NEUROSCIENCES – RADIOLOGY

• The patient has incontinence and lower limb weakness, which suggests involvement of the lumbosacral spinal cord or cauda equina.
• A fall from height can lead to:
  • Spinal cord injury (SCI) at the lumbosacral level.
  • Cauda equina syndrome (CES) if the injury affects the nerve roots below L1-L2.
  • Conus medullaris syndrome if the conus (lower part of the spinal cord) is involved.
• Symptoms like bladder dysfunction (incontinence), saddle anesthesia, and leg weakness warrant urgent MRI of the lumbosacral region.

Why the Other Options Are Wrong:

1. Imaging of the dorsal spine should be done: ❌
   • The dorsal (thoracic) spine is unlikely to be the primary site of injury since it usually causes upper limb involvement or complete paraplegia, rather than isolated lower limb weakness and incontinence.
2. Involvement of cervical spine C4 level: ❌
   • A C4 spinal injury would result in quadriplegia (both upper and lower limb paralysis) and respiratory dysfunction due to diaphragm involvement. This does not match the patient’s presentation.
3. The middle cerebral artery is involved: ❌
   • MCA stroke affects the face, upper limb, and speech, but does not cause isolated lower limb weakness and incontinence.
4. The posterior cerebral artery is involved: ❌
   • PCA stroke affects vision and memory, not the spinal cord or lower limb function.

This 25-year-old male presents with:
✅ Flaccid areflexic quadriparesis (weakness in all four limbs, absent reflexes).
✅ History of diarrhea 3 weeks prior → Suggestive of a preceding infection (e.g., Campylobacter jejuni).
✅ Intact sensations with downgoing plantar reflex → Suggests a peripheral nervous system disorder rather than an upper motor neuron lesion.

These findings are highly suggestive of Guillain-Barré syndrome (GBS), an acute inflammatory demyelinating polyneuropathy that follows an infection and leads to ascending paralysis.

Why is Nerve Conduction Study (NCS) the Best Diagnostic Test?

• NCS shows features of demyelination, including:
  ✅ Prolonged F-wave latency
  ✅ Reduced conduction velocity
  ✅ Conduction block
  ✅ Prolonged distal latencies
• It helps confirm the diagnosis of GBS and differentiate it from other neuromuscular disorders.

Why not the other options?

• Serum electrolytes → Hypokalemia can cause weakness, but it usually presents with cramps and cardiac abnormalities, not a post-infectious, symmetrical, progressive paralysis.
• Cerebrospinal fluid detailed report (CSF DR) → Would show albuminocytologic dissociation (high protein, normal WBC) in GBS, but it is not the first diagnostic test; it is supportive rather than confirmatory.
• MRI cervical spine → Useful for spinal cord pathology (e.g., transverse myelitis, cord compression) but unnecessary here as sensory function is intact.
• CT brain → Not helpful since there are no cranial signs or upper motor neuron features.

Thus, nerve conduction studies (NCS) are the best diagnostic investigation for suspected Guillain-Barré syndrome.

MRI is the best imaging modality for detecting a slipped (herniated) intervertebral disc because it provides high-resolution images of soft tissues, including:

• Intervertebral discs
• Spinal cord
• Nerve roots
• Ligaments

MRI can accurately visualize disc herniation, nerve compression, and associated inflammation, making it the gold standard for diagnosing herniated discs.

Why the other options are incorrect:

1. Computed Tomography (CT) Scan:
   • CT scans are better for bone structures but provide limited soft tissue detail.
   • CT myelography (CT with contrast in the spinal canal) can detect nerve compression, but MRI is preferred for soft tissues.
2. Electroencephalography (EEG):
   • EEG measures brain electrical activity and is used for conditions like epilepsy, not for detecting spinal issues.
3. Electrocardiography (ECG/EKG):
   • ECG records heart electrical activity, primarily used for diagnosing cardiac conditions, not spinal disorders.
4. Ultrasound:
   • Ultrasound is not effective for evaluating intervertebral discs due to its limited penetration through bone.
   • It is mainly used for soft tissue and vascular assessments, not spine imaging.

A “bat-wing deformity” on brain MRI is a characteristic finding in agenesis of the corpus callosum (ACC). This deformity occurs due to the absence of the corpus callosum, leading to widening of the lateral ventricles and an abnormal appearance of the interhemispheric structures.

Key Features of Agenesis of Corpus Callosum (ACC):

✔️ Absent or underdeveloped corpus callosum (the major white matter tract connecting both hemispheres).
✔️ Bat-wing or racing car appearance on MRI due to:

• Widening of the lateral ventricles (colpocephaly).
• Elevation of the third ventricle into the interhemispheric fissure.
  ✔️ Associated with developmental delay, intellectual disability, and seizures (depending on severity).
  ✔️ May occur in isolation or as part of genetic syndromes (e.g., Aicardi syndrome, Andermann syndrome).

Since a bat-wing appearance is strongly associated with ACC, it is the most likely cause in this case.

Analysis of Each Option:

✅ Correct Option:
🔹 “Agenesis of corpus callosum”
✔️ True – The absence of the corpus callosum leads to ventricular widening, giving the brain an MRI appearance resembling a “bat-wing.”

🚫 Incorrect Options:

🔹 “Holoprosencephaly”
❌ Holoprosencephaly is a failure of forebrain (prosencephalon) division, leading to a single midline ventricle and abnormal facial development.
❌ MRI does not show a bat-wing deformity but instead shows fused cerebral hemispheres.

🔹 “Polymicrogyria”
❌ Polymicrogyria is characterized by abnormally small and excessive gyri, leading to a “pebble-like” cortex on MRI, not a bat-wing deformity.

🔹 “Lissencephaly”
❌ Lissencephaly (“smooth brain”) results from failed neuronal migration, leading to absent or underdeveloped gyri and sulci.
❌ The MRI shows a smooth brain surface, not a bat-wing deformity.

🔹 “Neuronal heterotopia”
❌ Neuronal heterotopia is a failure of neurons to migrate properly, leading to grey matter nodules in abnormal locations (e.g., periventricular nodular heterotopia).
❌ It does not produce a bat-wing deformity.

In T2-weighted MRI (T2WI), tissues with high water content appear bright (hyperintense). The intervertebral disc, particularly the nucleus pulposus (the inner gel-like core of the disc), contains a high amount of water. Therefore, it appears bright on T2WI. This brightness helps distinguish healthy discs from degenerated discs, which lose water content and appear darker.

Why the Other Options Are Incorrect:

1. Grey
   Grey (intermediate signal intensity) is not characteristic of the intervertebral disc on T2WI. Grey signals are typically seen in tissues with moderate water content, such as muscle or cartilage, but not in the highly hydrated nucleus pulposus.
2. Black
   Black (hypointense) signals on T2WI are seen in structures with low water content, such as cortical bone or calcified tissues. The intervertebral disc, being rich in water, does not appear black.
3. Jet black
   Jet black is an extreme form of hypointensity, typically seen in structures like air or dense calcifications. The intervertebral disc does not appear jet black on T2WI.
4. Dark
   Dark signals on T2WI are associated with low water content or fibrous tissues, such as the annulus fibrosus (the outer ring of the intervertebral disc). However, the nucleus pulposus, which is the dominant component of the disc, appears bright due to its high water content.

The major advantage of MRI over CT is its superior soft tissue contrast and resolution, making it the best imaging modality for detecting soft tissue abnormalities, such as:
✅ Brain and spinal cord pathology (e.g., tumors, demyelination, ischemia)
✅ Ligament and tendon injuries
✅ Muscle and joint disorders
✅ Detailed imaging of internal organs without radiation

Why is MRI better for soft tissue imaging?

• Uses strong magnetic fields and radio waves instead of ionizing radiation.
• Can differentiate between gray and white matter in the brain better than CT.
• Provides multi-planar imaging (sagittal, coronal, axial views).
• High sensitivity in detecting edema, tumors, and demyelinating diseases.

Why not the other options?

• Quick modality → CT is much faster than MRI, making it the preferred choice in emergencies (e.g., trauma, stroke).
• Does not require any prior preparation → MRI often requires screening for metal implants/pacemakers and may need contrast agents.
• Superior in detection of calcified lesions → CT is superior for detecting calcifications and bone pathology, not MRI.
• Use of ionizing radiation → MRI does not use ionizing radiation, whereas CT does.

Thus, the correct answer is “excellent soft tissue imaging with high contrast sensitivity,” making MRI the preferred choice for soft tissue evaluation.

A “bat-wing deformity” on brain MRI is a characteristic finding in agenesis of the corpus callosum (ACC). This deformity occurs due to the absence of the corpus callosum, leading to widening of the lateral ventricles and an abnormal appearance of the interhemispheric structures.

Key Features of Agenesis of Corpus Callosum (ACC):

✔️ Absent or underdeveloped corpus callosum (the major white matter tract connecting both hemispheres).
✔️ Bat-wing or racing car appearance on MRI due to:

• Widening of the lateral ventricles (colpocephaly).
• Elevation of the third ventricle into the interhemispheric fissure.
  ✔️ Associated with developmental delay, intellectual disability, and seizures (depending on severity).
  ✔️ May occur in isolation or as part of genetic syndromes (e.g., Aicardi syndrome, Andermann syndrome).

Since a bat-wing appearance is strongly associated with ACC, it is the most likely cause in this case.

Analysis of Each Option:

✅ Correct Option:
🔹 “Agenesis of corpus callosum”
✔️ True – The absence of the corpus callosum leads to ventricular widening, giving the brain an MRI appearance resembling a “bat-wing.”

🚫 Incorrect Options:

🔹 “Holoprosencephaly”
❌ Holoprosencephaly is a failure of forebrain (prosencephalon) division, leading to a single midline ventricle and abnormal facial development.
❌ MRI does not show a bat-wing deformity but instead shows fused cerebral hemispheres.

🔹 “Polymicrogyria”
❌ Polymicrogyria is characterized by abnormally small and excessive gyri, leading to a “pebble-like” cortex on MRI, not a bat-wing deformity.

🔹 “Lissencephaly”
❌ Lissencephaly (“smooth brain”) results from failed neuronal migration, leading to absent or underdeveloped gyri and sulci.
❌ The MRI shows a smooth brain surface, not a bat-wing deformity.

🔹 “Neuronal heterotopia”
❌ Neuronal heterotopia is a failure of neurons to migrate properly, leading to grey matter nodules in abnormal locations (e.g., periventricular nodular heterotopia).
❌ It does not produce a bat-wing deformity.

An electroencephalogram (EEG) is the gold standard for diagnosing seizures. It records the electrical activity of the brain and can detect abnormal patterns associated with epilepsy and other seizure disorders. EEG is particularly useful for:

1. Identifying the type of seizure (e.g., focal, generalized).
2. Locating the seizure focus in the brain.
3. Monitoring treatment effectiveness.

Why the Other Options Are Wrong:

1. Myelography:
   • Myelography is an imaging technique used to evaluate the spinal cord and nerve roots, not the brain. It is not used for diagnosing seizures.
2. Electroencephalogram (EEG) and Electromyography (EMG):
   • While EEG is used for diagnosing seizures, electromyography (EMG) is used to assess muscle and nerve function. EMG is not relevant for diagnosing seizures.
3. Nerve conduction:
   • Nerve conduction studies evaluate the function of peripheral nerves and are not used for diagnosing seizures.
4. Electromyography (EMG):
   • EMG assesses muscle and nerve function and is not used for diagnosing seizures.

In T2-weighted imaging (T2WI) of MRI, tissues with high water content appear bright (hyperintense). Since cerebrospinal fluid (CSF) is primarily water, it appears bright white on T2-weighted images.

• T1-weighted imaging (T1WI), in contrast, shows CSF as dark (hypointense).
• Grey or black appearances are typically seen in different tissue contrasts rather than CSF on T2WI.

Magnetic resonance imaging (MRI) is the first choice of modality for diagnosing and examining suspected spinal cord lesions, especially in patients who have suffered trauma. MRI provides detailed imaging of both the spinal cord and surrounding soft tissues, including the vertebrae, ligaments, and intervertebral discs. It is particularly effective at detecting spinal cord injuries, including those involving soft tissue damage, edema, or hemorrhage.

Here’s why the other options are less suitable:

1. Positron emission tomography (PET) scan: PET scans are typically used for metabolic imaging and detecting abnormalities in tissue function, not for evaluating acute trauma or spinal cord lesions.
2. X-ray: While X-rays are useful for detecting fractures in the bones of the spine, they do not provide detailed information about soft tissue damage, such as spinal cord injury or edema.
3. Computed tomography (CT) scan: CT scans are good for evaluating bone fractures and certain types of trauma but offer less detail than MRI when it comes to soft tissue, such as the spinal cord and surrounding structures.
4. Electroencephalography (EEG): EEG is used for detecting electrical activity in the brain and is not appropriate for evaluating spinal cord injuries.

Understanding the Clinical Scenario

This patient presents with:

• Lower limb weakness
• Incontinence (suggesting involvement of the sacral spinal cord or its pathways)
• History of trauma (fall from height)

Given this combination of neurological and bladder dysfunction, a spinal cord injury at the lumbosacral level is the most likely cause. Imaging of the lumbosacral region (MRI or CT scan) is essential to assess spinal cord compression, fractures, or nerve root injury.

Why the Other Options Are Incorrect

1. The middle cerebral artery is involved – Incorrect

   • The middle cerebral artery (MCA) supplies the lateral aspects of the frontal, temporal, and parietal lobes.
   • MCA infarcts typically cause contralateral upper limb and facial weakness, aphasia (if dominant hemisphere is affected), or neglect (if non-dominant hemisphere is involved).
   • It does NOT cause isolated lower limb weakness or incontinence, as the medial frontal lobe (leg motor area) is supplied by the anterior cerebral artery (ACA).

2. The posterior cerebral artery is involved – Incorrect

   • The posterior cerebral artery (PCA) supplies the occipital lobe, thalamus, and parts of the midbrain.
   • PCA strokes result in visual deficits (homonymous hemianopia), thalamic pain syndrome, and sometimes memory impairment.
   • It does not cause lower limb weakness or incontinence.

3. Involvement of cervical spine C4 level – Incorrect

   • The C4 spinal level is located in the cervical spine and controls diaphragm function (via the phrenic nerve).
   • Injury here would result in respiratory compromise, upper limb weakness, and quadriplegia, not isolated lower limb weakness and incontinence.

4. Imaging of the dorsal spine should be done – Incorrect

   • While the thoracic spine (dorsal spine) is important for motor control of the lower limbs, the bladder and bowel functions are controlled by the sacral segments (S2-S4).
   • If the patient has incontinence, the injury is more likely in the lumbosacral region than in the dorsal (thoracic) spine.

The absolute contraindication for MRI is the presence of ferromagnetic implants or devices, such as an indwelling cardiac pacemaker, because the strong magnetic field can interfere with or damage the device.

Why is an indwelling cardiac pacemaker contraindicated?

• Magnetic fields can disrupt pacemaker function, leading to arrhythmias or complete failure of the device.
• Induced electrical currents can overheat components, potentially damaging the pacemaker or surrounding tissue.
• Movement of metallic components can cause mechanical damage.

However, some modern pacemakers (MRI-conditional pacemakers) are designed to be safe under specific MRI conditions.

Why not the other options?

• Allergies → MRI does not use contrast in all cases (contrast allergies are a relative contraindication, not absolute).
• Dyspnea → Not a contraindication unless the patient has severe respiratory distress requiring continuous monitoring.
• Claustrophobia → A relative contraindication; can be managed with sedation or open MRI machines.
• Movement disorders → Patients may require sedation to minimize motion artifacts but can still undergo MRI.

Thus, the correct answer is indwelling cardiac pacemaker, as it is a potentially life-threatening contraindication for MRI.

X-ray (radiography) is the initial imaging modality of choice for fractures because:

• It is fast, widely available, and cost-effective.
• It provides excellent visualization of bones to detect fractures, dislocations, and alignment issues.
• It has lower radiation exposure compared to CT scans.

Why the other options are incorrect:

1. Myelography:
   • Myelography is used for evaluating spinal cord, nerve roots, and the subarachnoid space with contrast, not for fractures.
2. PET (Positron Emission Tomography):
   • PET scans are used to assess metabolic activity, primarily for cancer detection and brain disorders, not fractures.
3. CT (Computed Tomography):
   • CT scans are more detailed than X-rays, but they are usually used for complex fractures, such as spinal, facial, or intra-articular fractures, or when X-ray findings are unclear.
4. MRI (Magnetic Resonance Imaging):
   • MRI is excellent for soft tissue injuries (ligaments, tendons, muscles, bone marrow edema), but it is not the first-line choice for fractures.

MRI is the most suitable test for diagnosing spinal cord lesions because it provides detailed imaging of soft tissues, including:

• Spinal cord
• Intervertebral discs
• Nerve roots
• Surrounding soft tissue structures

It is particularly useful for detecting:

• Spinal cord tumors (ependymomas, astrocytomas, metastases)
• Multiple sclerosis (MS) plaques
• Spinal cord infarction or ischemia
• Syringomyelia (fluid-filled cavity in the spinal cord)
• Compression from herniated discs or trauma

T2-weighted MRI is especially helpful for identifying edema, inflammation, and demyelination in the spinal cord.

Why the Other Options Are Wrong:

1. Complete Blood Count (CBC) Report (✗) [Detects Blood Disorders, Not Spinal Lesions]
   • CBC is useful for infections, anemia, leukemia, but it does not provide imaging of the spinal cord.
   • Some infections (e.g., meningitis) may cause elevated white blood cells, but CBC alone cannot diagnose a spinal cord lesion.
2. X-ray (✗) [Limited to Bone Structures, Not Soft Tissue]
   • X-rays are useful for detecting fractures, vertebral alignment issues, or bone abnormalities.
   • They cannot visualize the spinal cord, tumors, or demyelinating lesions.
3. Computed Tomography (CT) Scan (✗) [Better for Bones, Less Sensitive for Soft Tissue]
   • CT is useful for detecting fractures, hemorrhages, and bony abnormalities.
   • Contrast-enhanced CT can provide some details of soft tissue, but MRI is far superior for spinal cord imaging.
4. Electroencephalography (EEG) (✗) [Used for Brain Activity, Not Spinal Cord]
   • EEG records electrical activity in the brain, used for diagnosing seizures, epilepsy, sleep disorders, and encephalopathy.
   • It has no role in diagnosing spinal cord lesions

Magnetic Resonance Imaging (MRI) is the preferred imaging modality for detecting spinal cord lesions because it provides high-resolution images of soft tissues, including:

• Spinal cord
• Nerve roots
• Intervertebral discs
• Ligaments and surrounding soft tissues

MRI is highly sensitive for identifying:

• Spinal cord tumors (ependymomas, astrocytomas, metastases)
• Multiple sclerosis (MS) plaques
• Spinal cord infarction or ischemia
• Syringomyelia (fluid-filled cavity in the spinal cord)
• Compression from herniated discs or trauma

T2-weighted MRI is especially useful for detecting edema, inflammation, and demyelination in the spinal cord.

Why the Other Options Are Wrong:

1. X-ray (✗) [Limited to Bone, Not Soft Tissue]
   • X-rays are useful for bony structures (fractures, vertebral misalignment), but they do not provide details of spinal cord pathology.
   • Cannot detect tumors, demyelination, or spinal cord compression.
2. PET/CT (✗) [Used for Metabolic Imaging, Not Structural]
   • Positron Emission Tomography (PET) is used for metabolic activity, mainly in cancer detection.
   • CT provides good bone detail but is not as effective as MRI for soft tissues.
3. Myelography (✗) [Invasive and Outdated for Most Cases]
   • Myelography (X-ray with contrast in CSF) was historically used for spinal cord imaging but has been largely replaced by MRI.
   • Still used when MRI is contraindicated (e.g., pacemaker patients).
4. CT Scan (✗) [Better for Bone, Inferior for Soft Tissue]
   • CT scans are best for fractures and bony abnormalities but provide poor resolution for spinal cord and soft tissue compared to MRI.
   • Contrast-enhanced CT can help in trauma cases but is not preferred over MRI for cord lesions.

the first-line imaging modality for assessing skull fractures, especially in cases of trauma. CT provides detailed bone imaging, detects fractures, and evaluates for intracranial hemorrhage, brain edema, or other injuries that may accompany the fracture.

Why the Other Options Are Incorrect:
X-ray – While X-rays can detect skull fractures, they are not the preferred modality in emergency settings because they lack sensitivity for detecting intracranial injuries. CT is superior for evaluating both bone fractures and associated brain injuries.

PET scan – Positron Emission Tomography (PET) is primarily used for metabolic and functional imaging, such as detecting tumors or neurodegenerative diseases. It is not useful for acute trauma or skull fractures.

MRI – Magnetic Resonance Imaging (MRI) is excellent for soft tissue and brain evaluation, but it is not the first choice for detecting skull fractures because it does not image bone well. MRI is used later if there are concerns about brain injuries, such as diffuse axonal injury or ligamentous injury in spinal trauma.

Myelography – This imaging technique involves injecting contrast into the spinal canal to assess spinal cord and nerve root compression. It is not used for skull fractures.

Hint to Solve the Question:
“In cases of trauma, which imaging modality is the fastest and most effective in assessing both bone fractures and brain injuries?”

Magnetic resonance imaging (MRI) is the first-choice modality for diagnosing and examining suspected spinal cord lesions in trauma patients. MRI provides:

1. High-resolution images of soft tissues, including the spinal cord, nerve roots, and surrounding structures.
2. Detailed visualization of spinal cord injuries, such as contusions, compression, or hemorrhage.
3. Multiplanar imaging (axial, sagittal, and coronal views), which is essential for assessing the extent of spinal cord damage.

MRI is superior to other imaging modalities for evaluating spinal cord lesions because it does not involve ionizing radiation and provides excellent contrast resolution for soft tissues.

Why the Other Options Are Not the First Choice:

1. X-ray:
   • X-rays are useful for assessing bony injuries (e.g., fractures, dislocations) but do not provide detailed images of the spinal cord or soft tissues.
2. Computed tomography (CT) scan:
   • CT scans are excellent for evaluating bony structures and can detect fractures or dislocations. However, they are less effective than MRI for visualizing soft tissue injuries, such as spinal cord lesions.
3. Electroencephalography (EEG):
   • EEG measures electrical activity in the brain and is used to diagnose conditions like epilepsy. It is not used for evaluating spinal cord lesions.
4. Positron emission tomography (PET) scan:
   • PET scans are used to assess metabolic activity and are primarily used in oncology, cardiology, and neurology (e.g., for brain tumors or epilepsy). They are not suitable for diagnosing spinal cord lesions.