Neuroanatomy: cauda equina syndrome: practice question

A Anatomy question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Anatomy · Neuroanatomy: cauda equina syndrome

Sample item

A 40-year-old man with a large central L4-L5 disc prolapse has saddle anaesthesia, urinary retention and reduced anal tone. Which finding favours a cauda equina lesion rather than a conus medullaris lesion?

ASensory loss restricted to pain and temperature with preserved proprioceptionBSymmetric spastic weakness with brisk reflexes and extensor plantar responsesCAsymmetric flaccid weakness with absent ankle jerks and severe radicular painDA sensory level at T4 with bilateral arm weakness

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. Asymmetric flaccid weakness with absent ankle jerks and severe radicular pain

The spinal cord ends at about L1 to L2, and below that the lumbosacral nerve roots form the cauda equina. Damage to these roots is a lower motor neuron lesion with asymmetric flaccid weakness, areflexia, severe radicular pain and saddle anaesthesia. Conus lesions are more symmetric, painless and may include upper motor neuron signs.

Option by option

A. Sensory loss restricted to pain and temperature with preserved proprioception
Dissociated sensory loss suggests an intramedullary cord lesion, not root compression.
B. Symmetric spastic weakness with brisk reflexes and extensor plantar responses
Spasticity and extensor plantars are upper motor neuron signs, which fit the conus or cord rather than roots.
C. Asymmetric flaccid weakness with absent ankle jerks and severe radicular pain (correct)
Correct. Root involvement gives asymmetric lower motor neuron signs and pain.
D. A sensory level at T4 with bilateral arm weakness
A thoracic sensory level and arm weakness imply a lesion far above the lumbar roots.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Anatomy question

What is the answer to this Anatomy question?

The best answer is C, Asymmetric flaccid weakness with absent ankle jerks and severe radicular pain. The spinal cord ends at about L1 to L2, and below that the lumbosacral nerve roots form the cauda equina.

Why is "Sensory loss restricted to pain and temperature with preserved propri…" not the answer?

Dissociated sensory loss suggests an intramedullary cord lesion, not root compression.

Why is "Symmetric spastic weakness with brisk reflexes and extensor plantar r…" not the answer?

Spasticity and extensor plantars are upper motor neuron signs, which fit the conus or cord rather than roots.

Why is "A sensory level at T4 with bilateral arm weakness" not the answer?

A thoracic sensory level and arm weakness imply a lesion far above the lumbar roots.

What concept does this question test?

It tests Neuroanatomy: cauda equina syndrome in Anatomy. Damage to these roots is a lower motor neuron lesion with asymmetric flaccid weakness, areflexia, severe radicular pain and saddle anaesthesia. Conus lesions are more symmetric, painless and may include upper motor neuron signs.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Neuroanatomy: cauda equina syndrome?

Learn every nerve by its route, its muscles and what a lesion looks like at the bedside. That one habit answers a large share of questions. Then use the flashcards and the other Anatomy questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.