DOI: 10.1148/rg.226025118
(Radiographics. 2002;22:1473-1505.)
© RSNA, 2002
From the Archives of the AFIP
Cerebral Intraventricular Neoplasms: Radiologic-Pathologic Correlation1
Kelly K. Koeller, CAPT, MC, USN and
Glenn D. Sandberg, LTC, MC, USA
1 From the Departments of Radiologic Pathology (K.K.K.) and Neuropathology (G.D.S.), Armed Forces Institute of Pathology, 14th St at Alaska Ave, Bldg 54, Room M-121, Washington, DC 20306-6000; and the Departments of Radiology and Nuclear Medicine, Uniformed Services University of the Health Sciences, Bethesda, Md (K.K.K.). Received July 3, 2002; revision requested July 15 and received August 6; accepted August 20. Address correspondence to K.K.K. (e-mail: koeller@afip.osd.mil).
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Abstract
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Intraventricular neoplasms are readily seen on cross-sectional images, but the myriad possibilities may make a focused differential diagnosis elusive. Consideration of the tissue within and composing the ventricular lining and the clinical findings provide the means to limit the differential diagnosis when analyzing an intraventricular mass on an imaging study. Ependymomas are typically calcified, are more common in children, are more common in the fourth ventricle, and show intense enhancement on contrast-enhanced images. Subependymomas and central neurocytomas have an affinity for the anterior portion of the lateral ventricle, and both commonly demonstrate a heterogeneous cystic appearance on cross-sectional images. Subependymomas are more common in older adults, whereas central neurocytomas are more common before 40 years of age. Subependymal giant cell astrocytomas always lie near the foramen of Monro and are characterized by frequent calcification, intense enhancement on contrast-enhanced studies, and the presence of other stigmata seen in tuberous sclerosis. When a mass is centered on the choroid plexus, a highly vascular tumor—either choroid plexus papilloma, choroid plexus carcinoma, meningioma, or metastasis—should be suspected. The characteristic heavily lobulated appearance of a choroid plexus tumor favors this diagnosis over other possibilities, although it is not always possible to distinguish between the more common benign form, the choroid plexus papilloma, and the less common malignant counterpart, the choroid plexus carcinoma. By using clinical, demographic, and imaging findings, one can significantly limit the differential diagnosis for many of the most common intraventricular neoplasms.
Index Terms: Astrocytoma, 1612.1832, 1612.3639 • Brain neoplasms, 16.36, 161.38 • Choroid plexus, neoplasms, 1617.3639 • Ependymoma, 161.3636, 164.3636 • Meninges, neoplasms, 161.366 • Neurocytoma, 161.369
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LEARNING OBJECTIVES FOR TEST 6
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After reading this article and taking the test, the reader will be able to:
- Describe the distinguishing imaging features of common cerebral intraventricular neoplasms.
- Identify the characteristic imaging appearances of the different types of intraventricular tumors that allow a specific diagnosis to be favored.
- Discuss the direct correlation of the imaging appearance with the gross pathologic appearance in cerebral intraventricular neoplasms.
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Introduction
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Neoplasms that arise within the cerebral ventricular system are especially conspicuous on cross-sectional images, in part because of the great contrast between these soft-tissue masses and the surrounding cerebrospinal fluid (CSF). Although they are relatively easy to visualize, it is more difficult to narrow the differential diagnosis for a lesion in this location without knowledge of the tissue types that give rise to these tumors. In this article, eight of the more common lesions to arise in this area of the brain are reviewed, by using case material from the Thompson Archives of the Department of Radiologic Pathology at the Armed Forces Institute of Pathology and with the tissue of origin used as a guide.
The ventricles are surrounded by a lining of ependymal cells and a subependymal plate composed of glial cells. Accordingly, these layers give rise to ependymomas, subependymomas, and subependymal giant cell astrocytomas (SEGAs). This lining and the septum pellucidum, a glial-lined structure, also give rise to a glial neuronal tumor, the central neurocytoma that is unique to the ventricular system. Central neurocytoma is a recently described tumor that, until its confirmation with electron microscopy, was frequently mistaken for an intraventricular oligodendroglioma with light microscopy. A central neurocytoma has a striking resemblance to a subependymoma on radiologic images. The central neurocytoma and SEGA predominate in the anterior portion of the lateral ventricle near the foramen of Monro, whereas the ependymoma and subependymoma are usually found in either the fourth or lateral ventricles. The choroid plexus is the most highly vascular portion of the ventricular system and produces CSF. Neoplasms from this tissue are highly vascular and commonly associated with hydrocephalus. They occur in a benign form, the choroid plexus papilloma, and less commonly, in a malignant counterpart, the choroid plexus carcinoma. Tumors, such as meningioma and metastatic disease, that are commonly associated with a generous vascular supply also arise from this site. Since the choroid plexus is most prominent in the atria, these masses are most commonly noted in the posterior portion of the lateral ventricles. Salient demographic and imaging features of these eight tumor types are listed in the Table.
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Neoplasms of the Ventricular Wall and Septum Pellucidum
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Ependymoma
Ependymomas are common neoplasms that arise from differentiated ependymal cells that line the cerebral ventricles and the central canal of the spinal cord (1). They constitute 3%–9% of all neuroepithelial neoplasms, 6%–12% of all pediatric brain tumors, and almost one-third of all brain tumors in patients younger than 3 years (1).
Ependymomas may manifest at any age, with a documented age range of 1 month to 81 years (1). There is no gender predilection (1). Most posterior fossa ependymomas arise in children, with a mean age of about 6 years (1). The mean age at presentation is higher for patients who have a supratentorial ependymoma (18–24 years) (2). Of those ependymomas that occur intraventricularly, 58% originate in the fourth ventricle, whereas the remaining 42% are located in the lateral and third ventricles (3). Supratentorial ependymomas are more commonly extraventricular, especially in children (1,2). It is speculated that ependymomas may arise from embryonic rests of ependymal tissue trapped within the developing cerebral hemispheres (1). Bizarre sites reported for ependymomas include the ovaries, soft tissues, mediastinum, and sacrococcygeal region (4).
As with other intraventricular masses, clinical signs and symptoms are largely secondary to the effects of increased intracranial pressure and hydrocephalus (1). Because the fourth ventricle is a predominant site for these tumors, some patients may present with cerebellar ataxia and paresis (1,5). Patients with supratentorial ependymomas tend to present with focal neurologic deficits and seizures (1). In general, children with ependymomas have a less favorable prognosis than adults, in part from the increased prevalence of a fourth ventricle location and the predilection of this group for more anaplastic forms of the disease (1).
The 5-year progression-free rate for children overall is about 50% (6), with children younger than 2 years having an especially poor prognosis (7). The 5-year and 10-year survival rates for adults are 57.1% and 45%, respectively (1). The treatment of choice is gross total resection, and the degree of resection directly correlates with a better prognosis (8). Patients with supratentorial ependymomas have a better survival rate than those patients with posterior fossa ependymomas (9). For all types of ependymomas, recurrence is common (2,10). Postoperative radiation therapy is advocated for partially resected ependymomas (10).
Intraventricular ependymomas are well-circumscribed, grayish-red masses that usually fill the ventricular lumen and occasionally may extend into the adjacent brain parenchyma (Fig 1) (1). When they arise in the fourth ventricle, these soft pliable tumors originate from the floor or roof of the ventricle and frequently extend through the foramen of Luschka into the cerebellopontine angle and even the foramen magnum (Fig 2) (1).
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Figure 1. Ependymoma. Photograph of an autopsy specimen sectioned through the level of the fourth ventricle shows a soft, friable heterogeneous mass (arrows) within the fourth ventricle. Scattered areas of hemorrhage are noted.
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Figure 2. Ependymoma. Photograph of a brain at autopsy shows extensive cerebellopontine angle extension (arrows) from a fourth ventricular ependymoma. Numerous areas of hemorrhage give the mass a heterogeneous appearance.
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At histologic analysis, ependymomas are moderately cellular tumors characterized by rare mitotic figures; perivascular pseudorosettes; and, less commonly, ependymal rosettes (Fig 3) (1). Accordingly, they are considered World Health Organization (WHO) grade II lesions (1). Several variant forms are also noted, based on histopathologic features, and include cellular ependymoma, papillary ependymoma, clear cell ependymoma, tanycytic ependymoma, and anaplastic ependymoma (WHO grade III) (1).
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Figure 3. Ependymoma. Photomicrograph (original magnification, x100; hematoxylin-eosin stain) of an ependymoma shows a moderately cellular matrix composed of glial cells with perivascular rosettes (arrowheads) and no mitotic figures.
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On nonenhanced computed tomographic (CT) images, intraventricular ependymomas are usually isoattenuated, partially calcified masses (11). The soft-tissue component shows intense enhancement on contrast material–enhanced images (11). The soft-tissue portion of the tumor is usually hypoattenuated to isoattenuated on nonenhanced CT images (12). Occasionally, intratumoral hemorrhage may produce a blood-fluid level (2). Calcification, ranging from small punctate foci to large masses, is common (40%–80% of cases) (Fig 4) (2,11). Contrast enhancement is variable but usually intense within the soft-tissue portions, although it spares the cystlike regions (2,11). In contrast to most posterior fossa ependymomas, supratentorial ependymomas are usually located in the cerebral parenchyma and frequently have a cystic appearance on cross-sectional images (2,11,13).
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Figure 4a. Ependymoma in a 16-month-old child. (a) Axial CT image shows a fourth ventricular mass that is slightly hyperattenuated compared with the surrounding cerebellum. Focal calcification (arrow) is noted. (b) Axial T1-weighted magnetic resonance (MR) image shows the mildly heterogeneous mass, which is slightly hypointense compared with the cerebellum. (c) On an axial T2-weighted image, the mass is hyperintense compared with the cerebellum, with no surrounding vasogenic edema. (d) On a contrast-enhanced axial T1-weighted image, the mass shows intense heterogeneous enhancement.
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Figure 4b. Ependymoma in a 16-month-old child. (a) Axial CT image shows a fourth ventricular mass that is slightly hyperattenuated compared with the surrounding cerebellum. Focal calcification (arrow) is noted. (b) Axial T1-weighted magnetic resonance (MR) image shows the mildly heterogeneous mass, which is slightly hypointense compared with the cerebellum. (c) On an axial T2-weighted image, the mass is hyperintense compared with the cerebellum, with no surrounding vasogenic edema. (d) On a contrast-enhanced axial T1-weighted image, the mass shows intense heterogeneous enhancement.
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Figure 4c. Ependymoma in a 16-month-old child. (a) Axial CT image shows a fourth ventricular mass that is slightly hyperattenuated compared with the surrounding cerebellum. Focal calcification (arrow) is noted. (b) Axial T1-weighted magnetic resonance (MR) image shows the mildly heterogeneous mass, which is slightly hypointense compared with the cerebellum. (c) On an axial T2-weighted image, the mass is hyperintense compared with the cerebellum, with no surrounding vasogenic edema. (d) On a contrast-enhanced axial T1-weighted image, the mass shows intense heterogeneous enhancement.
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Figure 4d. Ependymoma in a 16-month-old child. (a) Axial CT image shows a fourth ventricular mass that is slightly hyperattenuated compared with the surrounding cerebellum. Focal calcification (arrow) is noted. (b) Axial T1-weighted magnetic resonance (MR) image shows the mildly heterogeneous mass, which is slightly hypointense compared with the cerebellum. (c) On an axial T2-weighted image, the mass is hyperintense compared with the cerebellum, with no surrounding vasogenic edema. (d) On a contrast-enhanced axial T1-weighted image, the mass shows intense heterogeneous enhancement.
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On MR images, intraventricular ependymomas typically show isointensity compared with gray matter with short repetition time (TR) pulse sequences and hyperintensity compared with gray matter with long TR pulse sequences. A heterogeneous appearance is typical, reflecting the calcification, hemorrhage, and cystic changes that are often present (Figs 4–6). As seen on CT images, there is variable contrast enhancement (2). Supratentorial ependymomas typically show nonspecific hypointensity to isointensity with short TR pulse sequences and hyperintensity with long TR pulse sequences (2).
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Figure 5a. Malignant ependymoma in a 58-year-old woman with a history of ductal carcinoma and renal cell carcinoma. (a) Axial CT image shows a heterogeneously hypoattenuated mass (arrows) adjacent to the right frontal horn of the lateral ventricle. (b) Axial T1-weighted MR image shows the heterogeneous mass, with cystlike areas mixed with more hyperintense regions. (c) On an axial T2-weighted MR image, the mass is predominantly hyperintense with focal regions of more hypointense signal. (d) On a contrast-enhanced axial T1-weighted MR image, the mass shows intense but heterogeneous enhancement. At surgery, the mass involved both the lateral ventricle and the right frontal lobe. Histologic examination revealed ependymoma.
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Figure 5b. Malignant ependymoma in a 58-year-old woman with a history of ductal carcinoma and renal cell carcinoma. (a) Axial CT image shows a heterogeneously hypoattenuated mass (arrows) adjacent to the right frontal horn of the lateral ventricle. (b) Axial T1-weighted MR image shows the heterogeneous mass, with cystlike areas mixed with more hyperintense regions. (c) On an axial T2-weighted MR image, the mass is predominantly hyperintense with focal regions of more hypointense signal. (d) On a contrast-enhanced axial T1-weighted MR image, the mass shows intense but heterogeneous enhancement. At surgery, the mass involved both the lateral ventricle and the right frontal lobe. Histologic examination revealed ependymoma.
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Figure 5c. Malignant ependymoma in a 58-year-old woman with a history of ductal carcinoma and renal cell carcinoma. (a) Axial CT image shows a heterogeneously hypoattenuated mass (arrows) adjacent to the right frontal horn of the lateral ventricle. (b) Axial T1-weighted MR image shows the heterogeneous mass, with cystlike areas mixed with more hyperintense regions. (c) On an axial T2-weighted MR image, the mass is predominantly hyperintense with focal regions of more hypointense signal. (d) On a contrast-enhanced axial T1-weighted MR image, the mass shows intense but heterogeneous enhancement. At surgery, the mass involved both the lateral ventricle and the right frontal lobe. Histologic examination revealed ependymoma.
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Figure 5d. Malignant ependymoma in a 58-year-old woman with a history of ductal carcinoma and renal cell carcinoma. (a) Axial CT image shows a heterogeneously hypoattenuated mass (arrows) adjacent to the right frontal horn of the lateral ventricle. (b) Axial T1-weighted MR image shows the heterogeneous mass, with cystlike areas mixed with more hyperintense regions. (c) On an axial T2-weighted MR image, the mass is predominantly hyperintense with focal regions of more hypointense signal. (d) On a contrast-enhanced axial T1-weighted MR image, the mass shows intense but heterogeneous enhancement. At surgery, the mass involved both the lateral ventricle and the right frontal lobe. Histologic examination revealed ependymoma.
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Figure 6a. Ependymoma in a 29-year-old adult. (a) Sagittal T1-weighted MR image shows an isointense fourth ventricular mass (arrows) with inferior extension through the foramen magnum. (b) On an axial T2-weighted MR image, the mass is mildly hyperintense compared with the cerebellum and extends through the right foramen of Luschka into the cerebellopontine angle. (c) On a contrast-enhanced axial T1-weighted MR image, the mass shows intense but heterogeneous enhancement.
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Figure 6b. Ependymoma in a 29-year-old adult. (a) Sagittal T1-weighted MR image shows an isointense fourth ventricular mass (arrows) with inferior extension through the foramen magnum. (b) On an axial T2-weighted MR image, the mass is mildly hyperintense compared with the cerebellum and extends through the right foramen of Luschka into the cerebellopontine angle. (c) On a contrast-enhanced axial T1-weighted MR image, the mass shows intense but heterogeneous enhancement.
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Figure 6c. Ependymoma in a 29-year-old adult. (a) Sagittal T1-weighted MR image shows an isointense fourth ventricular mass (arrows) with inferior extension through the foramen magnum. (b) On an axial T2-weighted MR image, the mass is mildly hyperintense compared with the cerebellum and extends through the right foramen of Luschka into the cerebellopontine angle. (c) On a contrast-enhanced axial T1-weighted MR image, the mass shows intense but heterogeneous enhancement.
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MR imaging is considered the modality of choice to evaluate these lesions, although CT is superior in the detection of calcification (2). Postoperative imaging is considered crucial in documenting the presence of postoperative residual disease, which has a substantial negative impact on survival rates in patients with this tumor (14).
Subependymoma
In 1945, Scheinker (15) described seven cases of brain tumors arising from the subependymal glial layer surrounding the cerebral ventricles. These tumors were characterized by expansive growth and lacked an infiltrative pattern at histologic examination. Since that time, more than 100 similar cases have been reported in the literature. With the exception of a very small number of cases that occurred in the brain parenchyma, cerebellopontine angle, and spinal cord, the overwhelming majority of these tumors have occurred within the fourth and lateral ventricles (2,5,15–25). The true incidence of subependymomas is difficult to ascertain because many of the cases occurred in asymptomatic patients and were detected only incidentally at autopsy. In a review of 1,000 serial necropsies in asymptomatic patients, Matsumura at al (17) reported the prevalence as 0.4%, compared with a prevalence of 0.7% in 1,000 consecutive craniotomies performed in symptomatic patients. Despite four case reports of subependymomas occurring in siblings, including one set of identical twins, no genetic susceptibility for the tumor has been proved (19,21,26).
Most subependymomas are smaller than 2 cm in diameter (26). However, symptomatic subependymomas are usually larger, averaging about 3–5 cm in greatest dimension (5,22). Symptoms most commonly depend on the location and size of the tumor, with intratumoral hemorrhage being another possible influence (5). The clinical presentation is nonspecific. Most symptomatic patients (80%) present with symptoms related to hydrocephalus as a consequence of ventricular obstruction (16,26). Less commonly, focal neurologic deficits (27% of cases), seizures (9%), and subarachnoid hemorrhage (4.5%) have been reported (16).
Males are more commonly affected, and most reported cases (82%) have occurred in patients older than 15 years (16,26). At least half of the reported cases have occurred in the fourth ventricle, with most of the remainder arising in the lateral ventricle (2,5,15–26). In rare cases, subependymomas have been recorded arising from the septum pellucidum, the third ventricle, and in the cervical or cervicothoracic spinal cord (16, 23). Gross total surgical resection is the goal of therapy (16). Even if only partial resection is achieved, postoperative radiation therapy or chemotherapy is usually not indicated. Recurrence after surgical resection is rare (2,22).
Subependymomas have a white to grayish color and are well circumscribed with a firm texture (16). The tumors grow in a slow deliberate fashion, are usually avascular, and are attached to the ventricular wall by a narrow pedicle (16). Although the exact histogenesis is still uncertain, they most likely arise from subependymal glial cells (26). Other possible sites include astrocytes from the subependymal plate, ependymal cells, and a mixture of ependymal and astrocytic cells (26).
A dense fibrillary matrix interrupted by numerous small cysts and nests of isomorphic nuclei that resemble subependymal glia is typically seen at histologic examination (Fig 7) (26). Mitotic activity is usually low or absent; thus, subependymomas correspond histologically to WHO grade I (26). Although most tumors are pure subependymomas, about 10% may manifest as an admixture with an ependymoma (5,16,26). In addition, other reported combinations include those with melanin, rhabdomyosarcoma, and sarcomatous transformation of vascular stromal elements (26). The prognosis of a patient with an intraventricular subependymoma is good, with gross surgical resection being curative (26). A good clinical outcome is less certain when the tumor is mixed with an ependymoma (5).
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Figure 7. Subependymoma. Photomicrograph (original magnification, x40; hematoxylin-eosin stain) of a subependymoma shows scattered clusters of nuclei (arrowheads) separated by large, acellular regions of glial processes.
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The typical CT appearance of a subependymoma is a well-circumscribed, lobulated intraventricular mass that is predominantly isoattenuated to slightly hypoattenuated compared with the brain parenchyma (Fig 8) (16,22). Hydrocephalus is present in 85% of cases (16). When hemorrhage is present, the mass may show hyperattenuation compared with the brain parenchyma (17,18). Most (84%) show at least some enhancement, more likely focal in nature, on contrast-enhanced images (16). Calcification (31.8% of cases) and cystic degeneration (18%) are common (16,22). Dense calcification is not common (2,16,23). Occasionally, subependymomas may produce peritumoral edema on cross-sectional images (2,16). Although most are avascular, some may have a blush on angiographic studies from discrete tumor vascularization (17).
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Figure 8a. Subependymoma in a 53-year-old man. (a) Axial CT image shows a right frontal horn mass that is predominantly isoattenuated compared with the brain parenchyma. Curvilinear calcification (arrow) is seen. (b) Axial T1-weighted MR image shows isointensity within the mass, compared with the white matter. (c) Axial T2-weighted MR image shows heterogeneous hyperintensity within the mass and no evidence of periventricular edema. (d) Contrast-enhanced axial T1-weighted MR image shows scattered heterogeneous enhancement within the mass.
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Figure 8b. Subependymoma in a 53-year-old man. (a) Axial CT image shows a right frontal horn mass that is predominantly isoattenuated compared with the brain parenchyma. Curvilinear calcification (arrow) is seen. (b) Axial T1-weighted MR image shows isointensity within the mass, compared with the white matter. (c) Axial T2-weighted MR image shows heterogeneous hyperintensity within the mass and no evidence of periventricular edema. (d) Contrast-enhanced axial T1-weighted MR image shows scattered heterogeneous enhancement within the mass.
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Figure 8c. Subependymoma in a 53-year-old man. (a) Axial CT image shows a right frontal horn mass that is predominantly isoattenuated compared with the brain parenchyma. Curvilinear calcification (arrow) is seen. (b) Axial T1-weighted MR image shows isointensity within the mass, compared with the white matter. (c) Axial T2-weighted MR image shows heterogeneous hyperintensity within the mass and no evidence of periventricular edema. (d) Contrast-enhanced axial T1-weighted MR image shows scattered heterogeneous enhancement within the mass.
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Figure 8d. Subependymoma in a 53-year-old man. (a) Axial CT image shows a right frontal horn mass that is predominantly isoattenuated compared with the brain parenchyma. Curvilinear calcification (arrow) is seen. (b) Axial T1-weighted MR image shows isointensity within the mass, compared with the white matter. (c) Axial T2-weighted MR image shows heterogeneous hyperintensity within the mass and no evidence of periventricular edema. (d) Contrast-enhanced axial T1-weighted MR image shows scattered heterogeneous enhancement within the mass.
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In attempting to differentiate subependymomas from ependymomas with imaging studies alone, Lobato et al (16) noted that subependymomas tend to be intraventricular, whereas ependymomas tend be paraventricular. They also reported that hyperattenuation compared with the brain parenchyma, enhancement, calcification, and cyst formation were also more commonly seen in ependymomas than in subependymomas (16). However, none of these features are sufficiently pronounced to be pathognomonic for either lesion. The distinctions between these tumors are even less apparent for those that arise in the fourth ventricle (16).
On MR images, subependymomas are generally hypointense compared with white matter with short TR pulse sequences and hyperintense compared with white matter with long TR pulse sequences (Figs 8 –10) (22–24). Heterogeneity is typical, with cystlike areas interspersed within the mass (22,24). When hemorrhage is present, characteristic signal intensity representative of hemoglobin by-products is noted (23). Enhancement is quite variable on contrast-enhanced images (22,23). They may not enhance, enhance minimally, or show intense enhancement after the intravenous administration of a contrast agent (24). Even when intense enhancement is seen, it is usually heterogeneous (2,24). Extension of a subependymoma beyond the ventricular margins is rare (23,27). These features may be helpful in distinguishing subependymomas from ependymomas, since the latter frequently have intense enhancement and extraventricular extension (24).
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Figure 9a. Subependymoma in a 70-year-old woman in whom breast carcinoma had been diagnosed 7 years before. A metastatic lesion to the chest wall had been found 4 months before she experienced a sudden onset of weakness and slurred speech that prompted neuroimaging. (a) Sagittal T1-weighted MR image shows a mass that is isointense compared with the white matter and that extends inferiorly. A sellar mass of unknown pathologic characteristics erodes the floor of the sella turcica. (b) Axial T2-weighted MR image shows a fourth ventricular mass (arrows) that is slightly hyperintense compared with the white matter. A metastasis was suspected. (c) Intraoperative photograph shows the well-circumscribed, firm, glistening mass (arrows) in the inferior portion of the fourth ventricle. Findings from histologic examination confirmed subependymoma, not metastatic disease.
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Figure 9b. Subependymoma in a 70-year-old woman in whom breast carcinoma had been diagnosed 7 years before. A metastatic lesion to the chest wall had been found 4 months before she experienced a sudden onset of weakness and slurred speech that prompted neuroimaging. (a) Sagittal T1-weighted MR image shows a mass that is isointense compared with the white matter and that extends inferiorly. A sellar mass of unknown pathologic characteristics erodes the floor of the sella turcica. (b) Axial T2-weighted MR image shows a fourth ventricular mass (arrows) that is slightly hyperintense compared with the white matter. A metastasis was suspected. (c) Intraoperative photograph shows the well-circumscribed, firm, glistening mass (arrows) in the inferior portion of the fourth ventricle. Findings from histologic examination confirmed subependymoma, not metastatic disease.
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Figure 9c. Subependymoma in a 70-year-old woman in whom breast carcinoma had been diagnosed 7 years before. A metastatic lesion to the chest wall had been found 4 months before she experienced a sudden onset of weakness and slurred speech that prompted neuroimaging. (a) Sagittal T1-weighted MR image shows a mass that is isointense compared with the white matter and that extends inferiorly. A sellar mass of unknown pathologic characteristics erodes the floor of the sella turcica. (b) Axial T2-weighted MR image shows a fourth ventricular mass (arrows) that is slightly hyperintense compared with the white matter. A metastasis was suspected. (c) Intraoperative photograph shows the well-circumscribed, firm, glistening mass (arrows) in the inferior portion of the fourth ventricle. Findings from histologic examination confirmed subependymoma, not metastatic disease.
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Figure 10a. Subependymoma in a 48-year-old man with a history of nausea for several months. Results from a prior abdominal CT study and endoscopy were negative. After developing new headaches, he presented again for evaluation. (a) Sagittal T1-weighted MR image shows a soft-tissue mass (arrows) in the inferior portion of the fourth ventricle with extension through the foramen magnum. Note dilatation of the remaining portions of the ventricular system as a result of the mass. (b) On an axial T2-weighted MR image, the mass appears heterogeneous, with cystic and soft-tissue components. Note absence of vasogenic edema. (c) Contrast-enhanced sagittal T1-weighted MR image shows intense heterogeneous enhancement of the mass.
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Figure 10b. Subependymoma in a 48-year-old man with a history of nausea for several months. Results from a prior abdominal CT study and endoscopy were negative. After developing new headaches, he presented again for evaluation. (a) Sagittal T1-weighted MR image shows a soft-tissue mass (arrows) in the inferior portion of the fourth ventricle with extension through the foramen magnum. Note dilatation of the remaining portions of the ventricular system as a result of the mass. (b) On an axial T2-weighted MR image, the mass appears heterogeneous, with cystic and soft-tissue components. Note absence of vasogenic edema. (c) Contrast-enhanced sagittal T1-weighted MR image shows intense heterogeneous enhancement of the mass.
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Figure 10c. Subependymoma in a 48-year-old man with a history of nausea for several months. Results from a prior abdominal CT study and endoscopy were negative. After developing new headaches, he presented again for evaluation. (a) Sagittal T1-weighted MR image shows a soft-tissue mass (arrows) in the inferior portion of the fourth ventricle with extension through the foramen magnum. Note dilatation of the remaining portions of the ventricular system as a result of the mass. (b) On an axial T2-weighted MR image, the mass appears heterogeneous, with cystic and soft-tissue components. Note absence of vasogenic edema. (c) Contrast-enhanced sagittal T1-weighted MR image shows intense heterogeneous enhancement of the mass.
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Central Neurocytoma
In 1982, Hassoun et al (28) described two cases of calcified intraventricular tumors in two young adult men who presented with progressive memory loss and benign clinical courses. Although histologic examination revealed neuronal differentiation and a striking resemblance to oligodendroglioma in one case and ependymoma in the other, electron microscopy showed features that clearly indicated that these tumors were unique (28). Since that time, more than 200 similar cases have been reported in the literature (29). The term central neurocytoma should be reserved for those neoplasms occurring only in the lateral and third ventricles. Lesions with similar histologic characteristics that are located outside these locations should be referred to as extraventricular central neurocytoma (29). There have been numerous reports of such tumors in the brain parenchyma, the cerebellum, and the spinal cord (30–34).
Central neurocytomas constitute approximately 0.25%–0.5% of all intracranial tumors (35). The mean age at presentation is 29 years, with a wide age range (8 days to 67 years) (29). Nearly half of all cases reported occur in the 3rd decade of life, and almost 75% of patients present between 20 and 40 years of age (29). There is no gender predilection (29). A relatively short clinical course (mean, 3 months) is typical, with the symptoms being related to increased intracranial pressure, mental status changes, visual deficits (secondary to papilledema), or hormonal changes (particularly for those lesions involving the third ventricle) (29,36,37). In rare cases, these tumors may be associated with sudden death secondary to acute ventricular obstruction (38). There is one case report of a central neurocytoma associated with gigantism, either from growth hormone– releasing factor within the tumor itself or from pressure on the hypothalamus (39).
Gross total surgical resection is the treatment of choice and typically curative (29). Recurrence of disease in patients who undergo such a procedure is uncommon (29). However, patients in whom operative limitations prevent a complete resection have an increased risk of recurrence and tend to have a less benign clinical course (29). In these cases, postoperative radiation therapy, chemotherapy, or stereotactic radiosurgery (gamma knife) may be used (40–42). A poorer clinical outcome is also usually seen in patients with central neurocytomas that undergo extraventricular extension (43,44).
Central neurocytomas arise from the septum pellucidum or the ventricular wall (40). Half of the cases involve the lateral ventricles near the foramen of Monro, whereas 15% are located in both the lateral and third ventricles (29). About 13% of central neurocytomas are bilateral, and only 3% occur in the third ventricle as an isolated location (29). There is a single case report of a central neurocytoma that arose in the fourth ventricle (45).
At gross inspection, central neurocytomas are typically gray and friable and often contain calcification or hemorrhage (29). They are considered WHO grade II tumors (29). The histologic features are so strikingly similar to those of an oligodendroglioma—with uniform round cells having round or oval nuclei (the classic "fried egg appearance"), as seen with the standard hematoxylin-eosin stain—that misdiagnosis of many central neurocytomas as intraventricular oligodendroglioma was common (Fig 11). The identification of pineocytomatous rosettes distinguishes these tumors from oligodendrogliomas in most cases. Calcification is very common (50% of specimens) (29). Central neurocytomas usually express immunoreactivity for synaptophysin and neuron-specific enolase, both markers for neuronal differentiation, which also aids in differentiating these tumors from oligodendrogliomas (29). In difficult cases, the final determination rests with electron microscopy, which depicts finely speckled chromatin, a small distinct nucleolus, and cell processes exhibiting typical neuritic features including microtubules (29).
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Figure 11. Central neurocytoma. Photomicrograph (original magnification, x400; hematoxylin-eosin stain) of a central neurocytoma shows sheets of neoplastic cells with round, regular nuclei.
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There are an increasing number of cases reported in which the histologic characteristics did not correlate with the presence or absence of recurrence, and some investigators have focused on the proliferation index in search of a more reliable marker of aggressive biologic behavior (40). In general, patients who harbor a central neurocytoma with a higher proliferation index from standard techniques (eg, Ki-67 index with MIB-1 antibody) have a poorer clinical outcome than those patients whose tumors have a lower index (46). Because of this aggressive biologic behavior, some authorities have proposed the term atypical central neurocytoma for these lesions (46). Some neurocytomas have even demonstrated an increase in their proliferation index after being partially resected (45,47).
The histogenesis of central neurocytomas remains unclear. Although the immunohistochemical features support a neuronal lineage, there are recent cell-culture investigations that indicate that the tumors may be derived from bipotential progenitor cells that are capable of both neuronal and glial differentiation (29,48). These cells may be located in the subependymal plate, which would provide a possible explanation for why some neurocytomas are extraventricular (48). Because both cell lines may be involved in neurocytomas, they are considered neuroepithelial tumors (29,48).
The typical cross-sectional imaging appearance of a central neurocytoma is a well-circumscribed, heavily lobulated, intraventricular mass with numerous intratumoral cystlike areas (Figs 12, 13) (43). The mass is most commonly located in the lateral ventricle, usually in its anterior portion near the foramen of Monro. Accordingly, a solid majority of cases of central neurocytoma are affiliated with hydrocephalus or monoventricular dilatation (49). On CT images, the lesions are hyperattenuated compared with the brain parenchyma (43,50). Cystlike areas are noted in two-thirds of cases with imaging studies (43). Calcification, usually punctate in character, is present in half of the cases (36,43). Moderate enhancement is typical after the intravenous administration of contrast media on both CT and MR images (43).
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Figure 12a. Central neurocytoma. (a) Axial CT image shows a hyperattenuated mass with focal calcification (arrowhead) centered near the foramen of Monro. (b) Axial T1-weighted MR image shows mild heterogeneity within the mass. The septum pellucidum is displaced toward the contralateral side, and the ipsilateral ventricle is clearly enlarged. (c) On a coronal T2-weighted MR image, the mass has an even more heterogeneous appearance. (d) Contrast-enhanced coronal T1-weighted MR image shows patchy enhancement within the mass. (e) Intraoperative photograph shows the soft-tissue mass at the depths of the retractors (r).
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Figure 12b. Central neurocytoma. (a) Axial CT image shows a hyperattenuated mass with focal calcification (arrowhead) centered near the foramen of Monro. (b) Axial T1-weighted MR image shows mild heterogeneity within the mass. The septum pellucidum is displaced toward the contralateral side, and the ipsilateral ventricle is clearly enlarged. (c) On a coronal T2-weighted MR image, the mass has an even more heterogeneous appearance. (d) Contrast-enhanced coronal T1-weighted MR image shows patchy enhancement within the mass. (e) Intraoperative photograph shows the soft-tissue mass at the depths of the retractors (r).
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Figure 12c. Central neurocytoma. (a) Axial CT image shows a hyperattenuated mass with focal calcification (arrowhead) centered near the foramen of Monro. (b) Axial T1-weighted MR image shows mild heterogeneity within the mass. The septum pellucidum is displaced toward the contralateral side, and the ipsilateral ventricle is clearly enlarged. (c) On a coronal T2-weighted MR image, the mass has an even more heterogeneous appearance. (d) Contrast-enhanced coronal T1-weighted MR image shows patchy enhancement within the mass. (e) Intraoperative photograph shows the soft-tissue mass at the depths of the retractors (r).
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Figure 12d. Central neurocytoma. (a) Axial CT image shows a hyperattenuated mass with focal calcification (arrowhead) centered near the foramen of Monro. (b) Axial T1-weighted MR image shows mild heterogeneity within the mass. The septum pellucidum is displaced toward the contralateral side, and the ipsilateral ventricle is clearly enlarged. (c) On a coronal T2-weighted MR image, the mass has an even more heterogeneous appearance. (d) Contrast-enhanced coronal T1-weighted MR image shows patchy enhancement within the mass. (e) Intraoperative photograph shows the soft-tissue mass at the depths of the retractors (r).
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Figure 12e. Central neurocytoma. (a) Axial CT image shows a hyperattenuated mass with focal calcification (arrowhead) centered near the foramen of Monro. (b) Axial T1-weighted MR image shows mild heterogeneity within the mass. The septum pellucidum is displaced toward the contralateral side, and the ipsilateral ventricle is clearly enlarged. (c) On a coronal T2-weighted MR image, the mass has an even more heterogeneous appearance. (d) Contrast-enhanced coronal T1-weighted MR image shows patchy enhancement within the mass. (e) Intraoperative photograph shows the soft-tissue mass at the depths of the retractors (r).
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Figure 13a. Central neurocytoma. (a) Axial CT image shows a heterogeneous, hyperattenuated mass in the right lateral ventricle. Note the asymmetry of the lateral ventricles secondary to obstruction of CSF flow from the right lateral ventricle. (b) Coronal view from cerebral angiography following a right internal carotid artery injection shows a subtle blush (arrows) in the region of the right lateral ventricle. (c) Lateral view from the same study shows a similar blush (arrows).
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Figure 13b. Central neurocytoma. (a) Axial CT image shows a heterogeneous, hyperattenuated mass in the right lateral ventricle. Note the asymmetry of the lateral ventricles secondary to obstruction of CSF flow from the right lateral ventricle. (b) Coronal view from cerebral angiography following a right internal carotid artery injection shows a subtle blush (arrows) in the region of the right lateral ventricle. (c) Lateral view from the same study shows a similar blush (arrows).
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Figure 13c. Central neurocytoma. (a) Axial CT image shows a heterogeneous, hyperattenuated mass in the right lateral ventricle. Note the asymmetry of the lateral ventricles secondary to obstruction of CSF flow from the right lateral ventricle. (b) Coronal view from cerebral angiography following a right internal carotid artery injection shows a subtle blush (arrows) in the region of the right lateral ventricle. (c) Lateral view from the same study shows a similar blush (arrows).
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On MR images, the solid portions of the tumor are hyperintense compared with the white matter with short TR and long TR pulse sequences, whereas the cystlike regions are hypointense compared with white matter with the short TR pulse sequences (Figs 12–14) (43). A broad attachment to either the lateral ventricle wall or the septum pellucidum is almost always present (43). Prominent flow voids, in some cases caused by venous dilatation near the foramen of Monro, may be seen (36,43). The combination of calcification and flow voids with the hyperintensity of the soft-tissue portions creates a heterogeneous appearance in most cases (44).
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Figure 14a. Central neurocytoma in a 46-year-old man with mood changes, lethargy, and recent onset of right-sided weakness. (a) Axial T1-weighted MR image shows a mass entrapping the left lateral ventricle. Notice the different signal intensity (arrowhead) within the left lateral ventricle compared with the right side. The mass is mildly hypointense compared with the white matter but is heterogeneous with scattered focal areas of mild hyperintense signal. (b) Axial T2-weighted MR image shows the heterogeneous mass with numerous cystlike areas and vasogenic edema (arrows) in the adjacent centrum semiovale. (c) Contrast-enhanced axial T1-weighted MR image shows intense enhancement of most of the mass, with sparing of the cystlike regions. At surgery, the tumor was difficult to resect because of invasion into the adjacent brain parenchyma.
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Figure 14b. Central neurocytoma in a 46-year-old man with mood changes, lethargy, and recent onset of right-sided weakness. (a) Axial T1-weighted MR image shows a mass entrapping the left lateral ventricle. Notice the different signal intensity (arrowhead) within the left lateral ventricle compared with the right side. The mass is mildly hypointense compared with the white matter but is heterogeneous with scattered focal areas of mild hyperintense signal. (b) Axial T2-weighted MR image shows the heterogeneous mass with numerous cystlike areas and vasogenic edema (arrows) in the adjacent centrum semiovale. (c) Contrast-enhanced axial T1-weighted MR image shows intense enhancement of most of the mass, with sparing of the cystlike regions. At surgery, the tumor was difficult to resect because of invasion into the adjacent brain parenchyma.
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Figure 14c. Central neurocytoma in a 46-year-old man with mood changes, lethargy, and recent onset of right-sided weakness. (a) Axial T1-weighted MR image shows a mass entrapping the left lateral ventricle. Notice the different signal intensity (arrowhead) within the left lateral ventricle compared with the right side. The mass is mildly hypointense compared with the white matter but is heterogeneous with scattered focal areas of mild hyperintense signal. (b) Axial T2-weighted MR image shows the heterogeneous mass with numerous cystlike areas and vasogenic edema (arrows) in the adjacent centrum semiovale. (c) Contrast-enhanced axial T1-weighted MR image shows intense enhancement of most of the mass, with sparing of the cystlike regions. At surgery, the tumor was difficult to resect because of invasion into the adjacent brain parenchyma.
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In rare cases, central neurocytomas may be associated with intraventricular (36,51), intratumoral (38), or parenchymal hemorrhage (52). The angiographic appearance is extremely variable, with reports ranging from avascularity to a vascular blush (36). There is one case report of an aneurysm from the lenticulostriate artery that was associated with a central neurocytoma (53). Extraventricular extension may correspond with malignant transformation, although not all cases with this imaging feature have shown such changes (43,54). Hypermetabolic activity, increased blood flow, and increased blood volume on positron emission tomographic (PET) images are typical for these tumors (54,55). In a limited number of cases that have been analyzed with MR spectroscopy, central neurocytomas have shown higher choline-to-creatine and choline-to-N-acetylaspartate ratios compared with normal brain regions and a peak at 3.55 ppm that likely corresponds to inositol or glycine (56).
Subependymal Giant Cell Astrocytoma
SEGA is the most common cerebral neoplasm in tuberous sclerosis, the neurocutaneous phakomatosis characterized by an autosomal dominant pattern of inheritance in 20%–50% of cases and the presence of tubers and subependymal glial nodules in 90%–100% of patients (57–59). Still, the SEGA is an uncommon tumor, accounting for only 1.4% of 733 pediatric brain neoplasms in one series (60).
There is a wide age range for presentation (birth to the 5th decade of life), but most cases occur in the 1st and 2nd decades, with a mean age of 11 years (combining data from the two largest series reported) (57,58,60–62). Among all patients with tuberous sclerosis, about 6%–16% have a SEGA (58). Whether a SEGA can occur in patients who do not harbor any manifestations of tuberous sclerosis is controversial. Although there have been patients who have a SEGA without manifestations of tuberous sclerosis, the apparent absence of tuberous sclerosis may simply be a reflection of an insufficient period of time having elapsed before the clinical signs could be documented or an example of variable gene expression (57,60).
Because the tumor is virtually always located near the foramen of Monro, symptoms related to increased intracranial pressure and seizures are the typical clinical manifestations (58). Hemiparesis has also been reported (60). Since most patients do not have a change in their seizure pattern after removal of a SEGA, it is doubtful that the SEGA caused the seizures; rather, they are more likely secondary to the usually numerous other intracranial tubers and nodules present in a patient with tuberous sclerosis (60). Menor et al (59) noted a higher rate of prevalence (80%) of cardiac rhabdomyomas in their five patients with SEGA, compared with the other 22 tuberous sclerosis patients without a SEGA.
The tumor is characterized by slow growth and a benign biologic behavior, corresponding to WHO grade I in the latest WHO classification scheme (58). In a series of 21 patients with SEGA, earlier diagnosis was associated with increased survival (57).
Current neurosurgical opinion supports resection of a symptomatic SEGA or a SEGA with documented growth on MR images (60). The development of better neurosurgical techniques has led to decreased perioperative mortality and morbidity in the resection of these lesions (60). Recurrence after surgical removal is rare (60). Radiation therapy has not been effective in preventing growth of SEGAs (60).
SEGAs probably arise from subependymal nodules in the ventricular wall of patients with tuberous sclerosis (57). Why an otherwise unremarkable subependymal nodule in a tuberous sclerosis patient would transform into a SEGA is still a mystery, as is the natural history of this tumor (57). The histogenesis of SEGA is also unclear, with evidence supporting both neuronal and astrocytic lineage (57). SEGA is histologically characterized by a mixed glioneuronal pattern and has a low proliferative index, corresponding to its slow growth (Fig 15) (58). Malignant histologic features in a SEGA are rare (57).
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Figure 15. Subependymal giant cell astrocytoma. Photomicrograph (original magnification, x200; hematoxylin-eosin stain) of a SEGA shows collections of large, bizarre cells (arrowheads) in a glial background.
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On CT images, SEGA appears as an isoattenuated to slightly hypoattenuated intraventricular mass near the foramen of Monro (60). Calcification is common (Fig 16) (60). When hyperattenuation other than calcification is noted, hemorrhage within the SEGA is likely (63). Before modern neuroradiology became available, a SEGA was clinically declared by the presence of typical symptoms (57). Today, the radiologic hallmark of a SEGA on cross-sectional images is a markedly contrast-enhancing mass located at or very near the foramen of Monro. This enhancement distinguishes a SEGA from a subependymal nodule, which does not enhance (59,64).
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Abstract
LEARNING OBJECTIVES FOR TEST...
