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Cauda Equina Damage and its Management
Iqbal F Hussain

This chapter is reproduced with permission from "Neurology of bladder, bowel and sexual dysfunction" edited by Clare J. Fowler, Butterworth-Heinemann, 1999 (ISBN 0-7506-9959-0).

The shorter length of the spinal cord compared to that of the vertebral column means that the most caudal roots arising from the lumbo-sacral segments of the cord travel a considerable distance in the cauda equina. Within this structure they are at risk of damage. There are numerous mechanisms of injury, some catastrophic and immediately recognisable, while others can be insidious in onset with a variety of presentations. Diagnosis of a cauda equina lesion may be complicated and require neuroradiological imaging together with tests of bladder, bowel, sexual and somatic function. Management may be difficult and require prolonged intensive and long-term rehabilitation.

Anatomy of the Cauda Equina
It is often stated that the spinal cord terminates at the level of the intervertebral disc between L1 and L2, but in fact this is only true in about half of all cases studied at post-mortem. Depending on the length of the trunk and the degree of flexion, it may terminate at a level anywhere from opposite the body of T12 to the disc between L2 and L3 or even L3 and L41,2. The cord is enclosed by the dura, arachnoid and pia mater which are separated by a potential subdural space and an actual subarachnoid space containing cerebrospinal fluid. The caudal spinal cord is termed the conus medullaris and is continuous as a filament of connective tissue known as the filum terminale. The dura and arachnoid meninges surround the filum terminale for 15 cms and extend to the level of the S2 vertebral body. There is therefore a difference of approximately 5 vertebral bodies between the conus and the distal extension of the meninges and this is a good approximation to the length of the cauda equina (Figures 1 and 2).

Figure 1 Figure 2
 Figure 1: T1SE MRI of conus (sagittal view). The spinal cord terminates opposite the lower border of the L1 vertebral body.  Figure 2: T2FSE MRI of thecal sac (sagittal view). The thecal sac terminates opposite the S2 vertebral body.

In the cervical region, the spinal nerve roots exit from the vertebral column horizontally and above the respective vertebral segment. At the caudal end of the cord the nerve roots descend for varying distances, beyond the conus medullaris in the case of S3 and S4, before reaching the corresponding neural foramen. In this caudal region the neural foramen is located below and medial to the respective neural arch and it is at this point the dorsal root ganglion lies. This is a sensory ganglion containing the cell bodies of the afferent nerves.

The bladder, bowel and sexual organs all receive important connections from the sacral part of the spinal cord by way of the pelvic plexus and pudendal nerve. The efferent parasympathetic outflow to the bladder, its main excitatory input, is provided via the pelvic nerves (S2-4). They synapse on postganglionic neurones in the pelvic plexus or in ganglia located within the bladder wall itself. Parasympathetic innervation is also important for sexual function, such as reflex clitoral erection and vaginal lubrication in women, and is partly responsible for vasodilatation of erectile tissue in men. The parasympathetic afferents have their cell bodies in the dorsal root ganglia of these same segments (S2-4) before entering the dorsal horn. The urethral sphincter (rhabdosphincter) receives motor innervation from efferent somatic pathways via the pudendal nerve. The anterior horn cells that innervate it lie in the ventral horn of sacral segments S2-4, in a region known as Onuf's nucleus. Sympathetic supply to the pelvic organs arises from T10-L1 and innervates the bladder neck and prostate (among the other male pelvic organs) and is important in both erection and ejaculation. The corresponding sympathetic afferents reside in the T11 to L2 dorsal root ganglia.

The introduction of contrast-enhanced CT and surface-coil MRI has allowed detailed visualisation of the nerve roots within the thecal sac of the cauda equina. These roots are known to form a cresentic pattern that is arranged in pairs, the motor bundle is anterior and medial to its larger sensory bundle3. Cohen et al.4 traced the cauda equina nerve roots on CT and MRI scans and compared them to cadaveric specimens. They showed that in the region of the proximal cauda equina (L2/L3) the roots occupy most of the space within the thecal sac with the motor bundle lying anteriorly. More caudally, the nerve roots become separated in a cresentic distribution, there being more space within the thecal sac and the L5 and S1 roots lying more anteriorly and lateral, while S2-4 lie in the dorsal part of the thecal sac (Figures 3A - 3E). Coronal sections can be obtained to show the location of the dorsal root ganglia within the neural canal (Figures 4 and 5). Note that there is minimal space within the neural canal and a lesion in this vicinity can cause considerable spinal nerve root compression.

Figure 3A
Figure 3A
Figure 3B
Figure 3B
Figure 3A-E: T2FSE (axial views). Serial sections taken through the intervertebral disc between T10/11, L1/2, L2/3, L5/S1 and through the lower body of the S1 vertebrae. Note that the spinal cord is circular in the most cranial section. With progressing caudal descent, individual roots become visible. This is arranged in a crescentic shape.
Figure 3C
Figure 3C
Figure 3D
Figure 3D
Figure 3E
Figure 3E
Figure 4 Figure 5
Figure 4: T2FSE (coronal view). The collection of spinal nerve roots that make up the cauda equina are seen after the cord terminates opposite the L1 vertebral body. Figure 5: T2FSE (coronal view). The dorsal root ganglia associated with the S1 nerve can be seen in the S1 foramina.

Causes and Presentation of Cauda Equina Damage
Severe damage to the cauda equina can occur following high velocity impacts to the lumbosacral spine, as seen following road traffic accidents, falls from great height or from penetrating injuries from gunshot, shrapnel or stabbing5. These injuries are likely to be associated with other local and more distant damage to soft tissue and bony structures. In one report it was shown that 85% of the spinal cord damage occurs pre-operatively (all too often at the time of the injury), about 10% in the early post-operative period and the remainder as a late complication. Although these incidents are relatively rare, with increasing numbers and higher velocity of road traffic accidents, together with better emergency treatment, cases of cauda equina injuries are more likely to survive and require long-term care and rehabilitation.

Abnormalities of the cauda equina may be developmental and be evident at birth or even ante-natally. The commonest dysrhaphic anomaly of the lower cord is a tethered conus. The diagnosis is not invariably straightforward although in about 45% of patients there are associated external signs such as a skin dimple, angioma or a hairy patch6. Bladder dysfunction is common7. A meningocoele is an extension of the dural sac outside the spinal canal (usually through a posterior defect) and on foetal ultrasound scanning such an abnormality may be seen. Although the diagnosis may be clear there may be very difficult management decisions including the possibility of terminating the pregnancy. Fortunately, these and other congenital causes of cauda equina damage (see Table 1) are rare and their management tends to be referred to dedicated paediatric centres.

Congenital Dermoid sinus
Congenital Midline Tumours: dermoid, epidermoid, teratoma, lipoma

Infectious: Neurosarcoidosis, Schistosomiasis, Abscess formation
Traumatic: Road traffic accident, Fall from height, Penetrating injuries - gunshot, stabbing
Degenerative: Central disc prolapse
Neoplastic: Primary – Ependymoma, Neurofibroma, Meningioma, Secondary metastasis
Vascular: Arteriovenous malformations
Iatrogenic: Anaesthetic, Orthopaedic and Neurosurgical procedures, Lumbar arachnoiditis following radiculogram
Table 1: Causes of cauda equina damage.

A much more common cause of cauda equina damage is prolapse of an intervertebral disc causing cord or root compression. The evolution of bipedal man is partly responsible for one of the most frequent reasons for seeking medical advice – back pain. In the lumbar vertebral segments, the commonest site for disc herniation, the anterior spinous ligaments are immensely strong so that anterior disc herniation is rare. The lumbar discs are particularly prone to herniation through the posterolateral projections with compression of neural structures, although less frequently, midline posterior herniation may also occur8. Symptoms of cauda equina root compression include back pain, sciatica, saddle anaesthesia, bladder and bowel dysfunction and leg weakness. There is a considerable debate as to the optimum timing of surgical decompression of an acute central disc prolapse, as will be discussed later.

Back pain is also frequently the presenting symptom of root compression from tumours of the cauda equina. These include neurofibromas, glial tumours such as ependymomas, astrocytomas and congenital midline tumours such as dermoid, epidermoid, teratoma and lipoma. Less common are meningiomas, arachnoid cysts, meningeal cysts and malignant melanoma9. The cauda equina may also be a site for metastatic disease and these are commonly from an intra-cranial primary such as medulloblastoma and pinealoma10. Symptoms from cauda equina tumours are rarely specific and are often insidious resulting in the possibility of late presentation and delayed diagnosis11. The common symptom of back pain may occasionally be ignored by the patient or medical practitioners until there is a development of signs such as sensory loss, leg weakness or, rarely, urinary retention. It is said that pain which disturbs sleep is characteristic of cauda equina tumour in contrast to pain from disc disease which is eased by rest and recumbency, although this is not always the case. Sensory deficit in the perineal saddle region or sphincter disturbance should prompt investigation for cauda equina damage. Although rarely reported at presentation, sexual dysfunction in both men and women may occur12,13 and may feature prominently in legal settlements where negligence has been proven following cauda equina damage.

A rare cause of cauda equina damage is a spinal arteriovenous malformation (AVM). AVMs are a heterogeneous group of conditions that can produce neurological deficit by direct cord compression or more commonly secondary to an alteration in the cord blood flow. The cord receives its blood supply from the anterior and posterior spinal arteries, while the dural supply is segmental and from branches of the intercostal arteries. The presence of the malformation results in increased pressure in the draining coronal and medullary spinal veins leading to a reduced arteriovenous pressure gradient, reduced blood flow and cord ischaemia (Aminoff 1974). This may be one explanation for the presentation of a cauda equina type syndrome despite the lesion being considerably more rostral. In one report Djindjian has showed that most AVMs are thoracolumbar (60%) with only 12% being cervical and the remaining 28% thoracic14.

In all causes of cauda equina damage, symptoms of bladder dysfunction can vary from complete urinary retention (either acute or chronic) to incontinence (both urge and stress incontinence). Significant and predominant bladder symptoms may result in such patients being referred to a urological surgeon and indeed some patients undergo urological surgical intervention before the correct neurological diagnosis is made. Predominant bowel symptoms are those of atonia with a variable degree of constipation, occasionally with overflow diarrhoea. Male subjects may present with erectile dysfunction although decreased penile tactile sensation and ejaculatory dysfunction may be additional components. Women may report loss of erotic sensation in the perineal region and an inability to appreciate sexual stimuli.

Somatic dysfunction is confined to the lower limbs and the peri-sacral region. Sensory deficit may be evident in the sacral, perineal and scrotal area. Back pain is common, although the symptom if solitary is unlikely to be initially attributed to a cauda equina lesion. Lower limb weakness is often reported and confirmed on clinical examination. The ankle reflexes may be absent and there may be an extensor plantar response if there is also cord or conus involvement.

Investigation of Cauda Equina Damage
Investigations are carried out to make a diagnosis, plan therapeutic intervention or follow progression and allow a prognosis to be made. Cauda equina lesions give rise to bladder, bowel, sexual and somatic dysfunction and the investigation of these is best carried out in a combined pelvic function laboratory.

Radiological Investigations
A plain X-ray of the spine is almost invariably carried out in the initial investigation of cauda equina lesions although most useful information is obtained from computed tomography (CT) or magnetic resonance imaging (MRI). Excellent images of tissue contrast and discrete spatial resolution can be rapidly obtained non-invasively and it is possible to carry out three-dimensional reconstructions. Where AVMs are suspected, selective spinal angiography is helpful both in confirming the diagnosis and planning interventional radiological therapeutic strategies such as embolisation of fistulae. The features of relevance is to know the origin of the AVM, the number of feeding vessels and to find the exact location of the AVM with respect to the spinal cord. Successful selective embolisation has avoided open surgical intervention in some cases of spinal AVMs presenting with Cauda Equina Syndrome.

Urological Investigations
The predominant urological symptom in patients with cauda equina lesions is of voiding difficulty. Patients report reduced flow, double and incomplete voiding and in severe cases complete retention with overflow incontinence. These symptoms can be investigated by a flow rate, measure of residual volume and cystometry. Patients with solitary cauda equina damage commonly demonstrate reduced urinary flowrate and incomplete voiding15.

Assessment of the detrusor muscle by cystometry may show a trace typical of the areflexic bladder which has previously been reported in cauda equina lesions16,17. There are, however, also reports of hyperreflexic cystometric findings following cauda equina damage. Possible mechanisms for this might include a direct and additional higher cord pathology such that a large tumour of the cauda may extend upwards to cause unexpected cystometric findings or there may be secondary ischaemic damage to the cord at a higher level following a primary lesion affecting the cauda.

Additional information about the sphincter mechanism may be obtained if cystometry is combined with fluoroscopic examination of the bladder. Most studies confirm an incompetent bladder neck18 although it is not an universal finding in cauda equina lesions and the degree of incompetence may not correlate with the level of nerve injury19. Stress incontinence from bladder neck incompetence is a particularly troublesome symptom and when it occurs in men is almost always associated with a lower motor neurone injury.

Colo-rectal Investigations
Patients with cauda equina lesions may have troublesome bowel symptoms. Typically they have an atonic bowel and are liable to severe and chronic constipation although they may get occasional overflow faecal incontinence. It is thought this may be as a result of parasympathetic denervation of the sigmoid and rectum. Incontinence to faeces and flatus may also result from a denervated anal sphincter. Anatomical and functional investigations of colo-rectal disturbances may be helpful. Barium studies and colonoscopy can provide useful anatomical information. Functional studies include anorectal manometry and defecography, which may be performed in specialised combined pelvic function laboratories.

Investigation of Sexual Dysfunction
In cases of cauda equina damage there is rarely a need to perform specific tests of sexual function. However, it is important to clearly document all symptoms reported by the patient. Men may volunteer their loss of erectile function while women may be more reluctant to report their symptoms. At a later date this documentation may be required for medico-legal purposes.

In men, it is important to demonstrate that pharmacologically induced erection is possible (with intracavernous injection or transurethral application of prostaglandin E1). This rules out a vascular cause for the underlying pathology and can also be used as a useful therapeutic intervention. The introduction of sildenafil citrate (Viagra) has been a significant advance not only in developing a new pharmacological agent to aid male erectile dysfunction but also to publicise sexual dysfunction in general. This is helping initiate studies of the management of female sexual disorders and there are clinical trials being carried out to establish if Viagra may be of benefit to women. The impact of sexual dysfunction on the quality of everyday life is unknown. Questionnaires are being validated that may become important tools in the assessment of sexual dysfunction in the future. As the therapeutic options increase with the development of safe and efficacious oral treatment, there is clearly an urgent need for tools which may help the clinician establish the burden of sexual dysfunction in both men and women.

Neurophysiological Investigations Various neurophysiological techniques may be used to demonstrate the root damage that occurs with a cauda equina lesion.

Management of Cauda Equina Damage
A wide range of conditions can give rise to cauda equina damage and the management reflects the underlying pathology. However, there are general principles that can be followed. An accurate assessment, reliant on history, examination, investigation and special reports from personnel involved in the continuing care of the patient are very necessary. The immediate management of acutely injured distal spinal cord will often require orthopaedic or neurosurgical intervention. Instability of the spine must be accurately identified and promptly stabilised. Root compression must be relieved and there is considerable debate (and medico-legal interest) about the expediency with which such surgical decompression is carried out. During the period of spinal shock an indwelling catheter should drain the bladder and clean intermittent self-catheterisation can be introduced later.

Cauda equina damage from an acute compressive lesion raises two important issues – is it the degree or duration of compression that is clinically important? The classical teaching has always maintained that immediate decompression is vital for recovery. There have been two important animal studies that have examined the problem. In female beagle hounds, Bodner20 demonstrated that neurological function evaluated by cystometry (CMG), cortical evoked potentials (CEP) and histology was dependent on the degree of compression of the cauda equina. 25% compression resulted in minimal change to the CMG and an increase in the CEP mean latency of only 3.2%. However with 75% compression, the CMG trace was a flat line, hallmark of an atonic bladder from lower motor neurone damage, and there was a 17.2% increase in the mean CEP latency.

Delamarter21, using a similar animal model for Cauda Equina Syndrome, studied neurological recovery following immediate, early and late decompression following 75% compression to the cauda equina. Following compression, all the animals had significant lower extremity weakness, tail paralysis and urinary incontinence. However, there was no statistically significant difference in recovery between the immediate, early or late decompression groups. This information may be helpful in the consent of the patient prior to surgical intervention and may explain the residual neurological deficit following early decompression.

Ultimately, many patients with cauda equina lesion will be severely disabled and require a multi-disciplinary approach which may involve occupational therapists, social workers, continence advisors and sexual therapists in addition to medical personnel. Medico-legally, in cases of cauda equina damage where negligence can be proven, there is potential for large settlements to be made. This is not surprising since these are often a young group of patients who, as a result of their injury, lose the capacity to maintain faecal and urinary continence, they may have considerable loss of mobility and additionally the loss of sexual performance may result in relationship disharmony. Symptomatic treatment of bladder, bowel, sexual and somatic dysfunction may go some way to alleviate the distressing symptoms of a cauda equina lesion.

(Source: "Neurology of Bladder and Sexual Dysfunction" in the Butterworth Heineman Blue Book Series of Practical Neurology)
Reference List

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  • Bedorook GM. Injuries of the spine and spinal cord. Part I. Oxford: North-Holland Publishing Company Ltd.; 1976; 17, Injuries of the thoracolumbar spine with neurological symptoms. p. 437-66.
  • Naidich TP, King DG, Moran CJ, Sagel SS. Computed tomography of the lumbar thecal sac. J.Comput.Assist.Tomogr. 1980;4(1):37-41.
  • Cohen SM, Wall EJ, Kerber CW, Abitol J-J, Garfin SR. The anatomy of the cauda equina on CT scans and MRI. The Journal of Bone and Joint Surgery 1991;73-B(3):381-4.
  • Robertson DP, Simpson RK. Penetrating injuries restricted to the cauda equina: a retrospective review. Neurosurgery 1992;31(2):265-70.
  • Hendrick EB, Hoffman HJ, Humphreys RP. McLaurin RE, editors.Myelomeningocele. New York: Grune and Strathan; 1977;Tethered Cord Syndrome.
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  • Ransohoff J. Clinical Neurosurgery. 1901; XIX, Lesions of the Cauda Equina. p. 331-43.
  • Mathew P, Todd NV. Intradural conus and cauda equina tumours: a retrospective review of presentation, diagnosis and early outcome. J.Neurol.Neurosurg.Psychiatry 1993;56:69-74.
  • Greenwood J, Rose JE. Rosenberg RN, Grossman RG, Schochet SS, Heinz ER, Willis WD, editors.The Clinical Neurosciences. New York: Churchill Livingstone Inc.; 1983; 16, Spinal Cord Tumours. p.
  • Fearnside MR, Adams CBT. Tumours of the cauda equina. J.Neurol.Neurosurg.Psychiatry 1978;41:24-31.
  • Comarr AE, Vigue M. Sexual counseling among male and female patients with spinal cord and/or cauda equina injury. PART I. American Journal of Physical Medicine 1978;57(3):107-22.
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  • Djindjian R. Angiography of the spinal cord. Surg.Neurol. 1974;2:179-85.
  • Murayama N, Yasuda K, Yamanishi T, Kitahara H, Shimazaki J. Disturbances of micturition in patients with spinal arteriovenous malformations. Paraplegia. 1990;27:212-6.
  • Nordling J, Meyhoff HH, Olesen KP. Cysto-urethrographic appearance of the bladder and posterior urethra in neuromuscular disorders of the lower urinary tract. Scand.J.Urol.Nephrol. 1982;16:115-24.
  • McGuire EJ, Wagner FCJn. The effect of sacral denervation on bladder and urethral function. Surg.Gynec.&Obst. 1977;144:343
  • Light JK, Beric A, Petronic I. Detrusor function with lesions of the cauda equina, with special emphasis on the bladder neck. J.Urol 1993;149:539-42.
  • Barbalias GA, Blaivas JG. Neurologic implication of the pathologically open bladder neck. J.Urol 1983;129:780
  • Bodner DR, Delamarter RB, Bohlman HH, Witcher M, Biro C, Resnick MI. Urologic changes after cauda equina compression in dogs. J.Urol 1990;143:186-90.
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Additional chapter of interest:

Chapter 6: Cauda equina disorders, by J.D. Stewart (Montreal, PQ, Canada) in the book
Neurologic Bladder, Bowel and Sexual Dysfunction edited by Clare J Fowler.

Neurologic Bladder, Bowel and Sexual Dysfunction
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Page Last Updated: 10 June 2005

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