Neoplasms of the cauda equina (differential)

The differential diagnosis for masses of the cauda equina region is often considered separately to the remainder of the spinal cord. It is often difficult to determine whether masses in this region are intramedullary or intradural-extramedullary.

Most common tumours

• myxopapillary ependymoma
  • by far the most common tumour of the conus medullaris and filum terminale, representing more than 90% of tumours in this region ¹⁰
  • most commonly present in young adult males
  • marked homogeneous enhancement is typical
  • often have associated haemorrhage; may calcify or undergo cystic degeneration
  • if large, may expand the spinal canal, cause scalloping of the vertebral bodies and extend out of the neural exit foramina
• schwannoma
  • second most common tumour in this region
  • most are solitary and sporadic, however, there is an association with neurofibromatosis type 2
  • small tumours may be distinguished from myxopapillary ependymomas by their origin from nerve roots (myxopapillary ependymomas arise from the filum terminale)
  • virtually all enhance
  • haemorrhage may occur but less commonly than with myxopapillary ependymoma
  • may be associated with intrinsic vascular changes (thrombosis; sinusoidal dilatation), cyst formation and fatty degeneration

Less common tumours

• paraganglioma
  • although spinal paragangliomas occur almost exclusively in the cauda equina, they represent only 3.5-3.8% of neoplasms in this region ²
  • serpentine flow voids are typically seen along the surface of and within the tumour nodule (however, flow voids may also be seen in hemangioblastomas)
  • haemorrhage is common, leading to a "cap sign" on T2 weighted images
  • the characteristic “salt-and-pepper” appearance of neck and skull base paragangliomas may be seen
  • intense enhancement is virtually always present
• intradural metastases
  • lesions are often multiple
  • “sugar coating” of the spinal cord and nerve roots may be seen
  • in the paediatric population, they are most commonly “drop metastases” from a CNS primary; in adults, non-CNS primary tumours are more common
• hemangioblastoma
  • focal flow voids, especially in larger lesions
  • vivid enhancement
  • an associated tumour cyst or syrinx is common (50-100%) ^6,9 
  • mostly sporadic however there is an increased incidence in patients with von Hippel-Lindau syndrome (multiple lesions are typical)
• meningioma
  • occurrence within the conus/cauda equina is uncommon
  • usually isointense with the spinal cord on T1 and T2 weighted images
  • calcification may be present (calcified lesions are hypointense on T1 and T2 weighted images, may show only minimal enhancement)
  • haemorrhage is uncommon
  • there is an increased incidence in patients with neurofibromatosis type 2
• astrocytoma
  • isolated conus medullaris involvement is seen in 3%. Involvement of the filum terminale is rare ⁶
  • the vast majority enhance
  • haemorrhage is uncommon
• spinal PNET
  • the most common sites of spinal involvement are the filum terminale and cauda equina (57%) ⁷
  • diffuse heterogeneous enhancement pattern
  • because CSF seeding commonly occurs, leptomeningeal enhancement may be seen
• ganglioglioma
  • only rarely involve the conus medullaris
  • predominantly in children and young adults
  • mixed signal intensity on T1 weighted images (due to the dual cellular elements of the tumour)
  • most demonstrate patchy enhancement
  • calcification is common

Benign masses that mimic tumours

• lipoma of the filum terminale
  • common (present in up to 5% of the general population ⁴)
  • usually an incidental finding, however, may be associated with signs and symptoms of tethered spinal cord
  • signal follows that of fat on all sequences (hyperintense on T1 and T2, saturation on fat saturated sequences)
  • no enhancement
  • can demonstrate chemical shift artefact on T2* / gradient weighted sequences
• dermoid cyst
  • 20% are located in the cauda equina ⁵
  • patients are usually younger than 20 years of age
  • usually contain fatty elements
  • no enhancement or mild rim enhancement
• epidermoid cyst
  • similar intensity to CSF on T1 and T2 weighted images
  • typically non-enhancing, however, a thin rim of contrast enhancement may be seen
  • diffusion restriction on DWI