.A., C. F. FUNG, F.R.C.S.(EDIN), F.R.C.S.(GLAS), AND V. W. FAN, F.R.C.S.(EDIN)
Department of Pathology and Division of Surgical Neurology, Department of Surgery, University of Hong Kong, Hong Kong I A case of a benign epithelial cyst in the posterior cranial fossa is described. It had the unique histological feature of a double-layered cuboidal epithelial lining. Detailed immunohistochemical and electron microscopic ,
studies supported an endodermal origin. The differential diagnosis and the histogenesis of epithelial cysts in the central nervous system are discussed. KEY WORDS •
epithelial cyst • neurenteric cyst • cerebellopontine angle
epithelium-lined cyst in the posterior cranial fossa is a very rare occurrence. There is considerable controversy over the nature and origin of these cysts, whether they are endodermal or neuroepithelial in origin. 2,3.10.12.20 Other authors, however, have reported rare cases of neurenteric cysts lined by mucus-producing cells.".•' 4 °''' Most of these neurenteric cysts were diagnosed by simple histochemical examination only. Immunohistochemical staining and electron microscopic examination, which can yield important information regarding the histogenesis of these cysts, have rarely been performed."' We describe an epithelial cyst in the left cerebellopontine angle with detailed histological, immunohistochemical, and electron microscopic studies. We have not found a cyst with similar histological features in the literature. We believe this is a histological variant of neurenteric cyst with an endodermal origin.
A
N
Case Report
This 28-year-old man presented in May, 1989, with a 2-year history of progressive blurring of vision associated with nocturnal headache and vomiting. The headache had become more severe during the 3 months preceding admission. Examination. The corneal reflex was impaired on the left side, otherwise neurological examination was unremarkable. There was no nystagmus or hearing loss. Plain skull x-ray films were normal. Computerized to278
mography showed a well-demarcated low-density cyst in the left cerebellopontine angle, the attenuation value of which was just above that of cerebrospinal fluid; there was no enhancement with administration of contrast material (Fig. 1). The cyst was compressing the brain stem and was not contiguous with the fourth ventricle.
Operation. On May 30, 1989, a left suboccipital craniectomy was performed with the patient in the left lateral position. A large cyst with a whitish wall was found in the subarachnoid space between the cerebellum and petrous bone (Fig. 2). The contents of the cyst were slightly milky. The cyst wall was excised under the operating microscope. There was only minimal adhesion between the cyst wall and the surrounding structures. Postoperative Course. The postoperative course was uneventful and the patient was discharged 2 weeks after surgery. Computerized tomography was repeated 3 months postoperatively, showing no evidence of cyst recurrence.
Pathological Examination. The gross specimen consisted of a fragment of pale brownish membranous tissue with irregular folding, measuring 2 x 1 cm when opened and 1 to 2 mm in thickness. The cyst lining was composed of a double layer of cuboidal cells abutting on a continuous basement membrane (Fig. 3 left). Outside the basement membrane lay J. Neurosurg. / Volume 74 / February, 1991
Epithelial cyst in the cerebellopontine angle
FIG. 1. Contrast-enhanced computerized tomography scan
showing a low-density cyst in the left cerebellopontine angle.
collagenous fibrous tissue. The epithelium was irregularly folded with papillary formations (Fig. 3 right). The cells were cytologically benign with eosinophilic cytoplasm and microvilli in the luminal border. Occasional mucin globules were noted in the epithelial cells as evidenced by positive staining with alcian blue, periodic acid-Schiff, and carcinoembryonic antigen. Immunohistochemical studies using the peroxidase technique on paraffin sections demonstrated strong positive staining for cytokeratin (Mak 6 and Cam 5.2) in the luminal layer of cells while the outer layer was negative (Fig. 3 right). Both layers of cells failed to stain for S-100 protein, neurofilament, or glial fibrillary acidic protein.
FIG. 2. Operative photograph showing a cyst with a whitish semitranslucent wall between the cerebellum and the petrous bone.
Electron microscopic examination revealed a double layer of epithelial cells separated from the collagenous matrix by a double-layered basal lamina (Fig. 4 left). The cells in the lumina' border showed round nuclei with marginated chromatin. Abundant short microvilli were present which were coated by fine reticular electron-dense material (Fig. 4 right). Rootlets were not noted in the microvilli. There were no cilia. Tight junctions were present in the luminal border. There was extensive interdigitation between adjacent epithe-
FIG. 3. Left: Photomicrograph demonstrating the double-layered cuboidal cells resting on a continuous well-formed basement membrane, outside which is collagenous fibrous tissue. Gordon and Sweet silver reticulin, x 125. Right: Photomicrograph showing that only the luminal layer of cells is positive for cytokeratin. The cyst wall is irregularly folded with papillary formations. Cam. 5.2, x 63.
J. Neurosu►g. Volume 74 / February, 1991
279
S. Y. Leung, et al.
FIG. 4_ Lek Electron micrograph showing a double layer of cells resting on the basal lamina. There are tight junctions and extensive interdigitation with well-developed desmosomes. Microvilli are noted in the
luminal border. The cytoplasm contains abundant dilated endoplasmic reticulum. x 6000. Right: Higher magnification showing the microvilli coated by fine reticular electron-dense material. x 40,000.
lial cells with well-formed desmosomes. The cytoplasm contained lipid droplets and dilated smooth endoplasmic reticulum filled with secretory materials (Fig. 4 left). The outer layer of cells was smaller and lay directly on the basal lamina. There were prominent bundles of tonofilament in the cytoplasm. They also formed extensive interdigitation with adjacent cells. Numerous pinocytotic vescicles were noted adjacent to the basal lamina (Fig. 5). Discussion
Posterior Fossa Cysts Various kinds of cyst can occur in the posterior cranial fossa. In origin, they can be epithelial, such as endodermal (neurenteric) or neuroepithelial (ependymal and choroidal epithelial) cysts; mesenchymal, such as arachnoid cysts; or mixed, such as teratomatous cysts. In the present case, the histological appearance of a double-layered cuboidal epithelium with luminal microvilli and positive staining for cytokeratin and negativity for vimentin speak against a diagnosis of arachnoid cyst. The absence of a mixture of various types of epithelial and mesenchymal elements makes the diagnosis of teratomatous cyst unlikely. Thus, the picture is that of an epithelial cyst of the posterior cranial fossa. An epithelial cyst of the posterior fossa is very rare. There is considerable controversy over the source and origin of such cysts. A thorough survey of the literature reveals 16 such cysts reported in the posterior cranial fossa, with 10 considered to be neuroepithelial in origin 23,10-12,18,20.21 and six to be neurenteric cysts. 1 • 5-6 . 14 . 22,23 Most of these cases were diagnosed on histological examination alone. Immunohistochemical and electron microscopic studies, which can yield important 280
information regarding the histogenetic origin of these cysts, were performed in only six cases; there were three endodermal cysts"' and three neuroepithelial cysts.' la
Neuretueric vs. Neuroepithelial Cysts The present case has a unique feature of doublelayered cuboidal epithelium. It would be impossible to determine whether the cyst was neurenteric, ependymal, or choroidal in origin without the aid of immunohistochemical and electron microscopic studies. The structure of a double-layered cuboidal epithelium resting on a continuous well-formed basement membrane is not a feature of ependymal cysts. Both cilia and
FIG. 5. Electron micrograph showing the basal cells with bundles of tonofilaments (arrow). Many pinocytotic vescicles are noted adjacent to the double-layered basal lamina. x 25,000.
J. Neurosurg. / Volume 74 / February, 1991
Epithelial cyst in the cerebellopontine angle blepharoplasts, which are to be expected if the lesion is
of ependymal origin, were characteristically absent. The positive staining of the luminal cells with cytokeratin also argues against ependymal origin. The lack of staining with S-100 protein, glial fibrillary acidic protein, or neurofilaments would exclude a neuroepithelial cyst. Electron microscopic examination is a useful tool in the diagnosis of cysts. The presence of fine reticular material coating the microvilli is a feature of endodermal cells and such coating has not been described in cells of the central nervous system. • Although epithelial cells of the choroid plexus possess microvilli, they are well developed and club-shaped with terminal expansions,' unlike the finger-like projections in our case. The tightly packed abundant tonofilaments in the basal layer of cells are not seen in neuroepithelium. Moreover, the presence of well-developed desmosomes is not typical in ependymal or choroidal cells.' Thus, the overall features in this case are in favor of a neurenteric cyst.
Basal Cells in Epithelial Cysts The presence of basal cells is also supportive of an endodermal origin. Electron microscopic examinations performed by different authors have demonstrated basal cells in some cases.• Unlike the findings in our cases, these basal cells do not form a continuous layer. Ghatak, et al.,' considered these basal cells identical to the basal cells characteristically seen in various surface and visceral epithelia including the upper respiratory tract' and the gastrointestinal tract. These cells are considered to be the stem cells capable of differentiation in the different directions. The epithelial lining of ducts in the gastrointestinal tract (such as the parotid duct or the pancreatic duct) commonly have double-layered cuboidal epithelium. In summary, the cyst in our case is most likely derived from the endoderm with differentiation toward stratified cuboidal ductal epithelium.
Jlistogenesis of Epithelial Cysts Ultrastructural examinations have shed light on the histogenesis of epithelial cysts of the central nervous system. Based on their electron microscopic features, Hirano, et al., 7.9 and Matsushima, et al.,' proposed that colloid cysts of the third ventricle,' neurenteric cysts of the spinal cord," 5 Rathke's cleft cyst, and pretectal and posterior cranial fossa cysts" all have a common origin from endoderm. These cysts are characterized by columnar ciliated and nonciliated epithelial lining. The ciliated cells are not present in every case but, if present, show the 9+2 structure with no granular coating material. Nonciliated cells with microvilli are present in every case, with characteristic surface granular coating indicative of an endodermal origin. They possess features of secretory function including Golgi apparatus, dilated endoplasmic reticulum distended with electron-dense reticular material,' or secreJ. Neurosurg.
I Volume 74 / February, 1991
tory globules. They have regular nuclei with marginated chromatin and prominent interdigitation of the adjacent cell border with well-developed desmosomes. Tight junctions are present in some cases. Basal cells are occasionally present' but never form a continuous layer as in our case. Because these cysts arise in the midline, Hirano, et al., and Matsushima, et al., have called them "midline developmental cysts." However, since Nishioka, et described a similar cyst in the left pretectal region and our case arose from the left cerebellopontine angle, endodermal-derived cysts may not be limited to the midline. Unlike neurenteric cysts of the spinal cord, the embryogenetic mechanism of these endodermal-derived cysts in the intracranial region is still obscure.
References 1. Afshar F, Scholtz CL: Enterogenous cyst of the fourth ventricle. Case report. J Neurosurg 54:836-838, 1981 2. Andrews BT, Halks-Miller M, Berger MS, et al: Neuroepithelial cysts of the posterior fossa: pathogenesis and report of two cases. Neurosurgery 15:91-95, 1984 3. Fukushima T, Hirakawa T, Tanaka A, et al: Choroidal epithelial cyst of the prepontine region: case report and ultrastructural study. Neurosurgery 22;128-133,1988 4. Ghatak NR, Kasoff 1, Alexander E Jr: Further observation on the fine structure of a colloid cyst of the third ventricle. Acta Neuropathol 31:101-107, 1977 5. Giombini S, Lodrini S, Migliavacca F: Intracranial enterogenous cyst. Surg Neurol 16:271-273,1981 6. Hirai 0, Kawamura J, Fukumitsu T: Prepontine epithelial-lined cyst. Case report. J Neurosurg 55:312-317, 1981 7. Hirano A, Ghatak NR: The fine structure of colloid cysts of the third ventricle. J Neuropathol Exp Neurol 33: 333-341,1974 8. Hirano A, Ghatak NR, Wisoff HS, et al: An epithelial cyst of the spinal cord. An electron microscopic study. Acta Neuropathol 18:214-223, 1971 9. Hirano A, Matsui T, Zimmerman HM: [The fine structure of epithelial cyst in the central nervous system.] Neurol Surg 3:639-646,1975 (Jpn) 10. Ho KL, Chason JL: A glioependymal cyst of the cerebellopontine angle. Immunohistochemical and ultrastructural studies. Acta Neuropathol 74:382-388, 1987 11. Hoenig EM, Ghatak NR, Hirano A, et al: Multiloculated cystic tumor of the choroid plexus of the fourth ventricle. Case report. J Neurosurg 27:574-579, 1967 12. Inoue T, Kuromatsu C, Iwata Y, et al: Symptomatic choroidal epithelial cyst in the fourth ventricle. Surg Neurol 24:57-62, 1985 13. Koto A, Horoupian DS, Shulman K: Choroidal epithelial cyst. Case report. J Neurosurg 47:955-960, 1977 14. Lach B, Russell N, Atack D, et al: Intraparenchymal epithelial (enterogenous) cyst of the medulla oblongata. Can J Neurol Sci 16:206-210, 1989 15. Matsushima T, Fukui M, Egami H: Epithelial cells in a so-called intraspinal neurenteric cyst: a light and electron microscopic study. Surg Neurol 24:656-660, 1985 16. Nishioka T, Kondo A, Kusaka H, et al: Epithelium-lined cyst of the pretectal region: case report and electron microscopic study. Surg Neurol 31:448-453, 1989 17. Odland GF, Reed TH: Epidermis, in Zetickson AS (ed):
281
S. Y. Leung, et al. Ultrastructure of Normal and Abnormal Skin. Philadelphia: Lea & Febiger, 1967 18. Parkinson D. Childe AE: Colloid cyst of the fourth ventricle. Report of a case of two colloid cysts of the fourth ventricle. J Neurosurg 9:404-409, 1952 19. Rhodin JAG: Histology. New York: Oxford University Press, 1974 20. Schelper RL, Kagan-Hallet KS, Huntington HW: Brainstem subarachnoid respiratory epithelial cysts. Report of two cases and review of the literature. Hum Pathol 17: 417-422, 1986 21, Schwartz AM, Jensen ME, Saks DA, et al: Epithelial cyst in the cerebellopontine angle with xanthogranulomatous changes simulating cholesterol granuloma. Surg Neurol 31:454-458, 1989
282
22. Walls TJ, Purohit DP, Aji WS, et al: Multiple intracranial cysts. J Neurol Neurosurg Psychiatry 49:438-441, 1986 23. Zalatnai A: Neurenteric cyst of medulla oblongata — a curiosity. Neuropediatrics 18:40-41, 1987
Manuscript received February 15, 1990. Accepted in final form August 6, 1990. Address reprint requests to: Suet Y. Leung, M.B.,B.S., Department of Pathology, Queen Mary Hospital, University of Hong Kong, Hong Kong.
J. Neurosurg. / Volume 74 / February, 1991
