Conus Medullaris Syndrome

As the spinal cord tapers to its end at the conus medullaris, it contains the lowest segments of the cord — those that supply the pelvic organs and the saddle region — packed into a short length. Just below the conus, the canal contains a bundle of nerve roots called the cauda equina. Because the conus is part of the spinal cord itself, an injury here can produce a mixture of "upper" and "lower" nerve patterns, and it tends to affect both sides fairly symmetrically. The nearby cauda equina roots may also be involved, which is why the two syndromes can overlap.

The commonest cause is a fracture of the spine at the thoracolumbar junction — the transition between the stiff chest region and the mobile lower back — where the conus typically sits and where injuries are concentrated. A burst fracture, in which bone is pushed backwards into the canal, is a frequent culprit. Other causes include a large disc herniation at this level and, outside of trauma, tumours or other lesions affecting the conus.

The characteristic feature is early, prominent and usually symmetrical disturbance of bladder, bowel and sexual function — for example difficulty passing or controlling urine. There is often numbness in the saddle area, and leg weakness that is typically less severe and more symmetrical than in cauda equina syndrome. Back pain is common, but the intense leg (radicular) pain seen with cauda equina syndrome is often less prominent. The exact combination depends on how much of the conus, and how many of the neighbouring nerve roots, are involved.

New difficulty passing urine, loss of bladder or bowel control, numbness around the back passage or genitals, or new leg weakness — particularly after an injury to the lower back — are red-flag symptoms that require immediate assessment. Prompt recognition allows the spine to be protected and imaged and any compression to be identified without delay.

Diagnosis combines the clinical examination with imaging. An MRI scan is the key test, showing the conus, the surrounding nerve roots and any compression from bone, disc or other cause. A CT scan shows the bones and the pattern of any fracture. Careful assessment of bladder function, saddle sensation and leg strength helps to define the extent of the injury and to distinguish conus medullaris syndrome from cauda equina syndrome, though in practice the two often overlap.

Where there is compression of the conus and its surrounding structures — for example from a burst fracture pushing bone into the canal — treatment usually involves surgery to relieve the pressure and to stabilise the spine. The precise operation depends on the level and pattern of injury. The timing of surgery in these injuries is debated and is decided on an individual basis, taking account of the neurological findings, the imaging and the person's overall condition. As with all spinal injuries, rehabilitation is central, with particular attention to bladder, bowel and sexual function and to mobility.

Recovery is variable and depends on the severity of the initial injury and the structures involved. Bladder, bowel and sexual function, once affected, can be slow and incomplete to recover, and specialist management of these is an important part of care. Leg strength often has a better prospect of recovery than the pelvic functions. Overall, patient outcomes are influenced by how severe the initial injury is, how quickly compression is relieved where present, and the quality of rehabilitation.

Because the conus and the cauda equina lie close together, the two syndromes are often discussed side by side and can overlap. In broad terms, conus medullaris syndrome affects the end of the spinal cord itself, tends to cause early and symmetrical bladder and bowel problems with less leg pain, whereas cauda equina syndrome affects the nerve roots below the cord and tends to cause more severe, asymmetrical leg pain and weakness. Our traumatic cauda equina syndrome page covers the latter in more detail. The distinction guides examination and expectations, but the urgent priority in both is the same: prompt assessment and imaging.

Myth: "The spinal cord runs the whole length of the back." Fact: In most adults it ends near the bottom of the ribcage, tapering into the conus medullaris.

Myth: "Conus and cauda equina syndromes are the same thing." Fact: They are related but distinct — one affects the end of the cord, the other the nerve roots below it — though they can overlap.

Myth: "Bladder problems after a spinal injury always recover fully." Fact: Bladder, bowel and sexual function can be slow and incomplete to recover, which is why specialist management matters.

This page is for general education and does not replace an individual assessment. Treatment depends on a person's specific symptoms, examination findings, imaging findings and overall health, and should always be discussed with a suitably qualified healthcare professional.

The spinal cord does not run the whole length of the back; in most adults it ends at about the level of the first or second lumbar vertebra, near the bottom of the ribcage, in a tapered tip called the conus medullaris. Conus medullaris syndrome is an injury to this terminal segment of the cord. Because the conus contains the nerve centres that control the bladder, bowel and sexual function, an injury here tends to affect these functions early and prominently, along with numbness in the "saddle" area (the parts of the body that would touch a saddle) and a variable degree of leg weakness. It is closely related to, but distinct from, cauda equina syndrome, which affects the nerve roots just below the conus. This page explains the syndrome, how it is assessed, and what treatment involves.

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• —Ahuja CS, Wilson JR, Nori S, et al. Traumatic spinal cord injury. Nat Rev Dis Primers. 2017;3:17018. doi:10.1038/nrdp.2017.18
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• —National Institute for Health and Care Excellence (NICE). Spinal injury: assessment and initial management. NICE guideline NG41. 2016.
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• —Guideline note: NICE NG41 reviewed for initial assessment. AO Spine thoracolumbar classification informs injury description. No stand-alone AAOS clinical practice guideline specific to conus medullaris syndrome was identified at the time of writing.

This information is for general patient education and is not a substitute for an individual consultation. Always seek personalised advice from a qualified spinal specialist.