Spontaneous contrast enhancement fluctuation in adult pilocytic astrocytoma

Follow-up imaging is crucial in managing primary brain tumors, with changes in contrast enhancement often used as a marker of tumor activity. However, fluctuations of enhancement independent of tumor progression have been described in low grade tumors in the paediatric population. This study aims to characterize the phenomenon of spontaneous contrast enhancement fluctuations in pilocytic astrocytoma and other low-grade primary brain tumors in the adult population.

A retrospective review of our MRI database (2011-2021) identified cases of pilocytic astrocytomas, pilomyxoid astrocytoma and rosette-forming glioneuronal tumors with stable tumor size with enhancement changes in clinically stable adult patients off medical treatment. After excluding those without serial MRIs, we reviewed the MRIs and clinical records of 238 patients. Number of cases with enhancement fluctuations, mean duration of increasing enhancement prior to stability or decline and number of fluctuation cycles were recorded.

The cohort included 9 adult patients, 6 pilocytic astrocytomas, 1 pilomyxoid astrocytoma and 2 rosette-forming glioneuronal tumors. Four of these were unresected (44%), while five were residual or recurrent tumors (56%). Despite stable tumor size and clinical status, a variety of enhancement patterns over time were observed: 44% of cases (4/9) demonstrated new or increasing enhancement on follow-up, with subsequent regression of enhancement over a 1-4 year follow-up period. An additional 44% of cases (4/9) displayed cyclical increasing and decreasing enhancement over a longer 7-15 year follow-up period. Mean duration of increasing enhancement prior to stability or decline was 12.3 months (SD 7.1). One case exhibited complete spontaneous resolution of enhancement. Fluctuation in morphology of enhancement was also observed in 44% of cases (4/9).

This is the first study to describe spontaneous fluctuation of enhancement in pilocytic astrocytoma and other circumscribed low-grade brain tumors in an adult population. Awareness of this phenomenon is crucial to prevent misinterpretation of enhancement changes as evidence of tumor progression or regression in clinically stable patients, circumventing unnecessary treatment changes and interventions.