Conus Medullaris

Conus Medullaris

The medulla spinalis or spinal cord comprise the central nervous system’s (CNS) core. It originates from the base of the brain passing via the vertebral canal, tapering and terminating at the upper lumbar region, in between the L1 and L2 lumbar vertebras. The farthest section i.e. Conus Medullaris is a cylindrical bunch of nerve fibers which is somewhat round in shape.

Other Names & Parts

The narrowing of the medulla spinalis starts from the conus medullaris extending into the ‘filum terminale.’ Hence it is sometimes called ‘Conus Terminalis’ which is a Latin expression meaning cone-shaped endpoint. Conus Medullaris is also a Latin term that means ‘medullary cone.’ ‘Medullary’ relates to the ‘medulla oblongata’ or the medulla of any body part that comprises of or resembles the bone marrow.

The filum terminale that extends from where the Conus Terminalis is a soft and slim strand composed of fibrous tissue. Conus medullaris links to the posterior end of the tailbone (coccyx) through the filum terminale. The linkage with the coccyx furnishes stability to the spinal cord.

The spinal cord starts to peter out after its ‘medullary cone’ section where the nerve fibers branch off in a crosswise fashion to form the ‘cauda equina’ which is, the tapering end of the conus medullaris. It has a form that resembles the tip of a horse’s tail.

Anatomy

The medullary cone in adults usually spans from the last rib pair (T12) of the thoracic vertebrae to the first pair of the rib of the lumbar vertebrae (L1). However, it sometimes lies in between the first and second rib pair (L1 and L2) of lumbar vertebrae. The medullary cone’s superior or upper end is not very prominent or well-defined.

Physiological functions

The nerves transmitting through the furthermost section of the spinal cord control functioning of the lower limbs, bowels, urinary bladder, and the genitals.

Emergence & Development

The conus medullaris, at the time of regular fetal development, originates and emerges from the vertebral column’s (spine) sacral area. It takes its final position, usually opposite to the nucleus pulposus (the jelly-like space inside the intervertebral discs) in disc spaces between L1 and L2 during birth. Nevertheless, in some cases, the ascent and positioning completes when the baby is two months old.

Development of the medulla spinalis is complete when the tip of conus medullaris (its lowermost section) settles in the intervertebral disc in between L1 &L2.

Arteries & veins supplying blood to Conus Medullaris

Three spinal arteries supply the maximum blood to the medullaris cone, the left and right ‘posterior spinal arteries’ and the ‘anterior spinal artery.’ Other arteries, including the branches of the median sacral artery, internal iliac artery, lateral sacral artery, and the aorta also supply blood but in smaller quantities.

Clinical Significance

Conus Medullary Syndrome

Owing to its location in the lumbar section of the spine, any lesion, wound or condition in this segment could have an adverse effect. Any injury or damage to the medullary section is known in medical parlance as ‘Conus Medullary Syndrome.’ CMS entails a bundle of indicators including low back pain, radicular pain, and urinary bladder and bowel dysfunctions.

Cauda Equina Syndrome

Another significant disorder associated with the vertebral column and occurring right below the medullary terminus is the ‘cauda equina syndrome’ (CES). The Conus Medullaris serves as a vital diagnostic checkpoint for establishing the presence of bulbocavernosus reflex in patients plagued by urinary retention. This crucial pointer for lesions or injuries to the pelvic nerves becomes marked in the latter stages of CES.

Pathophysiology: Conus Medullaris Syndrome

Any disorder, disease or condition of the medullary cone is referred to as ‘Conus Medullary Syndrome.’ They imply the improper functioning or malfunctioning of the bundle of nerve fibers passing through this distal spinal cord section. The condition could be caused by a partial injury, damage or lesion in the spinal cord resulting in sensory loss beneath the affected area.

The nerves fail to function appropriately owing to unwarranted constriction or stress. This unnatural pressure in the nerves could be attributed to a host of factors including but not limited to:-

  • Spinal swellings or tumors
  • Infection
  • Spinal stenosis (thinning or narrowing of the backbone)
  • Facet joint osteoarthritis (variously known as spinal arthritis or degenerative arthritis)
  • Trauma
  • Deep vein thrombosis (DVT) of the veins in the spine

Signs & Symptoms

Unlike some spinal nerve conditions like ‘Brown-Sequard Syndrome,’ ‘anterior cord syndrome,’ ‘cauda equina syndrome’ or ‘Hemiplegia’ that is one-sided, Conus Medullaris Syndrome is bilateral. In other words, injuries or lesions to medullary end up affecting both sides equally. Signs and symptoms of early-stage CMS which are felt abruptly on either side of the body are unlikely to cause paraplegia or paralysis of the lower half of the body.

However, a patient is more likely to be diagnosed with an advanced stage when the symptoms are severe including urinary bladder and bowel dysfunction, impotence, and compromised motor function. Someone whose normal lifestyle is affected by these symptoms is advised to opt for emergency medical intervention without delay to avoid the onset of paralysis.

Following are some of the usual signs/symptoms:

  • Pain in the lower back
  • Tingling in the lower back along with pain
  • A sensorial loss in the inguinal region (groin), legs, thighs, and the feet
  • Partial or total dysfunction of the urinary bladder and the bowels
  • Sexual dysfunction
  • Radicular pain
  • Achilles reflex (or ankle jerks) affected
  • Urinary incontinence
  • Fecal incontinence
  • Bilateral Sciatica
  • Impaired or weakened motor function in the lower extremities with sensory deficits
  • Absent or reduced reflexes in the lower extremity

However, numerous symptoms are similar to indicators of a few less severe spinal syndromes like sciatica, foraminal stenosis, and bulging discs. Hence, it is extremely crucial to consult a medical professional who’ll prescribe appropriate diagnostic assays and the right treatment plan.

Causes

It is not an isolated condition but manifests and develops as an outcome or aftereffect of partial spinal trauma. It could result from a road accident, gunshot or any mishap that injures the spine. However, signs could also become apparent because of a spinal tumor, arteriovenous malformations of the vertebral column (from stenosis) or an infection. Following are some causes of CMS:

  • Infections in the spinal cord
  • Injuries to the lower back resulting from a car mishap or gunshot
  • Congenital or hereditary malformations or deformities of the vertebral column

Diagnosis

MRI (magnetic resonance imaging) scan of the spinal column and lower back. On the other hand, the injury type and extent of the same (when mild or severe) are thoroughly considered for correctly diagnosing the condition. Once identified, the doctor prescribes a suitable treatment.

Treatment

  • Therapies: The physician might prescribe one or more therapies depending on the cause of the disorder and its extent. The treatment plans include radiation therapy, spinal decompression surgery, and antibiotics in combination for coping with the symptoms. Radiation therapy is the most effective treatment if the symptoms indicate malignant or cancerous spinal cord tumor.
  • Surgery: In case the tumor is benign, or if the malfunctioning is due to a spinal obstruction like a splinter or bullet, spinal decompression surgery is the opportune treatment. This helps in getting rid of the impediment and renews normal functioning. If the symptoms surface because of an infection caused by severe injury, oral antibiotics and intravenous therapies are the way to go.

Action plans for dealing with CMS

Exercising caution is exceedingly vital for medically monitoring serious cases. Any patient diagnosed with symptoms of bilateral lower extremity debilitation, urinary bladder, and bowel dysfunction or loss of sensation in the saddle joint should go through routine treatment initially. If preliminary therapeutic practices in the first 24 hours do not help in relieving the symptoms, then conducting (spinal) decompression surgery becomes imperative for minimizing risks of irreversible neurologic injury. Spinal decompression surgery could help mitigate:

  • Extensive or acute compaction of the medullary cone
  • CMS arising out of disc herniation: Vertebral canal or spinal canal decompression is facilitated through laminectomy or laminotomy procedure followed by an abjuration and discectomy (surgical removal of the intervertebral disc).
  • Chronic cases: If symptoms are less severe or acute, timely intervention and surgery prevent irreparable neurologic damage.
  • CMS with acute symptoms: Surgery helps in getting rid of the tumor and smoothen the decompression process. Laminectomy or discectomy, supplementary or analogous care related to surgery includes the myocutaneous flap, skin grafts and debridement (surgical removal of dead tissues and foreign bodies) for expediting wound healing

Effectiveness of Surgery

Numerous clinical accounts have showcased data about the outcomes of surgical decompression processes conducted at different stages of CMS. It is interesting to note that the surgical procedure’s timing made no noticeable difference as far as the extent of recovery or healing was concerned. Nevertheless the findings notwithstanding, timely surgical intervention significantly diminished the likelihood of severe neurological injury that could lead to paralysis.

Postoperative care & rehabilitation

Patients are transferred to a postoperative care ward after the decompression surgery. After that, they’re shifted to an intensive rehabilitation unit from where they’re either moved to subacute care unit or discharged and advised long-term supervision, depending upon the extent of disablement.

A team of expert medical professionals comprising the spinal cord rehabilitation specialist, physical and occupational therapists closely coordinate for laying down the recovery objectives. The rehabilitation aims are intended to expedite the social, professional, educational, psychological, physical, and medical roles of the recuperating patient.

Physical therapy

Physical therapies entail performing a wide range of strengthening and motion workouts. When it comes to recovering physically, the patient will be able to make steady progress if he or she performs the following activities routinely:

  • Ambulation or walking-about exercises
  • Going forward and backward on a wheelchair
  • Community programs and family training
  • Home-based workouts
  • Ambulating with spinal braces or splints and lower extremity supports for improving overall balance
  • Exercises involving a standing table

Occupational therapy

Occupational therapy techniques usually include the following activities:-

  • Training or preparation for transferring from acute or subacute care unit to home
  • Wheelchair training (for extensive use of a wheelchair)
  • Training for motor coordination to facilitate the holistic functioning of body parts responsible for motion
  • Training for effectively performing normal, everyday activities including using a toilet, bathing, grooming, and feeding
  • Rehearsing for a home-based workout schedule
  • Training to perambulate using assistive devices
  • Training to live harmoniously with a family and in a family setting

Medication approaches

CMS patients should take analgesics, palliatives or painkillers prescribed by the physician for getting relief from pain. NSAIDs might prove immensely useful in keeping the injury or wound from aggravating or exacerbating. There are several other classes of medicines that could help alleviate a range of complications linked to or associated with conus medullary syndrome:

  • Anticoagulants (for dealing with pulmonary embolism/deep vein thrombosis)
  • Benzodiazepines (for stimulating muscle relaxation in the medulla spinalis)
  • Skeletal muscle relaxants (induces relaxation of skeletal muscles by regulating their contractions)
  • Neuromuscular toxins (for checking conduction of excitatory impulses across synapses of neuromuscular tissues)

Monitoring & management in the long run

Consistent consultations or sessions with the rehabilitation specialists is a must as the professionals help to manage integration with the family and the community. They also assist the patient with improving ambulation, performing daily activities, regaining strength, and so on. Moreover, keeping in touch with a physician overseeing primary care is also necessary as the professional offers recommendations on postsurgical/postoperative diagnostic tests and medications.

Recurrent follow-ups is important for patients with erectile dysfunction, urinary bladder or kidney problems. Patients having these complications are increasingly vulnerable to renal calculi (kidney stones) and urinary tract infection (UTI). Patients who have undergone vesicostomy or suprapubic cystostomy should opt for cystoscopy at least once in a year to keep themselves updated on signs of emergent bladder malignancy.

 Conus Medullaris Syndrome vis-à-vis Cauda Equina Syndrome

Diagnosis is either for conus medullaris syndrome or cauda equine syndrome or both. The signs and symptoms of conus medullaris syndrome combine upper motor neurons (UMN) and lower motor neurons (LMN) effects. Cauda equina syndrome’s symptoms, generally involces the lower motor neurons.

CMS (conus medullaris syndrome) and CES (cauda equina syndrome) are both spinal cord syndromes that cause injury or damage to its endmost section and the segment just inferior to where it separates into cauda equina respectively. Both have distinct signs, symptoms, causes, onset history and other distinguishing characteristics that help in differentiating one from the other.

Comparison Table

The table below presents the symptoms of these two kinds of spinal cord injuries by specific prognostic aspects:

Conus Medullaris Syndrome Cauda Equina Syndrome
Sudden bilateral presentation Gradual and one-sided
Mild radicular pain Intense radicular pain
Patellar or knee-jerk reflexes maintained, but ankle jerks (variously called Achilles reflex)  compromised Both patellar & ankle jerk reflexes are affected
Lower back pain is the severe Low back pain is moderate or sometimes absent
Symmetric hyperreflexia partial paralysis of the extremities of lower limbs which is not distinctly noticeable. There is a possibility of the presence of fasciculations or muscular twitches. Asymmetric areflexic paralysis of the lower half of the body which is more pronounced. Atrophy of muscle fibers is more common, but fasciculation is atypical.
Numbness or lack of sensation (sensory symptom) is marked in the anal region. It affects both sides of the body symmetrically typified by dissociated sensory loss Numbness is more distinguishable in perineum, buttocks, and the posterior surfaces of the thighs. Mostly unilateral and asymmetric, sensory loss from the hip to the toes in particular dermatomes characterized by partial paralysis. Partial or total sensory loss in the tip of penis or clitoris.
Sphincter muscle impairment is exemplified by urinary incontinence where the patient fails to hold urine from flowing out for a reasonable period Urinary retention that becomes pronounced in the later stages
Impotence is more common Impotence is somewhat infrequent though the patient may experience erectile dysfunction. It is characterized by failure to have erections accompanied by the absence of sensation in clitoris or glans penis.

Ganglioglioma of Conus Medullaris (HX)

Ganglioglioma is the rarest of rare disorders of the spine where the affected individual suffers from a brain tumor. Development of a tumor in the medullary cone is the primilary sign. Surgical excision of the tumor is the most effective treatment for curing ganglioglioma.

Conus Medullaris Syndrome arising from disc herniation in dura matter (HX)

CMS could also occur because of an intervertebral disc herniation. Though extremely rare, conus medullaris syndrome could result from the herniation of the intervertebral disc between the L1 and L2 vertebras. Arthroscopy of the knees helps in detecting the condition. If a hernia also entails the extrusion of the T12-L1 disc, then the nucleus pulposus could spill out and enter the vertebral column, eventually leading to severe paralysis of the lower extremities. Performing an incidental durotomy or dural tear can help relieve the condition.

References

  1. https://www.lipkinhiggins.com/injury-advice/conus-medullaris-syndrome-what-you-need-know
  2. https://www.laserspineinstitute.com/back_problems/spinal_anatomy/spinal_cord/conus_medullaris/
  3. https://emedicine.medscape.com/article/1148690-overview#a0101
  4. http://www.innovateus.net/innopedia/what-conus-medullaris
  5. https://www.britannica.com/science/human-nervous-system/The-spinal-cord#ref605754
  6. https://www.ispn.guide/congenital-disorders-of-the-nervous-system-in-children/embryology-of-the-central-nervous-system-in-children-homepage/ascent-of-the-conus-medullaris/
  7. https://onlinelibrary.wiley.com/doi/pdf/10.7863/jum.2006.25.11.1397
  8. https://www.sciencedirect.com/topics/neuroscience/conus-medullaris
  9. https://www.spinalcord.com/conus-medullaris-syndrome

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