DOI: 10.1148/rg.242035069
RadioGraphics 2004;24:598-600
© RSNA, 2004
Oligoastrocytoma1
David K. Naugle, MD,
Timothy D. Duncan, MD and
Guerard P. Grice, MD
1 From the Departments of Radiology (D.K.N., T.D.D.) and Pathology (G.P.G.), Naval Medical Center San Diego, 34730 Bob Wilson Dr, Bldg 1, San Diego, CA 92134. Received March 13, 2003; revision requested May 30 and received June 30; accepted July 1. Address correspondence to D.K.N. (e-mail: docnog_99@yahoo.com).
Index Terms: Brain neoplasms
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History
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A 27-year-old woman experienced a generalized tonic-clonic seizure at home, witnessed by her husband. She presented to the emergency department and subsequently had another witnessed generalized seizure while being evaluated. She had no laboratory abnormalities, but a right temporoparietal mass was detected at unenhanced computed tomographic (CT) evaluation of the head. The mass was further evaluated with CT angiography and magnetic resonance (MR) imaging. The lesion was subsequently resected and the patient underwent radiation therapy.
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Imaging Findings
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Unenhanced axial CT images of the brain (Fig 1) demonstrated a 5 x 3-cm area of homogeneous low attenuation in the right temporoparietal region. There was no associated edema or hydrocephalus. Subtle scalloping of the adjacent inner table was visible.
On T1-weighted images, the same lesion appeared homogeneously hypointense (Fig 2a), without significant enhancement (Fig 2b). The lesion was homogeneously hyperintense on T2-weighted images (Fig 3), without adjacent edema.
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Figure 2a. Axial T1-weighted MR images obtained with (a) and without (b) contrast material demonstrate an area of homogeneously low signal intensity in the right temporoparietal region that does not significantly enhance after gadolinium administration.
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Figure 2b. Axial T1-weighted MR images obtained with (a) and without (b) contrast material demonstrate an area of homogeneously low signal intensity in the right temporoparietal region that does not significantly enhance after gadolinium administration.
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Pathologic Evaluation
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At surgical resection, tan tissue protruded from the craniotomy site (Fig 4). Gross pathologic evaluation of the mass revealed several samples of tan-colored tissue, the largest of which measured 2.5 x 1.1 cm.
Analysis of microscopic sections revealed a highly cellular tumor with both oligodendroglial and astrocytic components. The oligodendroglial portion constituted approximately 70% of the lesion; the astrocytic portion, approximately 30%. In some areas, these two components were intimately intermingled, whereas in others they were distinctly separate. The oligodendroglial component contained a large number of background minigemistocytes, nuclear pleomorphism, and increased mitotic activity (Fig 5). The intermingled astrocytic component was predominantly of the gemistocytic type, with marked nuclear pleomorphism, high cellularity, and multinucleated tumor cells. The scattered foci of a distinctly separate astrocytic component were composed of fibrillary astrocytes with hyperchromatic, pleomorphic, ovoid nuclei (Fig 6). No necrosis or microvascular proliferation was identified. These features are consistent with an anaplastic oligoastrocytoma grade III.
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Figure 5. Photomicrograph (original magnification, x400; hematoxylin-eosin stain) demonstrates tumor cells with high cellularity and pleomorphism. A typical neoplastic oligodendrocyte is seen with a round nucleus and perinuclear halo (long thin arrow). A neoplastic astrocyte (large arrowhead) appears as a "naked" nucleus because cytoplasm is not discernible. A "minigemistocyte" (small arrowhead) and a gemistocytic astrocyte (short thin arrow) are seen side by side below the neoplastic astrocyte. Long thick arrow = mitotic figure.
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Figure 6. Photomicrograph (original magnification, x400; hematoxylin-eosin stain) reveals a distinct astrocytic component of the oligoastrocytoma. This slide reveals pleomorphic, hyperchromatic, oval nuclei with no or barely discernible fibrillary astrocytic cytoplasm.
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Discussion
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Oligoastrocytomas are part of the glial cell continuum that includes both astrocytic and oligodendrocytic components. These tumors are graded, based on the World Health Organization (WHO) classification, as either low grade (WHO grade II) or anaplastic (WHO grade III). The anaplastic oligoastrocytoma exhibits histologic characteristics indicative of malignancy, including high cellularity, cellular pleomorphism, nuclear atypia, and increased mitotic activity. Microvascular proliferation and necrosis may also be present but are not required for the diagnosis (1).
These tumors typically occur in young adults (mean age at diagnosis, 35–45 years) and manifest with partial or generalized seizures (2). Although less common, patients may present with headaches or may have no symptoms at all (3). In a series by Beckmann and Prayson (4), most oligoastrocytomas occurred in the frontal (57% of cases) or temporal (30%) lobes. In addition, 19 of their 30 patients with oligoastrocytoma were male. Favorable prognostic factors include age at presentation of less than 40 years, lower grade of tumor, and better extent of resection (5). Of these, grade of tumor appears to be the most significant prognosticator (6).
Initial radiologic evaluation of patients with a suspected intracranial mass is usually performed with unenhanced CT of the head. On CT scans, oligoastrocytomas typically appear as intraaxial low-attenuation regions with little to no associated edema. Because of their slow growth, the associated mass effect of these tumors tends to be less severe compared with that of similar high-grade lesions (7). Further evaluation with MR imaging typically reveals a lesion that is hypointense on T1-weighted images and hyperintense on T2-weighted images. Contrast material enhancement is present in approximately half of the oligoastrocytoma cases in a series by Shaw et al (8).
A median survival time of 6.3 years as well as 5- and 10-year survival rates of 58% and 32%, respectively, have been reported by Shaw et al (8). Factors associated with longer survival include younger age at operation, total resection of the tumor, and postoperative radiation therapy (1,8).
Oligodendrogliomas tend to be chemosensitive and, therefore, may be treated with adjuvant chemotherapy. Conversely, astrocytomas are not chemosensitive. Oligoastrocytomas, in comparison with oligodendrogliomas, respond less favorably to chemotherapy, which is most likely because of the chemoresistance of their astrocytic component (3,9,10).
Histologically distinguishing pure oligodendrogliomas from the other gliomas assists in determining if chemotherapy may be an effective treatment. A characteristic gene alteration—allelic loss of chromosomes 1p and 19q—may help to identify an oligodendroglial component (2,10). In these tumors, some advocate use of chemotherapy after resection to help postpone radiation therapy and its potential neurologic side effects (2,3).
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Acknowledgments
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The authors gratefully thank medical photographer Teresa Hawkins, BA, for her excellent intraoperative photography.
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References
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- Reifenberger G, Kros JM, Burger PC, Louis DN, Collins VP. Oligoastrocytoma. In: Kleihues P, Cavenee WK, eds. Tumours of the nervous system. Lyon, France: IARC Press, 2000; 65-67.
- Behin A, Hoang-Xuan K, Carpentier AF, Delattre JY. Primary brain tumours in adults. Lancet 2003; 361:323-331.[CrossRef][Medline]
- Olson JD, Riedel E, DeAngelis LM. Long-term outcome of low-grade oligodendroglioma and mixed glioma. Neurology 2000; 54:1442-1448.[Abstract/Free Full Text]
- Beckmann MJ, Prayson RA. A clinicopathologic study of 30 cases of oligoastrocytoma including p53 immunohistochemistry. Pathology 1997; 29:159-164.[CrossRef][Medline]
- Shaw EG, Scheithauer BW, O’Fallon JR, Tazelaar HD, Davis DH. Oligodendrogliomas: the Mayo Clinic experience. J Neurosurg 1992; 76:428- 434.[Medline]
- Allam A, Radwi A, El Weshi A, Hassounah M. Oligodendroglioma: an analysis of prognostic factors and treatment results. Am J Clin Oncol 2000; 23:170-175.[CrossRef][Medline]
- Ricci PE, Dungan DH. Imaging of low- and intermediate-grade gliomas. Semin Radiat Oncol 2001; 11:103-112.[CrossRef][Medline]
- Shaw EG, Scheithauer BW, O’Fallon JR, Davis DH. Mixed oligoastrocytomas: a survival and prognostic factor analysis. Neurosurgery 1994; 34:577-582.[Medline]
- Fortin D, Cairncross GJ, Hammond RR. Oligodendroglioma: an appraisal of recent data pertaining to diagnosis and treatment. Neurosurgery 1999; 45:1279-1291.[Medline]
- Smith JS, Perry A, Borell TJ, et al. Alterations of chromosome arms 1p and 19q as predictors of survival in oligodendrogliomas, astrocytomas, and mixed oligoastrocytomas. J Clin Oncol 2000; 18:636-645.[Abstract/Free Full Text]
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History
Imaging Findings
