ASFNR Clinical State of Practice Statement on Imaging of Chronic Subdural Hematoma

BACKGROUND: The efficacy of middle meningeal artery embolization (MMAE) for chronic subdural hematoma (cSDH) has heightened interest in imaging biomarkers that may reflect neomembrane activity, predict recurrence, and identify patients most likely to benefit from treatment. Characterization of hematoma internal architecture, referred to as the imaging phenotype, may provide indirect information regarding the biological activity and maturation of the neomembrane. However, imaging phenotype has not been incorporated into randomized trials or validated treatment-selection algorithms, and standardized definitions and reporting remain lacking. METHODS: The American Society of Functional Neuroradiology Clinical Practice Committee developed this State of Practice statement through expert consensus and review of the available literature. KEY MESSAGE: Noncontrast CT (NCCT) remains the primary imaging modality for cSDH assessment. Hematoma burden should be characterized by maximum thickness measured perpendicular to the inner table, midline shift, and, when appropriate, volume. Volume may be estimated using the ABC/2 formula, whereas segmentation is more accurate for irregular, crescentic, or multiloculated collections when available. Internal architecture should be described using the Nakaguchi framework of homogeneous, laminar, separated, and trabecular phenotypes, with mixed or transitional features explicitly reported. Advanced techniques, including dual-energy CT, photon-counting CT, MRI, and arterial spin labeling, may provide information regarding membrane activity but are supported by limited, largely single-center evidence and currently have a problem-solving rather than routine role. Standardized reporting and prospective validation are needed before imaging phenotype or advanced-imaging biomarkers can guide treatment selection.