From the Guidelines
Neurological examination findings in conus medullaris lesions typically include symmetric lower extremity weakness, saddle anesthesia, and bowel/bladder dysfunction. Patients present with bilateral, often symmetric lower motor neuron signs including decreased muscle tone, flaccid paralysis, and diminished or absent deep tendon reflexes in the lower extremities, as seen in cases of cauda equina syndrome 1. Sensory deficits manifest as decreased sensation in a saddle distribution (perineum, buttocks, posterior thighs), which corresponds to sacral dermatomes. Urinary retention, overflow incontinence, and decreased anal sphincter tone are hallmark findings due to disruption of autonomic pathways. Sexual dysfunction is common. Pain may be present but is typically less severe than in cauda equina syndrome. Upper motor neuron signs are absent since the lesion affects the terminal end of the spinal cord rather than descending tracts.
These findings result from damage to the conus medullaris (S2-S5 spinal segments) where lower motor neurons and autonomic fibers originate. The symmetric nature of symptoms helps distinguish conus lesions from cauda equina syndrome, which often presents with more asymmetric findings, such as multifocal deficits and progressive neurologic deficits 1. Early recognition is crucial as prompt surgical intervention may prevent permanent neurological deficits. Key symptoms to look out for include:
- Symmetric lower extremity weakness
- Saddle anesthesia
- Bowel/bladder dysfunction
- Decreased muscle tone
- Flaccid paralysis
- Diminished or absent deep tendon reflexes in the lower extremities
- Urinary retention
- Overflow incontinence
- Decreased anal sphincter tone
- Sexual dysfunction
It is essential to note that the imaging study of choice in the evaluation of suspected conus medullaris lesions is MRI, due to its ability to accurately depict soft-tissue pathology, assess vertebral marrow, and assess the spinal canal patency 1.
From the Research
Neurological Examination Findings
The neurological examination findings on conus medullaris lesion can be summarized as follows:
- The bulbocavernosus reflex (BCR) is an important indicator of the type of lesion, with its presence indicating an upper motor neuron (UMN) lesion and its absence indicating a lower motor neuron (LMN) lesion 2
- The BCR can help distinguish conus medullaris from cauda equina syndromes 2
- Sensory or motor function in the most caudal sacral segments can define sacral sparing, which is part of the International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI) 2
- Sphincter dysfunctions can be addressed in the International Standards for the Assessment of Autonomic Function after SCI (ISAFSCI), although the BCR is not included in this classification 2
- The type of lesion (UMN or LMN) has important prognostic and therapeutic implications for bowel, bladder, and sexual function 2
Clinical Presentation
The clinical presentation of conus medullaris lesions can vary, but common features include:
- Urinary symptoms, such as loss of bladder function 3
- Minimal sensorimotor dysfunction in the lower lumbar and sacral segments 3
- Flaccid and areflexic motor paralysis in some cases 3
- Sensory loss in the perineal region or lumbar dermatomal distribution 3
Diagnostic Imaging
Diagnostic imaging, such as MRI, can be used to visualize the conus medullaris and diagnose lesions:
- Axial images of the conus-epiconus region can be more informative than sagittal images 3
- MRI can show pathological spinal cord expansion, gadolinium-enhancement, and tumoral cyst formation, which can help differentiate neoplastic from non-neoplastic lesions 4
Electrophysiological Monitoring
Electrophysiological monitoring, such as the BCR, can be used to assess the function of the conus medullaris: