Neuroimaging And Cerebrospinal Fluid Analysis
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USMLE Step 2 CK › Neuroimaging And Cerebrospinal Fluid Analysis
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.
Neutrophilic pleocytosis with low CSF glucose
Oligoclonal IgG bands with elevated IgG index
Xanthochromia with persistent RBCs
Eosinophils with very high CSF protein
Markedly elevated CSF opening pressure
Explanation
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.
A 24-year-old woman presents with 2 days of fever, severe headache, and progressive confusion. She has nausea and vomited twice. Past history includes recurrent oral HSV-1 lesions. Medications: oral contraceptive only. On exam, T 39.4°C, BP 118/72 mm Hg, HR 112/min. She is disoriented to place and has word-finding difficulty. Cranial nerves are intact. She has mild right arm weakness (4/5) and hyperreflexia on the right. Neck is mildly stiff. CBC shows WBC 14,800/µL. Basic metabolic panel is normal. Concern for CNS infection is high, but focal neurologic deficits raise concern for increased intracranial pressure or a focal lesion. The team must decide on the safest next diagnostic step before CSF sampling to avoid herniation risk and to support empiric management decisions.
Noncontrast head CT before lumbar puncture
No imaging; start antibiotics only and reassess
MRI spine with contrast
Carotid CT angiography
Immediate lumbar puncture with opening pressure
Explanation
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 focal weakness, guiding the choice of head CT. The correct answer, B, is appropriate because it aligns with the clinical presentation and current guidelines, providing rapid assessment for mass effect or increased ICP before lumbar puncture. Choice A is incorrect due to risking herniation without ruling out contraindications, which often results from underestimating focal deficits. 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 36-year-old man presents with progressive ascending weakness for 4 days after a diarrheal illness. He has difficulty climbing stairs and tingling in his feet. No fever now. Exam shows symmetric lower-extremity weakness (3/5), areflexia at the knees and ankles, and intact sensation to pinprick. Cranial nerves are intact. Respiratory rate is 18/min. MRI spine is unremarkable. Lumbar puncture is performed to support the suspected diagnosis and help guide monitoring. Which CSF finding is most consistent with Guillain-Barré syndrome?
Low glucose with neutrophilic pleocytosis
Oligoclonal bands with elevated IgG index
Xanthochromia with elevated RBCs
High protein with normal WBC count
Marked eosinophilia with very low glucose
Explanation
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 ascending weakness and areflexia, guiding the choice of lumbar puncture. The correct answer, A, is appropriate because it aligns with the clinical presentation and current guidelines, providing evidence of albuminocytologic dissociation in Guillain-Barré syndrome. Choice B is incorrect due to suggesting infection, which often results from confusing inflammatory responses. 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 30-year-old woman presents with 1 day of fever, headache, photophobia, and confusion. She had a generalized tonic-clonic seizure in the ED. Exam shows disorientation and a subtle right arm pronator drift. T 39.0°C. Because she has a new seizure and focal neurologic deficit, the team obtains neuroimaging before lumbar puncture. Which neuroimaging modality is most appropriate for the initial evaluation to assess for mass effect or hemorrhage quickly?
MR angiography of the head
CT of the cervical spine
Transcranial Doppler ultrasonography
MRI brain with and without contrast
Noncontrast CT of the head
Explanation
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, confusion, seizure, and focal signs, guiding the choice of initial neuroimaging. The correct answer, A, is appropriate because it aligns with the clinical presentation and current guidelines, providing quick assessment for contraindications to lumbar puncture. Choice B is incorrect due to being time-intensive, which often results from overprioritizing detail in emergencies. 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 26-year-old woman presents with fever, headache, and neck stiffness for 4 days. She is HIV-negative and recently returned from a camping trip. Exam shows photophobia and mild confusion without focal deficits. CT head shows no mass lesion. Lumbar puncture reveals WBC 220/µL (90% lymphocytes), protein 90 mg/dL, glucose 62 mg/dL (serum 100 mg/dL). Gram stain is negative. The team suspects viral meningitis and must identify which CSF profile best fits the suspected diagnosis to avoid unnecessary broad-spectrum antibiotics.
Eosinophilic pleocytosis with low glucose
Lymphocytic pleocytosis with normal glucose
Xanthochromia with falling RBC count by tube
Neutrophilic pleocytosis with very low glucose
No WBCs with markedly elevated protein
Explanation
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, and lymphocytic CSF, guiding the choice of profile matching. The correct answer, A, is appropriate because it aligns with the clinical presentation and current guidelines, providing support for viral meningitis diagnosis. Choice B is incorrect due to indicating bacterial infection, which often results from overinterpreting pleocytosis. 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 72-year-old man develops progressive headache and mild confusion over 2 weeks after a fall in which he struck his head. He takes aspirin daily. No fever. Exam shows mild left arm weakness and slowed speech. Vitals are stable. Noncontrast head CT shows a crescent-shaped extra-axial collection over the right cerebral hemisphere with midline shift. The team must determine the most likely diagnosis based on the imaging description to guide neurosurgical consultation.
Subarachnoid hemorrhage
Subdural hematoma
Intraparenchymal hemorrhage
Lacunar infarct
Epidural hematoma
Explanation
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 progressive headache and weakness post-fall, guiding the choice of CT interpretation. The correct answer, B, is appropriate because it aligns with the clinical presentation and current guidelines, providing identification of subdural hematoma's crescent shape. Choice A is incorrect due to typical lens shape in epidural, which often results from confusing hematoma types. 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 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?
Xanthochromia with persistent RBCs
Elevated opening pressure with normal CSF composition
Oligoclonal bands with elevated IgG index
Low opening pressure with elevated protein
Neutrophilic pleocytosis with low glucose
Explanation
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 67-year-old man with atrial fibrillation (not on anticoagulation) develops sudden right facial droop and right arm weakness 45 minutes ago. He has difficulty speaking but follows commands. No headache or trauma. On exam, BP 158/86 mm Hg, HR 108/min irregularly irregular, glucose 112 mg/dL. Neurologic exam shows expressive aphasia and right arm drift. NIHSS is 9. The emergency team must rapidly distinguish ischemic from hemorrhagic stroke to determine eligibility for thrombolysis and possible thrombectomy. No contraindications to CT are present. The question is which neuroimaging test is most appropriate first in this setting.
MRI brain with diffusion-weighted imaging
PET scan of the brain
CT myelography
Noncontrast CT of the head
MR venography
Explanation
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 focal weakness and aphasia, guiding the choice of noncontrast head CT. The correct answer, B, is appropriate because it aligns with the clinical presentation and current guidelines, providing rapid exclusion of hemorrhage before thrombolysis. Choice A is incorrect due to being time-consuming in the acute window, which often results from over-relying on 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.
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?
Carotid duplex ultrasonography only
Lumbar puncture for CSF analysis
MRI brain with gadolinium
CT angiography of the head and neck
Skull radiographs
Explanation
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.
A 40-year-old man presents with acute onset headache and fever. He is confused and has left arm weakness. CT head shows a right frontal ring-enhancing lesion with surrounding edema and mild midline shift. The team suspects a brain abscess and is considering lumbar puncture to evaluate for meningitis. Which is the most appropriate next step regarding CSF sampling in this patient?
Perform lumbar puncture only if CSF glucose is normal
Perform lumbar puncture immediately to confirm diagnosis
Avoid lumbar puncture due to herniation risk; treat and consult neurosurgery
Repeat CT head after lumbar puncture
Perform lumbar puncture after giving mannitol only
Explanation
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 headache, fever, and CT ring-enhancing lesion, guiding the choice of avoiding lumbar puncture. The correct answer, A, is appropriate because it aligns with the clinical presentation and current guidelines, providing risk reduction of herniation in brain abscess. Choice B is incorrect due to ignoring mass effect, which often results from underestimating imaging findings. 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.