- Which of the following findings would be most consistent with a diagnosis of neurocysticercosis?
Answer: Multiple small parenchymal calcifications
Neurocysticercosis, an infection with the larval stage of the tapeworm Taenia solium, is a common cause of adult-onset seizures in patients from endemic areas (like Latin America). The imaging findings vary with the stage of the parasite's life cycle. Seizures are often triggered by the inflammation surrounding a dying cyst, but the most common chronic and incidental finding on CT is multiple small, punctate calcifications representing dead, calcified cysticerci. This is the inactive phase of the disease. The other options represent brain metastases (A), a brain abscess or primary tumor (B), or hypoxic-ischemic injury (D).
- A 28-year-old woman presents with acute unilateral vision loss and eye pain worsened by movement. She also reports intermittent numbness in her right hand over the past year. Exam shows decreased visual acuity and a relative afferent pupillary defect. MRI brain demonstrates multiple periventricular plaques, and MRI cervical spine shows a short-segment T2 hyperintense lesion. A lumbar puncture is obtained to strengthen diagnostic certainty. Which additional test would confirm the suspected condition based on the CSF profile?
Answer: CSF oligoclonal bands by isoelectric focusing
This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes vision loss and MRI plaques, guiding the choice of additional CSF testing. The correct answer, A, is appropriate because it aligns with the clinical presentation and current guidelines, providing support for multiple sclerosis via oligoclonal bands. Choice B is incorrect due to targeting infection, which often results from misinterpreting demyelination. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.
- What is the most likely diagnosis?
Answer: Viral meningitis
This cerebrospinal fluid (CSF) profile is classic for viral (aseptic) meningitis. The key features are a moderate pleocytosis with a lymphocytic predominance, normal to mildly elevated protein, and a normal glucose level. Bacterial meningitis would show a neutrophilic predominance, high protein, and low glucose. Tuberculous meningitis would show a lymphocytic predominance but with low glucose and very high protein. Subarachnoid hemorrhage would show a large number of red blood cells and xanthochromia.
- A 58-year-old man presents with fever, severe headache, and confusion for 1 day. He is immunocompetent. On exam, T 39.1°C, BP 130/78 mm Hg. He is lethargic and has photophobia. Neurologic exam shows no focal weakness. He has neck stiffness. Noncontrast head CT shows no mass effect or midline shift. Lumbar puncture reveals opening pressure 210 mm H2O, WBC 1,200/µL (85% neutrophils), protein 220 mg/dL, glucose 28 mg/dL (serum glucose 100 mg/dL). Gram stain is pending. The team must decide immediate management based on CSF profile and typical etiologies.
Answer: Start IV ceftriaxone and vancomycin plus dexamethasone
This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes fever, headache, confusion, and neutrophilic CSF, guiding the choice of empiric antibiotics. The correct answer, B, is appropriate because it aligns with the clinical presentation and current guidelines, providing coverage for bacterial meningitis with adjunctive steroids. Choice A is incorrect due to targeting viral causes inappropriately, which often results from misinterpreting CSF profiles. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.
- Which of the following is the most appropriate next step to differentiate between the two most likely diagnoses?
Answer: Initiation of empiric therapy for toxoplasmosis
In an HIV-positive patient with a low CD4 count, multiple ring-enhancing brain lesions, and positive Toxoplasma serology, the differential diagnosis is primarily between cerebral toxoplasmosis and primary CNS lymphoma. The standard of care is to first initiate empiric therapy for toxoplasmosis (e.g., pyrimethamine, sulfadiazine, and leucovorin). A follow-up MRI is typically performed in 2 weeks. Clinical and radiographic improvement supports the diagnosis of toxoplasmosis. If there is no improvement or worsening, a brain biopsy is then considered to diagnose lymphoma. Lumbar puncture, SPECT/PET, and biopsy are typically reserved for cases that fail to respond to empiric treatment.
- A 19-year-old college student presents with fever, headache, and stiff neck for 12 hours. He is photophobic and vomited once. Exam shows T 39.2°C, petechial rash on the trunk, and nuchal rigidity. He is alert without focal deficits. Platelets are 180,000/µL; INR is normal. The ED plans immediate antibiotics and lumbar puncture. There is no papilledema, seizure, or focal neurologic deficit. Which is the most appropriate next step regarding neuroimaging and CSF sampling?
Answer: Perform lumbar puncture immediately after blood cultures
This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes fever, headache, rash, and no contraindications, guiding the choice of immediate lumbar puncture. The correct answer, A, is appropriate because it aligns with the clinical presentation and current guidelines, providing rapid CSF sampling in suspected meningococcemia without delays. Choice C is incorrect due to unnecessary in low-risk cases, which often results from overapplying CT criteria. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.
- In addition to a lymphocytic pleocytosis, which of the following findings in the cerebrospinal fluid would be most characteristic of this condition?
Answer: Elevated red blood cells
The constellation of fever, altered mental status, seizures, and focal neurologic findings localized to the temporal lobe on MRI is classic for Herpes Simplex Virus (HSV) encephalitis. Due to the necrotizing nature of the infection, HSV encephalitis often causes a hemorrhagic inflammatory response. This leads to the presence of an elevated number of red blood cells (RBCs) in the cerebrospinal fluid (CSF) in the absence of a traumatic tap. While a lymphocytic pleocytosis and mildly elevated protein are common, the presence of RBCs is a key diagnostic clue for HSV encephalitis.
- Which of the following neuroimaging findings would support the suspected diagnosis?
Answer: Disproportionately enlarged ventricles
The clinical triad of gait disturbance, dementia, and urinary incontinence ("wet, wacky, and wobbly") is classic for Normal Pressure Hydrocephalus (NPH). The characteristic finding on MRI or CT is ventriculomegaly (enlarged lateral ventricles) that is out of proportion to the degree of cortical atrophy (sulcal widening). This finding suggests impaired CSF reabsorption rather than hydrocephalus ex vacuo (ventricular enlargement due to loss of brain parenchyma).
- A 57-year-old man presents with acute onset vertigo, nausea, and gait instability that began 1 hour ago. Exam shows left-sided limb ataxia and dysmetria; strength is full. No headache. Concern exists for posterior circulation stroke. Noncontrast head CT is obtained and shows no hemorrhage. The team wants the most sensitive imaging to detect early ischemia in the posterior fossa and guide management. Which neuroimaging modality is most appropriate next?
Answer: MRI brain with diffusion-weighted imaging
This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes acute vertigo and ataxia, guiding the choice of MRI with DWI. The correct answer, A, is appropriate because it aligns with the clinical presentation and current guidelines, providing sensitive detection of posterior circulation ischemia. Choice B is incorrect due to low sensitivity early on, which often results from relying on CT alone. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.
- A 63-year-old woman presents with sudden left-sided weakness and neglect that began 2 hours ago. She has atrial fibrillation on apixaban. Glucose is 98 mg/dL. Noncontrast head CT shows no hemorrhage. Because she is on a direct oral anticoagulant, IV thrombolysis is not planned. The stroke team considers whether she may benefit from mechanical thrombectomy and needs imaging to identify a large-vessel occlusion rapidly. Which neuroimaging modality is most appropriate next?
Answer: CT angiography of the head and neck
This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes acute weakness on anticoagulation, guiding the choice of vascular imaging. The correct answer, A, is appropriate because it aligns with the clinical presentation and current guidelines, providing rapid detection of large-vessel occlusion for thrombectomy. Choice B is incorrect due to being less efficient for vessels, which often results from preferring detailed over urgent imaging. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.
- Analysis of the cerebrospinal fluid is most likely to show which of the following findings?
Answer: Oligoclonal bands
This patient's presentation of optic neuritis, a relapsing-remitting course of neurologic symptoms, and young female demographic is highly suggestive of multiple sclerosis (MS). A key diagnostic finding in the cerebrospinal fluid (CSF) of patients with MS is the presence of oligoclonal bands that are not present in the serum, which indicates intrathecal immunoglobulin synthesis. Albuminocytologic dissociation (high protein, normal cell count) is classic for Guillain-Barré syndrome. Elevated opening pressure and low glucose are seen in fungal or tuberculous meningitis. Neutrophilic pleocytosis is characteristic of bacterial meningitis.
- A 41-year-old woman with obesity presents with daily headaches for 2 months, worse when lying down, with transient visual obscurations. She denies fever or focal deficits. Exam shows bilateral papilledema and normal motor/sensory testing. BP 128/80 mm Hg. Pregnancy test is negative. MRI brain shows no mass lesion; MR venography shows no venous sinus thrombosis. A lumbar puncture is planned to confirm suspected idiopathic intracranial hypertension and guide management. Which CSF finding is most consistent with this condition?
Answer: Elevated opening pressure with normal CSF composition
This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes headaches and papilledema, guiding the choice of lumbar puncture. The correct answer, A, is appropriate because it aligns with the clinical presentation and current guidelines, providing confirmation of elevated pressure in idiopathic intracranial hypertension. Choice B is incorrect due to suggesting other pathologies like GBS, which often results from misattributing pressure changes. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.
- A 45-year-old woman presents with 3 weeks of worsening headaches and morning vomiting. She reports blurred vision and has had 2 episodes of brief confusion. Exam shows papilledema and mild left-sided weakness. Vitals are normal and she is afebrile. Because increased intracranial pressure from a mass lesion is a concern, clinicians must choose initial neuroimaging before considering lumbar puncture. Which neuroimaging modality is most appropriate for the initial evaluation?
Answer: MRI brain with and without contrast
This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes worsening headaches, papilledema, and weakness, guiding the choice of brain MRI. The correct answer, A, is appropriate because it aligns with the clinical presentation and current guidelines, providing detailed evaluation for mass lesions causing increased ICP. Choice B is incorrect due to herniation risk without imaging, which often results from rushing to LP. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.
- A 33-year-old woman reports 2 episodes of neurologic symptoms over 8 months. The first was painful vision loss in the left eye that improved over weeks. The second is 5 days of numbness and tingling in both legs with unsteady gait. She has fatigue and heat sensitivity. No fever. Exam shows decreased visual acuity in the left eye with a relative afferent pupillary defect, mild spasticity in both legs, hyperreflexia, and an upgoing plantar response on the right. Sensation to vibration is reduced in the feet. CBC and CMP are normal. MRI brain shows multiple ovoid periventricular T2 hyperintense lesions; one lesion enhances with gadolinium. A lumbar puncture is performed to support the suspected diagnosis and guide counseling about disease-modifying therapy.
Answer: Oligoclonal IgG bands with elevated IgG index
This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes recurrent neurologic episodes with MRI lesions, guiding the choice of lumbar puncture. The correct answer, B, is appropriate because it aligns with the clinical presentation and current guidelines, providing evidence of intrathecal IgG synthesis supportive of multiple sclerosis. Choice A is incorrect due to suggesting bacterial infection, which often results from confusing inflammatory patterns. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.
- Which of the following is the most likely diagnosis based on these neuroimaging findings?
Answer: Brain abscess
The combination of a subacute presentation with fever, neurologic deficits, and a ring-enhancing lesion on contrast-enhanced CT in a patient with a risk factor for bacteremia (IV drug use) is highly suggestive of a brain abscess. The ring enhancement represents a well-formed inflammatory capsule surrounding a necrotic, purulent center. While glioblastoma and metastasis can also present as ring-enhancing lesions, the presence of fever and risk factors for infection makes abscess the most likely diagnosis. An active MS plaque typically enhances more homogeneously or incompletely and is less likely to have a necrotic center.
- An MRI of the brain is most likely to show an infarct in which of the following locations?
Answer: Left lateral medulla
This constellation of symptoms is characteristic of Wallenberg syndrome, or lateral medullary syndrome. This is typically caused by an infarct in the territory of the posterior inferior cerebellar artery (PICA), which supplies the lateral medulla. The findings correspond to damage to specific structures in this area: the vestibular nuclei (vertigo, nystagmus), nucleus ambiguus (dysphagia, hoarseness), spinal trigeminal nucleus (ipsilateral facial numbness), spinothalamic tract (contralateral body sensory loss), and inferior cerebellar peduncle (ipsilateral ataxia).
- These CSF findings are most consistent with which of the following diagnoses?
Answer: Bacterial meningitis
The cerebrospinal fluid profile is classic for acute bacterial meningitis. Key features include a very high white blood cell count (pleocytosis) with a marked neutrophilic predominance, very low glucose (hypoglycorrhachia), and significantly elevated protein. In contrast, viral meningitis typically presents with a lymphocytic pleocytosis, normal glucose, and normal to mildly elevated protein. Tuberculous and fungal meningitis usually have a subacute presentation with lymphocytic pleocytosis, low glucose, and high protein.
- A 70-year-old woman presents with acute right-sided weakness and slurred speech that began 30 minutes ago. She has a history of intracerebral hemorrhage 2 years ago. BP is 210/110 mm Hg. She is somnolent. The team needs rapid imaging to evaluate for recurrent hemorrhage and guide blood pressure management and neurosurgical planning. Which neuroimaging modality is most appropriate for the initial evaluation?
Answer: Noncontrast CT of the head
This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes acute weakness, hypertension, and prior ICH history, guiding the choice of noncontrast head CT. The correct answer, A, is appropriate because it aligns with the clinical presentation and current guidelines, providing rapid detection of recurrent hemorrhage. Choice B is incorrect due to being less urgent for bleed, which often results from delaying with advanced imaging. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.
- What is the pathophysiologic process represented by these specific DWI/ADC findings?
Answer: Cytotoxic edema
The hallmark of acute ischemic stroke on MRI is restricted diffusion, which appears as a bright signal on diffusion-weighted imaging (DWI) and a dark signal on the apparent diffusion coefficient (ADC) map. This pattern represents cytotoxic edema, which is the result of cellular energy failure (due to ischemia) leading to failure of the Na+/K+ pump, intracellular ion influx, and subsequent cellular swelling. This swelling restricts the random (Brownian) motion of water molecules, causing the characteristic signal changes. Vasogenic edema, seen with tumors or abscesses, does not typically restrict diffusion to this degree. Demyelination and hemorrhage have different MRI appearances.
- These specific MRI lesions, often referred to as Dawson's fingers, are highly characteristic of which of the following conditions?
Answer: Multiple sclerosis
The description of multiple ovoid T2-hyperintense lesions in the periventricular white matter, particularly those oriented perpendicular to the lateral ventricles (Dawson's fingers), is a pathognomonic finding for multiple sclerosis (MS). These lesions represent demyelinating plaques that follow the orientation of the deep medullary veins. ADEM typically presents with large, poorly demarcated lesions that are monophasic. PML involves subcortical white matter, often asymmetrically. CADASIL typically involves the temporal poles and external capsule.
