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.
Markedly elevated CSF opening pressure
Xanthochromia with persistent RBCs
Oligoclonal IgG bands with elevated IgG index
Eosinophils with very high CSF protein
Neutrophilic pleocytosis with low CSF 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 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 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?
Transcranial Doppler ultrasonography
MR angiography of the head
MRI brain with and without contrast
CT of the cervical spine
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 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?
Neutrophilic pleocytosis with low glucose
Oligoclonal bands with elevated IgG index
Low opening pressure with elevated protein
Elevated opening pressure with normal CSF composition
Xanthochromia with persistent RBCs
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.
PET scan of the brain
MR venography
CT myelography
Noncontrast CT of the head
MRI brain with diffusion-weighted imaging
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 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
Avoid lumbar puncture due to herniation risk; treat and consult neurosurgery
Repeat CT head after lumbar puncture
Perform lumbar puncture after giving mannitol only
Perform lumbar puncture immediately to confirm diagnosis
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.
A 46-year-old woman presents with abrupt onset severe headache that peaked within 1 minute while showering. She has photophobia and vomiting. No focal deficits. Exam shows nuchal rigidity. Vitals: BP 162/94 mm Hg, T 36.9°C. Noncontrast head CT obtained 10 hours after onset shows no hemorrhage. Lumbar puncture is performed. CSF shows: RBCs 18,000/µL in tube 1 and 17,500/µL in tube 4, protein mildly elevated, glucose normal. The sample is centrifuged. The team must interpret whether these findings support aneurysmal subarachnoid hemorrhage versus traumatic tap to determine need for urgent aneurysm evaluation.
Clearing RBC count from tube 1 to tube 4
Low CSF glucose with neutrophils
Elevated CSF opening pressure alone
Xanthochromia in centrifuged CSF supernatant
Positive CSF cryptococcal antigen
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 thunderclap headache with nuchal rigidity, guiding the choice of CSF analysis. The correct answer, B, is appropriate because it aligns with the clinical presentation and current guidelines, providing distinction of SAH from traumatic tap via xanthochromia. Choice A is incorrect due to indicating traumatic tap, which often results from ignoring persistent RBCs. 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 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?
Obtain MRI brain before lumbar puncture
Defer lumbar puncture until rash resolves
Obtain noncontrast head CT before lumbar puncture
Perform lumbar puncture immediately after blood cultures
Perform CT angiography before lumbar puncture
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, 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.
A 61-year-old man presents with sudden severe headache and neck stiffness. Noncontrast head CT is negative. Lumbar puncture is performed 2 hours after symptom onset and shows RBCs 2,000/µL in tube 1 and 200/µL in tube 4, normal glucose, and no xanthochromia. He improves with analgesics. The team must decide whether this CSF pattern is more consistent with traumatic tap or subarachnoid hemorrhage to guide further workup.
Bacterial meningitis due to elevated RBCs
Subarachnoid hemorrhage due to normal glucose
HSV encephalitis due to absence of xanthochromia
Multiple sclerosis due to normal opening pressure
Traumatic tap due to marked decline in RBCs across tubes
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 sudden headache and decreasing CSF RBCs, guiding the choice of interpretation. The correct answer, A, is appropriate because it aligns with the clinical presentation and current guidelines, providing distinction of traumatic tap without xanthochromia. Choice D is incorrect due to not matching the pattern, which often results from overcalling early 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.
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
Xanthochromia with falling RBC count by tube
Neutrophilic pleocytosis with very low glucose
No WBCs with markedly elevated protein
Lymphocytic pleocytosis with normal 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 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 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.
Immediate lumbar puncture with opening pressure
Carotid CT angiography
Noncontrast head CT before lumbar puncture
MRI spine with contrast
No imaging; start antibiotics only and reassess
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.