We describe a case of lumbosacral plexopathy caused by an isolated aneurysm of the common iliac artery. The patient presented with worsening low back pain, progressive numbness and weakness of the right leg in the L2-L4 distribution. This had previously been diagnosed as sciatica. A CT scan showed an aneurysm of the right common iliac artery which measured 8 cm in diameter. Despite being listed for emergency endovascular stenting, the aneurysm ruptured and the patient died.

It is important to distinguish a lumbosacral plexopathy from sciatica and to bear in mind its treatable causes which include aneurysms of the common and internal iliac arteries.

We obtained samples of spinal accessory nerve from patients undergoing radical surgery for tumours or nerve grafting in the neck. These were analysed by light and electron microscopy for the type of fibre. All contained fibres consistent with non-proprioceptive sensory function including pain.