Exam (elaborations)
USMLE STEP 1 PATHOLOGY QUESTION BANK 3
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U WORLD QUESTION BANK FOR PATHOLOGY FOR STEP 1 USMLE-SET 3
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1. A 43-year-old male with advanced HIV is hospitalised forevaluation of recent-onset headaches and personality changes.
Imaging of the brain shows a solitary mass within the temporal
lobe. Biopsy of the mass reveals uniform cells containing the
Epstein-Barr virus genome. This patient most likely suffers from
which of the following?
A. Pilocytic astrocytoma
B. Glioblastoma
C. Oligodendroglioma
D. Ependymoma
E. Medulloblastoma
F. Primary CNS lymphoma
G. Meningioma
H. Craniopharyngioma
I. Schwannoma
J. Pituitary adenoma
Answer: F
Explanation:
The most frequent CNS tumour in immunosuppressed patients is a
primary CNS lymphoma. This CNS tumour is commonly associated with
AIDS.
Primary CNS lymphomas appear microscopically as dense, cellular
aggregates of uniform, atypical lymphoid cells. The majority of primary
CNS lymphomas arise from B-cells. Diffuse large B-cell lymphoma is the
most common subtype. The cells of CNS lymphomas are commonly
positive for the B-cell markers CD20 and CD79a.
Primary CNS lymphomas are universally associated with the Epstein-
Barr virus (EBY). The clinical presentation is non-specific. Mental status
changes, seizures, or progressive focal neurologic deficits may occur.
,Most of CNS lymphomas are high-grade and respond poorly to
chemotherapy.
(Choice G) Meningiomas are not associated with immunosuppressive
diseases, nor are they associated with EBY. Meningiomas are located
adjacent to the brain surface and are attached to the dura mater.
(Choice H) Craniopharyngiomas are located in the suprasellar region
and can be calcified. Craniopharyngiomas can cause visual disturbances
and endocrinopathies (such as hypopituitarism).
(Choice I) intracranial schwannomas are most commonly located at the
cerebellopontine angle. They cause symptoms of CN VIII compression
(hearing loss, tinnitus, loss of balance).
2. A 56-year-old man with a 1-week history of hemiplegia and expressive
aphasia has a CT imaging study that reveals an area of hypodensity in
his brain. A section of tissue from this region is obtained. Histologic
findings after staining for lipids are show n in the photograph, below .
,The cells marked most intensely by the lipid stain represent which of the
following cell types?
A. oligodendrocytes
B. ependymal cells
C. fibroblasts
D. astrocytes
E. schwann cells
F. neutrophils
G. microglia
Answer: G
Explanation:
An ischemic infarct results when blood flow to an area of the brain is
interrupted due to thrombosis or embolism. Macroscopic changes in the
, brain first appear 12 hours after the onset of ischemic injury. During the
first week after an acute stroke, CT imaging studies will reveal the
ischemic area to be hypodense and poorly delineated from the
surrounding tissue. Edema and loss of distinction of the gray-white
matter junction are also seen.
Microscopically, neurons in the area display signs of irreversible damage
during the first 48 hours after injury ("red neurons"). Neutrophils initially
move into the area, followed by microglia (derived from monocytes) 3-5
days after the onset of ischemia. Infiltration of the brain tissue by
microglia (arrow) is seen on light microscopy at this time. As the neurons
disintegrate, their fragments begin to be phagocytized by microglia. The
abundance of lipids seen in the cytoplasm of the microglia results from
extensive phagocytosis of myelin breakdown products. These histologic
findings are consistent with the given clinical history of 1 week of focal
deficits.
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