Management of Cauda Equina Tumors

Epidemiology and Pathology

Cauda equina tumors (CETs) represent a distinct entity of spinal cord neoplasms that arise from the cauda equina, with an estimated prevalence rate is 0.03 per 100,000 persons (in the age-adjusted 2000 US population). According to 2004–07 data from the Surveillance, Epidemiology and End Results (SEER) database, CETs account for 3.5% of all primary spinal canal tumors in the United States, with benign representing the overwhelming majority, that is, 80%. Most CETs are encountered in young adults, with a mean age of presentation at 47 years. There is a slight male predominance, that is, 54% versus 46%. Interestingly, there is a significant correlation between age and tumor pathology: ependymomas tend to occur in younger patients (34.6 ± 16 years) compared with nerve sheath tumors (51 ± 17 years). ^, Paragangliomas lie in between (48.6 ± 18 years).

Most tumors are slow-growing and arise from intrinsic structures of the region, including the filum terminale (myxopapillary ependymoma), peripheral nerve sheath (schwannoma and neurofibroma), intrinsic vessel well (hemangioblastoma or hemangioma), connective tissue (lipoma, sarcomas), embryologic remnants (teratoma), or other nervous structures (e.g., paraganglioma). Occasionally, they can occur in the context of neurocutaneous syndromes (phakomatoses), typically neurofibromatosis or von Hippel-Lindau disease. Furthermore, CETs might be associated with occult dysraphism in infants and young children. Given very low prevalence, the majority of evidence on these tumors is derived from case reports and small case series.

Clinical Presentation

Radiculopathy is the common symptom at the time of initial evaluation (present in 81% of cases), followed by low back pain (60%) and sphincter dysfunction (25%). , Overall, limited range of motion is seen in half of patients, with associated paravertebral spasm in 28%. Motor and sensory deficits are present in 40% and 50% of reported cases, respectively. Finally, lower extremity amyotrophy might be seen in 33% and 8.5% of cases, respectively, but they are never seen in isolation. Bilateral symptoms should raise suspicion for ependymoma.

According to literature, the interval to presentation ranges from 1 month to 264 months.

In a large French series by Wager et al., the mean time to diagnosis was 24.6 months. A strong association was observed with tumor histology: 20 months for ependymomas versus 50 months for neurofibromas and paragangliomas. Rarely, patients might present with a clinical picture of acute cauda equina syndrome secondary to intratumoral bleeding precipitated by trauma or progressive visual loss, papilledema, and optic nerve atrophy due to giant cauda equina ependymoma (with high CSF protein levels and arachnoiditis being potential mechanisms).

Diagnostic Evaluation

Aside from a thorough history and physical examination, the evaluation of a patient with concern for CET also entails diagnostic imaging. Electrophysiologic studies, including electromyography and motor/somatosensory evoked potentials, have limited clinical value in the preoperative setting.

Plain lumbosacral x-rays are obtained in most patients; however, they are unrevealing in up to two-thirds of cases. Observed findings may include scoliosis, bone scalloping, or erosion of the posterior vertebral body wall. The latter are typically a mark of slower-growing tumors.

Computed tomography of the lumbosacral spine can also be an important adjunct. It is of paramount importance that the entire lumbar spinal canal is adequately visualized; otherwise, tumors can be missed if the CT scan focuses on the lower three levels. Furthermore, care should be taken to avoid misinterpreting a hypodense tumor that fills the spinal canal as the absence of compression.

Magnetic resonance imaging comprises the gold standard for diagnosis. T1 and T2 sequences with and without gadolinium administration are necessary in order to better delineate the presence and size of the tumor, underlying vascularity, presence of cystic components, or intra-tumoral bleeding, as well as the relationship to bony structures and the conus. More importantly, it allows for a preliminary histopathologic diagnosis that can aid with surgical decision-making and aggressiveness of resection.

Primary differential diagnosis includes metastatic lesions, which share similar imaging features but do not always constitute a surgical entity. Although typically primary intraosseous lesions, chordomas may also develop inside the dural sac despite the absence of clear connection with the sacrum or the spine. Finally, astrocytomas arising from the conus medullaris may also involve the proximal part of the nerve roots; however, they are not true CETs.