Conus and cauda equina tumors represent a unique group of tumors due to their specific location in the spinal canal. The conus medullaris forms the last portion of the spinal cord from where the axons of the distal nerve roots originate and where the spinal bowel and bladder centers are located. The cauda equina is the conglomeration of the nerve roots of the lumbar and sacral spinal nerves distally to the conus area. These two areas form a transition between the central nervous system and the peripheral nervous system. Conus lesions will primarily affect the central functions, while cauda lesions will affect peripheral functions. As these two areas are in close proximity, lesions in one area can affect the function of the other area. Lesions in each area give rise to specific deficits and are appropriately called cauda equina syndrome (CES) and conus medullary syndrome (CMS). In this review, the tumors causing these syndromes are described.
Primary spinal cord tumors are less common than metastatic spinal tumors. Tumors of the spinal canal are classified in three ways depending on the tissue compartment in which they are found:
Tumors arising within the lumbar spine may involve either the vertebrae, the distal end of the spinal cord (conus medullaris), or the nerve roots (cauda equina). These tumors may be primary or metastatic, benign or malignant, and may have a broad range of presentations. The most common tumors involving the vertebrae are metastatic lesions with the most commonly involved area being the vertebral body. The most common tumors arising from the conus medullaris are ependymoma and astrocytoma. A metastatic lesion within the conus medullaris is possible but very uncommon. The most common tumor involving the cauda equina is a schwannoma.
Tumors of the vertebrae are quite frequently metastatic with primary bone or cartilaginous tumors much less common. Metastatic lesions are typically from 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). 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 which is an intradural extramedullary tumor that 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 have a dural tail. There are many etiologies for CES and CMS which are important to enumerate as they are part of the differential diagnosis when dealing with tumors in these areas.
Etiologies of CES includes:
2. Infection: typically from spinal epidural abscess complicating discitis or vertebral osteomyelitis. Although there is a compressive effect from the mass, there is vascular compromise resulting from local septic thrombophlebitis.
5. Degenerative: spinal stenosis
6. Postoperative lumbar spinal surgery complications
Etiologies of CMS includes:
2 Infection: spinal epidural abscess complicating discitis or vertebral osteomyelitis.
3 Ischemic: from poor arterial supply to the area
Cauda equina syndrome and conus medullaris syndrome are rare, with an estimated prevalence of 1-3 in 100,000 people per year and the annual incidence is between 1.5 to 3.4 per million people. Approximately 1-2 % of lumbar disc requiring surgery will present with a cauda 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 a metastasis. Approximately 40% of spinal lesions are intradural extramedullary. These are generally meningiomas of the dural sac or 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).
Symptoms may arise from either compression and dysfunction of the neural elements or from 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 causing 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.
Patients will typically present with a combination of back pain, radiculopathy, or myelopathy. The typical presentation of these lesions is back pain with a varying degree of neurological deficit related to compression of the neural elements. The patient with metastatic disease will give a history of weight loss, general malaise, night sweats, or a history of cancer. The patient with a CES will give a history of back pain with radicular symptoms depending on the level of compression. The patient with a CMS will give 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 some time. The most common sensory deficit is “saddle anesthesia” where the patients will complain 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/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 only have the Achilles tendon involved while 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 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:
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 (MRI) with and without contrast should be obtained to identify any possible mass lesions. The MRI is the gold standard for the evaluation of nontraumatic spinal lesions. If a metastatic mass lesion is suspected, then an appropriate workup would include a computed tomographic (CT) scan of the chest, abdomen, and pelvis or a full-body 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.
Anti-inflammatory agents and steroids can be effective in patients with inflammatory processes and tumors.
Surgical indications are aimed at decompression of the neural elements, gross total tumor resection if possible, and stabilization of the spine should there be any instability. As always, a multidisciplinary approach is best to determine the appropriate treatment based on long term prognosis as well as other indicated systemic treatments. Schwannoma and meningioma lesions usually are benign. 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. 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 is 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. Gross 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 always should 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. Is there is not a known primary, a biopsy is warranted.
Prophylaxis for deep venous thrombosis and/or pulmonary embolism should be started in the perioperative period.
Spinal arteriovenous malformation
Spinal cord infarct
Amyotrophic lateral sclerosis
Prognosis will depend on the pathology and the preoperative neurological deficits. The timing of surgical decompression is a significant factor in the prognosis and outcome; where the best results are obtained when surgery is done within the first 48 hours after the presentation of symptoms. Some reports give the benefits until the 72-hour mark. Bladder dysfunction has a negative prognostic factor for poor outcome. The return of bladder function is estimated to occur in approximately 50% of CES patients.
Neurological deficit (mild weakness to paraplegia)
Postoperative worsening or new neurological deficits, infections, and cerebrospinal fluid leak
Physical medicine and rehabilitation
The patient should be oriented about the diagnosis and management, so he can do informed decisions that will ultimately influence the outcome. After the pathology is obtained, the patient should be informed about the result and the possibility of further treatments with radiotherapy and chemotherapy. The patient needs education to cope with persistent deficits. An interprofessional team is necessary to maximize the medical, physical, psychological, educational, vocational, and social functions of the patient and improve outcomes.
Because the diagnosis and management of these patients is challenging, the patient should be managed by an interprofessional team that includes a neurosurgeon, neuropathologist, neuroradiologist, hematologist-oncologist, radiation oncologist, and pain specialist. The outcomes for patients with spinal cord tumors depend on many factors including age, comorbidities, the extent of resection, tumor spread, neurological deficits, and the pathology. Overall, the prognosis for most patients is guarded.
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