Management of possible idiopathic inferior vena cava compression during stereotactic body radiation therapy for lung cancer.

A man in his 80s undergoing a four-dimensional CT scan for lung cancer treatment developed acute symptoms of sweating, nausea and vomiting, which resolved when seated. Imaging suggested possible idiopathic inferior vena cava (IVC) compression, where the IVC was pinched between the right kidney and a tortuously positioned aorta when lying on his left side, exacerbating symptoms. The patient's blood pressure changed with position (seated: 155/92 mm Hg, supine: 149/84 mm Hg, left lateral: 130/63 mm Hg), indicating positional effects on IVC compression. While IVC compression is typically relieved by a left lateral position in pregnant women, this patient's symptoms worsened in that position due to unique anatomical variations. This case emphasises the importance of considering positional changes in the differential diagnosis of unexplained hypotension, particularly in patients without typical risk factors.