MSFinals-3184

MSFinals-3184

A 28-year-old woman presents with sudden-onset severe and unremitting occipital headache. On examination, she is drowsy and confused, with a blood pressure of 180/95 mmHg. You suspect that she may have had a subarachnoid haemorrhage and arrange a computed tomography (CT) scan. This is normal. She undergoes a lumbar puncture and the results are shown below:
Pot 1: red cells 490 × 109/l, white cells 10 × 109/l, no organisms seen
Pot 2: red cells 154 × 109/l, white cells 8 × 109/l, no organisms seen
Pot 3: red cells 51 × 109/l, white cells <5 × 109/l, no organisms seen
Which of the following is the most likely explanation for these results?