Oligodendroglioma and surgery

  Does anyone have statistics on how many oligodendrogliomas are inoperable and what impact this lack of surgery has on prognosis?
There is not a great deal of information  dealiing with  your precise question, however I have
located a large series published (in English )in 1988 ,which may answer
your question, the key line I will also quote from the abstract states that
" Patients with gross total tumor resection (n=47) had a median survival
time and 5-year survival rate of 3.3 years and 84% compared to 1.2 years
  and 42% for patients with subtotal resection (n=41).
  As you can see in this series 88 of 89 patients had surgery.
Dehghani F.  Schachenmayr W.  Laun A.  Korf HW.
Dr. Senckenbergische Anatomie, Anatomisches Institut II,
Johann-Wolfgang-Goethe-Universitat, Frankfurt/Main, Germany.
Prognostic implication of histopathological, immunohistochemical
and clinical features of oligodendrogliomas: a study of 89 cases.
Acta Neuropathologica.  95(5):493-504, 1998 May.