Acta Neurochir (Wien) (1994) 129:131-139 :Acta . . Nduro&lrurglca 9 Springer-Verlag 1994 Printed in Austria Pilocytic Astrocytomas of the Posterior Fossa A Follow-up Study in 33 Patients C. Hojer 1, G. Hildebrandt 1, H. Lanfermann 2, R. Schr6der 3, and W. F. Haupt 4 Departments of ~Neurosurgery, 2Radiology, 3pathology, and 4Neurology, University of Cologne, Cologne, Federal Republic of Germany Summary The extent of resection in pilocytic astrocytoma of the posterior fossa often remains undefined and the indications for further treat- ment in incompletely resected tumours are a matter of debate. It has been also realized that the problem of hydrocephalus in patients with pilocytic astrocytoma of the posterior fossa has not yet been solved and the diagnostic impact of postoperative CT findings re- mains questionable. We retrospectively reviewed the data from 33 patients harbouring a pilocytic astrocytoma of the posterior fossa to evaluate the impact of surgical technique in terms of radicality and of postoperative imaging results upon prognosis and adjunctive treatment. In addi- tion, the issue of hydrocephalus was considered and related to dif- ferent treatment modalities. Thirty patients underwent surgical treatment whereas 3 had open biopsy of the tumour. Macroscopically gross total resection of the tumour was performed in 20 patients, whereas resection was partial in 10. Follow-up was obtained in 29 patients for a period which ranged between 2 and 184 months (85 months + 56months). Outcome was good in 24 patients who had only slight neurological deficit and poor in 3 patients, who were severly disabled. Two patients died during the follow-up period. Recurrent tumour growth occurred in 2cases with incompletely resected tumours. From the series presented, it was concluded that long-term fol- low-up with CT seems mandatory in cases with contrast-enhancing residual tumour. Recurrent tumour growth should be assumed in postsurgical patients with an enlarging area of enhancement shown in follow-up CT studies. Permanent ventriculoperitoneal shunting is required in certain patients with pre- or postoperative hydrocephalus. While percutaneous irradiation treatment is not curative, the role of radiosurgery has to be defined in the future. Keywords." Pilocytic astrocytoma; posterior fossa; operative pro- cedure; neuro-imaging techniques. Introduction Cranial pilocytic astrocytomas, initially described by H. Cushing in 19315, are grouped together with low- grade glial neoplasms because of their benign biological behaviour 4. They represent slowly growing tumours in whom malignant transformation occurs very rarely 18. Histologically, these neoplasms are well defined by the occurrence of elongated and slender hair-like cells con- taining stout neuroglial fibrils 1~ 24 As a consequence of improved neuro-imaging and surgical techniques as well as postoperative intensive care, morbidity and mortality of patients with pilocytic astrocytomas of the posterior fossa has decreased in recent years 16. Nevertheless, this entity accounts for considerable morbidity and mortality mainly in young patients. We evaluated the findings of 33 patients with pilo- cytic astrocytoma of the posterior fossa in order to elucidate the peculiarities in the management of this lesion such as: surgical technique, pre- and postoper- ative treatment of hydrocephalus, the influence of re- sidual tumour considering long-term survival and the impact of imaging results upon further treatment. Methods The retrospective analysis included the historical, clinical, neuro- imaging and intra-operative data of 33 patients presenting with pil- ocytic astrocytoma of the posterior fossa. The patients were treated at the Neurosurgical Department of the University of Cologne from