Neuraxial Anatomy — MCQs
A resident at the emergency department is preparing for a lumbar puncture in a 26 years old female with suspected subarachnoid bleeding. Although she presented with altered sensorium, CT brain was found to be normal. During LP, which structure is pierced after the spinal needle crosses interspinous ligament?
Best site for administering spinal anesthesia is the intervertebral space between.
Epidural space lies between:
Through which route does prostate cancer primarily spread to the vertebral column?
Where is the epidural venous plexus located?
Number of vertebrae in human vertebral column is
Anterior Spinal artery is a branch of?
In spinal anesthesia, the drug is deposited between
In all of the following conditions, neuraxial blockade is absolutely contraindicated, EXCEPT:
In spinal anesthesia, the needle is pierced up to which space?
Neuraxial Anatomy Indian Medical PG Practice Questions and MCQs
Question 1: A resident at the emergency department is preparing for a lumbar puncture in a 26 years old female with suspected subarachnoid bleeding. Although she presented with altered sensorium, CT brain was found to be normal. During LP, which structure is pierced after the spinal needle crosses interspinous ligament?
- A. Supra/inter spinous ligament
- B. Skin
- C. Sub cutaneous fascia
- D. Dura mater
- E. Arachnoid mater
- F. Ligamentum flava (Correct Answer)
Explanation: The enriched explanation is the original text provided because none of the references were sufficiently relevant to the anatomy of a lumbar puncture. Ligamentum flava - After passing the interspinous ligament, the next significant structure pierced by the spinal needle during a lumbar puncture is the ligamentum flava. - This ligament is crucial for stabilizing the vertebral column and is located anterior to the interspinous ligament, connecting the laminae of adjacent vertebrae. *Supra/inter spinous ligament* - The question explicitly states that the needle has already crossed the interspinous ligament, making this an incorrect choice for the next structure. - The supraspinous ligament lies superficial to the interspinous ligament, both of which are encountered before the ligamentum flava. *Skin* - The skin is the very first layer pierced when performing a lumbar puncture. - The question is asking what is pierced after the interspinous ligament, not what is pierced first. *Sub cutaneous fascia* - The subcutaneous fascia is located directly beneath the skin and is encountered very early in the lumbar puncture procedure. - It lies superficial to all ligaments of the vertebral column, including the interspinous ligament. *Dura mater* - The dura mater is pierced after the ligamentum flava. - It is the outermost meningeal layer, which, once penetrated, indicates entry into the epidural space, followed by the subarachnoid space. *Arachnoid mater* - The arachnoid mater is a thin, delicate membrane that lies immediately deep to the dura mater. - It is pierced almost simultaneously with the dura mater, and its penetration allows entry into the subarachnoid space where CSF is collected. *Return of CSF* - The return of CSF is the result of successfully traversing all necessary layers and entering the subarachnoid space. - It is not an anatomical structure that is pierced itself, but rather the clinical endpoint of the procedure.
Question 2: Best site for administering spinal anesthesia is the intervertebral space between.
- A. L1 - L2
- B. L2 - L3
- C. L3 - L4 (Correct Answer)
- D. L5 - S1
Explanation: ***L3 - L4*** - The **spinal cord** typically ends at the level of **L1-L2** in adults, making the L3-L4 intervertebral space a safe choice to avoid inadvertent cord injury. - This interspace is easily identified by drawing an imaginary line between the highest points of the **iliac crests**, which usually intersects the L4 vertebra or the L3-L4 interspace. *L1 - L2* - This interspace is generally considered too high for routine spinal anesthesia due to the risk of directly puncturing the **spinal cord**, which often extends to this level in adults. - Puncturing the spinal cord can lead to severe neurological complications, so it is usually avoided. *L2 - L3* - While safer than L1-L2, the **L2-L3 interspace** is still relatively high and carries a slightly increased risk of spinal cord injury compared to lower levels. - The **L3-L4** or **L4-L5** interspaces are generally preferred as they offer a wider margin of safety. *L5 - S1* - The **L5-S1 interspace** is often difficult to access due to the angulation of the **vertebrae** and the presence of the **iliac crests**, making needle insertion challenging. - While anatomically safe in terms of spinal cord termination, the technical difficulty makes it a less preferred site for routine lumbar punctures or spinal anesthesia.
Question 3: Epidural space lies between:
- A. Dura and arachnoid
- B. Pia and arachnoid
- C. Dura and vertebral column (Correct Answer)
- D. Pia mater and grey matter
Explanation: ***Dura and vertebral column*** - The **epidural space** is located between the dura mater and the surrounding vertebral column (specifically the **periosteum** lining the vertebral canal). - This space contains **fat, connective tissue**, and a **venous plexus**, acting as a protective cushion for the spinal cord. *Dura and arachnoid* - The space between the dura mater and the arachnoid mater is the **subdural space** [1]. - This is normally a **potential space** but can become a real space in pathological conditions like a subdural hematoma [1]. *Pia and arachnoid* - The space between the pia mater and the arachnoid mater is the **subarachnoid space** [1]. - This space normally contains **cerebrospinal fluid (CSF)** and blood vessels [1]. *Pia mater and grey matter* - The pia mater is directly apposed to the surface of the brain and spinal cord, including its **grey matter**. - There is no distinct "space" between the pia mater and the neural tissue it covers.
Question 4: Through which route does prostate cancer primarily spread to the vertebral column?
- A. None of the options
- B. Batson plexus (Correct Answer)
- C. Inferior hypogastric plexus
- D. Superior hypogastric plexus
Explanation: Batson plexus - The Batson plexus is a valveless network of veins that connects the deep pelvic veins (including those draining the prostate) to the internal vertebral venous plexuses. - The absence of valves in this plexus allows for the retrograde flow of tumor cells, facilitating the direct spread of prostate cancer to the vertebral column and other bones without passing through the pulmonary circulation. Inferior hypogastric plexus - The inferior hypogastric plexus is a nerve plexus containing sympathetic and parasympathetic fibers, primarily involved in innervating pelvic organs. - It is a neural structure, not a vascular pathway, and therefore does not play a direct role in the hematogenous spread of cancer cells. Superior hypogastric plexus - The superior hypogastric plexus is also a nerve plexus, located anterior to the sacral promontory, involved in autonomic innervation of pelvic organs. - Like the inferior hypogastric plexus, it is a neural structure and not a venous pathway for metastatic spread of cancer. None of the options - This option is incorrect because the Batson plexus is a well-established and critically important route for the metastatic spread of prostate cancer to the vertebral column. - The involvement of this valveless venous system is a hallmark in understanding the predilection of prostate cancer for bone metastases.
Question 5: Where is the epidural venous plexus located?
- A. At the junction of middle and posterior cranial fossa
- B. In vertebral canal above dura mater (Correct Answer)
- C. Basal ganglia adjacent to pons
- D. In vertebral canal below dura mater
Explanation: ***In vertebral canal above dura mater*** - The **epidural venous plexus** (also known as **Batson's plexus**) is located in the **epidural space**, which is external to the dura mater. - In the spinal canal, this space is found between the **vertebral canal** (specifically, the periosteum lining the canal) and the **dura mater**. *At the junction of middle and posterior cranial fossa* - This location relates more to specific cranial nerves or arterial structures at the skull base and is not where the epidural venous plexus of the spine is primarily found. - The epidural space in the cranium is a potential space, and the venous plexuses associated with it are typically referred to as **dural venous sinuses**. *Basal ganglia adjacent to pons* - The **basal ganglia** are deep brain structures involved in motor control, and the pons is part of the brainstem, both located within the cranium. - This location is entirely within the brain parenchyma and not in the epidural space of the vertebral canal. *In vertebral canal below dura mater* - Below the dura mater is the **subdural space** (a potential space) and then the **subarachnoid space**, which contains cerebrospinal fluid and is where the spinal cord and nerve roots are located. - The epidural venous plexus is explicitly located *above* (external to) the dura mater, not below it.
Question 6: Number of vertebrae in human vertebral column is
- A. 30
- B. 33 (Correct Answer)
- C. 32
- D. 31
Explanation: ***Correct Option B: 33*** - The human vertebral column consists of **33 individual vertebrae** in total during early development. - These include **7 cervical**, **12 thoracic**, **5 lumbar**, **5 sacral** (which fuse to form the sacrum), and **4 coccygeal** (which fuse to form the coccyx) vertebrae. *Incorrect Option A: 30* - This number is incorrect; it does not account for all the vertebrae present either individually or in their fused state within the vertebral column. - The total number of vertebrae is higher when counting both individual and fused segments. *Incorrect Option C: 32* - This number is incorrect and falls short of the actual count of vertebrae in the human vertebral column. - It does not correctly represent the full complement of cervical, thoracic, lumbar, sacral, and coccygeal segments. *Incorrect Option D: 31* - This number is incorrect; it does not accurately reflect the total number of vertebrae, including both the individual and completely fused components of the sacrum and coccyx. - It is often confused with the number of 31 pairs of spinal nerves (which is a different count).
Question 7: Anterior Spinal artery is a branch of?
- A. Labyrinthine artery
- B. Vertebral artery (Correct Answer)
- C. Basilar artery
- D. Internal Carotid artery
Explanation: ***Vertebral artery*** - The **anterior spinal artery** is formed by the union of two small branches, one from each **vertebral artery**, at the level of the foramen magnum. - This artery runs inferiorly along the entirety of the spinal cord in the **anterior median fissure**, supplying the anterior two-thirds of the spinal cord. *Labyrinthine artery* - The **labyrinthine artery** (internal auditory artery) typically arises from the **anterior inferior cerebellar artery (AICA)** or, less commonly, directly from the **basilar artery**. - It supplies the inner ear structures, including the **cochlea** and **vestibular apparatus**, and is not involved in spinal cord supply. *Basilar artery* - The **basilar artery** is formed by the union of the two **vertebral arteries** and gives rise to several branches that supply the brainstem and cerebellum, such as the pontine arteries, AICA, superior cerebellar artery, and posterior cerebral arteries. - While the vertebral arteries are its originators, the basilar artery itself does not directly give rise to the anterior spinal artery; rather, the vertebral arteries do, **prior to their union** to form the basilar artery. *Internal Carotid artery* - The **internal carotid artery** primarily supplies the cerebrum and structures within the cranium, giving off branches like the ophthalmic artery, posterior communicating artery, anterior choroidal artery, middle cerebral artery, and anterior cerebral artery. - It is part of the **anterior circulation** to the brain and has no direct branches supplying the spinal cord.
Question 8: In spinal anesthesia, the drug is deposited between
- A. Dura and arachnoid
- B. Pia and arachnoid (Correct Answer)
- C. Dura and vertebra
- D. Into the cord substance
Explanation: ***Pia and arachnoid*** - Spinal anesthesia involves injecting anesthetic into the **subarachnoid space**, which is the anatomical region located between the pia mater and the arachnoid mater. - This space contains **cerebrospinal fluid (CSF)**, allowing the anesthetic to mix and spread, blocking nerve impulses at the spinal cord roots. *Dura and arachnoid* - The space between the dura mater and arachnoid mater is the **subdural space**, and it is typically a potential space rather than an actual one for anesthetic injection. - Injecting here would lead to a **subdural block**, which is distinct from spinal anesthesia and has different characteristics and risks. *Dura and vertebra* - The space between the dura mater and the vertebral canal is the **epidural space**. - **Epidural anesthesia** involves injecting anesthetic into this space, but it is distinct from spinal anesthesia as the drug does not mix directly with CSF and requires a larger dose. *Into the cord substance* - Injecting anesthetic directly into the **spinal cord substance** (intrathecal injection into the cord) would be highly dangerous and cause severe neurological damage. - Anesthetic drugs exert their effect by blocking nerve roots as they exit the spinal cord, not by acting directly on the cord parenchyma.
Question 9: In all of the following conditions, neuraxial blockade is absolutely contraindicated, EXCEPT:
- A. Patient refusal
- B. Severe hypovolemia
- C. Coagulopathy
- D. Pre-existing neurological deficits (Correct Answer)
Explanation: ***Pre-existing neurological deficits*** - Pre-existing neurological deficits are generally considered a **relative contraindication**, not an absolute one, for neuraxial blockade. The decision depends on the nature of the deficit, potential for worsening, and risk-benefit analysis. - While it requires careful consideration and thorough documentation, it does not always preclude the use of neuraxial techniques. *Patient refusal* - **Patient refusal** is always an absolute contraindication to any medical procedure, including neuraxial blockade. Consent is a fundamental ethical and legal principle in medicine. - Performing a procedure against a patient's will constitutes battery. *Severe hypovolemia* - **Severe hypovolemia** is an absolute contraindication because neuraxial blockade causes vasodilation due to sympathetic block, which can exacerbate hypotension and lead to cardiovascular collapse in an already compromised patient. - The reduced preload combined with vasodilation can critically impair organ perfusion. *Coagulopathy* - **Coagulopathy**, whether from anticoagulant therapy or an underlying bleeding disorder, is an absolute contraindication due to the significant risk of **spinal hematoma**. - A spinal hematoma can compress the spinal cord, leading to permanent neurological damage.
Question 10: In spinal anesthesia, the needle is pierced up to which space?
- A. Subarachnoid space (Correct Answer)
- B. Intrathecal space
- C. Epidural space
- D. Subdural space
Explanation: ***Subarachnoid space*** - In **spinal anesthesia**, the anesthetic agent is injected directly into the **cerebrospinal fluid (CSF)**, which is located in the subarachnoid space. - This space is targeted to achieve rapid and widespread blockade of spinal nerves, leading to anesthesia and paralysis below the level of injection. *Epidural space* - The **epidural space** is located outside the **dura mater** and contains fat and blood vessels; it is targeted in **epidural anesthesia**, not spinal anesthesia. - Anesthetic agents in the epidural space provide a slower onset and a more segmental block compared to spinal anesthesia. *Intrathecal space* - The term **intrathecal space** broadly refers to the space containing CSF, which includes the subarachnoid space, but is a less precise anatomical term for the site of injection in spinal anesthesia. - While technically correct in referring to an injection into the CSF, "subarachnoid space" is the specific anatomical term for where the needle tip rests. *Subdural space* - The **subdural space** is a potential space between the **dura mater** and the **arachnoid mater**; it is not the intended target for either spinal or epidural anesthesia. - Accidental injection into the subdural space during spinal or epidural procedures can lead to an unpredictable block with delayed onset and variable spread.
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