Conus medullaris Syndrome: Symptoms, Diagnosis, Treatment And Prognosis
Conus medullaris syndrome occurs due to trauma to conus medullaris and nerve roots of the spine. Most often T12 to L2 vertebrae are involved.
Conus medullaris vs cauda equine syndrome
conus medullaris syndrome
The term “cauda equina syndrome” is usually used to indicate a group of symptoms and signs caused by a compression radiculopathy of two or more nerve roots in the lumbar canal. Although there are various caiises of this syndrome, this communication is concerned only with those associated with lumbar disc herniation. There were no cases of the rare, severe cauda equina paralysis from massive disc extrusion which has been reported previously (O’Connell 1950, Robinson 1965, Spangfort 1972).
It is generally accepted that a disc herniation commonly causes compression of a single root, and this is easily explained both on anatomical and clinical grounds. Since the posterior longitudinal ligament reinforces the annulus in the midline, most disc herniae occur in the lateral part of the floor of the spinal canal, where the disc material compresses the adjacent lower root as it courses in the lateral recess on its way to the exit foramen. In recent years, however, disc lesions causing atypical or multiple root involvement, simulating an expanding lesion, have been demonstrated both myelographically and operatively. Muscle weakness is generally mild, and lower limb weakness associated with CES is predominantly asymmetrical in patients with an incomplete injury.
Although damage to the cauda equina may be caused in a variety of ways, the term cauda equina syndrome has come to be applied specifically to the neurological dysfunction that follows massive central or centrolateral lumbar disc prolapse. Fortunately, this occurrence is rare, accounting for only 2–3% of all lumbar disc operations. Whilst injury to the cauda equina can occur from a disc prolapse as high as T11/12 or T12/Ll, at this level the conus medullaris is affected. The clinical picture therefore is somewhat different from the more common occurrence, which is for the prolapse to occur at the L4/5 and L5/S1 levels.
Nerve fibres have differing susceptibilities both to ischaemia and mechanical trauma. Reversibility is dependent upon relief of both the mechanical pressure, which is obstructing axoplasmic flow, and the resolution of ischaemia/venous congestion. Because peripheral nerves possess Schwann cells they are, in theory, capable of regen- eration. However, if compression causes Wallerian degeneration at the level of or proximal to the cell body (as is the case for the parasympathetic nerves and the sensory fibres before they reach the root sleeve) regeneration will not occur.
Three other factors are also worthy of note when considering compression of the cauda equina. Firstly, a lower motor neuron lesion involving the autonomic nerves to the bladder is not synonymous with a similar lesion in a somatic nerve. Bladder musculature does not become flaccid simply as a consequence of pre- ganglionic motor denervation; it only loses reflex.
Cause of conus medullaris
Conus medullaris is near the nerve roots and any trauma there damages the nerves.
It could be caused due to:
Trauma like fractures
Tumor – vertebral body
Vascular lesion like arteriovenous fistula
Clinical features of conus medullaris
Back pain which is often severe
Bladder and bowel reflex is lost
Numbness, upper and lower limb weakness
The most distressing consequence of complete cauda equina damage is generally loss of bladder control. Not only does it pose a risk to health as a consequence of renal failure, but it may make work and social life very difficult. Loss of anal control is, in many respects, easier to manage.
When the urinary bladder and urethral sphincters are denervated there is lack of awareness of the need to void. Either straining or manual pressure on the lower abdomen is needed to micturate because detrusor function is lacking. The typical picture is of dribbling overflow urinary incontinence.
Genital function is also impaired and sensibility of the external genitalia is lost. Penile erection of sorts may be achievable at times, but ejaculation will be weak and may be lost altogether if the bladder neck has been opened surgically to facilitate micturition. Anorectal continence is also lost, although seldom is this noticed acutely because of an inability to appreciate filling of the rectum.
Bladder musculature does not become flaccid simply as a consequence of pre- ganglionic motor denervation; it only loses reflex activity. An atonic bladder is the result of muscular rather than neural injury (i.e. over-distension). Secondly, conduction in a single nerve fibre is an all or none phenomenon. Thirdly, the distinction between an incomplete and a complete lesion of the cauda equina is extremely important. Studies of major sacral resections for tumour indicate that complete unilateral loss of the sacral nerves is consistent with near-normal pelvic autonomic function. Partial loss of cauda equina function therefore may cause little or no disability
Diagnosis of conus medullaris
Diagnosis can be made by MRI or CT scan
Treatment and prognosis of conus medullaris
Doctor holding X-ray
The prognosis depends upon the severity of the case, underlying diseases. If timely diagnosis and treatment is done then this will be improve the prognosis. Emergency surgery, by its very nature, is often carried out under Cauda equina syndrome. Relief of cauda equina compression can be considerably more difficult than routine lumbar disc surgery. If there is no benefit to be gained from emergency operation then it should be scheduled for a time when there is least risk of adding to the existing neurodisability.