Conus Medullaris Syndrome

Original Editor - Chioma Clara Okeakpu
Top Contributors - Chioma Clara Okeakpu and Vidya Acharya

Definition

Conus Medullaris Syndrome (CMS) is a serious medical emergency. It could lead to long-term damage if not treated and can seriously impair a person's capacity to perform daily tasks. It occurs when the conus medullaris (CM), a cone-shaped structure tapered at the end of the lumbar enlargement of the spinal cord is compressed. The most frequent causes are infections, lumbosacral disc herniation, trauma, tumours, aortic pathology, inferior vena cava thrombosis, congenital conditions including spinal dysraphism, and iatrogenic after surgery or epidural anaesthesia.

Clinically Relevant Anatomy

Conus Medullaris

The Conus medullaris is the region where the spinal cord terminates and this is located at the vertebral levels, L1 & L2. It is considered as a transition area from the central to the peripheral nervous system, and injury to this area can result in specific neural symptoms.On average, the conus is at the middle third of the L1 vertebra but can also be located as high as the middle third of the T11 vertebra or as low as the middle third of L3 vertebra. The conus medullaris serves to stabilise the spinal cord by connecting to the coccyx via the coccygeal ligament. It equally gives rise to the lumbar sympathetic, sacral somatic and sacral parasympathetic nerves which continue downward within the cauda equina.

The following vessels provide circulatory supply to the conus medullaris:

1. The anterior spinal artery, which passes via the anterior median fissure and terminates at the filum terminale.

2. Two posterior spinal arteries, which travel through the spinal cord's posterolateral portion alongside the posterior nerve roots.

3. At the lower end of the cord, the vascular basket of the conus medullaris is made up of one or two tiny arteries that emerge from the anterior spinal artery and circumferentially join it with the posterior spinal arteries. Conus malformations and arteriovenous fistulas are commonly associated with this feature.

4. Radicular arteries: The anterior and posterior spinal arteries, alongside the eight anterior and twelve posterior arteries, form longitudinal arterial trunks and serve the corresponding nerve roots. The arteries of Adamkiewicz, which supply the lumbosacral area of the cord, are large anterior arteries located at the T1 and T11 segmental levels. These radicular arteries are clinically important as they are end arteries, and occlusion leads to spinal cord ischemia.

5. The iliolumbar artery gives rise to the artery of Desproges-Gotteron, a rare anatomic variation that travels up to the conus via the L5 or S1 nerve roots before anastomosing with the conal basket.

The conus is where the spinal nerves S3–S5 begin, and they provide motor and sensory innervation to the lower limbs, bowel, bladder, and perineum. They are essential for sexual function as well. The spinal nerves L2-L5, S1-S5, and Co1 continue inferiorly as the cauda equina . Conus medullaris or cauda equina syndromes can result from compression of these nerves.

Epidemiology

1. Conus medullaris syndrome is extremely uncommon; it affects 3% of all disc herniations and is thought to affect 1 in 30,000 to 100,000 persons annually.
2. The annual incidence is between 1.5 to 3.4 per million.
3. The prevalence of conus medullaris syndrome and cauda equina syndrome is highest in young males, due to their increased vulnerability to compressive thoracolumbar trauma..

Etiology

The following are the cause of conus medullaris syndromes( CMS).

1. Compression due to
   • Tumor: Least likely metastases, glioma, and ependymoma (often with a haemorrhagic intertumoral component). In this region, ependymoma is frequently referred to as myxopapillary ependymoma.
   • Trauma: fractured bone fragments
2. Infection: spinal epidural abscess complicating discitis or vertebral osteomyelitis
3. Ischemia: due to poor arterial supply to the area
4. Inflammation

Clinical Presentation

1. Onset & Pain: CMS presents with bilateral symptoms which may include severe back pain and perineal pain. This distinguishes it from cauda equina syndrome (CES) which normally presents with asymmetrical symptoms.
2. Motor: Patients present with mixed upper and lower motor neurons signs. Upper motor neuron signs are more prevalent and they include; symmetrical paralysis in the lower limbs, spasticity, and hyperreflexia. Lower motor neuron signs may include segmental areflexia (such as the ankle reflex).
3. Sensory: Presence of symmetric saddle anesthesia and early bladder/bowel reflex arc involvement.
4. Autonomic: Presence of early bowel problems & incontinence. Sexual dysfunction, such as impotence due to S2–S4 involvement.

Diagnostic Procedures

Diagnostic Procedures involves Examination/ Assessment and Imaging .

Examination

1. History : A thorough history is necessary, with detailed questions regarding recent falls, trauma or injuries, use of anticoagulation, presented spinal instrumentation, intravenous drug use, history of malignancy, chiropractic manipulation, and constitutional symptoms like fevers/chills
2. Physical exam assessing neurological symptoms which includes;
   • Motor or Sensory deficits : presents bilaterally in CMS
   • Saddle anaesthesia
   • autonomic signs like palpable bladder indicating urinary retention
   • absence or decreased bulbocavernosus reflex, etc.

It is important to note that this symptoms are similar with cauda equina syndrome but in conus medullaris syndrome, deficits of the lower extremities are more often bilateral and symmetric unlike cauda equina syndrome which presents as unilateral and asymmetrical deficits . Also, upper motor neuron signs can be present in conus medullaris syndromes, such as spasticity and hyperreflexia but cauda equina syndrome always presents with only lower motor neuron signs.

Imaging

1. The gold standard method of evaluating CMS is obtaining urgent MRI imaging with sagittal and axial T1 and T2 sequences with an ideal goal of one hour from the patient presentation.
2. CT myelogram is a viable option for patients with contraindications to MRI, such as those with metal implants. This imaging modality has limited utility as it requires injecting contrast through a spinal tap to visualize the spinal cord and its associated structures.
3. A bladder scan checking for a post-void residual volume should also be obtained to evaluate for urinary retention.

Treatment / Management

Treatment is mostly surgical, with decompression by laminectomy/discectomy or sequestrectomy; hence, orthopaedic and neurosurgical consultation is required.

Surgical management: Fast neurosurgical/orthopedic consultation; surgical decompression (discectomy, laminectomy, or tumor removal) ideally within 48 hours, preferably within 24 hours according to WFNS guidelines.

Rehabilitation: A thorough rehabilitation program may be necessary following surgery to address any lingering impairments and functional deficiencies in mobility and activities of daily living, as well as to address any concomitant neurogenic bladder, bowel, and sexual dysfunction.

Differential Diagnosis

Non-compressible causes of spinal cord dysfunction such as:

• Spinal cord infarct
• HIV-related myelopathy
• Transverse myelitis
• Multiple sclerosis
• Syringomyelia
• Spinal arteriovenous malformation

Cauda equina syndrome: asymmetric radiculopathy, Lower motor neuron signs, late autonomic involvement bulbocavernosusreflex.

Prognosis

There are changes of good prognosis if earlier surgical decompression is done <48 h of symptoms, Intact sacral pin prick sensation for good recovery of bladder function & Intact bulbocavernosus reflex.

Poor prognosis if surgical decompression is performed after 48 h of symptoms onset & presence of hemorrhage within spinal column on MRI.