Oligodendrogliomas

Oligodendroglial tumors

Oligodendroglial tumors represent approximately 4-7% of all gliomas; however, in some series the incidence has been reported to be as high as 10-20% because of improved histological appreciation and recently recognized molecular signatures. Oligodendroglial tumors are classified as being low-grade oligodendroglial tumors, high-grade anaplastic oligodendroglial tumors or mixed oligo-astrocytic tumors. The mixed tumors can again be low-grade or high-grade. The recent European Organization for Research and Treatment of Cancer and Radiation Therapy Oncology Group randomized trials have provided level 1 evidence regarding the best management of these tumors. This review provides an overview of oligodendroglial tumors and discusses contemporary and evolving treatment strategies.

Oligodendroglioma: an analysis of prognostic factors and treatment results

This study, an analysis of variable prognostic factors affecting the treatment outcome for patients with oligodendroglioma, included a retrospective analysis of the medical charts of patients diagnosed with oligodendroglioma treated at our institution between 1975 and 1997. The endpoints analyzed were the progression-free survival (PFS), as well as the overall survival. The factors analyzed included extent of surgery, postoperative radiotherapy, pathologic grade, performance status, age, and sex. Of a total of 37 cases, 19 were male and 18 were female. The median age at diagnosis was 30 years. The most common presenting symptoms were headache (78%), seizures (43%), motor symptoms (38%), and to a lesser extent behavioral changes (16%). The median duration of symptoms was 9 months. The most common location on computed tomography or magnetic resonance imaging scans was the frontal region (43%). Low grade tumors (grades I and II) were found in 60% of patients, and the remaining 40% had high grade tumors (grades III and IV). Eight patients had complete surgical excision, whereas 27 patients had partial excision, and two patients had biopsy only. The operative mortality rate was 14%. There were 24 patients who received postoperative radiotherapy, and only 3 patients received adjuvant chemotherapy. The median postoperative radiation dose was 5,580 cGy. With a median follow-up of 7 years, the 5-year PFS and overall survival for the whole group were 58% and 67%, respectively. The pathologic grade of the tumor was the only prognostic factor significantly affecting both PFS and overall survival. The 5-year PFS for patients with low grade tumors was 79% in comparison to 32% for patients with high grade tumors (p < 0.01). Patients with good performance status at initial presentation (performance status of 1 and 2) had a higher 5-year PFS in comparison to those with poor performance status (62% vs. 38%, respectively); however, this difference did not reach statistical significance. Similarly, patients who were subjected to complete surgical excision had a marginally higher PFS in comparison to those who had biopsy or partial excision (75% vs. 53%). There was no difference in the 5-year PFS between patients who received postoperative irradiation versus those who did not (51% vs. 47%, respectively). Patients with high grade oligodendrogliomas have a relatively poor prognosis. The pathologic grade of the tumor was the single most important prognostic factor significantly affecting both the PFS and overall survival. A prospective randomized clinical trial is needed to address the impact of postoperative irradiation on PFS of those tumors. In view of the poor outcome for patients with high grade oligodendroglioma, the use of adjuvant systemic chemotherapy should be studied in future multicenter randomized trials.

The treatment of cerebral oligodendrogliomas with particular reference to features indicating malignancy: report of seventy-seven cases

Oligodendrogliomas are relatively rare tumors that arise from the oligodendrocyte or its precursors. The role of postoperative radiotherapy (RT) in these tumors still remains unclear. Data concerning a study on 77 histologically verified cases of oligodendrogliomas of the brain among a total number of 1884 cases of an intracranial glioma treated at the Hacettepe Medical Centre between 1964 and 1991 were reviewed and analyzed (6.5%). One patient died in the early postoperative period and 8 patients in pediatric age group with an aggressive from of the tumor died within 6 months of treatment. The results suggest that oligodendrogliomas which arise in childhood primarily in the intraventricular region should be considered potentially more malignant than other lesions of this type. Because of this, we believe that postoperative radiotherapy is necessary to prevent the recurrences.

Prognostic factors in oligodendroglioma

BACKGROUND

A reliable marker for tumor oligodendroglial cells is not yet available, so that the histological recognition of the tumor still encounters uncertainties. There is no general agreement also on prognostic factors in oligodendroglioma. The inconsistency concerns mainly the histopathological factors. The aim of the study was recognition of prognostic factors in oligodendroglioma.

METHODS

In a series of ninety-eight oligodendrogliomas, including twenty mixed oligoastrocytomas, clinical [sex, age at surgery, tumor location, symptoms at presentation], therapeutic [extent of resection, year of surgery, post-operative Karnofsky score, post-operative radiotherapy, post-operative chemotherapy], histological [cell density, nuclear pleomorphism, vascular endothelial proliferation, necrosis, microcysts, mitoses, mitotic index (MI), apoptosis, apoptotic index (AI)] and immunohistochemical parameters [MIB-1 and PCNA Labeling Indexes (LIs), staining for GFAP, positivity for p53] were correlated with survival in uni- and multivariate analysis in order to identify their prognostic significance.

RESULTS

Age at surgery, extent of surgical resection, year of surgery, post-operative Karnofsky score and MIB-1 LI were associated with survival in both uni- and multivariate analysis. Location, symptoms at presentation, mitoses, MI, AI, and PCNA LI showed a significant correlation with survival in uni- but not in multivariate analysis. The twenty cases of oligoastrocytomas did not show any difference in survival from pure oligodendrogliomas.

CONCLUSIONS

Some clinical and therapeutic factors together with MIB-1 LI play a prognostic role. MIB-1 LI is prognostic with a cutoff of 8%. Histology gives a limited contribution to the prognosis. Oligoastrocytomas had the same outcome and prognostic factors as pure oligodendrogliomas.

Prognostic factors in oligodendrogliomas

An outcome analysis was performed on 96 patients with pure cerebral oligodendrogliomas operated in the 30-year period 1962 to 1991. The most important predictive prognostic factors were youth and no neurological deficit, demonstrated as a median survival for the group younger than 20 years of 17.5 years and for the group older than 60 years of 13 months. The group without neurological deficits had a 5-years survival of 43 per cent while the group with deficits had a 5-years survival of 5 per cent. The 5-years survival for oligodendroglioma of grade II was 46 per cent and for grade III 10 per cent. We found no effect of radiotherapy on survival, neither in the whole material or in any subgroup.

Low-grade gliomas of the cerebral hemispheres in children: an analysis of 71 cases

Low-grade gliomas constitute the largest group of cerebral hemispheric tumors in the pediatric population. Although complete tumor resection is generally the goal in the management of these lesions, this can prove difficult to achieve because tumor margins may blend into the surrounding brain. This raises several important questions on the long-term behavior of the residual tumor and the role of adjuvant therapy in the management of these lesions. To examine these issues, the authors reviewed their experience in 71 children with low-grade cerebral hemispheric gliomas who were treated at their institution between 1956 and 1991 and assessed the relationship between clinical, radiographic, pathological, and treatment-related factors and outcome. Only seven patients in the series died, one from perioperative complications, five from progressive disease, and one (a child with neurofibromatosis) from a second neoplasm. For the 70 patients who survived the perioperative period, overall actuarial survivals at 5, 10, and 20 years were 95%, 93%, and 85%, respectively; progression-free status was maintained in 88%, 79%, and 76%, respectively. On univariate analysis, the factor that was most strongly associated with both overall and progression-free survival was the extent of tumor resection (p = 0.013 and p = 0.015, respectively). A relationship between extent of resection and progression-free survival was present both in patients with pilocytic astrocytomas (p = 0.041) and those with nonpilocytic tumors (p = 0.037). Histopathological diagnosis was also associated with overall survival on univariate analysis; poorer results were seen in the patients with nonpilocytic astrocytoma compared to those with other low-grade gliomas, such as pilocytic astrocytoma, mixed glioma, and oligodendroglioma (p = 0.021). The use of radiotherapy was not associated with a significant improvement in overall survival (p = 0.6). All three patients who ultimately developed histologically confirmed anaplastic changes in the vicinity of the original tumor had received prior radiotherapy, 20, 46, and 137 months, respectively, before the detection of malignant progression. In addition, children who received radiotherapy had a significantly higher incidence of late cognitive and endocrine dysfunction than the nonirradiated patients (p < 0.01 and 0.05, respectively). The authors conclude that children with low-grade gliomas of the cerebral hemispheres have an excellent overall prognosis. Complete tumor resection provides the best opportunity for long-term progression-free survival. However, even with incomplete tumor excision, long-term progression-free survival is common.(ABSTRACT TRUNCATED AT 400 WORDS)

Seizures in patients with supratentorial oligodendroglial tumours. Clinicopathological features and management considerations

In this study of 34 consecutive histologically confirmed oligodendroglial brain tumours (15 oligoastrocytoma, 12 oligodendroglioma, 7 anaplastic oligodendroglioma) twenty five patients (75%) presented with symptoms related to seizures. Although the seizure incidence was lowest in anaplastic oligodendroglioma (57%) it was not statistically different from either pure (75%) or mixed (80%) oligodendroglial tumours. Patients with seizures had a significantly lower age (p < 0.001) at diagnosis (median 36 years) than those without seizures (57 years). The types of seizure disorder, that were present for a median of 15 months prior to surgery, were variable with 32% having generalised, 36% partial and 32% mixed patterns. There were no significant differences between either the type or incidence of seizures and the particular cerebral location of the oligodendroglial tumour. Twenty four of the patients presenting with seizures underwent surgery (5 stereotactic biopsy, 5 stereotactic guided resection and 14 conventional craniotomy and resection) without intraoperative electrocorticography (ECoG). Eighteen (75%) of these patients also had postoperative radiotherapy (40 to 54 Gy in 30 fractions. Following these treatments the percentage of patients fit free at 6, 12, and 24 months were 67%, 56%, and 53%, respectively. Median time to first post operative seizure was 32 weeks (range 5 weeks to 5.3 years). After a median follow up time of 30 months 20 of the 25 patients who presented with seizures were still alive. Eight (40%) were seizure free and three other patients (15%) had experienced less than three postoperative seizures in follow-up periods ranging from 42 to 62 months. Although the numbers of patients on preoperative (87%) and postoperative (83%) anticonvulsant medications were similar, some had their medications either withdrawn (17%) or reduced (4%) whilst others had it introduced (12%) after interventional management. Only five (20%) patients who presented with seizures, compared to 6 (67%) who had not presented with seizures had died during median follow-up of 28 months. Three of nine patients (33%), who were initially seizure free, developed seizures between 25 and 36 months after initial surgery and radiotherapy. This study (i) confirms the high incidence of epilepsy in supratentorial oligodendroglial tumours; (ii) has shown that seizures associated with these tumours are significantly more common in younger patients; (iii) suggests that younger age, but not the presence of seizures, is a significant independent prognostic variable; (iv) that seizure control following a second operation is generally disappointing and (v) suggests that tumour resection and radiotherapy often facilitate control of the seizures by anticonvulsants. Because of the multiple clinicopathological and management variables involved a prospective study would be required to assess the optimal management of patients with seizure disorders associated with oligodendroglial brain tumours.

Cerebral oligodendroglioma: prognostic factors and life history

The records of 137 patients with supratentorial oligodendroglioma treated surgically between 1953 and 1986 were reviewed. The tumors were rated histologically benign or malignant. In the 105 patients followed up with a minimum observation time of 5 years to December 1991, the mean postoperative survival was 90.2 months (standard error, 9), the median 64 months (standard error, 9.6), the 5-year survival rate 52.4%, and the 10-year survival rate 24%. Sixteen possible prognostic factors, broken down into two or more variables each, were considered in the survival study on univariate methods (5-year survival rate, survival curves, and Cox's hazard function) and on multivariate analysis according to Cox's stepwise proportional hazards model. The latter showed that variables correlated positively with survival were benign histological findings (P, 0.000), postoperative radiation therapy (P, 0.004), and time of operation from 1977 to 1986 (P, 0.044) in 105 patients of the whole series, and period of surgery from 1977 to 1986 (P, 0.000), subtotal or total surgical resection of the tumor (P, 0.001), and radiation therapy (P, 0.005) in the subgroup of 79 patients operated on for benign tumors. However, the most interesting point to emerge from the study was the relevance of admission clinical status to the survival of patients who did not receive radiation therapy and to the prognostic response of those who did. Of the 40 patients with seizures and negative neurological status--Clinical Syndrome A--the 10 who did not receive radiation therapy had survived as long as the 30 who did (5-year survival rate, 80 versus 67%; P, not significant; median survival, 122 versus 85 months; Breslow and Mantel-Cox P, not significant), whereas of the 65 patients with intracranial hypertension and/or neurological deficits--Clinical Syndrome non-A--the 18 who did not receive radiation therapy had short survival times, and the 47 who did fared significantly better (5-year survival rate, 11 versus 53%; P, 0.002; median survival, 32 versus 64 months; Breslow and Mantel-Cox P, 0.000). These findings were not significantly affected by the exclusion of malignant neoplasms and in the group of benign tumors, in which the histological characteristics have not been found to be significantly different between those with A and those with non-A clinical syndrome, did not depend on different frequencies of subtotal or total tumor removal.(ABSTRACT TRUNCATED AT 400 WORDS)

The role of postoperative irradiation in the treatment of oligodendroglioma

PURPOSE

Controversy regarding the role of adjuvant radiation therapy for the treatment of oligodendroglioma continues to exist. To better define the utility of postoperative irradiation for this tumor, the experience at the University of Washington was retrospectively examined.

METHODS AND MATERIALS

The histologic samples of 63 patients given the diagnosis of oligodendroglioma were reviewed by a panel of neuropathologists and 41 were classified as pure oligodendroglioma. The two treatment groups included 14 patients treated with surgery only and 27 who received surgery and postoperative radiation and were analyzed using univariate and multivariate analysis with respect to prognostic factors, freedom from relapse, and survival.

RESULTS

Univariate statistical analysis of 14 clinical variables showed that a poorer prognosis was associated in patients with high cell density (p = .008), necrosis (p = .017), hemiparesis (p = .026), and papilledema (p = .091), while patients presenting with seizures had a better prognosis (p = .0096). Multivariate analysis showed necrosis (p = .001) and hemiparesis (p = .02) to be associated with decreased survival. Multivariate and univariate analysis of the treatment groups found them to be homogenous with respect to prognostic factors. Survival times were significantly longer in the group treated with postoperative irradiation (median survival time 84 vs. 47 months, p = .032). The 5 and 10 year survival rates were 83% and 46%, respectively, for the irradiated patients compared with 51% and 36% for those treated with surgery alone. Freedom from tumor recurrence times were also longer in irradiated patients (median relapse free time 79 vs. 42 months, p = .01).

CONCLUSION

Based on the results of this study, we recommend continuing the practice of treating oligodendroglioma with postresection irradiation until a prospective multicenter clinical trial is conducted to thoroughly evaluate the role of postoperative irradiation in the treatment of this tumor.

The prognostic implications of histologic classification and bromodeoxyuridine labeling index of mixed gliomas

To clarify the biological and clinical behavior and prognosis of mixed gliomas, 47 patients underwent intraoperative bromodeoxyuridine (BrdU) labeling studies. The mean age was 27.8 years at symptom onset and 31.8 years at labeling (median, 36 years). Forty-five tumors were supratentorial, 30 were frontal, and two were cerebellar; 16 were recurrent at labeling. The median labeling index (LI) was 1% (range, < 1 to 15.1%). Forty-six tumors has oligodendroglial and astrocytic elements, and one had astrocytic and ependymal elements. The median LI was 4.4% in recurrent tumors and < 1% in primary tumors. A higher BrdU LI correlated with an increased risk of recurrence and a shorter time to recurrence. During a median follow-up of 16 months, four patients died; each had a BrdU LI > or = 4.4%. The median time to recurrence was 4.5 months for tumors with BrdU LI's > 5% but was not reached for tumors with LI's < 5% (p < 0.003). The histologic grade of the oligodendroglial component correlated with the median time to recurrence (8 months for Smith Grade C tumors, not reached for Smith Grade B tumors; p < 0.05); there were too few cases to evaluate the median times to recurrence of Smith Grade A and Grade D tumors. The median time to recurrence was not reached for any astrocytic grade, and there were no significant differences in the Kaplan-Meier survival curves. These findings suggest that the BrdU LI and the grade of the oligodendroglial component of mixed gliomas have prognostic significance.

Oligodendroglioma. The Princess Margaret Hospital experience (1958-1984)

BACKGROUND

Oligodendrogliomas are rare central nervous system (CNS) tumors. Although surgery remains the primary treatment, the role of postoperative radiation treatment remains a matter of controversy. This study assesses whether postoperative radiation improves survival and local tumor control when compared with surgical treatment alone.

METHODS

The medical records of 72 patients with the diagnosis of oligodendroglioma, registered at the Princess Margaret Hospital (PMH) between 1958 and 1984, were reviewed retrospectively. The data of 68 patients were evaluated, but 4 patients were excluded from the analysis because of inadequate follow-up. The median follow-up period at the time of analysis was 7.5 years. Tumors were classified as oligodendrogliomas, malignant oligodendrogliomas, or mixed oligoastrocytomas. Fifty-eight (85%) patients received postoperative irradiation at initial diagnosis, and 10 (15%) patients were treated with surgery alone. In most patients (76%), the radiation dose was 5000 cGy in 25 fractions given during a period of 5 weeks.

RESULTS

Five- and 10-year overall survival was 66% and 30%, respectively. Forty-two (62.0%) patients experienced disease relapse during the follow-up period. The median time to relapse from initial diagnosis was 2.6 years. Most tumor recurrences were at the primary site. Two patients developed distant metastasis within the CNS axis. Histologic subtype was the only significant prognostic factor for survival. The patients with oligodendroglioma and malignant oligodendroglioma had 5-year survival rates of 73% and 32%, respectively (P = 0.033).

CONCLUSIONS

The authors drew three conclusions. (1) Most patients eventually died with this tumor from local recurrence without distant metastasis. Local tumor control remains the major problem. (2) Tumor histologic subtype is a significant prognostic factor. (3) No statistically significant benefit can be attributed to postoperative irradiation; however, the number of patients not receiving radiation therapy was small (10). Thus, the role of radiation therapy remains a matter of controversy.

Intratumoral histologic heterogeneity of gliomas. A quantitative study

Quantitative data for intratumoral histologic heterogeneity were obtained by investigating ten small and ten large punched samples from 50 unembedded supratentorial gliomas. The 1000 samples were diagnosed according to the World Health Organization (WHO) classification and six histopathologic features associated with malignancy were evaluated (cellular density, nuclear pleomorphism, necroses, histologic architecture, vessels, and mitoses), each with defined gradations. The slides were read independently by two observers. The initially high interobserver variability (grade, 22.2%; type, 10.3%; and tumor presence/absence, 7.1%) was for the most part due to intermediate grades and types and was reduced to 1.7% after mutual review. Small samples showed lower mean grade than large samples and more often absence of tumor (7.6% versus 2.4%). Of all gliomas, 48% showed differently typed samples, 82% differently graded samples, and 62% benign and malignant grades. Intratumoral heterogeneity was higher for the necroses than for the other histopathologic features. Our results underscore the importance of extensive tissue sampling.

[Oligodendroglioma of the cerebellopontine angle: 16 years' course. Review of the literature and considerations on the pathology]

The authors after a meticulous bibliography research have found 43 cases of oligodendrogliomas in the posterior fossa. Out of these 43 cases they came to know that two of them were located in the cerebello pontine angle. The authors describe one more case of this pathology in this rare localization and call attention to the fact that the evolution of this case has been confirmed during the last sixteen years.

Lack of histopathological correlation of malignant ependymomas with postoperative survival

It is widely believed that an important determinant of clinical behavior and prognosis in patients harboring an ependymoma is the histological grade of malignancy of the tumor. Excluding from the present analysis examples of ependymoblastoma (a highly cellular, embryonal tumor occurring in children, with a notably poor prognosis and a tendency to subarachnoid spread), an attempt was made to correlate 15 cases of histologically malignant ependymoma with clinical recurrence and postoperative patient survival times. Ten patients (67%) were alive from 15 months to 14 years after surgery (median survival time 8.8 years); one patient had a histologically benign recurrence 11 years after surgical resection. Five patients (33%) died from a local recurrence of their tumor; their postoperative survival times ranged from 13 months to 6 years (median 2.5 years). The prognosis of malignant ependymomas is therefore highly variable. No correlation was possible between the tumor's histological features, site, or likelihood of recurrence. This lack of clinicohistopathological concordance contrasts with the known correlations that exist in astrocytomas.

Oligodendroglioma. A comparison of two grading systems

In order to compare the grading system for oligodendrogliomas described by M.T. Smith (1983) with the conventional grading system according to Kernohan (1938), specimens from 72 patients were graded according to both systems, and survival times of the patients were compared. Survival rates decline in older patients. No interaction between the age of the patient and the degree of the tumor was found. No influence of localization of the tumor on survival was found. Similar to the system of Kernohan, the grading system of Smith distinguishes between only three groups of patients with significantly different survival times. In Smith's Grade A and Kernohan's Grade 1 the longest survivals are found; while in Smith's Grade D and Kernohan's Grade 4 the shortest survivals are found. Smith's Grades B and C as well as Kernohan's Grades 2 and 3 were intermediate with respect to the survival times of the patients and did not significantly differ from each other. With the independently significant features (cell density, pleomorphism, and necrosis) evaluated according to simple on-off scoring, and with the reduction from four grades to three, the grading system according to Smith would provide a simple and good, concise grading system for oligodendrogliomas of the brain.

Oligodendroglial tumors. An immunohistochemical and electron microscopic study

Fifty-five cases of oligodendrogliomas and mixed oligoastrocytomas were evaluated using immunohistochemical (IH) study for glial fibrillary acidic protein (GFAP) and electron microscopic (EM) study. Most of the tumors in both of these groups showed many neoplastic oligodendroglial cells with GFAP-positive staining in their cytoplasm by IH study. By EM study too, many tumor cells showing features of oligodendroglial cells contained intermediate filaments. Our observations suggested the presence of a transitional form of cells in these tumors. The current study supports the contention that both oligodendrogliomas and oligoastrocytomas arise from a common progenitor cell capable of differentiation into both oligodendrocyte and astrocyte. The nature and degree of differentiation depends probably on gene expression and/or some microenvironmental factors.

Oligodendroglioma. An analysis of the value of radiation therapy

The role of radiation therapy in the treatment of supratentorial oligodendrogliomas is controversial. To evaluate the role of radiation therapy, the Duke University Medical Center series was retrospectively analyzed. Clinical history, radiation dosages, and pathologic materials were reviewed. Seventy-one patients were identified as having histologically proven oligodendroglioma. Analysis of the patient population demonstrated it to be similar in all major parameters to other populations previously reported in the literature. Multivariate statistical analysis of the demographic, clinical and radiographic variables of these patients showed that a poorer prognosis was associated with persons of increased age (P = 0.052) and black persons (P = 0.014), and in those with papilledema (P = 0.07), hemiparesis (P = 0.001), intellectual deficits (P = 0.0002), and necrosis (P = 0.041). All patients had a surgical procedure as first treatment while 18 and three patients, respectively, underwent a second and third surgical procedure. Thirty-seven patients had a subsequent course of radiotherapy. Univariate and multivariate statistical analysis comparing the patients treated with surgery alone those treated with surgery plus radiotherapy revealed no significant population or prognostic differences between the groups. The median times until clinical deterioration were 39 versus 27 months, the median times until documented tumor recurrence were 27 versus 28 months and the median survival times were 4.5 versus 5.2 years, for nonirradiated versus irradiated patients. These data, from a large and rigidly evaluated population, demonstrated no statistically significant difference in the symptom-free interval, time until tumor recurrence, or survival between the groups nor did radiation appear beneficial to any subgroup evaluated. The results suggest the need for a prospective clinical trial to evaluate the true role of radiation therapy in the treatment of this tumor.

Statistical analysis of clinicopathological features, radiotherapy, and survival in 170 cases of oligodendroglioma

The postoperative survival time of 170 nonrandomized patients treated for cerebral oligodendrogliomas in Norway from 1953 to 1977 was studied. Survival times were significantly prolonged if postoperative irradiation was performed in addition to surgery (median survival time 26.5 vs. 38 months, p = 0.039). In the group without postoperative radiotherapy, the 5-year rate of survival was 27% compared with 36% in the irradiated patients. The respective survival rates after 8 years were 14% versus 17%; thus, there was little effect on long-term survival. Irradiation appears not to be of benefit after "total" removal. Patients with partly resected lesions appeared to benefit from postoperative radiotherapy; the median survival period after subtotal tumor resection was 37 months with and 26 months without radiotherapy (p = 0.0089). The findings also indicate that irradiation doses between 40 and 50 Gy were as effective as doses between 50 and 60 Gy in increasing the patients' probability of surviving 5 years after subtotal tumor resection. Since the risk of radiation necrosis is proportional to the dose applied, the lower dose is recommended. These conclusions were also valid when adjustments were made for prognostically significant histological and clinical features.

Clinicopathologic correlations in the oligodendroglioma

To determine the prognostic significance of histologic variables in oligodendroglial neoplasms, the presence and degree of 15 such variables were correlated with postoperative survival rates in 71 patients. By univariate analysis, prognostically significant factors, in order of decreasing importance, were mitoses (log), necrosis, nuclear cytologic atypia, vascular hypertrophy, and vascular proliferation. When studied by stepwise regression, necrosis and the number of mitoses contained all of the prognostically useful information. When each of the five variables significant by univariate analysis was tested in the Cox model by adding a variable to the model containing the other four, necrosis was found to be the only independently significant variable. There were significant positive pairwise correlations between each of the five significant histologic variables except for cytologic atypia with necrosis. The only histologic variable with a significant association with older age was the number of mitoses. These results suggest that necrosis and, to a lesser extent, the mitotic count are features that, in the appropriate setting, can be used to identify the "anaplastic" oligodendroglioma.

A clinicopathological study of 323 patients with oligodendrogliomas

All patients with oligodendrogliomas (554) from the repository of the Armed Forces Institute of Pathology were retrospectively analyzed. The pathological diagnosis was confirmed in 323 patients and each case was graded according to a previously established grading system. The clinical features of these 323 verified cases of oligodendroglioma are presented, analyzed, and compared with findings in previous studies. There is a significant age skew according to tumor grade, with 68% of patients with grade A tumors under 40 years and 83% of patients with grade D tumors over 40 years of age. Headache was the most common symptom, followed by seizure, visual loss, papilledema, paralysis, and dementia. No symptoms showed a statistically significant correlation with tumor grade. However, tumor grading allowed significant prognostic statements to be made. Attention is drawn to several often neglected symptoms of oligodendrogliomas: ataxia, hemorrhage, stroke, and cerebrospinal fluid spread. This is, to our knowledge, the largest clinicopathological study of oligodendrogliomas to date.

Oligodendroglioma: incidence and biological behavior in a defined population

The cases of 208 patients with histologically confirmed oligodendrogliomas were studied. The incidence represents 4.2% of all primary brain tumors diagnosed in the Norwegian population over a 25-year period. All of these tumors were cerebral and the majority affected the frontal lobe. The patients' median age at diagnosis was 47 years, with a range from 3 to 76 years; 6% of the oligodendrogliomas occurred in children. The median duration of symptoms before diagnosis was 20.5 months (mean 43 months). Plain skull x-ray films showed calcified deposits in 28% of the tumors. At operation, most of the tumors were poorly defined, without cyst formation, hematoma necrosis, or calcification. The median duration of disease from onset of symptoms until death was 14 months in nine untreated cases. In surgically treated oligodendroglioma patients the median survival time from onset of symptoms was 74 months. The median postoperative survival time was 35 months (mean 52 months). Tumor calcification, as seen on plain skull x-ray films, was associated with a significantly longer survival period. The surgical findings of gross necrosis, gross hypervascularity, and soft tumor consistency were all related to a shorter total duration of disease. Grossly well demarcated lesions were associated with a significantly longer postoperative survival. The length of postoperative survival correlated with the preoperative clinical status. The cumulative proportion of patients surviving 5 years was 0.342. The patient's age and sex did not have a statistically significant influence on survival time. The extent of surgical excision only seemed to play a role when the neurosurgeon considered that he had removed the whole lesion: these patients had a median postoperative survival period 14 months longer than the other oligodendroglioma patients. The ABO blood group of the oligodendroglioma patient was of prognostic value. In particular, patients with blood group A had a distinctly poorer prognosis than patients with O or B blood. The survival data from this unselected series indicate that cerebral oligodendrogliomas have a less favorable prognosis than has generally been believed.

Oligodendroglioma of the posterior fossa in childhood

Oligodendrogliomas are uncommon intracranial tumors of childhood, especially when these tumors arise in the posterior fossa. Oligodendrogliomas are usually treated with local radiation therapy. The authors report four children, median age 7.5 years, cared for over a 7-year period, who had oligodendrogliomas (all histologically malignant) of the cerebellar region. Three patients received local radiation therapy and all had recurrent disease at a median of 11 months posttreatment outside their radiation field; at the time of relapse, disease at the primary tumor site was stable. One child treated with craniospinal and local radiation therapy is disease-free 15 months after diagnosis. These results suggest that oligodendrogliomas of the posterior fossa should be considered potentially malignant lesions and treated with local plus presymptomatic craniospinal radiation therapy.

Oligodendroglial tumors in childhood

A series of 20 hemispheric tumors in children less than 16 years of age, over a period of 20 years, is presented. Among them, 8 were oligodendroglial tumors, a proportion well above the level reported in the literature. The World Health Organization (WHO) classification, which includes mixed oligoastrocytomas, in the oligodendrogliomas was used. This addition does not explain this unusually high proportion. Selection of cases and the correct histological diagnosis are probably important.

Grading of oligodendrogliomas

The purpose of this study was to determine the effectiveness of histologic grading of oligodendrogliomas in a retrospective study. 323 cases with adequate clinical information and confirmatory histological material were acquired from the files of the AFIP. A grading system was devised using the following criteria: endothelial proliferation, necrosis, nuclear/cytoplasmic ratio, cell density and pleomorphism. The grading system separated 23% of the cases into grade A, 49% into grade B, 22% into grade C and 6% into grade D. Statistical analysis showed that the grading system significantly correlated with survival (P less than or equal to 0.01). Median survival periods for each grade were as follows: grade A, 94 months; grade B, 51 months; grade C, 45 months; grade D, 17 months. Of the five factors comprising grade, only pleomorphism was significantly correlated with survival by itself (P less than or equal to 0.01). It is concluded that grading of this form of glioma can be an effective estimate of prognosis.

Oligodendrogliomas of the spinal cord

The clinical, surgical, and pathological data from 35 published cases of oligodendroglioma and of one personal case are analysed and compared with those from other tumours of the cord and from cerebral oligodendrogliomas. Oligodendroglioma of the cord has a slightly lower average age than other gliomas and is closer to that of glioblastoma. In oligodendroglioma of the cord, as of the brain, acute onset or aggravation of the symptoms and an oscillating course are frequent. Two correlated data are particularly worth noting: a) the mean CSF protein content in oligodendroglioma of the cord is higher than in any other glioma; b) intracranial hypertension, in the form of papilloedema or hydrocephalus, or both, was present in 31% of cases. This signifies cerebral oligodendrogliomatosis, which was found in 6 out of 10 necropsied cases. At operation most oligodendrogliomas of the cord appear as infiltrating "gelatinous" tumours, though a minority have a firm consistency and apparently clearcut contours, which seem to be associated with a better prognosis. Postoperative radiotherapy seems to be useful.

Temporal lobe oligodendroglioma developing from infancy into adulthood

Clinical, radiological, surgical, and histological features are reported for a patient with a temporal lobe oligodendroglioma that had developed in infancy and was diagnosed and partially resected at age 10. The patient is presently 24 years old and still well. To the best of our knowledge this is the first report of an oligodendroglioma with probable onset at 5 months of life and satisfactory course over 24 years.