Molecular Imaging in Neurology — MCQs
Which of the following is a pathognomonic feature of Alzheimer's disease?
A lady presented with a 4 cm tumor in the left parietal lobe for which she underwent surgery and radiotherapy. After 3 months she presented with headache and vomiting. Which of the following would characterize the lesion in the patient?
Which common tracer in PET is usually administered in the form of a glucose sugar?
Radiation-induced necrosis can be diagnosed by:
A 60-year-old man with Parkinson’s disease presents with visual hallucinations and cognitive decline over the past year. He is on levodopa. What is the most likely diagnosis?
A patient presents with a suspected cervical spine injury following an accident. What is the first step in management?
A 2-year-old boy has been doing well despite his diagnosis of tetralogy of Fallot. He presented to an outside ER a few days ago with a complaint of an acute febrile illness for which he was started on a "pink, bubble-gum tasting antibiotic." His mother reports that for the past 12 hours or so he has been holding his head saying it hurts and he is less active than normal. On your examination, he seems to have a severe headache, nystagmus, and ataxia. Which of the following would be the most appropriate first test to order?
Which of the following statements is MOST accurate regarding herpes encephalitis?
Which of the following are enantiomers?
The best investigative modality for gallbladder stones -
Molecular Imaging in Neurology Indian Medical PG Practice Questions and MCQs
Question 1: Which of the following is a pathognomonic feature of Alzheimer's disease?
- A. Plaques and tangles (Correct Answer)
- B. Presence of Lewy bodies
- C. Presence of Pick bodies
- D. Red neuronal degeneration
Explanation: ***Plaques and tangles*** - The presence of **amyloid plaques** (extracellular deposits of beta-amyloid protein) and **neurofibrillary tangles** (intracellular aggregates of hyperphosphorylated tau protein) are the defining neuropathological hallmarks of Alzheimer's disease [1]. These are considered **pathognomonic** features upon post-mortem examination. - While other neurological conditions can have some tauopathy or amyloid deposition, the specific combination, distribution, and extensive nature of these two pathologies are unique to Alzheimer's [1]. [3] *Presence of Lewy bodies* - **Lewy bodies** are abnormal aggregates of alpha-synuclein protein that are characteristic of **Parkinson's disease** and **Lewy body dementia** [3]. - Their presence indicates a distinct neurodegenerative process, separate from Alzheimer's disease. *Presence of Pick bodies* - **Pick bodies** are cytoplasmic inclusions composed primarily of tau protein, but they are characteristic of **Pick's disease**, a type of frontotemporal dementia [2]. - Pick's disease has a different clinical presentation and neuropathological profile than Alzheimer's disease [2]. *Red neuronal degeneration (general feature)* - **Red neuronal degeneration** refers to the morphological changes seen in neurons undergoing acute irreversible ischemic injury, such as during a **stroke**. - It is a general feature of acute neuronal death and is not specific to, nor a pathognomonic feature of, Alzheimer's disease. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Central Nervous System, pp. 1292-1294. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Central Nervous System, pp. 1294-1295. [3] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Manifestations Of Central And Peripheral Nervous System Disease, pp. 721-722.
Question 2: A lady presented with a 4 cm tumor in the left parietal lobe for which she underwent surgery and radiotherapy. After 3 months she presented with headache and vomiting. Which of the following would characterize the lesion in the patient?
- A. Digital subtraction angiography with dual source CT scan
- B. Gd-enhanced MRI
- C. 99Tc-HMPAO SPECT brain
- D. 18FDG PET Scan (Correct Answer)
Explanation: ***18FDG PET Scan*** - This patient, presenting with new neurological symptoms after **surgery and radiotherapy** for a cerebral tumor, faces a diagnostic dilemma: differentiating between **tumor recurrence** and **radiation necrosis**. - **18FDG PET scans** effectively distinguish between these two conditions because viable tumor cells exhibit high metabolic activity and thus actively take up **fluorodeoxyglucose (FDG)**, while radiation necrosis is metabolically inactive and shows little to no FDG uptake. *Digital subtraction angiography with dual source CT scan* - **Digital subtraction angiography (DSA)** is primarily used to visualize **vascular structures** and is not the modality of choice for differentiating tumor recurrence from radiation necrosis. - A **dual-source CT scan** is useful for rapid imaging and dynamic studies but lacks the metabolic information needed for this specific differentiation. *Gd-enhanced MRI* - While **Gd-enhanced MRI** is excellent for detecting **structural changes** and **blood-brain barrier disruption**, it often cannot definitively differentiate between **tumor recurrence** and **radiation necrosis**. - Both conditions can present with similar **enhancement patterns** on MRI, making differentiation challenging without additional metabolic information. *99Tc-HMPAO SPECT brain* - **99mTc-HMPAO SPECT** measures **regional cerebral blood flow (rCBF)**, which can be altered in both tumors and areas of radiation injury. - However, it does not provide the specific metabolic information (glucose metabolism) needed to reliably distinguish between **viable tumor cells** and **radiation necrosis** as effectively as FDG PET.
Question 3: Which common tracer in PET is usually administered in the form of a glucose sugar?
- A. Aluminum - 12
- B. Fluorine 18 (Correct Answer)
- C. Carbon 11
- D. Oxygen 15
Explanation: ***Fluorine 18*** - **18F-FDG** (Fluorodeoxyglucose) is the most common PET tracer, utilizing **Fluorine-18** as its radioactive component. - FDG is a glucose analog, meaning it mimics glucose and is taken up by metabolically active cells, allowing for imaging of **glucose metabolism**. *Aluminum - 12* - **Aluminum-12** is not a common radionuclide used in PET imaging. - The most common tracers in PET are **positron emitters** like Fluorine-18, Carbon-11, Nitrogen-13, and Oxygen-15. *Carbon 11* - **Carbon-11** can be used in PET tracers (e.g., 11C-methionine), but it is **less common** than 18F-FDG due to its shorter half-life. - Its short half-life (20 minutes) requires an **on-site cyclotron** for production, limiting its widespread use. *Oxygen 15* - **Oxygen-15** is employed in PET tracers (e.g., 15O-water for cerebral blood flow), but it has an **even shorter half-life** (2 minutes) than Carbon-11. - Its extremely short half-life makes it **impractical** for routine clinical use in the form of a glucose sugar.
Question 4: Radiation-induced necrosis can be diagnosed by:
- A. MRI
- B. CT
- C. PET
- D. Biopsy (Correct Answer)
Explanation: ***Biopsy*** - A **biopsy** is the definitive diagnostic method for radiation-induced necrosis, allowing for histological examination of tissue to confirm necrosis and rule out residual or recurrent tumor. [1], [2] - It provides a direct view of cellular changes, identifying **necrosis, atypical cells**, and ruling out **malignancy**. *MRI* - While **MRI** can show structural changes indicative of necrosis (e.g., mass effect, edema), it often cannot definitively differentiate between **radiation necrosis** and **tumor recurrence.** [2] - It often shows **T1 hypointensity** and **T2 hyperintensity**, but these findings are not specific. *CT* - **CT scans** are useful for detecting gross changes like **mass effect** and **edema** but have limited sensitivity for distinguishing necrosis from tumor recurrence. - It may show **low-density lesions** but lacks the resolution and specificity for precise diagnosis. *PET* - **PET scans** measure metabolic activity and can help distinguish between **tumor recurrence** (high uptake) and **radiation necrosis** (low uptake) in some cases. - However, false positives can occur, as some inflammatory processes in necrosis can also show increased uptake, making it **less definitive** than a biopsy. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Central Nervous System, pp. 1307-1308. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 340-341.
Question 5: A 60-year-old man with Parkinson’s disease presents with visual hallucinations and cognitive decline over the past year. He is on levodopa. What is the most likely diagnosis?
- A. Frontotemporal dementia
- B. Alzheimer's disease
- C. Lewy body dementia
- D. Parkinson’s disease dementia (Correct Answer)
Explanation: No changes were made to the text as none of the provided references met the relevance criteria (score >= 7) for characterizing the differential diagnosis between Parkinson’s disease dementia and Lewy body dementia, specifically the 'one-year rule' or the pathological progression from established Parkinson's disease motor signs to cognitive decline.
Question 6: A patient presents with a suspected cervical spine injury following an accident. What is the first step in management?
- A. perform imaging studies
- B. administer oxygen
- C. stabilize the cervical spine (Correct Answer)
- D. log roll the patient
Explanation: ***stabilize the cervical spine*** - In any suspected cervical spine injury, the **first and most critical step is to stabilize the cervical spine** to prevent further neurological damage. This is achieved through manual inline stabilization, followed by a **rigid cervical collar** and placement on a backboard. - This immediate stabilization is paramount before any other assessments or interventions that could potentially worsen the injury. *perform imaging studies* - While imaging studies (e.g., X-ray, CT scan) are crucial for diagnosing the extent of cervical spine injury, they should only be performed **after the spine has been adequately stabilized**. - Performing imaging prior to stabilization risks **further displacement** of vertebrae and spinal cord injury. *administer oxygen* - Administering oxygen is an important step in **maintaining adequate oxygenation** and is part of initial resuscitation, but it does not take priority over cervical spine stabilization in a trauma setting. - **Airway, Breathing, Circulation (ABC)** management should always incorporate cervical spine protection. *log roll the patient* - **Log rolling** is a technique used to move a patient with a suspected spinal injury, but it must be performed **only after the cervical spine is stabilized** and with sufficient personnel to ensure coordinated movement. - Log rolling is not the first step in management; rather, it is a technique for patient assessment and transfer once initial stabilization is achieved.
Question 7: A 2-year-old boy has been doing well despite his diagnosis of tetralogy of Fallot. He presented to an outside ER a few days ago with a complaint of an acute febrile illness for which he was started on a "pink, bubble-gum tasting antibiotic." His mother reports that for the past 12 hours or so he has been holding his head saying it hurts and he is less active than normal. On your examination, he seems to have a severe headache, nystagmus, and ataxia. Which of the following would be the most appropriate first test to order?
- A. CT or MRI of the brain (Correct Answer)
- B. Lumbar puncture
- C. Urine drug screen
- D. Blood culture
Explanation: ***CT or MRI of the brain*** - The patient's history of **tetralogy of Fallot** puts him at increased risk for a **brain abscess** due to right-to-left shunting, bypassing pulmonary filtration of bacteria. - New onset of severe headache, nystagmus, and ataxia in this context strongly suggests an **intracranial mass lesion**, making immediate imaging crucial. *Lumbar puncture* - Performing a **lumbar puncture** in the presence of signs of elevated intracranial pressure (severe headache, nystagmus, ataxia) or suspicion of a mass lesion (brain abscess) is **contraindicated** due to the risk of herniation. - While it can diagnose meningitis, the clinical picture with focal neurological signs makes a mass lesion a higher concern that needs to be ruled out first. *Urine drug screen* - The patient's symptoms (severe headache, nystagmus, ataxia) are not typical for drug intoxication in a 2-year-old, especially given the history of a recent febrile illness and a congenital heart defect. - There is no clinical indication for drug use in this young child, and this test would not address the serious neurological symptoms. *Blood culture* - While a blood culture might be useful to identify a systemic infection, it will not directly explain or diagnose the acute focal neurological deficits such as nystagmus and ataxia, and the severe headache. - Given the high suspicion of an intracranial lesion with risk of herniation, obtaining imaging is a higher priority than waiting for blood culture results, which would take time.
Question 8: Which of the following statements is MOST accurate regarding herpes encephalitis?
- A. Focal neurological symptoms are common.
- B. EEG findings are nonspecific and not diagnostic.
- C. The temporal lobe is commonly involved. (Correct Answer)
- D. MRI is a key diagnostic tool.
Explanation: ***The temporal lobe is commonly involved.*** - **Herpes simplex encephalitis (HSE)** characteristically targets the **temporal lobes** [1] and **orbitofrontal cortex**, leading to specific neurological deficits. - This predilection for the temporal lobes often results in symptoms such as **aphasia**, **seizures**, and **memory disturbances** [1]. *Focal neurological symptoms are common.* - While focal neurological symptoms such as **aphasia**, **hemiparesis**, and **seizures** are indeed common in HSE [1], this statement is less specific than the involvement of the temporal lobe. - The **localization** of the infection to the temporal lobes explains why these focal symptoms are so prevalent [1]. *MRI is a key diagnostic tool.* - **MRI findings**, particularly **T2-weighted** and **FLAIR sequences**, showing **edema** and **hemorrhage** in the temporal lobes and insular cortex, are highly suggestive of HSE. - However, the most definitive diagnostic tool remains the detection of **HSV DNA** in the **cerebrospinal fluid (CSF)** via **PCR**. *EEG findings are nonspecific and not diagnostic.* - **EEG** in HSE often shows **periodic lateralizing epileptiform discharges (PLEDs)** or **focal slowing** primarily over the temporal lobes, which are highly suggestive, although not entirely diagnostic on their own. - These findings can help guide further investigation and support a clinical diagnosis in conjunction with other tests.
Question 9: Which of the following are enantiomers?
- A. D-glucose and D-mannose
- B. D-glucose and D-galactose
- C. D-glucose and D-fructose
- D. D-glucose and L-glucose (Correct Answer)
Explanation: ***D-glucose and L-glucose*** - **Enantiomers** are stereoisomers that are **non-superimposable mirror images** of each other. - **D-glucose** and **L-glucose** fit this definition perfectly; they have the same chemical formula and connectivity but differ in the spatial arrangement of all their chiral centers, resulting in mirror images. - Any pair of D- and L- forms of the same sugar are enantiomers. *D-glucose and D-mannose* - These are **epimers**, specifically C-2 epimers, meaning they differ in the configuration at **only one chiral carbon atom** (the second carbon from the carbonyl group in their open-chain forms). - They are not mirror images of each other because the configurations at the other chiral centers are the same. *D-glucose and D-galactose* - These carbohydrates are **epimers**, specifically C-4 epimers, meaning their difference lies in the configuration around the **fourth carbon atom**. - As they differ at only one chiral center and have the same "D-" configuration for their penultimate carbon, they are not mirror images of each other. *D-glucose and D-fructose* - These are **constitutional isomers** (structural isomers), not stereoisomers. - D-glucose is an aldohexose (aldose sugar) while D-fructose is a ketohexose (ketose sugar). - They differ in the position of the carbonyl group, so they cannot be enantiomers.
Question 10: The best investigative modality for gallbladder stones -
- A. Oral cholecystogram
- B. Percutaneous transhepatic cholangiography
- C. Ultrasound (Correct Answer)
- D. Intravenous cholangiogram
Explanation: ***Ultrasound*** - **Ultrasound** is the **most widely accepted and accurate** non-invasive imaging modality for detecting gallstones. - It has a high sensitivity and specificity for visualizing stones within the gallbladder and assessing for associated complications like **cholecystitis**. *Oral cholecystogram* - This method involves ingestion of a contrast agent, which is then absorbed and excreted into the bile, outlining the gallbladder. - It has largely been replaced by ultrasound due to its **lower accuracy** and **dependence on gallbladder function**. *Percutaneous transhepatic cholangiography* - This is an **invasive procedure** involving direct puncture of a bile duct, typically reserved for visualizing the **biliary tree** when other methods are insufficient, especially in cases of obstructive jaundice. - It is **not the primary diagnostic tool** for uncomplicated gallstones but rather for complex biliary duct pathology. *Intravenous cholangiogram* - This involves intravenous injection of contrast, which is then excreted into the bile to visualize the biliary tree. - It is **rarely used today** due to its **limited diagnostic yield**, potential for adverse reactions, and the advent of superior imaging techniques like **MRCP** and **ERCP**.
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