L:\usmle review 7 - Sinoe medical homepage.

(including glioblastoma) > meningioma > pituitary tumor. Location at the junction of cortical gray
and white matter is also typical for metastatic disease, as is the round shape.
Astrocytomas (choice A) typically arise in the white matter and have an irregular shape.
Ependymomas (choice B) are uncommon and arise from the ependymal lining of the ventricles.
Glioblastoma multiforme (choice C) is an aggressive form of astrocytoma that can cause a
“butterfly lesion,” crossing between the cerebral hemispheres.
Meningiomas (choice D) can cause spherical lesions and are usually located on the surface of
the brain.
22. A 37-year-old woman presents to the emergency department with a fever. Chest x-ray film
shows multiple patchy infiltrates in both lungs. Echocardiography and blood cultures suggest a
diagnosis of acute bacterial endocarditis limited to the tricuspid valve. Which of the following is
the most probable etiology
(A)
(B)
(C)
(D)
(E)
Congenital heart disease
Illicit drug use
Rheumatic fever
Rheumatoid arthritis
Systemic lupus erythematosus
22. The correct answer is B. The most probable etiology of bacterial endocarditis involving the
tricuspid valve is illicit IV drug use, which can introduce skin organisms into the venous system
that then attack the tricuspid valve. Staphylococcus aureus accounts for between 60% and 90%
of cases of endocarditis in IV drug users.