Functional Neuroimaging — MCQs
Structure of brain involved in emotion: a) Neocortex b) Limbic system c) Thalamus d) Hippocampus
Cerebral blood flow is regulated by all of the following except:
EEG waves prominent in occipital lobe are
All the following are indications for brain imaging in epilepsy, except:
Substance used for PET scan is
Radiation-induced necrosis can be diagnosed by:
Pine-tree bladder is a sign of.
Intra-tumoral calcification in the brain is seen in all except?
Which of the following techniques is the best for differentiating recurrence of a brain tumor from radiation therapy-induced necrosis?
Which of the following brain tumors is typically hyperdense on CT scan?
Functional Neuroimaging Indian Medical PG Practice Questions and MCQs
Question 1: Structure of brain involved in emotion: a) Neocortex b) Limbic system c) Thalamus d) Hippocampus
- A. Neocortex
- B. Thalamus
- C. Limbic system (Correct Answer)
- D. Hippocampus
Explanation: ***Limbic system*** - The **limbic system** is a complex set of brain structures located on top of the brainstem and underneath the cortex that is primarily associated with **emotion**, motivation, memory, and behavior. - Key components include the **amygdala** (crucial for fear and emotional responses), **hippocampus** (memory formation with emotional context), **hypothalamus** (autonomic responses to emotion), and **cingulate gyrus** (emotional processing). - This is the **primary neuroanatomical system** responsible for emotional processing and regulation. *Neocortex* - The **neocortex** is the outermost layer of the brain involved in higher-level functions such as **conscious thought**, sensory perception, motor commands, and language. - While it modulates and interprets emotions, it is not the primary center for generating basic emotional responses. *Thalamus* - The **thalamus** acts as a **relay station** for sensory and motor signals to the cerebral cortex. - While it processes emotional stimuli, it does not initiate or primarily control emotional responses itself. *Hippocampus* - The **hippocampus** is a crucial part of the limbic system primarily involved in **memory formation**, particularly the consolidation of short-term to long-term memory, and **spatial navigation**. - While it plays a role in recalling emotionally charged memories, it is not the primary structure for the generation or direct experience of emotion itself.
Question 2: Cerebral blood flow is regulated by all of the following except:
- A. Calcium ions (Correct Answer)
- B. Blood pressure
- C. Arterial PCO2
- D. Potassium ions
Explanation: ***Calcium ions*** - While **calcium ions (Ca²⁺)** are mechanistically essential for vascular smooth muscle contraction and relaxation, they are **not considered a primary regulatory signal** for cerebral blood flow (CBF) in the same way as the other factors listed. - Ca²⁺ acts as an **intracellular second messenger** that mediates the effects of other regulatory factors (like PCO2, K⁺, and vasoactive substances), rather than being a direct extracellular regulatory signal itself. - The question refers to primary regulatory factors that directly modulate CBF, not the intracellular mechanisms by which vascular smooth muscle responds. *Blood pressure* - **Cerebral autoregulation** maintains relatively constant CBF despite changes in **mean arterial pressure (MAP)** between approximately 60-150 mmHg. - Blood pressure is a **key regulatory factor** - when MAP falls below or exceeds this range, CBF becomes pressure-dependent. - This protective mechanism prevents cerebral ischemia or hyperemia with systemic blood pressure fluctuations. *Arterial PCO2* - **Arterial partial pressure of carbon dioxide (PaCO2)** is one of the **most potent direct regulators** of CBF. - **Hypercapnia** (increased PaCO2) causes cerebral vasodilation and increased CBF (approximately 1-2 mL/100g/min increase per 1 mmHg rise in PaCO2). - **Hypocapnia** (decreased PaCO2) causes vasoconstriction and reduced CBF, utilized therapeutically in managing elevated intracranial pressure. *Potassium ions* - **Increased extracellular K⁺** in the perivascular space causes **direct vasodilation** of cerebral arterioles. - This mechanism is crucial for **neurovascular coupling** (functional hyperemia) - when neurons are active, they release K⁺, which dilates nearby vessels to increase local blood flow. - K⁺-mediated vasodilation helps match cerebral perfusion to metabolic demand during neuronal activity.
Question 3: EEG waves prominent in occipital lobe are
- A. Gamma
- B. Alpha (Correct Answer)
- C. Beta
- D. Theta
Explanation: ***Alpha*** - **Alpha waves** are typically most prominent in the **occipital and parietal lobes** when an individual is awake but in a relaxed state with their eyes closed. - They are associated with a state of **relaxed awareness** and tend to disappear when the eyes open or during mental activity or sleep. *Gamma* - **Gamma waves** are the fastest brain waves and are associated with **higher-level cognitive functions**, such as learning, memory, and information processing across different brain regions. - While present throughout the brain, they are not specifically prominent in the occipital lobe in isolation during baseline resting states. *Beta* - **Beta waves** are characteristic of an **alert, awake state** and are often recorded over the frontal and central regions of the brain. - They are associated with active thinking, problem-solving, and concentration, and tend to be suppressed in the occipital region during rest. *Theta* - **Theta waves** are typically associated with **sleep stages 1 and 2**, as well as deep meditation and certain emotional states. - While they can be observed in various brain regions during specific activities or sleep, they are not primarily prominent in the occipital lobe during awake, relaxed states.
Question 4: All the following are indications for brain imaging in epilepsy, except:
- A. EEG shows a focal seizure source
- B. Control of seizures is difficult
- C. Seizures have focal features clinically
- D. Epilepsy starts after the age of 5 years (Correct Answer)
Explanation: Address the indications for brain imaging in epilepsy based on clinical guidelines. ***Epilepsy starts after the age of 5 years*** - The recommendation for **brain imaging** is typically suggested for epilepsy onset after the age of **16 years** to rule out structural causes, rather than age 5 [2]. An onset at age 5 does not exclude the possibility of idiopathic epilepsy, which often does not require imaging [1]. - While it's a good practice to image any new onset epilepsy, age 5 by itself is not a specific indication that *demands* imaging beyond standard workup if no other red flags are present. *EEG shows a focal seizure source* - A **focal seizure source identified on EEG** strongly indicates a structural lesion in the brain that could be responsible for the seizures [2]. - **Brain imaging** (e.g., MRI) is essential to identify the underlying **structural abnormality**, such as a tumor, malformation, or scar tissue [2]. *Control of seizures is difficult* - Poorly controlled or **refractory seizures** warrant further investigation with brain imaging to look for an **underlying structural cause** that might be amenable to surgical intervention or require alternative therapies [2]. - This suggests the possibility of a lesion that is not responding to standard anti-epileptic drugs, necessitating a search for the **etiology of intractability** [3]. *Seizures have focal features clinically* - **Focal clinical features** (e.g., twitching of one limb, sensory disturbances on one side) strongly point to a specific area of the brain where the seizures originate [4]. - **Brain imaging** is crucial to identify any **structural lesion** (e.g., tumor, malformation, stroke) corresponding to the clinically localized area of seizure onset [2].
Question 5: Substance used for PET scan is
- A. Gadolinium
- B. Gastrografin
- C. Iodine
- D. 18F-FDG (Correct Answer)
Explanation: ***18F-FDG*** - **18F-FDG (Fluorodeoxyglucose)** is a glucose analog labeled with a **positron-emitting radioisotope**, fluorine-18 (18F). - It is the most commonly used radiotracer in PET scans, as it accumulates in cells with high metabolic activity, particularly **cancer cells** and activated brain cells. *Gadolinium* - **Gadolinium** is a paramagnetic contrast agent primarily used in **MRI scans** to enhance the visualization of blood vessels and abnormal tissues. - It does not emit positrons and is therefore not suitable for PET imaging. *Gastrografin* - **Gastrografin** is an oral, water-soluble contrast agent containing **iodine**, typically used in **X-rays** and **CT scans** of the gastrointestinal tract. - It is not a radioactive tracer and has no application in PET imaging. *Iodine* - **Iodine** in various forms can be used as a contrast agent in **X-rays** and **CT scans**, or as a radioactive isotope (e.g., **I-131**) for **thyroid imaging** and treatment. - While some isotopes of iodine are radioactive, they are not typically used for PET imaging, which relies on positron emission.
Question 6: 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 7: Pine-tree bladder is a sign of.
- A. Pelvic abscess
- B. Bilharziasis (Correct Answer)
- C. Intraperitoneal bladder rupture
- D. Neurogenic bladder
Explanation: ***Bilharziasis*** - The "pine-tree bladder" appearance on a retrograde cystogram is characteristic of **chronic bilharzial cystitis**, also known as **schistosomiasis of the bladder**. - This appearance results from **fibrosis**, **granulomas**, and **calcification** of the bladder wall leading to multiple irregular diverticula and trabeculations, which resemble pine-tree branches. *Pelvic abscess* - A pelvic abscess causes an **extrinsic compression** on the bladder, leading to mass effect or displacement, rather than intrinsic wall changes. - It would typically present with symptoms of infection, such as fever and localized pain, and imaging would show a fluid collection. *Intraperitoneal bladder rupture* - An intraperitoneal bladder rupture would lead to extravasation of urine into the peritoneal cavity, which would be visible on imaging as **free fluid** around abdominal organs. - The bladder itself would appear flaccid and potentially collapsed, without the characteristic "pine-tree" appearance. *Neurogenic bladder* - Neurogenic bladder is characterized by **detrusor-sphincter dyssynergia** or loss of bladder sensation, leading to features like **trabeculation**, cellules, and diverticula due to high intravesical pressure. - While it can cause some bladder wall changes, the specific "pine-tree" pattern is not its hallmark, and it is usually associated with neurological deficits.
Question 8: Intra-tumoral calcification in the brain is seen in all except?
- A. Craniopharyngioma
- B. Meningioma
- C. Oligodendroglioma
- D. Hemangioblastoma (Correct Answer)
Explanation: **Explanation:** The correct answer is **Hemangioblastoma**. In neuroradiology, identifying the presence or absence of calcification is a high-yield diagnostic marker for intracranial tumors. **1. Why Hemangioblastoma is the correct answer:** Hemangioblastomas are highly vascular, WHO Grade 1 tumors typically located in the posterior fossa (cerebellum). Characteristically, they present as a **cystic lesion with a highly enhancing mural nodule**. Crucially, hemangioblastomas **do not calcify**. Their primary imaging features are related to vascularity (flow voids on MRI) and associated erythropoietin production, which may lead to polycythemia. **2. Why the other options are incorrect:** * **Oligodendroglioma:** This is the "classic" answer for calcified brain tumors. Calcification is seen in **70–90%** of cases, often described as chunky or ribbon-like. * **Craniopharyngioma:** In the pediatric population (adamantinomatous type), calcification is a hallmark, occurring in approximately **90%** of cases. It follows the "90% rule": 90% are cystic, 90% calcify, and 90% enhance. * **Meningioma:** These are extra-axial tumors that frequently show calcification (about **20–25%**). When the calcification is diffuse and gritty, they are histologically termed "Psammomatous meningiomas." **NEET-PG High-Yield Pearls:** * **Mnemonic for Calcified Brain Tumors (Old Men Are Posh):** **O**ligodendroglioma, **M**eningioma, **A**strocytoma, **P**ineal tumors/ **P**apilloma (Choroid plexus). * **Most common calcified tumor in children:** Craniopharyngioma. * **Most common calcified tumor in adults:** Oligodendroglioma. * **Hemangioblastoma Association:** Frequently associated with **Von Hippel-Lindau (VHL) syndrome**; look for retinal angiomas and renal cell carcinoma in clinical stems.
Question 9: Which of the following techniques is the best for differentiating recurrence of a brain tumor from radiation therapy-induced necrosis?
- A. MRI
- B. Contrast-enhanced MRI
- C. PET scan (Correct Answer)
- D. CT scan
Explanation: **Explanation:** The differentiation between **tumor recurrence** and **radiation necrosis** is a common diagnostic dilemma because both entities appear similar on conventional imaging (enhancing mass with surrounding edema). **Why PET Scan is the Correct Answer:** The distinction is based on **metabolic activity**. * **Tumor Recurrence:** Malignant cells are hypermetabolic and demonstrate high glucose uptake. Therefore, they appear as **"Hot" lesions** on FDG-PET (Fluorodeoxyglucose) or Amino Acid PET (e.g., Methionine-PET). * **Radiation Necrosis:** This represents dead tissue and inflammatory changes, which are metabolically inactive. These appear as **"Cold" lesions** (photopenic) on PET scans. This functional assessment makes PET the gold standard for differentiation. **Why Other Options are Incorrect:** * **MRI & Contrast-enhanced MRI (CE-MRI):** While MRI is the investigation of choice for initial diagnosis, it cannot reliably distinguish recurrence from necrosis. Both conditions cause a breakdown of the blood-brain barrier, leading to similar contrast enhancement and T2/FLAIR signals. * **CT Scan:** CT lacks the soft-tissue resolution required for neuro-oncology and provides no metabolic information, making it the least sensitive modality for this purpose. **NEET-PG High-Yield Pearls:** * **MR Spectroscopy (MRS):** If PET is not an option, MRS is the next best functional MRI technique. Recurrence shows **increased Choline** (cell turnover) and **decreased NAA** (neuronal loss), whereas necrosis shows a "dead" spectrum (low peaks across the board or a Lactate/Lipid peak). * **Perfusion MRI (rCBV):** Tumor recurrence typically shows **increased** relative Cerebral Blood Volume (rCBV) due to neoangiogenesis, while necrosis shows **decreased** rCBV. * **Gold Standard:** Histopathology remains the definitive gold standard, but PET is the best non-invasive imaging technique.
Question 10: Which of the following brain tumors is typically hyperdense on CT scan?
- A. Ependymoma
- B. Medulloblastoma (Correct Answer)
- C. Oligodendroglioma
- D. Astrocytoma
Explanation: **Explanation:** The density of a tumor on a non-contrast CT (NCCT) scan is primarily determined by its **cellularity** and the **nuclear-to-cytoplasmic (N:C) ratio**. **1. Why Medulloblastoma is correct:** Medulloblastoma is a "Small Round Blue Cell Tumor." These tumors are characterized by extremely high cellular density and very little cytoplasm. Because DNA and cellular proteins attenuate X-rays more than water or lipids, the high concentration of cells makes the tumor appear **hyperdense** relative to the normal brain parenchyma on NCCT. This is a classic radiological hallmark of medulloblastoma, typically seen in the midline (cerebellar vermis) of pediatric patients. **2. Analysis of Incorrect Options:** * **Ependymoma:** Usually appears isodense or heterogeneous on CT. While they often contain calcifications (which are hyperdense), the soft tissue component itself is not typically hyperdense. * **Oligodendroglioma:** These are known for having the highest incidence of **calcification** (up to 90%), which is hyperdense. However, the tumor mass itself is usually hypo-to-isodense. * **Astrocytoma:** Most low-grade astrocytomas are **hypodense** due to high water content and associated edema. High-grade gliomas (GBM) are usually heterogeneous due to necrosis and hemorrhage. **3. High-Yield Clinical Pearls for NEET-PG:** * **Hyperdense tumors on CT (Mnemonic: "M-L-G"):** **M**edulloblastoma, **L**ymphoma (Primary CNS), and **G**erm cell tumors/Meningioma. * **Medulloblastoma:** Most common malignant brain tumor in children; associated with "drop metastases" (seeding via CSF). * **Calcification Mnemonic:** "Old Elephants Can't Dance" (**O**ligodendroglioma, **E**pendymoma, **C**raniopharyngioma, **D**ysembryoplastic Neuroepithelial Tumor).
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