Cyst wall enhancement in pilocytic astrocytoma: neoplastic or reactive phenomena

Cystic pilocytic astrocytomas (CPA) consist of a mural nodule and an accompanying cyst, which may prominently enhance on MRI after contrast administration. This raises the question whether an enhanced wall represents a tumor and thus should be resected together with the solid nodule, as radical tumor surgery is associated with better prognosis. Until now, no systematic histopathological examinations of cyst walls have been reported in correlation with MRI, intraoperative appearance and postoperative clinical and MRI follow-up. We present 3 patients with CPAs and brightly enhanced cyst walls on MRI. Because of the benign, transparent appearance of the cyst wall intraoperatively, it was biopsied but not resected, and only radical removal of the nodule and its immediate surroundings was performed. Separate specimens taken from the cyst wall showed no tumor. MRI performed annually, up to 48-56 months after surgery showed no recurrence of the cyst or the tumor. In such cases of CPA, we suggest that enhancement of cyst walls may represent reactive rather than tumoral tissue, and may be left intact without risking worse prognosis. Mechanisms leading to cyst wall enhancement and the optimal surgical treatment are discussed.