Radiopaque ring sign as a distinct finding at the entry site of gunshot wounds on postmortem CT

Postmortem computed tomography (PMCT) is widely used in the evaluation of gunshot wounds, particularly for the assessment of projectile trajectories and osseous injury patterns. Radiologically hyperdense findings at the wound margin are frequently attributed to gunshot residue (GSR), yet their morphology and underlying mechanisms remain insufficiently differentiated. In particular, different types of hyperdense patterns at the entry site have not been systematically distinguished, despite their potential forensic relevance.

Fifty forensic cases with gunshot wounds to the head and neck were retrospectively analyzed using PMCT. Two readers independently assessed GSR-related hyperdensities, while bone fragments, projectile fragments, and the radiopaque ring sign were evaluated by consensus. Interrater agreement was assessed using Cohen's kappa.

GSR-related hyperdensities were identified in 82% and 72% of cases (κ = 0.55). Hyperdense findings were common and morphologically heterogeneous. A radiopaque ring sign was identified in 3 of 50 cases (6%) and appeared as a compact circumferential structure at the entry site. In contrast, other hyperdense findings at the wound margin and within the surrounding tissue were often difficult to distinguish from bone fragments, potentially leading to false-positive interpretations.

Hyperdense findings at the wound margin represent a heterogeneous spectrum rather than a single entity. A true radiopaque ring sign is a distinct phenomenon confined to the entry site and may be associated with specific shooting conditions, underscoring the importance of morphological differentiation for accurate forensic interpretation.