Biphasic growth and subsequent spontaneous regression of posterior fossa meningioma with progressive calcification: illustrative case.

backgroundSpontaneous regression of meningiomas is rare, and the association between tumor growth dynamics and progressive calcification remains not well elucidated. OBSERVATIONS: A 76-year-old female was incidentally noted to have a calcified posterior fossa mass during evaluation for head trauma. Retrospective review of serial noncontrast CT examinations spanning approximately 17 years revealed a biphasic volumetric course consisting an initial slow-growth phase, followed by tumor enlargement and subsequent spontaneous regression. Quantitative slice-by-slice volumetric analysis demonstrated continuous progression of intratumoral calcification across tumor evolution phases. As the tumor volume decreased, calcification progressively became the dominant lesion component. MRI performed 3 months following the latest CT study demonstrated a dural-based lesion with homogeneous enhancement and a dural tail sign, findings consistent with meningioma. LESSONS: This case illustrates that meningiomas may undergo dynamic biological transitions over extended periods, including growth phases and spontaneous regression. Progressive intratumoral calcification observed throughout tumor evolution may represent a tumor aging and biological involution indicator rather than reflecting slow tumor growth. https://thejns.org/doi/10.3171/CASE26353.