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This young man in his 20’s has a recurrent spinal tumour. He has significant sensory loss, mainly in the left thigh, and is partially incontinent. The MRI shows tumour at T10-T12, and a second tumour mass from L5-S1. The liklihood is that the 2 tumours are connected – it just doesn’t show clearly on the MRI. The MRI indicates that the tumour is pushing the cord posteriorly at T10-T12, and anteriorly L5. The cauda equina appears full of tumour, with a large bulge of tumour at S1 which seems to extend outside the vertebra.
I am using my standard monitoring protocol for scoliosis patients – monitoring EMG from L2. L3, L4, L5, S1, and S4/5 using respectively the adductors (L2/3), quadriceps (L4), peroneus longus (L5), medial gastrocnemius (S1), and the anus (S4/5). The adductors and anus use a channel each for both left and right sides; all other channels are unique to left and right.
I am using a cortical electrical stimulator to evoke MEPs, as well as using free running EMG and triggered EMG (via stimulating probe).
1100 – The anaesthetist is using TIVA, any neuromuscular block has worn off, and I have established good baselines prior to the initial incision and subsequently after the laminectomy. The baselines appear normal on the right side with good amplitudes from all channels; those on the left side are mixed. There are good responses from L2, 3, 4 and 5 but no response from S1 or the anal sphincter.
1115 – The surgeon is starting at the L2-S1 tumour. Surgeon is using the stimulating probe to stimulate the midline of the cord – no response at 3mA using a monopolar probe.
1130 – Stimulating cortically when the surgeon does not have hands in the patient, good MEPs compared to baseline.
1230 – Tumour is out of the lumbosacral part of the spine. MEPs stable compared to baseline. Previous surgery at the T10-12 level, so this may be more difficult.
1445 – After a lengthy period, most of the laminectomy from T10 – L2 is now completed, and the task of tumour removal can begin. Lots of spontaneous activity from both sides as the bone is removed once the drilling is compeleted
1615 – After a break, surgeon is taking out tumour which is lying behind spinal cord. Because this is a recurrent tumour, and the remains of the previous tumour has been irradiated, there is no clear plane between cord and tumour and this is likely to be a lengthy process. MEPs standing up well, although the S1 and anus on right are now missing – I will try increasing the stimulation voltage.
1800 – Most tumour removed from L5-L3. Lots of spontaneous activity from both sides at L4 root level. Probe used to discriminate between tumour and nerve root.
1900 – L5-L3 section completed and moved to T10 -L2 section. MEPs still good both sides (to baseline). Lots of activity as fibrous tissue removed from top of spinal canal (this replaced the bone removed in the previous procedure).