Ependymoma

Primary extraneural ependymomas are rare tumors that arise in ectopic sites, including pulmonary, sacrococcygeal region, ovarian, and paraovarian tissues. Four such ependymomas reported in the literature involve the paraovarian tissues, including 2 broad ligament ependymomas. Here we describe a myxopapillary ependymoma of the broad ligament in a 22-year-old woman, which may be the first tumor of this type to be reported in this location. Cytology, histology, cytochemistry, immunohistochemistry, and flow cytometry ploidy analysis are studied and described. Identification of perivascular ependymal rosettes, ependymal canals, vimentin and glial fibrillary acidic protein immunoreactivity, cytochemical staining of blepharoplasts or terminal bars by phosphotungstic acid hematoxylin, and presence of multiple foci of myxoid degeneration among the ependymal rosettes characterized a myxopapillary ependymoma.

(Arch Pathol Lab Med. 2005;129:1338-1342)

Ependymomas, which account for up to 9% of primary central nervous system neoplasms and up to 70% of intramedullary neoplasms, most commonly arise from the ventricular system and only rarely metastasize or arise ectopically.1 Some reported sites where ependymomas have arisen include the mediastinum, lung, ovary, paraovarian tissues, and retrolumbar and sacrococcygeal subcutaneous and soft tissues.2,3 Only 4 cases of primary paraovarian ependymoma have been reported to date, including 1 from the uterosacral ligament,4 1 from the mesovariunV and 2 arising from the broad ligament.6 To our knowledge, we present the first reported case of a primary extraneural myxopapillary ependymoma of the broad ligament and the third reported case of an extramedullary ependymoma of the broad ligament. Cytologie, histologie, cytochemical, immunohistochemical, and DNA flow cytometric findings are studied and described.

REPORT OF A case

A 22-year-old, nulliparous, African American woman was found to have a left adnexal mass at the time of her first routine Papanicolaou test. She denied symptoms of pelvic pain, dyspareunia, or significant dysmenorrhee. Her history was significant only for chlamydia cervicitis, diagnosed 8 months previously. Treatment and negative test of cure had been documented, and the patient had never experienced symptoms consistent with pelvic inflammatory disease. Her Papanicolaou test revealed a lowgrade squamous intraepithelial lesion suggestive of human papillomavirus, with subsequent biopsy confirmation. The endocervical curettage was negative for dysplasia. Pelvic ultrasound confirmed a 6-cm, cystic, left adnexal mass containing echogenic debris and nonshadowing solid foci (Figure 1). The mass was immediately adjacent to a normal-appearing left ovary with evidence of a fat plane separating the 2 structures. A portion of the wall of the cystic mass was shared by the bladder anteriorly and was thinned, suggesting that the 2 structures were focally contiguous (Figure 1). The uterus and right ovary appeared normal. Results of laboratory studies, including complete blood count and chemistries, were unremarkable. The ovarian tumor marker, CA 125, was normal at 10.4 U/mL (reference range, 0-35 U/mL), and testing for human chorionic gonadotropin was negative. Based on these clinical findings, a differential diagnosis of hydrosalpinx, tubo-ovarian abscess, endometrioma, and neoplasm was considered, and a consultation to obtain a tissue diagnosis was pursued. The patient was taken to the operating room for laparoscopic evaluation and resection of the mass. Operative findings revealed a mass within the left broad ligament, predominantly anterior to the uterus and crossing the midline. The anterior leaf of the broad ligament was distorted by the mass, which was densely attached to the left dome of the bladder without a clear plane of dissection, confirming the ultrasound suggestion that the mass and bladder shared a "common wall." The mass was excised intact, including the shared common wall. The uterus, ovaries, fallopian tubes, appendix, and upper abdomen were all uninvolved by the tumor. Intraoperative frozen section con- ' sultation reported the mass to be a "stromal proliferation with neural like features" with a differential diagnosis including a "granulosa cell tumor, a degenerative fibroma or a degenerative ependymal tumor." The patient's postoperative course was uncomplicated. Follow-up radiographie surveillance with computed tomography and magnetic resonance imaging at 18 months did not disclose new masses or metastatic disease.

MATERIALS AND METHODS

The surgical specimen was submitted for intraoperative frozen section consultation and cytologie examination using rapid hematoxylin-eosin and Diff-Quick stains. The specimen was subsequently fixed in 10% buffered formalin, processed routinely, and embedded in paraffin for pathologic examination. Four-micrometer-thick sections were cut from the paraffin blocks and stained with hematoxylin-eosin for morphologic analysis. Selective paraffin blocks were immunohistochemically stained using the standard avidin-biotin-peroxidase method7 with primary antibodies against vimentin (monoclonal, 1:50; Biocare Medical, Walnut Creek, Calif), glial fibrillary acidic protein (GFAP; polyclonal, 1:1000; BioGenex, San Ramon, Calif), epithelial membrane antigen (monoclonal, 1:1600; DakoCytomation, Carpinteria, Calif), low- and high-molecular-weight cytokeratins (Kermix cocktail: 1:400; monoclonal CKl [DakoCytomation] and monoclonal AEl/AE3 [Cell Marque Corporation, hot Springs, Ark]), and CAM 5.2 (monoclonal, 1:50; Becton Dickinson, Franklin Lakes, NJ). Special cytochemical staining with phosphotungstic acid hematoxylin was also performed on selective paraffin blocks.

Ploidy analysis of DNA content was performed by using flow cytometric methods on a paraffin-embedded tissue blocks using the technique described by Dressier and Bartow.8 Briefly, a 50µm-thick section of tumor was deparaffinized in xylene, dehydrated in a series of graded alcohols, fragmented, and then trypsinized. The final suspension of nuclear material was subsequently stained with propidium iodide (excitation wavelength, 488 nm). The analysis was performed with a Coulter XL-MCL flow cytometer (Coulter Corporation, Miami, FIa).

PATHOLOGIC FINDINGS

Gross Findings

The surgical specimen, labeled "left broad ligament mass," was a 7.0 × 6.5 × 6.0-cm, smooth-surfaced, redto-tan, thin-walled cystic mass that was focaUy affixed to a portion of the bladder wall. Two raised circular nodules on the outer wall surface, measuring 1.0 cm and 0.3 cm in greatest dimension, that represented the 2 thickest areas of the cyst wall were sampled for frozen section intraoperative consultation. On incision, the inner cystic cavity was filled with serosanguineous fluid and the inner wall had a predominantly smooth lining.

Cytologie Findings

Cytologie preparations contained a predominantly monomorphous population of tumor cells with moderate eosinophilic cytoplasm with fine, elongated cytoplasmic processes (Figure 2). The nuclei were round to oval with finely speckled chromatin. Other nuclei were coarsely granular with small nucleoli or chromocenters. Mitotic figures were inconspicuous. Tumor cells were often found to be arranged around numerous, fine capillary vessels, which were either closely juxtaposed or loosely attached (Figure 3). Focal collections of mucinous material were also identified.

Histologic Findings

The large cystic cavity of the mass was lined by flat cuboidal to tall columnar cells with areas containing delicate pseudopapillary structures composed of relatively monomorphic small tumor cells radially arranged around small blood vessels (Figure 4). The oval to round tumor cell nuclei were separated equidistantly away from a central blood vessel by their tapering fibrillary eosinophilic cytoplasmic processes, which extended to the center to form perivascular pseudorosettes most typical of those seen in ependymal tumors (Figure 4, inset). The nuclei were pale to mildly hyperchromatic and contained finely to coarsely granular chromatin with inconspicuous to small distinct nucleoli or chromocenters. The cyst wall also disclosed classic ependymal perivascular pseudorosettes in cross section (Figure 5, a) and along the longitudinal aspect (Figure 5, b). Multifocal regions had perivascular ependymal rosette and canal formation, these structures being seen predominantly within myxoid (mucicarmine-reactive) and cystic regions characteristic of a myxopapillary ependymoma (Figure 6). Myxopapillary features, which included intercellular mucin deposition, microcysts containing mucin, and epithelial tumor cells surrounding small to large pools of mucin (Figure 6), were seen in multiple foci. A portion of the cystic mass showed benign bladder smooth muscle and serosa focally adhered to the outer cyst wall. Histologically, the fibrous cyst wall blended into the smooth muscle, but tumor cells did not involve the smooth muscle. Abundant lipid-laden and hemosiderin-laden histiocytes were found throughout the full thickness of the cyst wall as single cells or large collections of cells. Plasma cells were also identified. No evidence of teratomatous or other neuroectodermal elements or differentiation was identified. Necrosis, pronounced cytologie atypia, and mitotic figures were all absent.

Cytochemical Staining

Apical and luminal portions of the ependymal rosettes and canals were reactive to phosphotungstic acid hematoxylin staining, highlighting the terminal bars or anchoring basal bodies (blepharoplasts) of cilia lining these true ependymal structures (Figure 7), indicating differentiation toward cells that line the ventricular system of the brain.

lmmunohistochemical Staining

Individual ependymoma tumor cells and those in ependymal structures (ependymal canals and ependymal rosettes or "perivascular pseudorosettes") were vimentin and GFAP immunoreactive (Figure 8, a and b, respectively). Vimentin staining was diffuse and more prominent compared to GFAP staining, which was focal and occasionally weak. Staining for Kermix and epithelial membrane antigen was focally positive in the tumor cells and more prominent in ependymal cells lining the inner cystic cavity and pseudopapillary structures.

DNA Ploidy Analysis by Flow Cytometry

Measurements of ploidy status (nuclear DNA content) and proliferative capacity (S-phase fraction) of 30 000 cells were obtained by using the technique of flow cytometry. The tumor cells showed a normal diploid amount of DNA with an index of 1.0 and an S-phase fraction of 0.3% with a coefficient of variation of 4.3%.

COMMENT

Since the first report of an extramedullary ependymoma was described within the subcutaneous tissue overlying the coccyx in 1902, numerous subsequent reports have been published, including more than 50 sacrococcygeal cases,9 8 ovarian cases,10 4 paraovarian cases," and a few rare cases from other distant sites. Ependymomas are central nervous system tumors that infrequently disseminate via cerebrospinal fluid spread and very infrequently metastasize to such places as the spinal cord, lung, and bone.3 Myxopapillary ependymomas most frequently arise within the cauda equina, conus medullaris, or filum terminale and may rarely be seen as an extradural growth in the sacrococcygeal, presacral, or postsacral soft tissues.12 Primary extraneural (external to the central nervous system) ependymomas distant from the neuraxis, however, are truly exceptional. The present case, on our review, is only the third reported case of a primary broad ligament ependymoma, and to our knowledge, the first reported case of a primary extraneural myxopapillary ependymoma of the broad ligament.

Many hypotheses on the histogenesis of extramedullary ependymomas have been proposed. However, the exact origin cannot be determined for certain. The most cogent theory that supports the occasional finding of subcutaneous islands of ependyma in the postcoccygeal region in infants is that these lesions originate from extramedullary ependymal rests. These rests represent remnants of the extradural filum terminale or coccygeal medullary vestige (a derivative of the caudal neural tube persisting beneath the skin of the postanal pit as an ependyma-lined cleft).1 Pelvic ependymomas appear to occur only in females; however, these ependymal islands are not known to be associated developmentally with female pelvic structures. One possible exception is the rare finding of ependymallike structures in mature cystic teratomas of the ovary.10 Other suggestions of origin include ectopic glial tissue from retained fetal products of conception or neuroectodermal tissue that has undergone neometaplasia from peritoneal mesenchymal tissue.4,5

Our case was completely separate from the left ovarysurgically, pathologically, and radiologically. However, the cystic mass shared a common wall with the anterior bladder. The significance of this finding is unclear. Embryologically, the tissues that give rise to the developing mesonephros and its genitourinary derivatives are a considerable developmental distance away from the neural tube elements that give rise to ependyma. The closest juxtaposition of the 2 elements developmentally would be the distance between the urogenital ridge and the notochord and neural tube. At the 8-week developmental stage of the human embryo, a mesonephric transverse fold of tissue (future broad ligament) containing the paramesonephric ducts fuse at the midline with the anterior bladder wall and form a portion of the vagina and uterus. Thus, an ependymal rest trapped in the developing mesonephros could potentially migrate with the tissues of the incipient broad ligament and fuse with the anterior bladder wall. This ependymal rest could then give rise to a primary ependymoma located within the broad ligament and have a close association with the bladder wall, as was observed in the present case.

The findings of (mucicarmine-staining) intercellular mucin, mucinous microcysts, ependymal rosettes, epithelial tumor cell rosettes surrounding small to large pools of mucin, and ependymal canals were characteristic of myxopapillary ependymoma. The diagnosis of an ependymal neoplasm in our case was confirmed by cytoplasmic staining with GFAP, indicating the glial nature of the neoplasm, and positive phosphotungstic acid hematoxylin staining of blepharoplasts (anchoring basal bodies) outlining ependymal rosettes and canals, indicating differentiation toward ventricle-lining epithelium containing cilia.

Aneuploidy and DNA content analysis is being investigated in a variety of neoplasms to potentially serve as a prognostic indicator. One study has shown a significantly increased disease-free survival in patients with central nervous system ependymomas that show aneuploidy." In a case of primary ependymoma of the lung, the tumor showed DNA aneuploidy." Our current primary broad ligament case was diploid.

Extramedullary ependymomas, overall, are predominantly neoplasms of low malignant potential, but have been shown to recur as well as metastasize. Of 8 patients with primary ovarian ependymomas described in the literature, only 1 is known to have died of disease.1" Three of the 4 patients with primary paraovarian ependymomas, including 2 from the broad ligament, either had recurrence of disease or showed bladder or peritoneal metastases, yet all patients were alive with no evidence of dis ease after 18 to 24 months of follow-up.4 Many of these patients received either adjuvant chemotherapy or radiation therapy. Kline et aP reported that extradural myxopapillary ependymomas from the sacrococcygeal region behave more aggressively and tend to have a higher rate of metastasis than typical intradural ependymomas arising from the cauda equina. Our case showed no evidence of recurrence or metastatic disease 18 months postoperatively. Because of its rarity, it is not known how the present case of a primary broad ligament myxopapillary ependymoma will behave in the long term compared to both intradural and sacrococcygeal counterparts.

References

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2. Namiki H, Hardman JM, Yang H-Y. Ependymal tumors. In: Silvcrberg SG, DeLellis RA, Frable WJ, eds. Principles and Practice of Surgical Pathology and Cytopathology. 3rd ed. New York, NY: Churchill Livingstone; 1997:2956-2961.

3. Burger PC, Scheithauer BW. Tumors of the Central Nervous System. Washington, DC: Armed Forces Institute of Pathology; 1994. Atlas of Tumor Pathology, 3rd series, fascicle 10.

4. Duggan MA, Hugh J, Nation JG, Robertson Dl, Stuart GC. Ependymoma of the uterosacral ligament. Cancer. 1989;64:2565-2571.

5. Grody WW, Nieberg RK, Bhuta S. Ependymoma-like tumor of the mesovarium. Arch Pathol Lab Med. 1985;109:291-293.

6. Bell DA, Woodruff JM, Scully RE. Ependymoma of the broad ligament: a report of two cases. Am 1 Surg Pathol. 1984;8:203-209.

7. Giorno R. A comparison of two immunoperoxidase staining methods based on the avidin-biotin interaction. Diagn lmmunol. 1984;2:161-166.

8. Dressier LG, Bartow SA. DNA flow cytometry in solid tumors: practical aspects and clinical applications. Semin Diagn Pathol. 1989;6:55-82.

9. Kline MJ, Kays DW, Rojiani AM. Extradural myxopapillary ependymoma: report of two cases and review of the literature. Fed Pathol Lab Med. 1996;16:813-822.

10. Garda-Barriola V, Naranjo de Gomcz M, Suarez JA, Lara C, Gonzalez JE, Garcia-Tamayo ). Ovarian ependymoma: a case report. Pathol Res Pract. 2000; 196:595-599.

11. Guerrieri C, Jarlstelt I. Ependymoma of the ovary: a case report with immunohistochemical, ultrastructural, and DNA cytometric findings, as well as histogenetic considerations. Am I Surg Pathol. 1993;17:623-632.

12. Rosenbioom MK. Ependymal tumors: a review of their diagnostic surgical pathology. Pediatr Neurosurg. 1998:28:160-165.

Darren E. Whittemore, DO; Robert E. Crondahl, MD; Kondi Wong, MD

Accepted for publication June 16, 2005.

From the Departments of Pathology (Drs Whittemore and Wong) and Obstetrics/Cynecology (Dr Grondahl), Wilford Hall Medical Center, Lackland Air Force Base, Tex.

The authors have no relevant financial interest in the products or companies described in this article.

Corresponding author: Darren Whittemore, DO, Department of Pathology, Wilford Hall Medical Center, 2200 Bergquist Dr, Suite 1, Lackland Air Force Base, TX 78236 (e-mail: whittemore@bluebirdcom.net).

Reprints not available from the authors.

Copyright College of American Pathologists Oct 2005
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