Cauda Equina and Conus Medullaris Syndromes Clinical Presentation

Updated: Jun 13, 2018
  • Author: Segun Toyin Dawodu, JD, MD, MS, MBA, LLM, FAAPMR, FAANEM; Chief Editor: Nicholas Lorenzo, MD, CPE, MHCM, FAAPL  more...
  • Print


Patients can present with symptoms of isolated cauda equina syndrome, isolated conus medullaris syndrome, or a combination. The symptoms and signs of cauda equina syndrome tend to be mostly lower motor neuron (LMN) in nature, while those of conus medullaris syndrome are a combination of LMN and upper motor neuron (UMN) effects (see Table 1, below). The history of onset, the duration of symptoms, and the presence of other features or symptoms could point to the possible causes.

Table 1. Symptoms and Signs of Conus Medullaris and Cauda Equina Syndromes (Open Table in a new window)


Conus Medullaris Syndrome

Cauda Equina Syndrome


Sudden and bilateral

Gradual and unilateral


Knee jerks preserved but ankle jerks affected

Both ankle and knee jerks affected

Radicular pain

Less severe

More severe

Low back pain



Sensory symptoms and signs

Numbness tends to be more localized to perianal area; symmetrical and bilateral; sensory dissociation occurs

Numbness tends to be more localized to saddle area; asymmetrical, may be unilateral; no sensory dissociation; loss of sensation in specific dermatomes in lower extremities with numbness and paresthesia; possible numbness in pubic area, including glans penis or clitoris

Motor strength

Typically symmetric, hyperreflexic distal paresis of lower limbs that is less marked; fasciculations may be present

Asymmetric areflexic paraplegia that is more marked; fasciculations rare; atrophy more common



Less frequent; erectile dysfunction that includes inability to have erection, inability to maintain erection, lack of sensation in pubic area (including glans penis or clitoris), and inability to ejaculate

Sphincter dysfunction

Urinary retention and atonic anal sphincter cause overflow urinary incontinence and fecal incontinence; tend to present early in course of disease

Urinary retention; tends to present late in course of disease

Symptoms of cauda equina syndrome include the following:

  • Low back pain

  • Unilateral or bilateral sciatica

  • Saddle and perineal hypoesthesia or anesthesia

  • Bowel and bladder disturbances

  • Lower extremity motor weakness and sensory deficits

  • Reduced or absent lower extremity reflexes

Low back pain can be divided into local and radicular pain. Local pain is generally a deep, aching pain resulting from soft-tissue and vertebral body irritation. Radicular pain is generally a sharp, stabbing pain resulting from compression of the dorsal nerve roots. Radicular pain projects in dermatomal distributions. Low back pain in cauda equina syndrome may have some characteristic that suggests something different from the far more common lumbar strain. Patients may report severity or a trigger, such as head turning, that seems unusual.

Severe pain is an early finding in 96% of patients with cauda equina syndrome secondary to spinal neoplasm. Later findings include lower extremity weakness due to involvement of the ventral roots. Patients generally develop hypotonia and hyporeflexia. Sensory loss and sphincter dysfunction are also common.

Urinary manifestations of cauda equina syndrome include the following:

  • Retention

  • Difficulty initiating micturition

  • Decreased urethral sensation

  • Typically, urinary manifestations begin with urinary retention and are later followed by an overflow urinary incontinence.

Bell et al demonstrated that the accuracy of urinary retention, urinary frequency, urinary incontinence, altered urinary sensation, and altered perineal sensation as indications of possible disk prolapse justified urgent MRI assessment. [76, 77]

Bowel disturbances may include the following:

  • Incontinence

  • Constipation

  • Loss of anal tone and sensation

The initial presentation of bladder/bowel dysfunction may be of difficulty starting or stopping a stream of urine. It may be followed by frank incontinence, first of urine then of stool. The urinary incontinence is on the basis of overflow. It is usually with associated saddle (perineal) anesthesia (the examiner can inquire if toilet paper feels different when the patient wipes).


Physical Examination

The symptoms of cauda equina syndrome are associated with corresponding signs pointing to an LMN or UMN lesion. Refer to the images and tables below for assistance in examining the patient and documenting examination findings. In addition to the signs listed below, signs of other possible causes should be sought (eg, examination of the peripheral pulses to rule out possible vascular cause or ischemia of the conus medullaris).

Muscle groups, surface anatomy, peripheral sensory Muscle groups, surface anatomy, peripheral sensory innervation, and dermatomes of the anterior lower limb. This image should be correlated with Tables 1 and 2 in the text. Image courtesy of Nicholas Y. Lorenzo, MD.
Muscle groups, surface anatomy, peripheral sensory Muscle groups, surface anatomy, peripheral sensory innervation, and dermatomes of the posterior lower limb. This image should be correlated with Tables 1 and 2 in the text. Image courtesy of Nicholas Y. Lorenzo, MD.

Pain and deficits associated with nerve root involvement are shown in Table 2, below.

Table 2. Pain and Deficits Associated with Specific Nerve Roots (Open Table in a new window)

Nerve Root


Sensory Deficit

Motor Deficit

Reflex Deficit


Anterior medial thigh

Upper thigh

Slight quadriceps weakness; hip flexion; thigh adduction

Slightly diminished suprapatellar


Anterior lateral thigh

Lower thigh

Quadriceps weakness; knee extension; thigh adduction

Patellar or suprapatellar


Posterolateral thigh, anterior tibia

Medial leg

Knee and foot extension



Dorsum of foot

Dorsum of foot

Dorsiflexion of foot and toes



Lateral foot

Lateral foot

Plantar flexion of foot and toes






Bulbocavernosus; anal

Table 3. Root and Peripheral Nerve Innervation of the Lumbosacral Plexus (Open Table in a new window)






L2, 3, 4

Adductor longus


L2, 3, 4



L2, 3, 4

Quadriceps femoris


L2, 3, 4

Anterior tibial

Deep peroneal

L4, 5

Extensor hallucis longus

Deep peroneal

L4, 5

Extensor digitorum longus

Deep peroneal


Extensor digitorum brevis

Deep peroneal

L4, 5, S1

Peroneus longus

Superficial peroneal

L5, S1

Internal hamstrings


L4, 5, S1

External hamstrings


L5, S1

Gluteus medius

Superior gluteal

L4, 5, S1

Gluteus maximus

Inferior gluteal

L5, S1, 2

Posterior tibial


L5, S1

Flexor digitorum longus


L5, S1

Abductor hallucis brevis

Tibial (medial plantar)

L5, S1, 2

Abductor digiti quinti pedis

Tibial (lateral plantar)

S1, 2

Gastrocnemius lateral


L5, S1, 2

Gastrocnemius medial


S1, 2



S1, 2

Pain often is localized to the low back; local tenderness to palpation or percussion may be present. Pain in the legs (or radiating to the legs) is characteristic of cauda equina syndrome. Radicular pain is a common presentation in patients with cauda equina syndrome, usually in association with radicular sensory loss (saddle anesthesia), asymmetric paraplegia with loss of tendon reflexes, muscle atrophy, and bladder dysfunction. The presentation is somewhat similar to and is often confused with conus and epiconus lesions.

Reflex abnormalities may be present; they typically include loss or diminution of reflexes. Hyperactive reflexes may signal spinal cord involvement and exclude the diagnosis of cauda equina syndrome. Sensory abnormality may be present in the perineal area or lower extremities. Light touch in the perineal area should be tested. Anesthetic areas may show skin breakdown.

Muscle weakness may be present in muscles supplied by affected roots. Muscle wasting may occur in chronic cauda equina syndrome.

Poor anal sphincter tone is characteristic of cauda equina syndrome. Babinski sign or other signs of upper motor neuron involvement suggest a diagnosis other than cauda equina syndrome, possibly spinal cord compression.

In cauda equina syndrome, the peripheral nerve fibers from the sacral segments of the cord, as well as various lumbar dorsal and ventral nerve roots, may also be involved. This results in an asymmetric and higher distribution of motor and sensory symptoms and signs in the lower extremities. Incontinence of bowel and bladder is not severe and develops late for the same reason.

In conus and epiconus lesions, the sacral region neurons (S2-S4) are destroyed. The destruction of these neurons leads to an early and more severe involvement of bowel, urinary bladder, and sexual dysfunction than seen in those with CES. In contrast, for the same reason, the motor and sensory symptoms in the lower extremities are often not very severe and only the distal parts of the limb musculature are involved.

The anatomical proximity of the conus medullaris, the epiconus, and the cauda equina can lead to 2 of these anatomical structures being involved via a single lesion, resulting in an overlap of symptomatology.

The salient features and findings of cauda equina syndrome and conus medullaris syndrome are listed in Table 4, below.

Table 4. Cauda Equina Versus Conus Medullaris Syndrome (Open Table in a new window)


Cauda Equina Syndrome

Conus Medullaris

Vertebral level



Spinal level

Injury to the lumbosacral nerve roots

Injury of the sacral cord segment (conus and epiconus) and roots

Severity of symptoms and signs

Usually severe

Usually not severe

Symmetry of symptoms and signs

Usually asymmetric

Usually symmetric


Prominent, asymmetric, and radicular

Usually bilateral and in the perineal area


Weakness to flaccid paralysis

Normal motor function to mild or moderate weakness


Saddle anesthesia, may be asymmetric

Symmetric saddle distribution, sensory loss of pin prick, and temperature sensations (Tactile sensation is spared.)


Areflexic lower extremities; bulbocavernosus reflex is absent in low CE (sacral) lesions

Areflexic lower extremities

(If the epiconus is involved, patellar reflex may be absent, whereas bulbocavernosus reflex may be spared.)

Sphincter and sexual function

Usually late and of lesser magnitude;

lower sacral roots involvement can cause bladder, bowel, and sexual dysfunction

Early and severe bowel, bladder, and sexual dysfunction that results in a reflexic bowel and bladder with impaired erection in males


Multiple root level involvement; sphincters may also be involved

Mostly normal lower extremity with external anal sphincter involvement


May be favorable compared with conus medullaris syndrome

The outcome may be less favorable than in patients with CES

Cauda equina syndrome

In cauda equina syndrome, muscle strength in the lower extremities is diminished. This may be specific to the involved nerve roots as listed below, with the lower lumbar and sacral roots more affected, leading to diminished strength in the glutei muscles, hamstring muscles (ie, semimembranosus, semitendinosus, biceps femoris), and the gastrocnemius and soleus muscles.

Sensation is decreased to pinprick and light touch in a dermatomal pattern corresponding to the affected nerve roots. This includes saddle anesthesia (sometimes including the glans penis or clitoris) and decreased sensation in the lower extremities in the distribution of lumbar and sacral nerves. Vibration sense may also be affected. Sensation of the glans penis or clitoris should be examined.

Muscle stretch reflexes may be absent or diminished in the corresponding nerve roots. Babinski reflex is diminished or absent.

Bulbocavernosus reflexes may be absent or diminished. This should always be tested.

Anal sphincter tone is patulous and should always be tested since it can define the completeness of the injury (with bulbocavernosus reflex); it is also useful in monitoring recovery from the injury.

Urinary incontinence could also occur secondary to loss of urinary sphincter tone; this may also present initially as urinary retention secondary to a flaccid bladder.

Muscle tone in the lower extremities is decreased, which is consistent with an LMN lesion.

Conus medullaris syndrome

Patients may exhibit hypertonicity, especially if the lesion is isolated and primarily UMN.

Signs are almost identical to those of the cauda equina syndrome, except that in conus medullaris syndrome signs are more likely to be bilateral; sacral segments occasionally show preserved bulbocavernosus reflexes and normal or increased anal sphincter tone; the muscle stretch reflex may be hyperreflexic, especially if the conus medullaris syndrome (ie, UMN lesion) is isolated; Babinski reflex may affect the extensors; and muscle tone might be increased (ie, spasticity).

Other signs include papilledema (rare, occurs in lower spinal cord tumors), cutaneous abnormalities (eg, cutaneous angioma, pilonidal sinus that may be present in dermoid or epidermoid tumors), distended bladder due to areflexia, and other spinal abnormalities (noted on lower back examination) predisposing the patient to the syndrome.

Muscle strength

Physical examination for cauda equina or conus medullaris syndromes would be incomplete without tests for sensation of the saddle and perineal areas, bulbocavernosus reflex, cremasteric reflex, and anal sphincter tone, findings for all of which are likely to be abnormal.

Muscle strength of the following muscles should be tested to determine the level of lesion:

  • L2 - Hip flexors (iliopsoas)

  • L3 - Knee extensors (quadriceps)

  • L4 - Ankle dorsiflexors (tibialis anterior)

  • L5 - Big toe extensors (extensor hallucis longus)

  • S1 - Ankle plantar flexors (gastrocnemius/soleus)

ASIA impairment scale

In defining impairments associated with a spinal cord lesion, the American Spinal Cord Injury Association (ASIA) impairment scale is used in determining the level and extent of injury.

This scale should also be used in defining the extent of conus medullaris syndrome/cauda equina syndrome. The scale is as follows:

  • A - Complete; no sensory or motor function preserved in sacral segments S4-S5

  • B - Incomplete; sensory, but not motor, function preserved below the neurologic level and extends through sacral segments S4-S5

  • C - Incomplete; motor function preserved below the neurologic level, and the majority of key muscles below the neurologic level have a muscle grade less than 3

  • D - Incomplete; motor function preserved below the neurologic level, and the majority of key muscles below the neurologic level have a muscle grade greater than or equal to 3

  • E - Normal; sensory and motor function normal

The injury should be described using this scale, for example, ASIA class A. Most patients with cauda equina/conus medullaris syndrome are in ASIA class A or B initially and gradually improve to class C, D, or E.


Complications include the following:

  • Thromboembolic phenomena

  • Neurogenic bladder/bowel

  • Erectile dysfunction

  • Pressure ulcers

  • Heterotopic ossification

  • Osteoporosis

  • Chronic neuropathic pain

  • Spasticity/contractures

  • Recurrent urinary tract infections

  • Urethral stricture

  • Bladder calculi

  • Depression