Extradural Endodermal Cyst of Posterior Fossa: Case Report, Review ...

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consequences of limited cyst leakage in other cases suggests significant differences in cyst contents. Prevention of subarachnoid spread of cyst contents during resection of dermoid and epidermoid cysts is important. Helpful maneuvers include limiting the opening of the cyst wall, dissection of the arachnoid until the contents can be aspirated or resected, and using cottonoid paddies to occlude the subarachnoid space dependent to the site of resection. Such techniques are even more important during removal of true neoplasms of the posterior fossa with a tendency for subarachnoid spread, such as medulloblastoma, ependymoma, and choroid plexus carcinoma.

The report by Carvalho et al. describes the clinical course of a patient operated for a dysontogenic cyst. Although it seems that this entity would basically be considered a dermoid tumor were it not for the muscle fibers contained therein, a more complete description from a pathological point of view would add to the value of the report, as the term “dysontogenic” is not common. In addition, it is stated that fat breakdown may induce an inflammatory response secondary to cholesterol by-products; while I suppose that for certain fats this may be the case, most fats do not contain cholesterol. Overall, the report is of interest, especially in view of its long-term follow-up.

Griffith R. Harsh IV Stanford, California

Jack P. Rock Detroit, Michigan

Extradural Endodermal Cyst of Posterior Fossa: Case Report, Review of the Literature, and Embryogenesis Vaijayantee Kulkarni, M.B.B.S., Roy Thomas Daniel, M.Ch., Ramachandran Pranatharthi Haran, M.Ch. Department of Neurological Sciences, Christian Medical College Hospital, Vellore, India

OBJECTIVE AND IMPORTANCE: Posterior fossa endodermal cysts are rare. They are located in the midline, in ventral or ventrolateral locations, or intrinsic to the neural axis. Accordingly, various theories of embryogenesis have been proposed. We report the first case of an extradural, dorsolaterally situated endodermal cyst. CLINICAL PRESENTATION: An adult male patient presented with a short history of headache and cerebellar ataxia. Neuroimaging revealed an extra-axial cystic posterior fossa mass. INTERVENTION: An entirely extradural cyst was found and was totally excised. Immunohistochemistry confirmed the diagnosis of endodermal cyst. CONCLUSION: The extradural, dorsal location of the endodermal cyst suggests gaps at the cranial end of the notochord causing ectodermal-endodermal adhesions during early gastrulation and the persistence of endodermal remnants in the dorsal mesenchyme of the blastemal cranium. The literature is reviewed, and proposed theories of embryogenesis are discussed. (Neurosurgery 47:764–767, 2000) Key words: Endodermal cyst, Extradural, Posterior fossa

The main value of this case report is the fact that, despite the occurrence of aseptic meningitis in the immediate perioperative period, there were no long-term consequences of fat dissemination in the subarachnoid space that was presumably attributable to entrapment of the fat globules by the fibrous tissue. We wonder whether the use of the semi-sitting position by the authors promotes greater fat dissemination, in contrast to the half-lateral position, since it results in a greater amount of CSF drainage and the migration of the fat droplets along with air into the supratentorial cisterns. Laligam N. Sekhar Amitabha Chanda Annandale, Virginia

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ndodermal cyst is a rare developmental cyst lined by columnar epithelium of presumed endodermal origin (3). Spinal endodermal cysts are most frequently located in the cervicothoracic region and are usually associated with variable degrees of spinal dysraphism. Intracranial endodermal cysts are rare, and their embryogenesis is incompletely understood. They are frequently situated in the posterior fossa, and so far, approximately 50 cases of posterior fossa endodermal cysts have been reported (6). In all of the cases, the cyst was found to be intradural, lying in a ventral or ventrolateral location or intrinsic to the brainstem or cerebellum. We report the first case of an extradural, dorsolaterally positioned posterior fossa endodermal cyst and discuss its possible embryogenesis.

CASE REPORT A 40-year-old man presented with a 1-year history of intermittent right-sided occipital headache and progressive unsteadiness of gait. Clinical examination revealed right-sided cerebellar signs. Magnetic resonance imaging (Figs. 1 and 2) revealed a laterally situated, extra-axial posterior fossa mass. The lesion was hypointense on T1-weighted images and hyperintense on T2-weighted images, and it did not enhance after administration of gadolinium.

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axial cystic lesion. The histopathological features, such as cuboidal epithelium and goblet cells, suggested the endodermal origin of the lesion (3, 16). The immunopositivity of the cyst wall to carcinoembryonic antigen (a marker for gut epithelium) corroborated the diagnosis of endodermal cyst (8, 11).

FIGURE 1. Axial T2-weighted magnetic resonance image of the brain, showing an extraaxial hyperintense mass compressing the left cerebellar hemisphere.

Embryogenesis of neurenteric cyst

FIGURE 2. Gadoliniumenhanced coronal T1-weighted magnetic resonance image of the brain, showing the hypointense, nonenhancing mass. Note that the tentorium is elevated by the tumor, and there is erosion of the petrous bone by the mass.

Operation The patient underwent right retromastoid suboccipital craniectomy. The lesion was cystic and entirely extradural, containing thick, dark-greenish fluid and shining crystals. The capsule was thin and was adherent to the dura. There was no intradural communication. The contents and most of the capsule were removed.

Postoperative course Postoperatively, the patient displayed immediate improvement in cerebellar signs, and he was discharged on the 4th postoperative day.

Pathological findings Examination under light microscopy revealed a cyst lined by cuboidal epithelial cells and goblet cells. Immunohistochemical staining showed strong positivity for carcinoembryonic antigen (Fig. 3).

DISCUSSION Intracranial endodermal cysts occur mostly along the midline in the posterior fossa, the most common location being anterior to the brainstem or within the fourth ventricle. They have also been reported to occur within the brainstem, in the cerebellopontine angle, within the cerebellum, and in the

FIGURE 3. A, photomicrograph of the cyst wall showing columnar epithelium and goblet cells (hematoxylin and eosin; original magnification, ⴛ90). B, photomicrograph showing positivity of the cyst wall to immunostaining with carcinoembryonic antigen (original magnification, ⴛ90). cisterna magna (1). Most of these cysts were found to be adherent to the neurovascular structures of the cistern or the ventricle, making total resection (without causing neurological deficits) difficult (6). However, no recurrence of endodermal cysts has been reported, even after partial excision. Some of them exhibited intermittent leakage of their contents, causing recurrent aseptic meningitis. None of these cysts were associated with any cranial bony anomalies. The occurrence of an extradural endodermal cyst is extremely rare. Macdonald et al. (10) reported the case of a dorsally located neurenteric cyst in the paraspinal subcutaneous tissue; the cyst was associated with occult cervical spinal dysraphism. In our case, the cyst was situated dorsolaterally and was entirely extradural, with no intradural or extracranial communication. Other epidemiological features of our case, such as male predominance and presentation in the 4th decade, were consistent with previous reports (1). The magnetic resonance imaging features and the signal characteristics were those of an extra-

The occurrence of an epithelial cyst of endodermal origin in and around the neural axis suggests ectopic remnants of the primitive endoderm in the developing neuroectoderm during early embryogenesis. Neurenteric cysts are usually thought to represent a minor degree of endodermal-ectodermal malformation. Several theories have been proposed to explain their origin. To enhance understanding of these theories, a brief review of early neural embryogenesis is presented. During the second week of embryogenesis, prospective notochordal cells are located in Hensen’s node at the cranial end of the primitive streak. The notochordal process is formed between the ectoderm and endoderm by the ingression of these cells through the primitive pit in the center of the node. As the notochordal process elongates, the primitive streak regresses and Hensen’s node thus occupies a progressively more caudal position, ultimately coming to lie in a coccygeal location. The notochord extends cranially up to the prochordal plate; the cranial end thus forms the clivus, separating the endoderm of the primitive pharynx from the neuroectoderm of the diencephalichindbrain junction. The neurenteric canal, which is the central lumen of the notochordal process, is continuous with the amniotic cavity through the primitive pit. This process subsequently intercalates with the adjacent endoderm, which thereby places the notochordal canal in communication with both the amniotic cavity and the yolk sac. The neurenteric canal exists for approximately 48 hours, after which the notochordal process excalates from the endoderm and forms the definitive notochord (17). In 1912, Budde (2a) proposed that the failure of closure and abnormal caudal migration of the neurenteric canal might be responsible for the formation of


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endodermal cysts in the lumbosacral region. Bremer (2) discounted this assumption because the regressing primitive knot and the neurenteric canal lie at the tip of the coccyx, which makes it difficult to explain any anomalies dorsal to the coccyx on the basis of the anomaly of the neuroenteric canal alone. He thus postulated the formation of more rostral accessory neurenteric canals, which have been observed to form in animals. Harriman (7) proposed sequestrational malformation of the neurenteric canal, leading to heterotopias at various spinal levels, as the cause of endodermal cysts in the cervicodorsal region. These theories seemed inadequate, because remnants of the cells left behind by the regressing primitive knot or an aberration of intercalation or excalation of the notochord would explain enteric remnants only as far dorsal as the notochord, i.e., up to the vertebral body (the final position of notochord). Moreover, it seemed difficult to explain more severe midline clefts on the basis of simple remnants of cells. Rhaney and Barclay (12) thus proposed that the more dorsal defects might involve aberrant intercalation of the endoderm into more dorsally located neuroectoderm, the strands of cells traveling the split notochord, as had earlier been proposed by Saunders (13). The herniation of the endodermal layer through the defect in the notochord would thus result in endodermal-ectodermal adhesion. Although several authors have suggested the “split notochord” as the primary event leading to endodermal-ectodermal adhesions, the cause of this primary event is unclear (5, 8, 10). Indeed, the occurrence of a cleft in the notochord has to be invoked in any theory of embryogenesis of these lesions. That would also explain the existence of cases of endodermal derivatives occurring dorsal to the neural tube, as seen in stillborn fetuses with severe malformations involving the cervicothoracic spine, in which abdominal viscera herniate through the back of the fetus (10). Bentley and Smith (1a), in 1960, proposed a comprehensive classification of neurenteric malformation under the term “split notochord syndrome,” because this concept seemed fundamental to the mechanism of achieving connections between the endoderm and the dorsum of the embryo.

In extreme cases, persistence of complete clefts leads to the development of a midline fistula from the gut to the back. Further regression of the cleft could result in a diastematomyelia or an isolated neurenteric cyst (10). The cranial end of the notochord forms the posterior clinoid portion of the clivus and underlies the diencephalicmesencephalic junction; the epiblast overlying the notochord subsequently forms the neural tube (8, 17). It can be presumed that disturbances of early gastrulation (such as splitting of the notochord), beginning shortly after the onset of primitive streak regression, will interfere with the development of the foregut, cranial notochord, and cranial neuroepithelium and may contribute to the formation of posterior fossa endodermal cyst (8). The regression of most of the cellular elements of an endodermal-ectodermal connection would leave only a small collection of cells that could give rise to a thin-walled epithelial cyst located at any point (dorsoventral) along the course of the original adhesions in the presence of normal clivus and hindbrain. This theory of variable regression of endodermal-ectodermal adhesions at the cephalic end of the notochord can explain the occurrence of all the posterior fossa endodermal cysts reported so far. The lateral location of the cyst, such as in the cerebellopontine angle and within the cerebellar hemisphere, can be explained on the basis of lateral extension of the cerebellum during development (Fig. 4). In our case of extradural endodermal cyst, the migration of endodermal remnants would have occurred along with lateral extension of the occipital plates of the blastemal cranium (desmocranium), during the early part of second month of gestation.

CONCLUSION Endodermal cysts can occur at various levels of the neuraxis, from the posterior fossa to the coccyx. Spinal endodermal cysts are often associated with variable degrees of split cord malformation. Different theories have been proposed to explain the entire spectrum of these anomalies. With the occurrence of a dorsally located, extradural posterior fossa cyst, the theory of ectodermal-endodermal adhesions seems more plausible. Posterior

FIGURE 4. Schematic diagrams showing the possible embryogenesis of posterior fossa endodermal cysts. A, cross section of the embryo at third week of gestation, showing the split notochord with the endoderm elements displaced between the developing neural folds. B, cross section of the embryo at fifth week of gestation, showing rhombencephalon with the fourth ventricle and the roof plate. The dotted line refers to the path of regression of the endodermal elements. The curved arrow represents the lateral development of the hindbrain and the blastemal cranium. The shaded numbered circles refer to the different locations of sequestered endodermal remnants, which would give rise to the endodermal cysts at various locations, as shown in C. 1, prepontine; 2, intrapontine; 3, intrafourth ventricular; 4, cisterna magna; 5, lateral extradural; 6, intracerebellar; and 7, cerebellopontine cistern.


Extradural Posterior Fossa Endodermal Cyst fossa endodermal cysts probably represent a minor degree of aberration in the development of the cranial notochord during early gastrulation. Received, July 9, 1999. Accepted, May 10, 2000. Reprint requests: Roy Thomas Daniel, M.Ch., Department of Neurosurgery, Christian Medical College Hospital, Vellore 632004, India.

REFERENCES 1. Bejjani GK, Wright DC, Schessel D, Sekhar LN: Endodermal cysts of the posterior fossa: Report of three cases and review of the literature. J Neurosurg 89:326–335, 1998. 1a. Bentley JFR, Smith JR: Developmental posterior enteric remnants and spinal malformations: The split notochord syndrome. Arch Dis Child 35: 76–86, 1960. 2. Bremer JL: Dorsal intestinal fistula: Accessory neuroenteric canal—Diastematomyelia. Arch Pathol 54:132–138, 1952. 2a. Budde M: Die Bedeutung des Canalis Neurentericus fur die formale Genese de Rhachischisis anterior. Beitr Pathol Anat 92:91–129, 1912. 3. Burger PC, Scheithauer BW: Benign cystic lesions, in Tumors of the Central Nervous System, in Atlas of Tumor Pathology. Washington, DC, Armed Forces Institute of Pathology, 1994, 3rd series, pp 359–361, fascicle 10. 4. Deleted in proof. 5. Dodds GS: Anterior and posterior rhachischisis. Am J Pathol 17:861–872, 1941. 6. Eynon-Lewis NJ, Kitchen N, Scaravilli F, Brookes GB: Neurenteric cyst of the cerebellopontine angle: Case report. Neurosurgery 42: 655–658, 1998. 7. Harriman DGF: An intraspinal enterogenous cyst. J Pathol Bacteriol 75:413–419, 1958. 8. Harris CP, Dias MS, Brockmeyer DL, Townsend JJ, Willis BK, Apfelbaum RI: Neurenteric cysts of the posterior fossa: Recognition, management, and embryogenesis. Neurosurgery 29:893–898, 1991. 9. Deleted in proof. 10. Macdonald RL, Schwartz ML, Lewis AJ: Neurenteric cyst located dorsal to the cervical spine: Case report. Neurosurgery 28:583–588, 1991. 11. Mackenzie IR, Gilbert JJ: Cysts of the neuraxis of endodermal origin. J Neurol Neurosurg Psychiatry 54:572–575, 1991. 12. Rhaney K, Barclay GPT: Enterogenous cysts and congenital diverticula of the alimentary canal with abnormalities of the vertebral column and spinal cord. J Pathol 77:457–471, 1959. 13. Saunders RL: Combined anterior and posterior spina bifida in a living human female. Anat Rec 87:255–277, 1943. 14. Deleted in proof. 15. Deleted in proof. 16. Wilkins RH, Odom GL: Spinal intradural cysts, in Vinken PJ, Bruyn GW (eds): Tumors of the Spine and Spinal Cord: Part II—Handbook of Clinical Neurology. Amsterdam, North-Holland Publishing Co., 1976, vol 20, pp 55–102.

17. Williams PL, Warwick R, Dyson M, Bannister LH (eds): Gray’s Anatomy. Edinburgh, Churchill Livingstone, 1989, ed 37, pp 132–133, 161– 163.

COMMENTS In this interesting case report, Kulkarni et al. describe a rare dorsolateral, extradural location of an endodermal cyst. Endodermal cysts contain mucoid material within epithelium thought to originate from the endoderm. They are also known as neurenteric, enterogenous, respiratory, and bronchogenic cysts. Those in the posterior fossa usually lie intradural, ventral to the brainstem. Although most theories of the embryogenesis of endodermal cysts posit anomalies of notochord development as the cause of separation of endodermal cells from normal gut, they diverge regarding both the mechanism and the timing of this phenomenon. In embryogenic order, these theories include the following: 1) persistent fusion of endoderm and ectoderm interferes with the development of the notochord and produces an endodermal diverticula (4); 2) an abnormality of the notochord anlage prevents notochord fusion, which permits ingress by pluripotent precursors of the endoderm (5); 3) duplication of the notochord permits adherence of endoderm to ectoderm (1); 4) abnormal duplication of the neurenteric canal gives rise to displayed endodermal remnants (3). In general, the earlier in development the notochordal anomaly appears, the more profound the eventual anomaly, which can range from severe osseous and neural schisms to hemicords to small neurenteric cysts (3). The authors of this report argue persuasively that endodermal cysts can develop anywhere within the posterior fossa as fragments of endoderm are dispersed throughout the posterior hindbrain during its development (see Fig. 4 in the article). Awareness of the various possible locations of these cysts should aid in the differential diagnosis of posterior fossa lesions and may help guide the choice of surgical approach (2).

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1. Beardmore H, Wiglesworth H: Vertebral anomalies and alimentary duplications, clinical and embryological aspects. Pediatr Clin North Am 5:457–473, 1958. 2. Bejjani JK, Wright DC, Schessel D, Sekhar LN: Endodermal cysts of the posterior fossa: Report of three cases and review of the literature. J Neurosurg 89:326–335, 1998. 3. Bremer JL: Dorsal intestinal fistula: Accessory neurenteric canal—Diastematomyelia. Arch Pathol 54:132–138, 1952. 4. Dias M, Walker M: The embryogenesis of complex dysraphic malformations: A disorder of gastrulation? J Pediatr Neurosurg 18:229–253, 1992. 5. Saunders RL: Combined anterior and posterior spina bifida in a living human female. Anat Rec 87:255–277, 1943.

There is a wide differential for intracranial cystic lesions. This article describes one of the more unusual of these cysts occurring in an unusual location. Endodermal cysts are rare lesions that are presumed to be derived from the endoderm of the developing gastrointestinal tract (enterogenous cyst) or, less commonly, the respiratory tract. In this case, the intestinal nature of the epithelium is demonstrated by the presence of cuboidal cells and goblet cells that are immunohistochemically positive for carcinoembryonic antigen. The unusual location of this tumor in an extradural, dorsolateral position in the posterior fossa is explained by the authors on the basis of migration of endodermal remnants along with the lateral extension of occipital plates of the blastemal cranium during the second month of gestation. David R. Hinton Neuropathologist Los Angeles, California Kulkarni et al. report a rare case of an extradural neurenteric cyst without demonstrable ventral origin. Usually, these lesions occur at the lower cervical and upper thoracic region, and their ventral origin is suggested by defects in the vertebral bodies. The lesions may be either intra- or extradural. The present case is exceptionally unusual in that it was found in the posterior fossa. Perhaps fine-cut computed tomography of the temporal bone might have noted a connection, but the authors’ interesting discussion points out, the embryogenesis of this lesion is not clear.

Griffith R. Harsh IV Stanford, California


Jack P. Rock Detroit, Michigan