Anatomy

The conus medullaris represents the caudal end of the spinal cord. It narrows and continues as the filum terminale, a fibrous strand providing longitudinal support.  From the same level, nerve roots descend, forming the cauda equina, a bundle of lumbar, sacral, and coccygeal nerves. The conus medullaris typically terminates between the T11 vertebral body and the L2/L3 intervertebral disc.

Diagnostics

MRI is essential for assessing normal morphology and signal intensity, which remain consistent in healthy individuals but vary slightly across different imaging sequences. Routine MRI protocols for evaluating the conus medullaris typically include T1-weighted (T1W) and T2-weighted (T2W) sagittal and axial sequences, as well as fat-suppressed sequences for improved lesion detection. Additional imaging techniques, such as diffusion-weighted imaging (DWI) and contrast-enhanced studies can further aid in the characterization of various pathologies.

Presentation

The conus medullaris and cauda equina are susceptible to a broad spectrum of conditions, including congenital malformations, degenerative changes, postoperative complications, ischemic injury, inflammatory and infectious diseases, as well as neoplasms.

Clinical manifestations may vary depending on the underlying pathology but commonly include low back pain and sciatica, lower extremity weakness, sensory deficits, sphincter, and sexual dysfunction. The most severe form, conus medullaris syndrome (CMS), is characterized by a combination of bilateral lower extremity weakness, saddle anesthesia, urinary retention, and bowel incontinence. There is some overlap of CMS with cauda equina syndrome (CES), which presents mostly by lower motor neuron signs and symptoms, while those of CMS are a combination of lower and upper motor neuron. CMS presentation is usually symmetric, while CES is commonly asymmetric.

Pathological changes on imaging can manifest as an abnormal position of the medullary cone, altered signal intensity, abnormal enhancement, contour irregularities, and masses affecting the conus or adjacent structures.