Age-Related Volumetric Changes of the Posterior Cranial Fossa and its Structures in Stroke Patients.

The posterior cranial fossa (PCF) contains critical neural structures, including the cerebellum and brainstem, whose volumetric relationships play an essential role in normal neurological function. While cranial bone growth is completed in early adulthood, brain structures may undergo age-related changes, particularly prominent in patients with stroke, potentially altering craniocerebral relationships within the PCF. Data on volumetric changes of the PCF and its contents in the adult population are limited. The aim of the study was to evaluate age- and sex-related volumetric changes of the PCF and its main neural structures in adults using MRI- and CT-based volumetric analysis.This retrospective, multicenter study included 1,280 adult subjects who underwent neuroimaging for suspected or confirmed cerebellar stroke at 11 university hospitals in Germany. In most centers, segmentation and volumetric analysis were performed using Brainlab software (Brainlab AG, Munich, Germany). In selected centers, volumetric calculations were performed using the standard method according to local protocol.PCF, cerebellar, and brainstem volumes demonstrated significant age-related changes. Cerebellar volume showed a progressive decline with increasing age from 136 cm3 (IQR 123.6-147.2) to 115.2 cm3 (IQR 107.4-131.1) (p < .001), whereas posterior fossa cerebrospinal fluid volume (PCF-CSFv) increased, indicating age-related expansion of infratentorial cerebrospinal fluid spaces. Across most age groups, males exhibited larger PCF, cerebellar, and brainstem volumes than females. In the overall cohort, these differences remained statistically significant after Holm-Bonferroni correction (all p-corrected < 0.001), whereas PCF-CSFv did not differ significantly between females and males (p-corrected = 0.438).Aging is associated with a progressive reduction of infratentorial neural tissue volumes, particularly affecting the cerebellum, accompanied by a relative expansion of PCF-CSFv. Pronounced sex-related volumetric differences persist throughout adulthood, with males demonstrating larger infratentorial structures than females. These findings provide robust normative data that may aid in the interpretation of PCF pathology in clinical and research settings.