An Unusual Presentation of Isolated Contrecoup Injury.

A 38-year-old man sustained a traumatic brain injury (TBI) following a road traffic accident, presenting unconscious with vomiting and right ear bleeding. He had a prior history of head trauma with cranioplasty. On admission, he was deeply unconscious (Glasgow Coma Scale (GCS) E1VTM3) with unequal non-reactive pupils. Imaging revealed a significant left-sided acute subdural hematoma (SDH), burst temporal lobe, and midline shift, alongside an old cranioplasty mesh and right petrous bone fracture. Notably, there was minimal injury on the right (impact) side but extensive hemorrhagic damage on the left (opposite) side, suggesting a contrecoup injury. He underwent emergency decompressive craniotomy and postoperative ICU care, eventually recovering enough for discharge. This case highlights an unusual presentation of contrecoup injury in the absence of significant coup-related hemorrhage. The presence of a cranioplasty mesh likely influenced injury mechanics. The proposed mechanism involves both positive and negative pressure theories: the brain lagging behind skull motion (positive pressure) and rebound forces (negative pressure), creating damage on the opposite side. The mesh's rigidity compared to natural bone may have amplified injury through stress concentration at the mesh-bone interface. This unique biomechanical interaction may explain the disproportionate injury seen contralaterally. To our knowledge, no previous case reports describe such an isolated contrecoup injury pattern associated with a cranioplasty mesh. This report underscores the importance of considering altered skull biomechanics in patients with prior cranial surgeries and contributes novel insight into TBI dynamics.