eMedicine Specialties > Neurology > Introductory Topics

Cauda Equina and Conus Medullaris Syndromes

Author: Segun T Dawodu, MD, JD, MBA, FAAPMR, FAANEM, CIME, DipMI(RCSed), Former Clinical Instructor, Mount Sinai Medical School; Current Director, Pain and Injuries Rehabilitation Services, PMRehab Pain and Sports Medicine Associates
Coauthor(s): Nicholas Y Lorenzo, MD, Chief Editor, eMedicine Neurology; Consulting Staff, Neurology Specialists and Consultants
Contributor Information and Disclosures

Updated: Feb 10, 2009

Introduction

Background

The spinal cord tapers and ends at the level between the first and second lumbar vertebrae in an average adult. The most distal bulbous part of the spinal cord is called the conus medullaris, and its tapering end continues as the filum terminale. The upper border of the conus medullaris is often not well defined. Distal to this end of the spinal cord is a collection of nerve roots, which are horsetail-like in appearance and hence called the cauda equina (Latin for horse's tail). These nerve roots constitute the anatomic connection between the central nervous system (CNS) and the peripheral nervous system (PNS). They are arranged anatomically according to the spinal segments from which they originated and are within the cerebrospinal fluid (CSF) in the subarachnoid space with the dural sac ending at the level of second sacral vertebra.

Pathophysiology

The conus medullaris part of the spinal cord obtains its blood supply primarily from 3 spinal arterial vessels—the anterior median longitudinal arterial trunk and 2 posterolateral trunks. Less prominent sources of blood supply include radicular arterial branches from the aorta, lateral sacral arteries, and the fifth lumbar, iliolumbar, and middle sacral arteries. The latter contribute more to the vascular supply of the cauda equina, although not in a segmental fashion, unlike the blood supply to the peripheral nerves. The nerve roots may also be supplied by diffusion from the surrounding CSF. Moreover, a proximal area of the nerve roots may have a zone of relative hypovascularity.

In understanding the pathological basis of any disease involving the conus medullaris, keep in mind that this structure constitutes part of the spinal cord (the distal part of the cord) and is in proximity to the nerve roots. Thus, injuries to this area often yield a combination of upper motor neuron (UMN) and lower motor neuron (LMN) symptoms and signs in the dermatomes and myotomes of the affected segments. On the other hand, a cauda equina lesion is a LMN lesion because the nerve roots are part of the PNS. Cauda equina and conus medullaris syndromes are classified as clinical syndromes of the spinal cord; epidemiological data on the 2 syndromes are often not available separately from the general data on spinal cord injury.

Frequency

United States

Frequency is determined by the underlying etiology. Multiple conditions can result in a cauda equina or conus medullaris syndrome as outlined later in this article.

Mortality/Morbidity

Morbidity and especially mortality rates are determined by the underlying etiology. Multiple conditions can result in cauda equina or conus medullaris syndrome, as outlined later in this article.

Race

Currently, no published study looks at the incidence of these conditions based on race.

Sex

Currently, no published study looks at the incidence of these conditions based on gender.

Age

Currently, no published study looks at the incidence of these conditions based on age.

Clinical

History

The history of onset, the duration of symptoms, and the presence of other features or symptoms could point to the possible causes. 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 LMN in nature, while those of conus medullaris syndrome are a combination of LMN and UMN effects (Table 1).

Table 1. Symptoms and Signs of Conus Medullaris and Cauda Equina Syndromes

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Physical

The symptoms described in History are associated with corresponding signs pointing to an LMN or UMN lesion. Refer to Media files 1-2 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).

• Signs of cauda equina syndrome include the following:
  • 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.
• Signs of conus medullaris syndrome include the following:
  • 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 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)
• 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. Table 2. Root and Peripheral Nerve Innervation of the Lumbosacral Plexus

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    Table

    Muscle	Nerve	Root
    Iliopsoas	Femoral	L2, 3, 4
    Adductor longus	Obturator	L2, 3, 4
    Gracilis	Obturator	L2, 3, 4
    Quadriceps femoris	Femoral	L2, 3, 4
    Anterior tibial	Deep peroneal	L4, 5
    Extensor hallucis longus	Deep peroneal	L4, 5
    Extensor digitorum longus	Deep peroneal	L4,5
    Extensor digitorum brevis	Deep peroneal	L4, 5, S1
    Peroneus longus	Superficial peroneal	L5, S1
    Internal hamstrings	Sciatic	L4, 5, S1
    External hamstrings	Sciatic	L5, S1
    Gluteus medius	Superior gluteal	L4, 5, S1
    Gluteus maximus	Inferior gluteal	L5, S1, 2
    Posterior tibial	Tibial	L5, S1
    Flexor digitorum longus	Tibial	L5, S1
    Abductor hallucis brevis	Tibial (medial plantar)	L5, S1, 2
    Abductor digiti quinti pedis	Tibial (lateral plantar)	S1, 2
    Gastrocnemius lateral	Tibial	L5, S1, 2
    Gastrocnemius medial	Tibial	S1, 2
    Soleus	Tibial	S1, 2

    Muscle	Nerve	Root
    Iliopsoas	Femoral	L2, 3, 4
    Adductor longus	Obturator	L2, 3, 4
    Gracilis	Obturator	L2, 3, 4
    Quadriceps femoris	Femoral	L2, 3, 4
    Anterior tibial	Deep peroneal	L4, 5
    Extensor hallucis longus	Deep peroneal	L4, 5
    Extensor digitorum longus	Deep peroneal	L4,5
    Extensor digitorum brevis	Deep peroneal	L4, 5, S1
    Peroneus longus	Superficial peroneal	L5, S1
    Internal hamstrings	Sciatic	L4, 5, S1
    External hamstrings	Sciatic	L5, S1
    Gluteus medius	Superior gluteal	L4, 5, S1
    Gluteus maximus	Inferior gluteal	L5, S1, 2
    Posterior tibial	Tibial	L5, S1
    Flexor digitorum longus	Tibial	L5, S1
    Abductor hallucis brevis	Tibial (medial plantar)	L5, S1, 2
    Abductor digiti quinti pedis	Tibial (lateral plantar)	S1, 2
    Gastrocnemius lateral	Tibial	L5, S1, 2
    Gastrocnemius medial	Tibial	S1, 2
    Soleus	Tibial	S1, 2

Causes

The most common causes of cauda equina and conus medullaris syndromes are the following:

• Lumbar stenosis (multilevel)
• Spinal trauma including fractures¹
• Herniated nucleus pulposus (cause of 2-6% of cases of cauda equina syndrome)^2,3,4
• Neoplasm, including metastases, astrocytoma, neurofibroma, and meningioma: Twenty percent of all spinal tumors affect this area.
• Spinal infection/abscess, such as tuberculosis, herpes simplex virus, meningitis, meningovascular syphilis, cytomegalovirus, or schistosomiasis⁵
• Idiopathic, eg, spinal anesthesia⁶ : These syndromes may occur as complications of the procedure or of the anesthetic agent (eg, hyperbaric lidocaine, tetracaine).
• Spina bifida and tethered cord syndrome⁷
• Other, rare causes
  • Spinal hemorrhage, especially subdural and epidural hemorrhage causing compression within the spinal canal
  • Intravascular lymphomatosis
  • Congenital anomalies of the spine/filum terminale including tethered cord syndrome
  • Conus medullaris lipomas
  • Multiple sclerosis
  • Spinal arteriovenous malformations
  • Late-stage ankylosing spondylitis
  • Neurosarcoidosis
• Deep venous thrombosis of the spinal veins (propagated)

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