Losing a marble

A 44 year old woman with no medical history presented with abdominal pain, vomiting, and lack of bowel movement for four days. Apart from an increased bilirubin level (32 μmol/L, range: <21 μmol/L) blood markers were unremarkable. What is the eponymous radiological finding and diagnosis in this plain abdominal radiograph (fig 1⇓)? Fig 1 Rigler’s triad, pathognomic of …