A 28-year-old woman presents with subacute painful unilateral vision loss, reduced color perception, and a relative afferent pupillary defect. She reports a prior episode of right hemibody numbness 6 months ago. Examination reveals Lhermitte's sign and a sensory level at T6. MRI brain shows multiple ovoid T2/FLAIR hyperintense lesions in the periventricular white matter oriented perpendicular to the lateral ventricles, as marked **A** in the diagram. Gadolinium-enhanced imaging shows both active and chronic lesions. CSF analysis reveals oligoclonal bands and elevated IgG index. Which of the following best describes the pathological basis of the lesions marked **A**?
A. Perivenular inflammatory demyelination radiating along medullary veins in the periventricular white matter
B. Vasculitic destruction of large penetrating cortical vessels with secondary ischemia
C. Demyelination confined to the gray matter with sparing of white matter tracts
D. Axonal loss predominating over demyelination in the subcortical U-fibers
Explanation
Why "Perivenular inflammatory demyelination radiating along medullary veins in the periventricular white matter" is right
The lesions marked A are Dawson's fingers — a pathognomonic finding in multiple sclerosis. These are T2/FLAIR hyperintense lesions oriented perpendicular to the lateral ventricles in the periventricular white matter. The characteristic feature is that they represent perivenular inflammatory demyelination that radiates outward along the medullary veins draining into the lateral ventricles. This perivenular orientation is what distinguishes Dawson's fingers from other white matter lesions and is the hallmark of MS pathology. The clinical presentation (optic neuritis, transverse myelitis, Lhermitte's sign), CSF findings (oligoclonal bands, elevated IgG), and dissemination in space and time on MRI (periventricular, juxtacortical, infratentorial, and spinal cord lesions) confirm relapsing-remitting MS (Harrison's 21e).
Why each distractor is wrong
Demyelination confined to the gray matter with sparing of white matter tracts: Dawson's fingers are specifically periventricular white matter lesions, not gray matter lesions. While MS can affect gray matter, Dawson's fingers are a white matter phenomenon.
Vasculitic destruction of large penetrating cortical vessels with secondary ischemia: This describes vasculitis or stroke pathology, not MS. MS is an autoimmune demyelinating disease, not a vasculitic process. The perivenular inflammation in MS is immune-mediated, not vasculitic.
Axonal loss predominating over demyelination in the subcortical U-fibers: Axonal loss is a feature of chronic MS lesions but is not the primary pathological basis of acute Dawson's fingers. U-fiber lesions (juxtacortical) are a separate category of MS lesions; Dawson's fingers are periventricular, not juxtacortical.
High-YieldNEET PG
Dawson's fingers = periventricular T2 hyperintensities perpendicular to lateral ventricles = perivenular demyelination along medullary veins = pathognomonic for MS.
Harrison's 21e, Multiple Sclerosis
Practice similar questions
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.
