• Maximilian Patzig, Christoph Laub, Hendrik Janssen, Lorenz Ertl, and Gunther Fesl.
• Bmc Neurol. 2014 Jan 1; 14: 219.

BackgroundThe specificity of computed tomography (CT) for subarachnoid haemorrhage (SAH) is very high. However, physicians should be aware of rare false positive findings, also referred to as "pseudo-SAH". We present an unusual case in which such a finding was caused by chronic hypoxaemia.Case PresentationA 37-year-old male patient presented with headaches. His CT-scan showed multiple confluent subarachnoid hyperattenuations, which mimicked SAH. However, the headache was chronic and had no features typical for SAH. The patient suffered from severe chronic hypoxaemia due to congenital heart failure. On CT-angiography diffuse intracranial vessel proliferation was found and laboratory results revealed a highly raised level of haematocrit, which had both probably developed as compensatory mechanisms. A combination of these findings explained the subarachnoid hyperdensities. Magnetic resonance imaging (MRI) showed no signs of SAH and visualized hypoxaemia in cerebral veins. A diagnosis of pseudo-SAH was made. The patient's symptoms were likely due to a secondary headache attributed to hypoxia and/or hypercapnia. Therapy was symptomatic.ConclusionsSevere chronic hypoxaemia should be recognised as a rare cause of pseudo-SAH. Clinical evaluation and MRI help differentiate SAH from pseudo-SAH.

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