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Keywords:

  • Anaesthetic techniques;
  • regional;
  • spinal;
  • combined epidural-spinal;
  • Complications;
  • neurological. Anatomy;
  • spinal cord;
  • conus medullaris

Abstract

  1. Top of page
  2. Abstract
  3. Case 1
  4. Case 2
  5. Case 3
  6. Case 4
  7. Case 5
  8. Case 6
  9. Case 7
  10. Discussion
  11. Acknowledgments
  12. References

Seven cases are described in which neurological damage followed spinal or combined spinal-epidural anaesthesia using an atraumatic spinal needle. All patients were women, six obstetric and one surgical. All experienced pain during insertion of the needle, which was usually believed to be introduced at the L2−3 interspace. In all cases, there was free flow of cerebrospinal fluid before spinal injection. There was one patchy block but, in the rest, anaesthesia was successful. Unilateral sensory loss at the levels of L4–S1 (and sometimes pain) persisted in all patients; there was foot drop in six and urinary symptoms in three. Magnetic resonance imaging showed a spinal cord of normal length with a syrinx in the conus (n = 6) on the same side as both the persisting clinical deficit and the symptoms that had occurred at insertion of the needle. The tip of the conus usually lies at L1−2, although it may extend further. Tuffier's line is an unreliable method of identifying the lumbar interspaces, and anaesthetists commonly select a space that is one or more segments higher than they assume. Because of these sources of error, anaesthetists need to relearn the rule that a spinal needle should not be inserted above L3.

This report documents seven cases in which single-shot spinal or combined spinal-epidural (CSE) anaesthesia using an atraumatic spinal needle was followed by neurological symptoms involving more than one segmental nerve root. One has previously been reported in detail elsewhere [1]. Five of these cases were encountered in medicolegal practice and two in a survey [2]. Summaries of clinical and anaesthetic data are given in Table 1 and of the neurological outcome in Table 2.

Table 1.  Clinical and anaesthetic details of seven patients who suffered damage to the conus medullaris following spinal anaesthesia
Case no.Weight (kg)Type of block* ProcedurePosition of patientSize of needle (G)Presumed level and details of insertionDose of hyperbaric bupivacaine 0.5%Outcome of block
  1. *SSS, single shot spinal; CSE, combined epidural–spinal. †All patients complained of pain on insertion of the spinal needle. CSF, cerebrospinal fluid. ‡T11−12 later confirmed. ¶L1−2 later confirmed.

162SSSCaesarean sectionLeft lateral27L2-3; free flow of CSF2.5 ml with fentanyl 12.5 µgGood
247SSSCaesarean sectionSitting25L2-3; free flow of CSF2.6 mlGood
386CSECaesarean sectionLeft lateral25L2-3; CSF after needle withdrawn2.0 ml with fentanyl 25 µgT4
466SSSBreech deliveryUnknown25L2-3; CSF after needle withdrawn; pain on injection3.0 mlIncomplete on left side
565CSECaesarean sectionSitting26L2-3; free flow of CSF2.5 mlT4-6
6102CSECaesarean sectionSitting25L2-3/L3-4 (uncertain); no recorded difficulty with insertion2.3 ml with fentanyl 25 µgT4
7102CSEIncisional hernia repairSitting27L1-2/L2-3; difficult insertion3.0 mlGood
Table 2.  Neurological outcome in seven patients who suffered damage to the conus medullaris following spinal anaesthesia
Case no.Pain on insertionMRI appearance of conus medullarisNeurological outcome
Urinary problemsSensoryMotor
1Right legSyrinx right side (Fig. 1)YesL4-S1 on rightRight foot drop
2Left hipSyrinx left sideNoL5-S1 on leftLeft foot drop
3Back, left legSyrinx left side (Fig. 2)YesL4-S1 on leftLeft foot drop
4Right side?NormalNoT4-S2 on rightOnly lasted one week
5Right legSyrinx right side (Fig. 3)YesL4-S3 on rightRight foot drop
6?Left legHigh signal in conus at L1NoL4-S1 on leftLeft leg weakness
7Right legSyrinx right sideNoL5-S1 on rightRight foot drop

Case 1

  1. Top of page
  2. Abstract
  3. Case 1
  4. Case 2
  5. Case 3
  6. Case 4
  7. Case 5
  8. Case 6
  9. Case 7
  10. Discussion
  11. Acknowledgments
  12. References

A woman who had undergone two previous Caesarean sections was booked for elective Caesarean section under spinal anaesthesia. A 27-G Whitacre spinal needle was inserted at L2−3, with slight difficulty because the patient was restless. When the needle was inserted she complained of pain down her right leg, but there was a good flow of cerebrospinal fluid (CSF) from the needle. Hyperbaric bupivacaine was injected without pain and sensory block ensued as expected. Later the same day she complained of throbbing pain radiating down the right leg, with weakness in her right leg, pain in the right thigh and buttock, paraesthesia in the right big toe and numbness over the whole of the right leg and lateral border of her right foot. Reflexes were absent and motor power was reduced uniformly round all three joints in the right leg. A magnetic resonance imaging (MRI) scan of the lumbar spine was initially reported to show no abnormality, but on review showed a small syrinx to the right of the midline, at about the level of the body of the 12th thoracic vertebra (Fig. 1).

image

Figure 1. Magnetic resonance imaging scan using T1 weighting, in case 1. (a) The sagittal view shows cord and epidural fat as white and fluid as dark. The cord ends at the lower border of L1. A dark cleft is visible in the substance of the cord, which also appears as a dark spot on the right of the midline in (b), the axial image at T12.

Some months later, she still complained of persistent pain and numbness in the right leg and foot. On examination, light touch, pin prick and vibration sense were all reported to be absent below the level of T8−9. All reflexes were brisk except the right knee, ankle and plantar reflexes which were absent, and there was a persistent foot drop. There was also some difficulty initiating micturition, with poor bladder sensation. Electromyographic (EMG) changes suggested motor and sensory deficit at the levels of L4−5–S1 and that the damage was central, in the spinal cord or roots, rather than peripheral. The extent of authenticated damage could not be explained by damage to a single root.

Case 2

  1. Top of page
  2. Abstract
  3. Case 1
  4. Case 2
  5. Case 3
  6. Case 4
  7. Case 5
  8. Case 6
  9. Case 7
  10. Discussion
  11. Acknowledgments
  12. References

A primipara required an emergency Caesarean section when not in labour because of unprovoked decelerations in the fetal heart trace. It was decided that this should be under spinal anaesthesia. A 25-G pencil-point needle was inserted at L2−3. Insertion was easy but was associated with left hip pain. Clear CSF was obtained and hyperbaric bupivacaine injected without problem, producing a satisfactory block.

On the following day, she stayed in bed as her leg felt weak, but micturition was normal. Numbness, weakness and ‘pins and needles’ in the left leg persisted but with some improvement over the next few days. Neurological examination showed that sensation was reduced over the lateral side of the left lower calf, dorsum of the foot and the outer three toes. There was weakness of all movements in the left ankle joint and great toe, and the left ankle jerk was reduced.

The MRI scan showed no epidural abnormality or disc protrusion, but a cavity within the cord on the left side from the lower thoracic region to the conus, which ended at L1−2. The appearance was not consistent with a congenital abnormality and there was no evidence of vertebral damage to suggest a traumatic syrinx. She went home, after some improvement, on the sixth postpartum day. Mild foot drop and some abnormality of sensation persisted on the left side.

Case 3

  1. Top of page
  2. Abstract
  3. Case 1
  4. Case 2
  5. Case 3
  6. Case 4
  7. Case 5
  8. Case 6
  9. Case 7
  10. Discussion
  11. Acknowledgments
  12. References

A parous woman was booked for Caesarean section after failed induction of labour for mild pre-eclampsia at 41 weeks' gestation. A CSE technique was used, and although the anaesthetist stated that it was inserted in ‘the lower back’ the patient recalled that it was at about the level of her bra strap. During insertion of the spinal needle she reported severe pain radiating throughout her back and down the left leg. Cerebrospinal fluid emerged only after the needle was withdrawn slightly. She was given hyperbaric bupivacaine with fentanyl intrathecally with only transient slight pain, and a bilateral block to T4 resulted. The operation passed uneventfully and the epidural catheter was not used.

After the Caesarean section it soon became clear that her left leg was not recovering normally. She had persistent left leg weakness and pain, numbness from the groin downwards, headache and difficulty passing urine. On examination, she had sensory loss from L1 downwards in the left leg, severe weakness (slight movement only) round all joints and absent reflexes in the left leg. The MRI scan later that day showed no epidural abnormality, but a swollen conus with increased signal from T10 to T12, mainly on the left side (Fig. 2). This was diagnosed as a small haematoma within the cord.

image

Figure 2. Magnetic resonance imaging scan using T2 weighting, in case 3. The end of the cord is less clear in this sagittal image (a), which appears to show several vacuoles, but the syrinx is clearly visible on the left side in (b), the axial view at cut 17 in (a).

Headaches, foot drop, toe deformities, pain and some numbness in the left leg persisted, with sphincter disturbance which showed some improvement.

Case 4

  1. Top of page
  2. Abstract
  3. Case 1
  4. Case 2
  5. Case 3
  6. Case 4
  7. Case 5
  8. Case 6
  9. Case 7
  10. Discussion
  11. Acknowledgments
  12. References

This patient received a single-shot spinal anaesthetic during labour for assisted vaginal breech delivery. The spinal needle was sited by an experienced anaesthetist, who reported using the L2−3 interspace, although later examination suggested it was T11−12. On insertion of the needle, the patient screamed and reported a burning sensation on the right side. The needle was withdrawn and CSF aspirated. Hyperbaric bupivacaine was injected but there was pain on injection. The block was incomplete on the left side.

Initially on the first postpartum day there was sensory loss up to T4 on the right and T10 on the left. Motor function was grossly impaired but recovered completely in a week. Sensation returned to normal on the left over weeks, but remained abnormal on the right from T4 to S2 with dysaesthesia requiring medical treatment. There were no bladder symptoms. The MRI scan was reported as normal but the signs were believed to relate to damage to the spinothalamic tract.

Case 5

  1. Top of page
  2. Abstract
  3. Case 1
  4. Case 2
  5. Case 3
  6. Case 4
  7. Case 5
  8. Case 6
  9. Case 7
  10. Discussion
  11. Acknowledgments
  12. References

This patient had pre-eclampsia but with normal clotting. She had a CSE inserted reportedly at L2−3. During insertion of the spinal needle she experienced transient pain shooting down her right leg, but there was free flow of CSF and no pain on injection of bupivacaine. The resulting block height was as expected.

Postpartum recovery was incomplete in the right leg, and initial neurological examination revealed diminished sensation on the right from L4 to S3, with weak dorsal and plantar flexion at the ankle but normal reflexes. She had urinary retention requiring prolonged catheterisation. The MRI scan (Fig. 3) showed what was reported as a cleft within the right side of the conus at T12–L1. This was diagnosed as a conus infarct.

image

Figure 3. Magnetic resonance imaging scan using T2 weighting, in case 5. (a) Sagittal view. The syrinx shows to the right of the midline in (b), the axial view at the level of the T12–L1 disc.

She was reviewed 8 months later when her urinary problems had recovered, but dysaesthesia and foot drop continued in the right leg. On external examination, the site of skin puncture was found to be consistent with L2−3. It was considered impossible for the spinal needle to have reached the site of the lesion.

Case 6

  1. Top of page
  2. Abstract
  3. Case 1
  4. Case 2
  5. Case 3
  6. Case 4
  7. Case 5
  8. Case 6
  9. Case 7
  10. Discussion
  11. Acknowledgments
  12. References

This patient required Caesarean section under CSE because of deteriorating renal disease early in the third trimester of pregnancy. The level of CSE insertion was thought to be L2−3 or L3−4. The patient recalled pain on insertion, although no problems were recorded by the anaesthetist at the time. The level of block was T4 and surgery was uneventful.

Post partum, the patient complained of pain in the left leg as soon as the block began to wear off. The MRI scan showed a high signal on T2-weighted spin echo in the conus at the vertebral level of L1.

Pain, dysaesthesia and weakness in the left leg continued. Eighteen months later she had reduced temperature and vibration sensation below the left knee, allodynia in L5 and S1, and a numb great toe. There was some weakness at the hip, knee and ankle, with eversion the most severely affected.

Case 7

  1. Top of page
  2. Abstract
  3. Case 1
  4. Case 2
  5. Case 3
  6. Case 4
  7. Case 5
  8. Case 6
  9. Case 7
  10. Discussion
  11. Acknowledgments
  12. References

This obese patient with a history of difficult intubation presented for re-repair of an incisional hernia. It was decided to use spinal anaesthesia, but insertion was not easy and several attempts produced ‘pins and needles’ down the left leg. Eventually, and with difficulty, a CSE approach was tried on what felt to the patient like the right side. The subarachnoid space was entered successfully at a level that was thought to be either L1−2 or L2−3 (later confirmed by image intensifier as L1−2). This produced a sharp pain on the right side, but spinal anaesthesia produced a good block and surgery was successfully accomplished.

Postoperatively, she complained of pain and weakness in the right leg, and was found to have foot drop. This was initially attributed to tight antithromboembolism stockings, but symptoms persisted and 2 weeks later MRI revealed a syrinx within the right side of the conus. Electromyography confirmed an L5–S1 lesion. Her foot drop persisted.

Discussion

  1. Top of page
  2. Abstract
  3. Case 1
  4. Case 2
  5. Case 3
  6. Case 4
  7. Case 5
  8. Case 6
  9. Case 7
  10. Discussion
  11. Acknowledgments
  12. References

The seven patients whose cases are reported here all suffered damage to more than a single nerve root, three after single-shot spinals and four after CSEs. Their ages ranged from teens to fifties and their weights from 47 to 102 kg. That six of them were obstetric patients probably reflects the author's sphere of practice. In all cases an atraumatic spinal needle, usually a 25 or 27 G Whitacre, was used. In all cases the anaesthetist believed the needle was being inserted at L2−3 or thereabouts. In three cases there was free flow of CSF without any need for needle adjustment, yet all patients reported pain on insertion of the needle, and in only one was there also pain on injection of the anaesthetic. All patients received bupivacaine rather than lidocaine, the former having considerably less propensity to neurotoxicity [3, 4], while some but not all received fentanyl. In all but one case, spinal anaesthesia produced a block such as would be expected from the dose of bupivacaine that was given (Table 1). Case 4 might have been expected to suffer the most severe symptoms as the only case in which the local anaesthetic appeared to have been injected into the cord, with a resulting incomplete block. Indeed, sensory symptoms were the most extensive, but there was no sphincter disturbance and motor loss was short-lived. Symptoms were believed to relate to the spinothalamic tract, although such damage would be unlikely from a spinal needle as the spinothalamic tract is of course on the anterolateral aspect of the spinal cord. Uniquely in this case, no changes were said to be visible on MRI.

In all cases sensory and motor deficit of lower motor neurone distribution relating to one leg, usually with unilateral MRI changes in the conus, followed pain on spinal needle insertion on the same side (Table 2). In no case did the spinal cord appear to be unduly long.

Aetiology of conus lesions

When major neurological symptoms follow neuraxial blockade, the worried clinician turns to imaging techniques to exclude an epidural space-occupying lesion which would require urgent decompression. Epidural haematoma, abscess, prolapsed disc and spinal stenosis have all been reported in such circumstances [5, 6]. Subdural haematoma is also reported after spinal anaesthesia [7]. Compression in the lumbar region, as it is often exerted below the cord, usually gives rise to cauda equina syndrome. No such features were visible on MRI in any of the present cases.

Signs and symptoms relating to the conus medullaris may also result from compression by tumours [8, 9], syrinx [10], congenital cysts [11, 12] or vascular malformations, or from trauma [13–15], infarction [16–19] and tethered cord [20, 21].

Mathew & Todd [8] analysed the presentation in 62 patients with tumours in either the cauda equina or the conus. The commonest symptom in both groups was back pain, with bilateral leg pain being more common with conus and unilateral with cauda equina tumours. Unilateral or bilateral leg weakness, usually lower motor neurone, could occur in both groups, with bladder involvement present in 36% of conus and 26% of cauda equina tumours. Anal sphincter involvement was uncommon.

A congenital cyst differs from a syrinx in that the former is a congenital dilatation of the ventriculus terminalis (the terminal portion of the central canal, not normally visible on MRI) and is lined with ependyma [11]. Presenting symptoms are said to be non-specific and include low back pain, sciatica, leg weakness and bladder dysfunction [11, 12]. The MRI appearance of such a cyst is much larger than in the present series, and suggests that it virtually fills the vertebral canal, causing considerable compression of nervous tissue and accounting presumably for the common occurrence of back pain, a symptom that was prominent in case 6 in the present series.

Trauma may result from vertebral fracture [15], a shearing injury (as seen in leg injuries from motor cycle accidents) causing nerve root avulsion [13], or occasionally even manipulation [22] causing vascular damage. Pain and bladder symptoms are prominent [14].

Infarction of the conus medullaris is uncommon, because the blood supply to the conus is normally secure, being derived from the artery of Adamkiewicz with generous anastomoses. Occlusion of this artery may result in paraplegia, not cauda equina or conus syndrome. However, in a minority of individuals, perhaps 20%, the blood supply to the conus comes from sacral radicular arteries with fewer anastomoses, and may be more vulnerable. The usual victims are the elderly with arterial pathology [16–18]. Pre-eclampsia might have been a possible contributory factor in cases 3 and 5.

Tethered cord syndrome results from a congenital anomaly; it may occur in isolation, in some forms of scoliosis and typically diastematomyelia. It commonly presents with urinary symptoms [20, 21] and may be exacerbated by the lithotomy position. Although typically the conus is abnormally low, it may occasionally be at a normal level but tethered by a tight filum terminale. Tethered cord should represent a contraindication to neuraxial anaesthesia. None of the cases reported here showed evidence of it.

Intrathecal injection of a neurotoxic substance, such as irritant agents that were once used for spinal anaesthesia, can produce cauda equina syndrome, because the sacral roots are poorly myelinated and particularly vulnerable to chemical damage. Although Waters et al. [3] reported ‘conus medullaris injury’ following spinal anaesthesia using tetracaine and lidocaine in sequence, the cauda equina was the more likely site of such injury. Cauda equina syndrome is indeed described following continuous spinal anaesthesia using lidocaine [23]. Tedeschi et al. [24] reported a case of true conus injury following spinal anaesthesia in a 62-year-old diabetic woman, with the MRI appearance of gas within the cord and oedema surrounding it. Katz & Hurley [25] described the case of a parturient who was given repeated painful top-ups via an epidural catheter embedded within the conus. The resulting syrinx appeared to fill the vertebral canal, an MRI appearance similar to that of a congenital cyst. Greaves [26] reported a case of haematomyelia following attempted spinal anaesthesia believed to be at L3−4. The patient, another elderly woman, had a hip replacement under general anaesthesia following failed spinal anaesthesia. She had suffered severe pain reportedly in the left leg on injection of an estimated 0.3 ml of hyperbaric bupivacaine. An atraumatic spinal needle had not been used. Postoperatively, she had sensory deficit from T12 to L3 and a dense motor paralysis in the right leg. She died on the tenth postoperative day of pulmonary embolus, and at autopsy the needle track, identified at T12–L1, penetrated the conus and was associated with a haemorrhage within the cord extending 4.5 cm cephalad, on the right of the midline. The anomalous side of the initial pain was apparently unnoticed by the author, editor and all referees of this paper. This case is important because, although there was no MRI, the nature of lesion was verified at postmortem examination, and also because of the proven error of perhaps three segments in the level of spinal insertion.

Three anatomical factors

1 Although the cord commonly ends opposite the lower border of L1 or the L1−2 interspace, it may extend as low as L3. Thomson [27] found that it reached L2 in 43% of women but only 27% of men. The frequency distribution of the segmental level at which the spinal cord ends was assessed by Reimann & Anson [28] in 129 cadavers, and by Saifuddin et al. [29] in a more recent MRI study of 504 adults. Their results are summarised in Fig. 4. Considering the angle of entry of a spinal needle, if inserted at L1−2 it might reach a conus that ended at the lower border of L1, which according to Fig. 4 would encompass between 63 and 78% of individuals. Using the same argument, if inserted at L2−3 it might be possible to reach the conus in 4–20% of people.

image

Figure 4. Proportion of adults in whom the cord would be present at each spinal level. Cumulative data derived from Reimann & Anson [28] (▪) and Saifuddin et al. [29] (◆); L2 lower = the lower third [29] or half [28] of the body of L2; L2 mid = middle of the body of L2 (interpolated in upper curve); L2 upper = upper third [29] or half [28] of the body of L2; L1/2 = L1−2 interspace; L1 lower = the lower third [29] or half [28] of the body of L1.

2 Tuffier's line, that joining the iliac crests, while commonly used to identify lumbar interspaces, does not bear a constant relationship to them. Although the mode is the lower border of L4 to the L4−5 interspace [30, 31], the level may vary from L3−4 to L5–S1, hence a major source of error.

3 At the level of the conus the nerve roots form a highly organised overlapping pattern in close proximity to the cord, and bound to it by an intricate web of arachnoid membrane [32].

Possible mechanisms in the cases reported here

The consistent histories in these seven cases, with damage to more than one root, strongly suggest that the needle-tip alone can cause conus damage. In all cases the symptoms were mainly unilateral, unlike with more severe conus lesions, but this is perhaps not surprising because the MRI lesions appeared small and unilateral (Figs 1–3). The MRI changes that were observed are consistent with fluid collection, intramedullary haemorrhage or a small infarct. Yet most of those involved did not believe the needle could have reached the spinal cord. This may be a misapprehension (see below) but it is possible, perhaps, that a needle inserted among the tightly knit terminal roots could tear the surrounding membrane causing a small haemorrhage.

Why this cluster of cases? Can they be attributed to the current fashion for atraumatic needles? It is true that an atraumatic spinal needle has at least 1 mm of blind tip beyond the hole and there may be a tendency to insert it further into the subarachnoid space than is necessary with a Quincke needle. Yet this 1 mm is unlikely to be the whole answer.

For many years spinal anaesthesia was in the doldrums, while epidural blockade flourished, and anaesthetists learnt to site epidural needles at all manner of levels. Then, with the re-introduction of atraumatic needles and the use of less noxious local anaesthetic solution, the practice of spinal anaesthesia made a comeback, particularly in obstetric practice, and it is now the most popular form of anaesthesia for Caesarean section [33]. So now, many anaesthetists with liberal attitudes to lumbar interspaces that are, moreover, condoned by many textbooks [34], have taken to using spinal and CSE anaesthesia. It should be emphasised, however, the cephalad tilt given to the spinal needle at CSE using the needle-through-needle technique is not the only problem, as three of the cases reported here related to single-shot spinal anaesthesia.

Although many anaesthetists are confident that they can identify lumbar interspaces accurately, van Gessell et al. [35] demonstrated that 59% of dural punctures were performed one or two spaces higher than assumed. More recently, Broadbent et al. [36] found that when a group of experienced anaesthetists believed they had identified L3−4, in 85% of observations the space selected was one to four segments higher than this. Given the inaccuracy of methods of identifying lumbar interspaces, and the variability of the position of the conus, it cannot be logical to aim to insert a needle intrathecally above the spinous process of L3.

If a spinal needle causes pain, it is obviously correct to avoid injection although it may be too late to prevent nerve damage. It would also be wise to establish by radiological means the interspace that has been used. The moral of these stories is not to avoid atraumatic needles but to avoid upper lumbar interspace at all times, exercising particular care in women.

Acknowledgments

  1. Top of page
  2. Abstract
  3. Case 1
  4. Case 2
  5. Case 3
  6. Case 4
  7. Case 5
  8. Case 6
  9. Case 7
  10. Discussion
  11. Acknowledgments
  12. References

I am most grateful to Drs Philippa Groves, Paul Harvey and Paul Wilson for information about three of these patients, and to Dr Mark Scrutton for reading this report with a critical eye and improving it.

References

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  2. Abstract
  3. Case 1
  4. Case 2
  5. Case 3
  6. Case 4
  7. Case 5
  8. Case 6
  9. Case 7
  10. Discussion
  11. Acknowledgments
  12. References
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