Conus and Cauda Equina Tumors

Etiology

Tumors of the vertebrae are quite frequently metastatic, with primary bone or cartilaginous tumors much less common. Metastatic lesions are typically from the lung, breast, prostate, or kidney. Tumors within the conus medullaris may arise from the astrocytes of the spinal cord (astrocytoma) or the ependymal lining of the central canal of the spinal cord (ependymoma). Metastatic lesions are much less common. Tumors of the cauda equina typically arise from the Schwann cells lining the nerve roots (schwannoma).[4][5][6] Sometimes, they have a dumbbell shape due to their propensity to grow out of the neural foramina. Neurofibroma from a nerve root can also be commonly found. Meningioma is a benign lesion that is an intradural extramedullary tumor, which may arise anywhere along the lumbar spinal canal, causing compression of the nerve roots or the conus medullaris. It arises from the arachnoid cap cells and often has a dural tail. There are several etiologies for cauda equina syndrome (CES) and conus medullaris syndrome (CMS), which are important to consider as part of the differential diagnosis when dealing with tumors in these areas.

Etiologies of CES

1. Compressive
   • Massive herniated lumbar disc
   • Tumor: (metastatic disease to the spine with epidural extension, schwannoma, neurofibroma, meningioma)
   • Trauma: (fractured bone fragments)
   • Spinal epidural hematoma (spontaneous, iatrogenic, traumatic)
2. Infection: Typically from spinal epidural abscess complicating discitis or vertebral osteomyelitis. Although there is a compressive effect from the mass, vascular compromise results from local septic thrombophlebitis.
3. Ischemic
4. Inflammatory
5. Degenerative: Spinal stenosis
6. Postoperative lumbar spinal surgery complications

Etiologies of CMS

1. Compressive
   • Tumor: ependymoma (frequently with a hemorrhagic intratumoral component), glioma, and, least likely, metastases. Ependymoma in this area is commonly known as myxopapillary ependymoma. Myxopapillary ependymomas are typically positive for several immunophenotype markers, including GFAP, S100, vimentin, CD99, AE1/AE3, and NCAM1.
   • Trauma: fractured bone fragments
2. Infection: spinal epidural abscess complicating discitis or vertebral osteomyelitis
3. Ischemic: from poor arterial supply to the area
4. Inflammatory

Epidemiology

Cauda equina syndrome and conus medullaris syndrome are rare, with an estimated prevalence of 1-3 cases per 100,000 people per year, and an annual incidence between 1.5 and 3.4 per million people.[7] Approximately 1% to 2 % of lumbar discs requiring surgery will present with a cauda equina syndrome.

Approximately 55% of spinal lesions are extradural and involve the vertebral column. Of these, 20% are located in the lumbar spine. The most common lesion is metastasis. Approximately 40% of spinal lesions are intradural extramedullary. These are generally meningiomas of the dural sac, as well as schwannomas and neurofibromas of the nerve roots. Approximately 5% of spinal lesions are intramedullary (greater than 90% are ependymoma or astrocytoma of varying histological grades, and less than 2% are metastases).

Pathophysiology

Symptoms may arise from either compression and dysfunction of the neural elements or local tumor effects, causing ischemic and metabolic disorganization within the neurons. Tumors may lead to a combination of upper and lower motor neuron findings and bowel/bladder incontinence.  Back pain is the most common complaint. This can be mechanical pain related to a pathologic fracture or instability, or biological primary pain related to local tumor factors on the nerve roots, or secondary to involvement of the lumbar vertebrae. Intradural tumors may compress the cauda equina, causing radiculopathy, or potentially grow large enough to compress the conus medullaris, thus leading to myelopathy. The lesion may compress the vasculature and possibly cause venous hypertension or arterial ischemia, thus leading to spinal cord edema and neuronal dysfunction. Intrinsic lesions of the conus medullaris cause compression of the spinal cord as they grow. Conus medullaris metastases release local tumor factors that cause spinal cord edema and metabolic disarray.

History and Physical

Patients will typically present with a combination of back pain, radiculopathy, or myelopathy. The typical presentation of these lesions is back pain, accompanied by a varying degree of neurological deficit related to compression of the neural elements.[8][9] The patient with metastatic disease has a history of weight loss, general malaise, night sweats, or cancer. The patient with a CES has a history of back pain with radicular symptoms, depending on the level of compression. The patient with a CMS has a history of back pain with myelopathic symptoms. The patients may only complain of the slow onset of numbness or tingling in the lower extremities, which can progress over time. The most common sensory deficit is “saddle anesthesia,” where the patient complains of decreased sensation in the perineal and perianal areas. A varying degree of upper or lower motor neuron findings may also be present, as well as bowel or bladder incontinence. The anal sphincter tone is diminished. Deep tendon reflexes may be diminished in the lower extremities, but a lesion in the cauda will typically only involve the Achilles tendon. At the same time, those with a conus lesion will also have the patellar knee reflex involved. The diagnosis may be delayed due to the slow onset of neurological symptoms. Many lesions in the conus will present with a similar history and physical exam as those in the cauda because the nerve roots compressed in the cauda originate from the conus area. Sexual dysfunction can be present in some patients.

Features distinguishing CES from CMS are described below:

• Onset: gradual and asymmetric in CES; sudden and bilateral in CMS
• Pain: severe and radicular in CES; rare and bilateral perineum/thighs
• Sensory: saddle anesthesia in both; asymmetric in CES; symmetric in CMS
• Motor: marked and asymmetric in CES, not marked and symmetric in CMS
• Reflex: only ankle jerk absent in CES; ankle jerk and knee jerk may be absent in CMS
• Autonomic: bladder dysfunction and impotence later in CES; bladder dysfunction and impotence early in CMS

Evaluation

The evaluation of a patient with back pain without neurological deficit should be conservative as long as there are no significant risk factors; however, should risk factors exist, then an evaluation with neuroimaging should be initiated. If the patient presents with a neurological deficit or bowel/bladder incontinence, then magnetic resonance imaging with and without contrast should be obtained to identify any possible mass lesions. The MRI is the gold standard for evaluating nontraumatic spinal lesions. If a metastatic mass lesion is suspected, an appropriate workup would include a computed tomographic scan of the chest, abdomen, and pelvis, or a full-body positron emission tomography (PET) scan, to evaluate for any primary malignancy. Lumbar radiographs may show pathological fractures, destroyed pedicles, angulation, or enlarged neural foramina. When necessary, a lumbosacral CT scan is performed to visualize the bony anatomy of the spine.

Treatment / Management

Anti-inflammatory agents and steroids can be effective in patients with inflammatory processes and tumors. Prophylaxis for deep vein thrombosis or pulmonary embolism should be initiated during the perioperative period.

Surgical indications are aimed at decompression of the neural elements, gross tumor resection if possible, and stabilization of the spine, should there be any instability. As always, a multidisciplinary approach is best for determining the appropriate treatment based on long-term prognosis, as well as other indicated systemic treatments. Schwannoma and meningioma lesions are usually benign.[10][11][12] If schwannoma or meningioma is suspected and the patient is asymptomatic, observation is usually appropriate if the lesion is small. However, should there be a large lesion or neurological symptoms, then surgical resection for decompression and gross total resection should be attempted.(B2)

For malignant tumors, radiation or chemotherapy options are used. For astrocytoma or ependymoma, initial surgical resection for decompression and gross total resection is recommended. The role of chemotherapy and radiation, and the timing of such treatments, are still controversial. The indications for radiation or chemotherapy do depend on tumor type, histological grade, and degree of resection. For intramedullary metastatic lesions, the indications for surgery, radiation, and chemotherapy are more complex and depend heavily on a multidisciplinary approach.[13] Total resection is very difficult to obtain, and very often, worsening of neurological deficits is produced if attempted. The treatment of a patient with metastatic disease should always include systemic control of the disease if possible. If a primary lesion is known, surgery is usually not performed to avoid the worsening of deficits. If there is no known primary, a biopsy is warranted. (B3)

Differential Diagnosis

Whenever a patient with conus or cauda equina tumors is assessed, the following differentials should be kept in mind:

• Astrocytoma
• Ependymoma
• Myxopapillary ependymoma
• Metastases
• Herniated disc
• Transverse myelitis
• Spinal arteriovenous malformation
• Spinal cord infarct
• Multiple sclerosis
• Diabetic neuropathy
• Guillain-Barré syndrome
• Amyotrophic lateral sclerosis
• Sarcoidosis

Prognosis

Prognosis will depend on the pathology and the preoperative neurological deficits. The timing of surgical decompression is a significant factor in prognosis and outcome, with the best results obtained when surgery is performed within the first 48 hours after symptom presentation.[14] Some reports indicate benefits up to the 72-hour mark. Bladder dysfunction is a negative prognostic factor for poor outcomes.[15][16] The return of bladder function is estimated to occur in approximately 50% of patients with CES.

Complications

Complications can arise from conus and cauda equina tumors themselves or from the modalities to treat these tumors. The following are some of these complications:

• Neurological deficit (mild weakness to paraplegia)
• Urinary incontinence/retention
• Fecal incontinence
• Sexual dysfunction
• Saddle anesthesia
• Radicular pain
• Postoperative worsening: new neurological deficits, infections, and cerebrospinal fluid leak